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T H E U S E O F P A S S I V E C O O L I N G T E C H N I Q U E S T OC O N C E N T R A T E S O L I D S I N W A T E R

b yM A R Y B E T H K E F F E R B R A Y , B . S . in C . E .

A T H E S I SIN

C I V I L E N G I N E E R I N G

S u b m i t t e d t o t he G r a d u a t e F a c u l t yo f T e x a s T e c h U n i v e r s i t y i nP a r ti a l F u l f i l l m e n t o ft h e R e q u i r e m e n t s f o rt h e D e g r e e o f

M A S T E R O F S C I E N C EIN

C I V I L E N G I N E E R I N G

A p p r o v e d

A c c e p t e d

D e c e m b e r 1 9 8 9

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THE USE OF PASSIVE COOLING TECHNIQUES TOCONCENTRATE SOLIDS IN WATER

byMARY BETH KEFFER BRAY, B.S. in C.E.

A THESISIN

CIVIL ENGINEERING

Submitted to the Graduate Facultyof Texas Tech Unive rsity inPartial Fulfillment ofthe Requirements forthe Degree of

MASTER OF SCIENCEIN

CIVIL ENGINEERING

Approved

Accepted

December 1989

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T3Mo. i^1

A C K N O W L E D G E M E N T S

Words are insufficient to express my sincere appreciat ion to Dr. R. Heywaxd RamseyI I I , Cha i rperson of my com m it tee, for h i s helpful guidance, perp etu al enco urag em ent ,and und ers ta ndin g. His profess ional exper t i se together wi th h is valuable ass i s tance,were major factors in the successful complet ion of this project .

Appreciat ion i s ex tended to Dr . Richard Tock and Dr . Tony MoUhagen for the t imeand effort they spent on my behalf while serving as committee members.

Special thanks are extended to Mr. J . Bradley Thornhi l l , a laboratory technician inthe Envi rorunental Science Laboratory in the Civi l Engineer ing Depar tment at TexasTech Universi ty, for his support in the experimental phases of this project .

Appreciat ion i s ex tended to Ms. Jean Ann Cantore, of the Engineer ing Communicat ions Center in the Engineering College at Texas Tech Universi ty, for her help withproof- reading .

Special thanks are al so extended to Dean Bray , Veen Chee Foong, June Wilcot tSl igar, and al l the other people who offered assistance and support throughout thisproject . Thei r presence i s appreciated more than they real ize.

The financial support received from the U. S. Air Force is also great ly appreciated.

11

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T A B L E O F C O N T E N T S

A C K N O W L E D G E M E N T S i iL IS T O F T A B L E S vL IS T O F F IG U R E S v iN O T A T IO N S v i iC H A P T E R

1 . I N T R O D U C T I O N 1The Need for Energy Conse rvat ion 1Background 1Object ives 3Thesis Out l ine 4

2. L I T E R A T U R E R E V I E W 5The Need for Econo mical M ethod s to Treat W ater 5

Usable W ater 6Dy nam ics of Cooling 7

Na tura l Cool ing Processes in a Ho t , Ar id Region 9Passiv e Cooling 10

Th e Cl ima te Near the Grou nd 12Pro per t ies of Ice 13

Sam pling Ice 15Ice Form at ion 16Freezing versus Ev apo rat ion 16Freez e-Cry stahza t ion Processes for PoU utant Rem oval 17V F M P T P r o ces s 18IFC Process 19Appl icat ions 20S u m m ar y 2 0

m

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3. P R O C E D U R E S 2 2Approach 22Research P l an and Procedures 23

Ou tdoor Tests 23Con trol led Co ndit ions Tests 24

Test Fac ility 25O utd oo r Test Faci l i ty 25Con trol led Test Faci l i ty 26

Ion Chrom atograp h 26D at a Analysis 27

Ou tdoor Tes t Pha se 27Cont ro l led Test Ph ase 29Revised Cont ro l led Test Pha se 29Step han 's Eq uat io n Analysis 30

4. R E S U L T S 3 1D ata Prese n t a t i on 31

Ou tdoor Test Pha se 31Cont ro l led Test Ph ase 32Revise d Con trol led Test Ph as e 33

Step han 's Eq uat io n Analysis 35Econom ic Analysis 36

5. C O N C L U S I O N 3 9Recommendat ions 39

B I B L I O G R A P H Y 4 1A P P E N D I X 4 5

IV

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LIST OF TABLES

1 Sodiimi Chloride in Solution 562 1988-89 W inter Nights with Freezing W eathe r in Lubb ock, Texas 583 W inter D at a Collection Problem s 594 W inter Resu lts 605 Prelim inary Results 616 Re sults of 500 m g/ L Test Gra ph 627 Resu lts of 1500 m g/ L Test Gra ph 638 Resu lts of 4500 m g/ L Test Gra ph 649 Econom ics of Passive Ice-Maker System 7110 Econom ics of IF C System 7211 Economics of V FM PT System 73

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LIST OF FIGURES

1 OSW Projects 462 Freeze-evaporation Process 473 Direct-refrigerant Freeze Process 484 Water Phase Diagram 495 Iranian Ice-maker 506 Ice Crystal 517 Natura l Arctic Ice 528 VFM PT Process 539 VFM PT Phase Diagram 54

10 IFC Process 5511 Test Unit 5712 Results from 500 m g/1 Test Run 6213 Resu lts from 1500 mg /1 Test Run 6314 Results from 4500 mg /1 Test Run 6415 Average Results 6516 Average Results with Seawater 6617 Proposed Passive Ice-maker Ponds 67

VI

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N O T A T I O N S

AT FB = Average Tem pera tu re Below Freez ingB T U = Br i t i sh Thermal Un i tEPA = Env i ronm en ta l P ro t ec t i on AgencyGP D = Gal lons per Day

h = Thickne ss of IceIC = Ion Chrom atograph

IC W M = In t eg ra l Crys t a l W asher /M el t e rIFC = Indi rect Freeze Co ncen t rat ion

k = Mean The rma l Conduct iv i tyL = Laten t Heat of W ater

m g/ L = Mi l l igram per Li terNa Cl = Sodium Chlor ide

NOA A = Nat iona l Ocean ic and Atmospher i c Adm in i s t r a t ionOS W = Office of Sahne W ater

Qc = Convective Flu xQe = Heat Transfer by Mass Tra nspo r tQk = Conduct ive FluxQ,. = Rad iat ive Flux

V l l

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RO = Reverse OsmosisS = Sum ma t ion of Degree Hours of Freezing

ST PV PU = Sub-Tr ip le Poin t Vapor Process ing Uni tt = Time

TD S = To tal Dissolved SolidsV F M P T = Vacu um Freez ing Mul t i p le Phase Trans fo rmat ion

a = Correct ion Factor for Step han 's Eq uat io np Density of Ice0 T em p er a t u r e

V l l l

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C H A P T E R 1I N T R O D U C T I O N

The Need for Energy Conservat ionT he w orld 's source s of gas and o il, the m ost des irable form of fossil-fuel energ y, a re

being d epleted . Th e U ni ted S tates is us ing o il fas ter th an any o ther nat ion in the wor ldbu t has less th a n 5 pe rce nt of the w orld 's oi l reserve s. Th e am oun t of oi l pro du ce d inthe United States is already decHning. Pakiz (23) predicts that the United States wil lru n ou t of oi l betw een th e years 2050 and 2100. The refore, i t is neces sary to ut i l izeother energy sources or to f ind methods that are less energy intensive for accomplishingtasks . A comfor table s tan da rd of l iv ing cannot be mainta ined in the fu ture w i thout achange in current energy-use pract ices .

BackgroundUti l izat ion of passive cooling is one way that fossi l -fuel energy consumption could

be decreased . Pass ive cool ing uses the natural envi ronment to reduce the temperatureof a subs tan ce ins tea d of using energy intensive devices. T his techniqu e has been u sedin Iran for air condit ioning, refrigerat ion, and to make ice (3). The ice-maker processconsists of a system of shal low ponds which are 10 to 20 meters wide and 100 meterslong or longer. An ad obe wall run s along the so uth side of the po nd an d pro videsshade during the day. The wall also acts as a wind block and prevents heat gain fromconvection. Water is added on winter nights. This water is cooled by the t ransfer of heatf rom the water to the atmosphere by radiat ion , evaporat ion , and conduct ion . However ,the water body gains heat through conduct ion f rom the under ly ing so i l . This heat must

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be removed by heat t ransfer to the atmosphere. The ponds lose a large amount of heatthrough radiat ion to the sky on clear nights. Heat is also lost when water molecules onthe surface ev apo rate . W he n the night is cool eno ugh , ice wil l form (3 ).

CooHng a m ater ia l involves the loss of hea t throu gh evap orat ion , radia t ion , or convect ion (2 5). This hea t loss is affected by th e specific he at of a subs tan ce , the h ea trequi red per un i t mass of the sub stance to raise it s t em pe ratu re by 1 degree C elsius(27) . Th e specific heat of water is 1 calorie per g ram p er degree Celsius and is th e

s tandard to which o ther mater ial s are compared .Ra diat ion i s heat t ransfer wi tho ut ma ss t ran spo r t . At n ight , the air wiU be cooler

than the water and heat wil l be t ransferred by radiat ion to the sky or black space.Conve ction is hea t t ransfer by f luid mo tion . Cool air passing over the water w ill

gain hea t from th e water wh ereas hot air passin g over the wa ter wiU he at th e water (3).Evaporat ion is the change of state from l iquid form to vapor. Heat is lost because

the water must overcome the latent heat of vaporizat ion which is the amount of heatrequ ired to chan ge a molecule of l iquid to a gas. Th e latent he at of crystaH zation is 80calories per gram (31).

Passive cooling ice-makers could also be applied as a t reatment process to removedissolved sol ids in water. W he n wa ter freezes, it tend s to freeze as a crys tal and dissolvedsolids wil l be excluded from the crystal matrix as the ice crystals develop. The ice formedwiU be more pure th an th e liquid por t io n , because th e lat ter includes the substanc esexcluded from the frozen crystal . This technique could be used to desal inate or removedissolved sol ids from waste water.

If this technique could be optimized, i t could be used during part of the year inmo st areas of the Un i ted Sta tes . Th e operat io nal scheme behind pass ive cooling i s to

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minimize the heat input in to the substance dur ing the day and maximizing the heatloss at night , al lowing the water to freeze. By optimizing the ways to l imit heat input ,passive cooling ice-makers may be an al ternat ive and more economical way to freezewate r . Th e resul ta nt ice would be a na tur al produ ct f rom envi ronm ental processes an dnot from energy inten sive -m etho ds. How ever, the re axe costs asso ciated with passivecooling. The operat ing costs for the system consist of energy costs to run the ice-removalequipm ent and pum p the water ; and ma intena nce costs , and labor costs . T he c api tal

costs for the system consist of si te acquisi t ion fees, and construct ion costs for the ponds,walls, appur tenances , and equipment costs for the ice removal and washing equipment .

Object ivesTh is stu dy wiU look at th e use of freezing to remove tota l dissolved solids ( TD S)

from wa ste wate rs. Th e purpo se is to find out if the freezing of wa ter und er wintercond it ions could be used as a m ore econom ical m ean s of rem oving dissolved sol ids. Th eobjectives are as follows:

1. To determine what qual i ty water can be obtained from ice formed fromwaters containing different amounts of the same type of dissolved sohds.

2. To determine if the passive freezing of ice can be used forreducing dissolved sol ids, and

3. To develop recommendat ions to ass i s t fu ture ice-making s tudies .

Thesis Out l ineThe next chapter includes a review of pert inent l i terature in the area of passive cool

ing, the dynamics of cooling, the cl imate of the ground layer, freezing technology, and

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the properties of water. Chapter 3 describes the acquisition of data used in this studyand the procedures that were adopted to perform the laboratory tests. A discussion ofthe results is presented in Chapter 4. Finally, the conclusions of this research as weU asrecommendations for future research are presented in Chapter 5.

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two freezing processe s (1 0). T he pla nts were to produc e 0.1 to 1 mil l ion gal lons pe r dayfor less tha n a dol lar per th ou san d gal lons . Figure 1 in the App end ix shows the p lantloca t ions .

De sal in at ion by freezing is th e focus of this study. The refore, freeze-eva porat ionan d direct refrigerant cooling will be exa m ined in mo re detai l . Tw o different techniqu eswere considered for the freeze separat ion processes. Plants ut i l izing each technique wereeve ntual ly bu il t . Th e fi rst pi lot pla nt bui l t ut i l ized a freeze-evapo rat ion process an d th esecond used a direct-refrigerant freezing process. In the freeze-evaporat ion process, thesal twater i s p laced in a h igh-vacuum chamber and f iash cooled to a temperature loweno ugh for ice crystals to form (26 ). Th e water vapor gen erate d in the process canalso be used as a source of desa l inated wa ter. Th e pi lot plant consists of four 60,000gallons per day modules. No cost analysis was avai lable for the operat ion (26). In the

direct-refrigerant technique, a refrigerant is placed in the brine to cause ice crystals toform. Use of the direct refrigerat ion process reduces the size of the compressor but addsthe problem of handling a second fluid which must be removed from the system (8).This 15,000 gal lon per day pi lot plant produces water in the range of 35 to 45 cents pertho usa nd gal lons (8) . Schemat ics of bo th p lan ts are shown in Figures 2 and 3 .

Usab le WaterTh e pr im ary appl icat ion th at wiU be addressed in th i s s tudy is the desal inat ion

of water containing high levels of inorganic dissolved soHds. For water to be used inmany appl icat ions , cer tain const i tuents must not exceed speci f ied l imi ts . These l imi tsare depe nden t upo n the in tende d use of the water . W ater that contains less than500 milligrams per liter of total dissolved solids is classified as fresh by the United

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State s Pub l ic He al th Service (31) . Also , the En vi ron me ntal Protec t ion Agency (EP A)reco mm end s th at dr inking water not exceed 500 miUigrams per li t er to tal d i sso lvedsolids (TD S) acco rding to the 1980 sta nd ar ds . At 500 m il l igrams per l i ter , the wa terwiU beg in to hav e a sal ty taste . Cit ies such as Lu bbo ck, T exa s, exceed this l imit withno app aren t occurrence of ma jor h eal th problem s. A sodium l imi t of 20 mi l l igrams pe rl i ter i s recommended but no maximum contaminant level has been set for TDS (22) .Water used for i r r igat ion can have 500 mi l l igrams per l i t er TDS. Waters can be used athigher sal ini ty levels except when the local water table is close to the ground surface.Waters wi th TDS concent rat ions of 5,000 mill igrams per Hter and greater are general lynot acceptable for any irr igat ion uses (37). Thresholds for cooling water sal ini ty levelsvary depending on corrosivi ty.

Dynamics of CoohngCooling is achieved thr ou gh th e loss or t ransfer of he at . W he n wa ter is cooled, it

loses hea t by radia t ion , evap orat ion , and conduct ion (38) . These metho ds t ransfer thewater 's heat to the air . More specifical ly, radiat ion is the emission, dissemination, ordiffusion of he at from th e water to the surrou ndin g mat eria ls. Ra dia t ion is a funct ion ofwater surface area and water tem pe ratu re. Eva pora t ion is the change of s tate f rom l iquidto vapor . Heat i s los t because the water must overcome the latent heat of vapor izat ion ,the am oun t of hea t req uired to cha nge a molecule of l iquid to a gas. A fluid in th eform of a gas must have more energy than i ts l iquid form. Liquid at the point where i tis about to evapora te and gas from the l iquid tha t has jus t e vapo rated m ay be at th esame te m pe ra tur e. Th e only d if ference b etween the two i s thei r energy levels . Th e e xt raenergy in the gas is contributed by the surrounding Hquid molecules before i t vaporizes.

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8

The heat lost through this process is diff icul t to determine since i t is dependent onam bient m etero logical condi t ions (38) . Th e phase d iagra m in Figure 4 shows the s tateswhich water can exist at different temperatures and pressures.

Co nduc t ion i s the t ransm iss ion or conveyance of heat throu gh a m ediu m or passagewi th out perce pt ib le mot ion of the medium . In a shallow pon d of wa ter , condu ct ionwould occur by the t ransf er of he at from th e basin soi l und erlying the wa ter to the w aterand then from the water to the atmosphere. Convection is the t ransfer or conveyance ofhe at by mo ving fluids. Flu id m otio n transfers heat betw een regions of un equ al de nsi tyboth in the body of water and between the water body and the over ly ing atmosphere.W ind p assin g over the wa ter ca n transfer some of i ts energy to the water as hea t or pickup heat f rom the water depending on the exis t ing temperature gradient . The wind canincreas e the hea t c ontent of the w ater a nd thu s wind effects in passive-cooling ice-make r

system s mus t be minim ized. Conv ection and conduction-l ike rad iat io n axe also diff icultto est imate because they, too, are funct ions of local meterological condit ions (38).

The optimal cooling scenario is a f iat pond that is exposed to the ent ire hemisphereof the nigh t sky. W he n th e sky is clear and the hum idity is low, 20 to 30 B T U persquare foot-hour per square foot of surface can be dissipated (33).

Th e inte rac t ion of the different m eth od s of he at t ransfer are described by Po un de rin the fol lowing energy balance equation (25):

Qk = Qr + Qc + Qc (2.1 )where Qk is the conductive flux, Qr is the radiative flux, Qc is the convective flux, andQe i s the heat of t ransfer by mass t ranspor t (evaporat ive or condensat ion of water ) .

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In 1 881, Ste pha n m ade the f irst m ath em at ic al descr ip t ion of ice growth or ice decay.His law is as follows (25):

ek - d t = L/9dh (2.2)hwhere k i s the mean thermal conduct iv i ty , 9 i s the temperature, t i s t ime, h i s thethickness of the ice, L is the latent heat , and p is the density of the ice.

Stephan 's equat ion considers heat t ransfer red by conduct ion through an ice layerth a t has alre ady formed on a large bo dy of wa ter. Th e calculated thickness is the iceth a t w ill grow or decay from th e bo tto m layer of the ice sheet due to hea t t ransfe rredby conduction. Since this equation only considers conductive heat t ransfer , i t is l imitedin i ts uses.

Natural Cool ing Processes in a Hot , Ar id RegionA related s tudy was conducted at Ar izona State Univers i ty in Tempe, Ar izona, to

examine the optimizat ion of cooling by solar ponds. Tests were run to determine theamount of cool ing due to each process and the to tal maximum cool ing that could beachieved through natural processes at n ight . Four water -proofed , insulated boxes wereused to hold the water. The fi rst box, with the top covered with foi l to prevent heat lossby radiat ion , measured the heat los t by convect ion . The second box was covered wi tha black plast ic f i lm to maximize radiat ion losses. The third box was uncovered to aUowevaporat ive losses while the fourth box ut i l ized spray evaporat ion to maximize cooling(16) .

The s tudy found that convect ion losses f rom the water gradual ly decreased watert em pera tu res and th i s lo ss l agged beh ind the d ry -bu lb t emp era tu re . W hen convec tion

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10

and radia t ion were u t if ized , the water tem pe ratu re fo llowed the dry-bulb tem pe rat ur e.The water temperature in the th i rd box fel l below the dry-bulb temperature shor t lyaf ter sunset and somet imes fel l below the wet -bulb temperature. In the four th box, thet em per a tu re fe ll be low bo th t he wet -bu lb and d ry -bu lb t empe ra tu res and somet imesthe water temperature dropped below the dewpoint before sunr i se . The temperature inth e spray -eva por at ion proce ss was the most effect ive. This process increa sed the coolingtem pe ratu res 15 to 25 percent over tha t of the o ther tes t uni t s (16) .

Pass ive CoohngPassive cool ing i s the use of the natural envi ronment to decrease the temperature

of a substance through the natural f iows of thermal energy under ambient condi t ions(24) . The second law of thermodynamics says that heat f iows from hot to cold regions

or from high pressure to low pressure zones. Passive cooHng techniques ut i l ize this lawby al lowing the excess heat in a system to f low to a sink exhibi t ing a lower temperature(33) . Passive cooling has the fol lowing advantages (1):

1. Requi res low manufactured energy input ;2. has few moving par t s which are durable , and , therefore, requi res

f i t t i e maintenance;3. Is simple and inexpensive to instal l , and;4. Is safe.

I t has two major d isadvantages (24) :1. A lower efficiency than an act ive system, and;2. A lack of publ ic acceptance.

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11

Pass ive cooling system s have evolved over the years to imp rove ma n' s comfort . Inar id , in ter ior , cont inental areas where the ambient ai r t emperature exhib i t s a largevariance from day to night , bui ldings are buil t with thick walls, domed roofs, andwith common walls or Utt le distance between adjacent structures. The thick walls offerinsulat ion a nd al so act as hea t reservoirs which dam pen the dai ly tem pe ratu re var iat ionsinside the home. The domed roofs and the clustered buildings help decrease the solarenergy inp ut into the hom e. Th e side-by-side constr uct io n of bui ldings also help sh adethe s t reets an d adjacent bui ld ings . These a dap tat ion s are examples of age-old techniques(3) . The pr incip les used in these adaptat ions can al so be appl ied today in o ther regions .

Other i imovations that have been used for years in the Middle East include the windtower, the cistern, and the ice maker. The wind tower sensibly and evaporat ively coolsair . The air is directed over an underground storage pond and then is circulated throughthe area to be cooled. Cisterns holding runoff from building roofs or water brought fromlocal supplies, can be the source of the coohng w ater , or can act as a heat-sin k fromthe air with in the buildin gs. T he ice-maker techn ique consists of a sys tem of pon dsand a n ice-storage building. W he n ice forms in the pond s, i t is remo ved an d s tored.To lower interior bui lding temperature, the ice storage faci l i ty is constructed part ial lyunderground to help preserve the ice. The ice-maker has been used to produce ice whenthe ambient air temperature is sHghtly above freezing condit ions (3).

Th e ice-mak er concept could have appHcations in othe r pa rts of the world. Th eice-ma ker syste m as used in Ira n consists of several shal low po nd s, 10 to 20 m ete rs wideand several hundred meters long (Figure 5). An adobe wall runs along the south sideof the pond and provides shade during the day. The wall also acts as a wind block atnight , preventing heat gain from convection. Several ponds and walls can be placed in

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12

paral lel . This placement increases the shielding effect from the wind. Water is added toth e pon ds on winter nig hts . Th e po nd w ater is the n cooled by the t ransfer of he at fromthe water to the atmo sphe re throug h the com binat ion of radia t ion , evapo rat ion , andconduct ion processes . However , the water body gains heat through conduct ion f rom theund erly ing soi l which mus t be dissipa ted to the air. T he wate r wil l lose a large a m ou ntof he at th rou gh these processes on clear nigh ts. W he n the night is cool eno ugh an dthese processes are act ive, i ce wiU form (3) . The am bient ai r t em pe rat ure determ ineshow muc h ice will form. On some nights , wa ter is adde d in centime ter increm ents atperio dic intervals durin g the night to increase the am oun t of ice formed. In areas similarin cUmate to Iran, passive cooling systems may be feasible and economical (3) . Thesesystems can only be appHed in cUmates that are similar to Iran.

The C l imate Near t he GroundTo unders tand why pass ive cool ing works , the chmate near the ground must be

exa m ined . W ater has a high specific heat an d thus acts as a hea t reservoir . Specificheat i s the heat requi red per uni t mass to rai se the temperature of the substance by1 degree C elsius (27). T he specific he at of wa ter is 1 calorie per g ra m degre e Ce lsiusand i s the s tandard to which o ther mater ial s are compared . For a dry mineral so i l , th i svalue is about 0.2 calories per gram per degree Celsius even if the specific composit ionof the soils varies (32).

Th e soi ls th at s urro und th e po nd s are im po rta nt in the form ation of ice. Differentsoil type s wiU transfer hea t at different ra tes . Th e optim al soi l would be a po or insu lator,l ike sand. The average specific heat capaci ty of soi l can be taken as the average of i tscon st i tue nts . In o ther words , a bod y of water wi ll change in tem pe ratu re m uch less

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13

th a n the adjacent la nd areas or the ai r bodies for the same weather condi t ions . Th especific he at of ice is inde pen de nt of i ts dens i ty an d th e specific hea t of any air bub ble str ap pe d in th e ice m ay be negle cted. Th e specific high he at of wa ter makes pa ssivecooling possible.

Smal l bodies of water wiQ show greater sensi t iv i ty to tem pe ratu re changes tha nlarger on es. A large bo dy of wa ter stores a m ore hea t . Sm all bodies of wa ter can befurthe r divided into pud dles and pools. Bo th wiU exhibi t some different cha rac terist ic s.A pud dle is shal low a nd has a small surface area w hile a po ol is deeper and wiU exhib i t asma ller dai ly te m pe ra tu re va riat ion s. A pu ddle wiU be great ly effected by shade . Bo thwiU hav e a cooler up pe r surface d ue to he at lost by evap ora tion . Ice wiU form first onsmall sohd objects at the surface of these small bodies and not at the banks. As thesize of the body of water increases, there is less change in the dai ly water temperatures

when compared to the seasonal var iat ions in temperature (14) .Condi t ions conducive to f reezing are determined by ambient ai r t emperature, c loud

cover, and the wind veloci ty. Favorable condit ions include low temperature, clear skies,an d low wind veloci t ies. Since the am bient air tem pe ra tur e is recorde d at a sta nd ar d 2meters above the ground level , the temperatures exper ienced at ground level general lywiU be lower. The refore, i t is possible to have ice when the me asu red air te m pe ra tu reat a s tandard weather s tat ion i s above f reezing .

Propert ies of IceSeawater i s 2 ,700 more t imes abundant then f resh water . The ocean could become

an inex hau st ibl e source of fresh wa ter if the dissolved sohds could be remov ed. Innature, the convers ion of sal twater to f resh water occurs regular ly through evaporat ion

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14

of freezing processes. For many years, people in the Soviet Union have col lected sea icefor use (31).

The propert ies of water and ice are the basis for the use of freezing as a separat ionproce ss . W he n wa ter freezes , i t forms a crystal l a t t ice. The lat t ice const ruc t ion processis select ive a nd wiU not accep t su bst i tute s for the hydrog en or oxygen ions with th eexception that f iuoride ions can be incorporated (25). Ice exists in a variety of forms,but the majori ty of ice is in the polymorphic form, which is shown in Figure 6 (25).Ice i s a hydrogen-bonded compound. Each oxygen atom associates wi th two hydrogenato m s. Bubble-f ree ice i s t rans pare nt and double ref ract ing (2) :

The oxygen atoms occupy the poin ts of a hexagonal la t t ice in which eachoxygen at om is te t rahedraU y coo rdinated wi th four o ther oxygen atom s. Th e0 - 0 d is tance i s 0 .267 nano m eters at 0 degrees Cels ius , which produce s theopen low-densi ty s t ructure shown, (p . 21)

W he n w ater freezes slowly, pure ice can be formed. Th e impu ri t ies in the w ater wil lnot be included in the crystal matrix, unless the water body freezes sol id or experiencesquick-freeze condit ions, which can occur at temperatures less than -20 degrees Celsius(25) .

When seawater freezes, the saHnity of the ice formed averages only 4,000 parts permil l ion. Seaw ater con tains betwee n 30,000 and 35,000 pa rts per miUion of TD S (31 ).For a given temperature, an equil ibrium condit ion exists at which ice and brine of agiven concentrat ion can coexist unt i l the eutect ic point of the solut ion is reached. Theeute ct ic poin t is th e con cen trat ion at which freezing wiU not o ccur or at which sal twiU pre cip i tat e before ice can be formed (12 ). Th erefore, the sal t can be inc orp ora tedin to the mat r ix when temperatures fal l below the eutect ic poin t . The eutect ic poin t forsodium chloride in seawater is -22.9 degrees Celsius (12). The freezing point of water

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is depressed -0.062 degrees Celsius when there are 1,000 parts per miUion of sodiumchloride in a solut ion.

SupercooUng alone does not cause ice to form. The ice must have a si te (an objector pa rt icl e) on which to form and grow. Th e solut ion m ust co ntain some centers forcrystal izat ion . Nucleat ion may occur spontaneously or be induced.

Th e var iat ion of the densi ty of water wi th tem pe ratu re is ano ther prop er ty tha tmakes ice formation by passive cooling possible. Water has i ts maximum specific gravi tyat 4 degrees Celsius. Th e ice formed whe n surface wa ter tem pe ra tur e reaches the freezingpoin t ex pa nd s and floats. There fore, ice can be remov ed from th e surface of the cooHngp o n d .

Ice has another property exhibi ted when i t is warmer than -15 degrees Celsius. Thecon tam inan ts t ra pp ed in the crystal l ine s t ru cture of the ice wi ll s lowly migrate downw ard

be cau se of gravi ty. Th e comb ined effects of these prope rt ies ma ke ice form ation bypassive cooHng a possibiUty.

Sampl ing IceThe procedure for ice sampling, col lect ion, and analysis is not exact . Typical ly, ice

wiU vary ( in a chem ical ly) significant m aim er in the vert ical direct ion but not in t hehorizontal direct ion (7). Cowgil l adds that there is ht t le data avai lable on the chemicalcom posi t ion of ice f rom lakes and ponds. The chem ical comp osi t ion includes e nt ra ppe ddus t and p l ank ton (7 ) .

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16Ice Formation

W hen th e air tem pe rat ure d rops , the body of water wiU be cooled. Th e coldestwater will sink until the whole pond is 4 degrees Celsius. Then, as the top water layercontinues to cool, it becomes less dense. Therefore, the warmest lake water will be inthe underlying layer with a maximum temperature of 4 degrees Celsius (18).

The first ice to form in a calm body of water (water velocities average less than0.5 m ete rs p er second) consists of spicules or plate-Uke crys tals. Frazil ice (disk-Ukeparticles of ice less 1 millimeter in d iame ter) form in faster flowing bodies of water. Th esmall crystals th at form first, grow into a network of dentries th at freeze together. Th econtinuous cover that is formed is called skim ice. When the ice sheet becomes stable,it continues to thicken downward (2). If the air temperature is cold enough, the latentheat of crystallization will be conducted upward through the ice and transferred to theair. Th e process of crystal growth downward in the water is called congelation, an dthe ice that is formed is called congealed ice. This ice is usually made up of column-shaped crystals with a vertical orientation. In a moving body of water, the ice needs anobstruction to coalesce upon before it can form (2).

Freezing versus EvaporationTh e freezing p oint of water is essentially indep endent of pressure, whereas the boihng

point of water is dependent on pressure. Also, the heat absorbed by vaporization is 7.5times the heat which is liberated at crystalization. This fact suggests that the energyrequired for each p oun d of vapor formed will produc e 7.5 pounds of ice. This concept wasseemingly illustrated in vacuum-freezing and vapor-compression devices (5). However,Dodge shows the energy required for freezing is not directly related to the latent heat

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(10) . In a thermodynamic energy balance, the work used in evaporat ion processesrequires 7.4 kilowatts per hour per 1,000 gallons while the work required in freezing is6.3 ki lowatts per hour per 1,000 gal lons for an ideaUzed si tuat ion. The small differenceis energy input is insignificant when compared to the large amounts of work needed tocom pen sate for the i rreversibif it ies of the freezing proce ss (10). Snyder conc urs (31) :

It is sometim es s tate d erroneou sly th at freezing is inhe rently m ore efficientthan dist i l lat ion because only 80 calories must be removed to freeze a gramof water , whereas 540 calories must be added to evaporate a gram. If noneof the energy n eede d for freezing or eva pora t ion were recovered, freezingwould indeed be cheaper , but carefu l thermodynamic design can recovermu ch of the energy inp ut ( into dist i l lat ion). Con seque ntly in ac tual pra ct icethe cycle efficiency is about the same whether desaHnation is performed byeva por at ion or freezing, (p. 44)

Freezing processes have problems that are not exper ienced in evaporat ion processes .For exam ple, the format ion of ice crystal s ma y som et imes ent rap b r ine. Ice crystal smust be large enough to be removed from the water , yet small enough so not to entraptoo much br ine. Figure 7 shows that th e pures t ice formed und er na tur al c ondi t ions ,in the A rct ic Sea in a top 10-centim eter layer of ice, will occur 1 cen time ter below thesurface (31). Also, the sepa rat ion of ice from wa ter is diff icult . Refrigerat ion system sare therm od yn am ica l ly inefficient and the cost of rem oving hea t from a unit volum e ofwater is high compared to the cost of adding heat (17).

Freeze-Crystahzat ion Processes for Pol lu tant RemovalTh ere are m an y indu stries utf lizing the of freeze -crystahz at ion processes for remov al

of con tam inan ts . Freeze -crystahzat ion i s a physical process tha t i s based on the pr inciple tha t ice crystals formed thro ug h freezing wiU essential ly con tain pur e wate r (6).Th e resu l tant ice can be removed, washed, and mel ted . Conversely , the con cen t rated

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brine may be recycled for reuse in some industries. Two different industrial freeze technologies have been developed in the 1980 's (11) ; the Vacuum Freezing Mul t ip le PhaseTrans fo rmat ion (V FM PT ) and the Ind i rec t F reeze Concen t ra t i on ( IFC ) p rocess . Theseprocesses can operate in s i tuat ions where TDS concent rat ions range f rom low to h ighand they are easy to scale-up f rom th e bench-scale tes t to the pro to ty pe un i t . Th e equipm ent used in thes e processes is relat ively insensi t ive to fouhng. Th e equipm ent costsless th an e vap ora t ion eq uip m en t. Since the laten t hea t of fusion is less th an the late ntheat of vapor izat ion , f reeze-concent rat ion uses less energy than evaporat ive processes .Also, the inf luent s t ream s to the system s do not typical ly requi re pre t rea tm en t . Theseadvantages al so decrease the operat ion and maintenance costs . Indiv idual systems havebee n tai lored to req uire less energy but freezing processes stiU rem ain ene rgy intensiveand expensive (6) .

V F M P T P r o c e s sTh e V F M P T (by Calyxes) process u t ihzes vacuum freezing . Both the ice and th e

vapor formed a t the t r iple poin t axe use d. Th e vapor provides a m ean s for m elt ingthe washe d ice crystals (6) . Th e V F M P T process is effective, reha ble, and efficient.This process i s achieved by a Sub-Tr ip le Poin t Vapor Process ing Uni t (STPVPU) andan In tegrated Crystal -Washer /Mel ter ( ICWM). These two devices help the process byhqui fy ing the vapor in the STPVPU and then mel t ing and washing the crystal s in theIC W M (6) . V F M P T claims to have the f irst comm ercially avai lable f reeze -crystahzat ionsystem. This process has advantages over both reverse osmosis (RO) and evaporat ionprocesses . V F M P T can conce nt rate so lu tions to thei r eu tect ic poin t whereas RO ca nonly conce nt rate u p to 7 or 8 percen t of the so lu t ions eutect ic poin t . This sy stem h as

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a longer Ufe tha n R O sy stem s and is not as sensi t ive to fouhng or scale form ation. Itcan handle ei ther acidic or basic solut ions and also solut ions containing oxidizing agentswhile RO can not . Also, this system is not as sensi t ive to corrosion problems as RO orevapora t i on equ ipmen t .

Th e V F M P T process is uniqu e. The pressure is decreased in the react ion c ham berso that the ice wil l subhmate or go direct ly from a sohd to a vapor at a lower-than-bo ihn g-p oin t - tem pe ratu re. Figure 8 shows the equipment used in th i s process whi leFigure 9 shows a phase diagram which explauis the operat ion of the devices (6).

IFC ProcessTh e IF C process is an indirec t freeze-concen trat ion (IFC ) system (by CB I). In an

indire ct freeze proces s, a refrigerant in the freeze-exchanger absorbs hea t thro ug h ametaUic barrier from a f iowing brine solut ion while coohng and part ial ly freezing thebrine. In the IFC system, ice crystals are formed in the bulk of the hquid without growthon the heat-r em ova l surface (11). Th e system provides an energy-efficient crysta lhzerand provides for a continuous working process.

Figure 10 shows the IFC process, which has a freeze-exchanger that produces icecrystal s ; a wash column for sepa rat ing and w ashing the crystal s ; a prec ip i tate separat ion device for growing and se par at ing prec ipi ta te crystals; and a refrigerat ion system .T he low te m pe ra tu re m inimizes metafl ic corrosion and allows the use of favorable cons t ruc t ion mate r ial s . Th e low tem pe ratu re al so helps enhance precip i tat ion because mostsubstan ces are less so luble at lower tem pe ratu res . No chemicals are added so the to ta lvolume of waste for ul t imate disposal is minimized. The system is adaptable to differentfeed conc en trat io ns a nd com posit ions since i t is a physical proce ss. Th e refrigerant is

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not contaminated by the waste because a closed indi rect sys tem is used . No ai r pol lu t ionis pro du ce d. Last ly , pre t rea tm en t i s not requi red (11) .

A p p h c a t i o n sFreez e-crysta hzat ion has been used in a var iety of indust r ies . Some of these in

dust r ies include mining , orange ju ice ma nufac turuig , p ickhng, indu st r ial waste concent rat ion , seawater desal inat ion , tex t i le manufacturers , chemical and alhed productsmanufac tu r ing , f ab r i ca t ed meta l p roduct ion , mach inery manufac tu r ing , e l ec t r i ca l manufac tur ing , pr odu ct ion of me asur ing , analyzing and controUing equipm ent , and in u t ih tyand cogenerat ion faciht ies (11).

S u m m a r yTh e combina t ion of shade, the tem pe ratu re regime near the ground , and winter

condi t ions ma ke passive ice format ion a process of the fu ture. The tem per atur es inshad ed areas wiU be several degrees cooler than the tem pera tures recorded in the sunnyloca t ions . Shade prevents a por t ion of the sun 's radiat ion f rom reaching the w ater .Bi rge repor ted t ha t th e pr ima ry factor in mel t ing i s the impac t of radia nt he at on theice (18). A decrease in the radiat ion wil l help prevent ice melt and keep water withoutan ice sheet cooler .

The temperature at ground level wi l l add to th i s ef fect . Temperature measurementswiU be cooler tha n the off icial recorded t em pe ratu re s ince the am bient ai r t em pe rat ureis record ed at a s tan da rd 2 m eters above the groun d level. In the winter , ground- levelair te m pe ra tu re s wiU be cooler . T he benefi ts offered by sha de and lower tem pe rat ur es

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show th a t th e freezing of wa ter is possible even whe n the official reco rded te m pe ra tu reis above freezing and thus enhance the use of passive coohng ice-makers.

Locat ing the ice-maker system away from the ci ty environment wil l also increase theamount of ice produced. In the ci ty, the houses, large office buildings, and factories forman i r regular surface that s lows ai r movements . These s t ructures wi l l absorb more heatdur ing th e day th an th e features found in count ry . At n ight , th is heat wiU be retain edfor a longer per iod th an i t would be in a cou ntry area . Ad de d to the surface i rreg ulari t iesi s an increase in ai rborne paxt iculates , which al so retain heat . This combinat ion resul t sin the form ation of a he at island th at conc entrate s heat in the center of the ci ty. Byoptimizing the cooler condit ions offered by shaded locat ions, ground level condit ions,and rural condi t ions , the ice-maker system operat ions are enhanced.

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23

Research P l an and ProceduresOutdoor Tes t s

The p lan was to s imulate and tes t the procedures used in the Iranian pass ive ice-m ake r . W ater w i th d if ferent c once nt rat ions of Na Cl was p laced in shallow insulated p ansin a shaded outdoor locat ion . A 7-day hyg rothe rm ogra ph, a device tha t cont inuouslyreco rds bo th humid i ty and t empera tu re , was used t o mon i to r t he t empera tu re o f t heshaded locat ion. The ice was to be harvested periodical ly and the inches of ice formeddur ing th e in terval were recorded. Ne xt , the ice would be washed to remove res idualbr ine . Th en , the ice would be me l ted at room tem pe ratu re and the me l ted volumerecorded . Samples of the ice col lected would be analyzed wi th an ion c hrom atogra ph(IC) to determine the concent rat ion of sodium contained in the ice.

The concentrat ions of the NaCl to be used were determined chemical ly. Since sodiumweighs 22.99 miUigrams per mole and chlorine weighs 35.45 miUigrams per mole, NaClweighs 58.44 milhgrams per mole. Therefore, sodium chloride is 39.34 percent sodium.The milhgrams per hter of sodium in solut ion were determined by dividing the weight ofsodium chlor ide in the so lu t ion by the percent of sodium in the compound (15) . Table1 in the Appendix shows the concent rat ions used in the exper iment .

The var iables in the exper iments conducted outdoors included temperature, humidi ty , wind, t ime , volume, and so lu t ion conc ent rat ion . Te m pera ture and t ime weremoni tored wi th a hygrothermograph. The NaCl concent rat ion was to be a cont ro l factor . Due to evaporat ion , precip i tat ion , and o ther weather related incidents , the so lu teconcentrat ion probably varied. The solvent volume was selected as a control , but f locksof bird s dran k the less co nce ntra ted sa m ples. The refore, the controls were not able tobe cont roUed.

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Contro l led Condi t ions TestsFreezing exper iments were conducted ins ide an upr ight f reezer uni t . Insulated cups

were placed inside the freezer and fiUed with the test solut ion. The temperature in thefreezer was m ainta ined b etwe en 0 and 25 degrees Fahre nhei t . A hyg rotherm ogra ph wasused to moni tor the temperature in the f reezer and the f reezmg t ime in terval . At theend of th e freezing t im e pe rio d, the ice which had formed was remove d and was hed. Th evolum es of ice an d unfrozen solut ion from each cup were m eas ured . An IC was used tomeasure the sodium concent rat ion in the mel ted ice and in the br ine so lu t ions coUectedat the en d of the freezing pe riod . Th e am ou nt of ice lost during the harve st an d w ashingphase could be found using a mass balance on the ini t ial and final volumes of the testsolut io ns. Th e m ass balan ce also require d values for the concen trat ions of sodiu m inthe ice forme d a nd in the residual brine. T he amo unt of usab le ice com pared to th eto ta l am ou nt ice formed w as also dete rm ined by differences in weight . Th e resul tsobtained f rom th is phase would be used for compar ison against the resul t s obtainedunder ambient weather condi t ions .

After the prel iminary f reezer exper iments , i t was determined that addi t ional factorsneeded to be controUed to provide stat ist icaUy vahd resul ts. Each bucket used in thetes ts was f iUed w ith 33 po un ds of sif ted san d. Th e t ime in the freezer w as a ccu ratelymo ni tore d so tha t eac h ru n was 7 hours long. Th e exper imen ts were swi tched from afrost-free freezer uni t which varied over a 30-degree Fahrenheit temperature range to anon-frost-free freezer uni t w hich exh ibi ted a lower rang e of te m pe ra tu re varia t ion (12.6degrees Fahrenhei t ) .

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Each tes t run concurrent ly used so lu t ions at the three tes t concent rat ions in orderthat a representat ive so lu te concent rat ion would exper ience the same condi t ions in eachru n. Dis tiUed water was used to m ix the so lu t ions used the exp er im ents . Th e infiuentwa ter was f irst t re at ed by reverse osm osis. Th en, the wa ter was sent thr ou gh th eBarnstead st iU which is used for dist iUation in the environmental lab. The water was ofa good quali ty and checks were run for verif icat ion. Only trace amounts of sodium, onth e order of 1 pa rt pe r imlho n, were found in the effluent w ater. Ea ch of the thre e cupsfiUed with 500 miUUiters of one of the test solutions. The first cup had 500 miUigramsper h ter of sodium; the second had 1,500; and the th i rd had 4 ,500. The cups containmgsolut ion w ere place d in cups in the bu cke ts, surroimded by sa nd, a nd frozen for 7 ho urs .The cups in the bucket were used to keep the amount of sand in each bucket consistentfor each run . Figu re 11 depicts the configurat ion of the test un i t . Ice formed by th eend of the test period was removed from each solut ion cup and weighed before and afterwash ing .

The variables of interest in each test run were both the f inal sal t concentrat ions inth e ice formed an d in the unfrozen solut ion left in th e test c ups. Sam ples of melte dice and res idual br ine were tes ted by an IC to determine the sodium concent rat ion inthe samples. The influent concentrat ion was controUed by applying the protocol set insolu t ion pre pa rat io n (Table 1 in the A ppe ndix ) .

Test FacihtyOutdoor Test Facih ty

The roof of the Texas Tech Universi ty CivU Engineering BuUding was the si te forthe o utdo or ph ase of the exp erun ents . Shade was provided by a wooden wal l set up

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on the south s ide of the exper imental area. The pans in which the tes t so lu t ions werep l aced were i n su l a t ed wi th pack ing mater i a l and ba t tu ig .

The ice removed from the test vessel was taken to the lab where i t was washedusing a s t raine r and th en m el ted . Th e volume of me l ted ice was me asured in volum etr icbeaker s .

ControUed Test FaciUtyThis phase was conducted using an upr ight f reezer uni t located in the Envi ronmental

Science La bo rato ry in the CivU Engineer ing De par tm ent at Texas Tech Univers i ty . Th ewashing and measuring of the ice ut ihzed the same procedures and facUit ies as theoutdoor phase. The tes t so lu t ions were prepared the same maimer .

Th e tes t so lu t ions used in the expe r iments were prepa red in the lab by adding sodiumchloride in specified am ou nts to distUled wa ter. Co nce ntrat io ns were dete rm ine d byweighing the sal t , used for each of the three test concentrat ions.

Ion Chromatograph. The IC i s an ins t rument that combines conduct iv i ty detect ionan d ionic sepa rat io n abiUties. A fil tered 100-m icrohter sam ple of hqu id is injected intothe IC and i s pumped through ion exchange res ins where the cat ions are sepaxated .Vaxious ions have paxticulax affinities for the resin and the ions in the test solution canbe identif ied by the rate at which they migrate through the IC column. An ion's aff ini tyis largely a funct ion of i ts size and valence. After migrat ion, the ions axe neutraUzedand sample ions are conver ted to thek corresponding s t rong base. The alkahni ty i s thenmeasured by a conductance ceU. The chromatographs formed by the sample const i tuentsare ou tpu t by a pr in te r on grap h pa pe r . Th e pea k heights are the n me asure d andcal ibra ted . Ca hb rat io n curves formed f rom sta nda rds run throu gh the IC are used to

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int er pr et s am ple res ul ts. Typica l ly, f ive different st an da rds w ith kno wn values of thecat ions of in teres t are used .

Data AnalysisD a ta was coUected ui different ph ase s. Th e first phas e mvolved an ou tdo or ex

periment and was used to help develop a plan for scal ing-up the passive cooling-pondconc ept . Th e second phas e, which was used to develop the proced ure for the f inal phas e,involved indoo r test in g in a freezer. Th e third pha se involved a controUed freezer experim en t . T he resul ts of this pha se were used to dete rm ine the qu ah ty of effluent pre dic tedfor the th ree different con cen trat ions of Na Cl in solut ion.

Ou tdoor Tes t PhaseThis phase involved tes t s conducted outs ide dur ing the months of February and

M arch 1989. M any problem s were exper ienced in th i s pha se. Equ ipm ent had to bedeve loped a nd an outdoo r locat ion for exp erim ent found. Th e roof of the Texas TechCivU Engineering Building was chosen because i t was close to the lab and because accessto the si te was controUed. Peop le and four-legged anim als were denied access to th eexp er im enta l un i t s . However , b i rds were a problem . They dran k water from the co nt ro luni t and f rom some of the uni t s that contained the lower NaCl concent rat ions .

Some problems were ant icipated . Pass ive cool ing i s whoUy dependent on the localchmat ic condi t ions and the f reezing condi t ions might be sporadic in occurrence. Therewas the logis t ical problem of t ranspor t ing the water to the roof and the ice to thelabo rator y . People and car t s were sohci ted to help move bo th the water and ice. Toduphca t e t he I r an i an - type coohng pond method be ing inves t i ga t ed , shade had to be

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provided, for th i s phase. The shade was provided by modi fy ing p lywood f rames foundon the roof which were lef t f rom a previous exper iment . The temperature in the shadeon the roof was moni tored cont inuaUy wi th a hygrothermograph.

Operat ional problems developed dur ing th is phase. The tes t so lu t ions f roze to sohdice in the expe r im enta l un i t s . An ext re me cold per iod was exper ienced and the tes tsolut ion in aU the u nit s a nd th e co ntrol froze sohd in a few hours t im e.

Another problem was that the NaCl tes t concent rat ions were approaching seawaterlevels. In the smaU volumes, there was l imited reservoir space in the experimental uni tfor these soUds to migrate to the brine supply when ice crystals formed. In the extremetemperatures experienced, the smaU volumes of the test solut ions froze too quickly foraccu ra t e , r epea t ab l e r esu l t s .

Houses, laxge office buildings, factories, and landscaping vegetat ion in the ci ty forman irregulax surface that slows air movement. Structures and paved surfaces wiU absorbmo re heat dur ing the day tha n land mass in the count ry . At n ight , th i s heat wiU beret ain ed for a longer perio d tha n in a ru ra l area . A dde d to the surface i rregulari t ies arethe increases in ai rborne pa r t icu la tes in the ci ty tha t a l so retain he at . The resul t is theform ation of a he at island which con cen trates he at in the center of the ci ty. Add it ionaU y,the ai r t emperature exper ienced at ground level dur ing the n ight hours i s lower thanthe layers of air above i t . Less ice could have been formed because the experiment waslocated on a roof in the center of Lubbock, Texas . The tes t uni t s may have gained heatf rom the bui ld ing and the ci ty itself.

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ControUed Test PhaseT he test un i t was a buck et in which three cups were place d. Th e cups were the n

ins ula ted by placing soi l in the voids betw een th em . Th e cups were fiUed with 500m iUih ters of solu tion a nd plac ed in a freezer un til sufficient ice form ed. A sketch of th etes t uni t i s shown in Figure 11.

Var iables in th i s phase included insulat ion , temperature, t ime, and concent rat ion .Th e so i l used as insulat ion for the cups was not uni form and be t ter insu lat ion may havebee n offered to one pa r t of the container when com pared to another a rea. The am oun tof soi l used also varied shghtly with each run. The freezer ini t ial ly used was frost-free.Therefore, th e tem pe ratu re var ied mo re tha n 20 degrees Fahren hei t dur ing the tes tpe riod . Th e t ime the solut ions were left inside the freezer had to be varied in orde rto get enoug h ice for the test run . Th ree different con cen trat ions of Na Cl were used .Ea ch run used three sam ples of the same conce nt rat ion in the tes t uni t . The f reezercondi t ions exper ienced by one run could vary for another run which make compar isonsbetween different runs difficult.

Revised Cont roUed Test PhaseModificat ions to the previous tests included the provision of a more uniform insula

t ion, a different freezer, and more precise procedures. The sand used for insiUation wassieved an d weighed before plac em ent in the test un i t . T he freezer uni t used was notfrost-free and did not have as high a cychc temperature variat ion as the unit used in thesecond p ha se . Th e tests were ru n for a specified t ime period (7 hou rs) which aUowedsufficient ice to form for the three test NaCl concentrat ions.

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Stephan ' s Equat ion Analys i sSte ph an 's equ at ion was used to es t im ate how much ice would form under th e d if ferent

cond i t ions of the exp er ime nt and to pred ict how much ice would form in a typical w interseason in Lubbock, Texas . By input t ing the constants in to Stephan 's equat ion i t canbe simphfied to (2):

h = 0.035S-^a (3.1)wh ere h is the thick ness of the ice in m ete rs, S is the s um m atio n of the nu m ber ofdeg ree-h ours of freezing, and a is a correct ion factor less th an 1 (2) . T his equ atio n wiUbe apphed to both the outdoor and cont roUed tes t phases . Al though, the equat ion onlydesc ribes ice grow th after ice form ation , i ts use wiU help describe how mu ch ice can b eformed if a conservat ive value is used for a. The l imi tat ions of the Ste pha n equa t ionwere p resen t ed i n Chap ter 2 .

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C H A P T E R 4R E S U L T S

This c hapte r is organized in to three d if ferent sec t ions -da ta pres entat io n of the icemaking tes t s ; i ce development us ing Stephan 's equat ion for analysis ; and an economicanalysis of several ice-making techniques. The resul ts of the ice-making techniques wiUbe discussed in the foUowing sect ions.

D a t a P r e s en t a t i o nOutdoor Tes t Phase

Tables 2, 3, and 4 prese nt the resu l ts obtain ed in this ph ase . Table 2 shows thenigh ts which were below freezing durin g the 1988-89 winte r per iod. Ea ch da te is followed by the average temperature below f reezing (ATBF) in degrees Fahrenhei t and i t sdurat ion . This data was obtained f rom NOAA records for the winter 1988-89 per iod inLub bock , Tex as . Th e AT BF along wi th the dura t ion of f reezing w eather for each daywas used to calculate t he de gree-h ours of freezing e xperience d in the 1988-89 w interper io d for Lu bboc k. This value wiU be used in Step han 's equa t ion . Th e te m pe rat ur eexper ienced in an ins t rum ent shel ter 2 m eters off the ground m ay be shght ly w arme r

th an te m pe ratu res at ground level, so the value of ice predicte d by Steph an 's equa t ionwiU be conservat ive.

Table 3 shows the days on which dat a coUect ion was at te m pte d . Days in the t imeinterval which are not hs ted between these dates are per iods in which no data wascollected because ice was not formed on the building roof. Some of the days shown inTable 2 did not have the cold persist long enough for ice to form in the sal ine solut ions.

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The resul t s f rom the outdoor tes t s shown in Table 4 are h ighly var iable . This factmay be due in par t to the var iat ion in the ice coUect ion procedure used on some daysduring the study interval shown in Table 4. The ice in the comers of the pans was soth ick tha t th e the ice could not be removed wi th a ham m er . Therefore, the ice in themiddle of the test uni t was coUected. By the end of the winter , the ice in the comers ofthe tes t uni t had buUt up s igni f icant ly . Dur ing mUder temperature per iods , the cornerice was coUected and mixed with the ice coUected from the center . The corner ice couldhave been of bet ter qual i ty than the new ice formed at the center of the unit since theNa Cl t r ap pe d in the ice in ters t ices wiU m igrate s lowly downw ard due to gravi ty .

Another factor is the possibUity that as the experiment continued, a residual bui ldup of sal t formed in the containers. In the rush to get off the roof and out of the cold,the pans were not washed thoroughly after each run which could have added to the sal tbuUdup. Var iat ions in temperature could al so cause the resul t s to vary . A colder daywiU freeze the w ater m ore quickly and thu s entr ap m ore dissolved sohds .

Cont roUed Test PhaseThis phase of the exper iment was used as a prehminary tes t procedure to design

the final exp er im ent . Th e m ajor problem s exper ienced in th i s pa r t of the expe r imen t

was the identif icat ion of a large number of variables which needed to be controUed bothduring the freezing interval and in the analysis phase. Evidence of the high variabihtyis shown in the Table 5 . The lower NaCl concent rat ions were not impacted by thesevar iables in the tes t procedure s as mu ch as the h igher concent rat ions . Th e s ta nd arddeviat ion for the 4500 milhgrams per hter solut ion is over 50 percent of the mean.Therefore, i t was necessary to develop a means to control these variables, as discussed

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in Ch ap ter 3 . Th e revised proced ures were used in order to ma ke the resul t s vahd andwor thwhi l e .

Revised Cont roUed Test PhaseTh is was the fmal labora tory p hase of the expe rhne nt . Tables 6, 7, and 8 show the

resul ts from the 500 miUigram per hter , 1,500 miUigram per hter , and 4,500 mUligrampe r h ter tes t conc ent rat ions of Na Cl , respectively . Each table al so shows the m ea n,st an da rd de viat ion, m ax im um , m inim um , and coefficient of varia t ion for the differentco nc en tra t ion s. Th e grap hs of the resul ts axe shown in Figure s 12, 13, and 14. Th egraphs show NaCl concent rat ion in the ice and in the res idual br ine so lu t ion .

The coefficients of variabihty displayed in Tables 6, 7, and 8 show that the resul ts aregood stat ist icaUy and that the modificat ions made in the test protocol were beneficial .The resul ts varied shghtly because the freezer exhibi ted a 12.6-degree Fahrenheit rangedur in g i t s ope rat ion al cycle. Th e cycle per iod las ted approxima tely 30 m inute s . An othe rcause of vaxiat ion may have been the sand used for insulat ion. The sand was sieved andweighed in each bucket , but i t was not homogeneous. Vaxiat ions in the sand mixturef rom one tes t uni t to the preparat ion of another al so cont r ibuted to the var iabih ty .

T he resul t s f rom the 500 miUigrams per h ter run had three o uthe rs . Th e outUers were

a resul t of poo r labora tory p roced ures . Th e samples were s tored over a weekend and notcovered sufficient ly, aUowing the NaCl concentrat ions to increase due to evaporat ion.Th e ou thers were not used to calculate the resul t s f rom th is run . Th e outUers tes t showedtha t t he d i scarded runs had NaCl concen t ra t i ons t ha t were approx imate ly g rea t e r t hantwo s tandaxd deviat ions above the mean.

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The 1,500 and 4,500 miUigrams per hter runs exhibi ted lower coefficients of variabU-i ty than the 500 miUigram per h ter . These numbers show that the runs are repeatableand Stat i s t icaUy vahd. When the three mns are graphed together a curve (Figure 15)can be drawn showing the removal rate for the condit ions used. More runs would helpvahdate this curve. However, i t does show an interest ing possibUity. The equation ofth e curve h as a correla t ion coefficient of 1 for a third-o rder p olyn om ial equa tion of thecurve (A value of 1 is opt im al) .

When seawater freezes, the ice has an average of 4,000 miUigrams per hter of sahnity,while the water i tself contains 33,000 miUigrams per hter (31). Seawater frozen naturaUyin the arct ic can be added as shown in Figure 16. The correlat ion coefficient is 1 fora th i rd-order polynomial equat ion . Fur ther s tudies in th i s area could help vahdate anequation for the concentrat ion of dissolved sohds in ice when natural , pond-hke freezingoccur s .

The resul ts show that an effluent of significant bet ter quahty can be obtained inice form ed un de r pon d-h ke freezing con dit ions . Dissolved sohds can be t ra pp ed in theinte rsti ce s of th e frazil ice as it forms a she et. The refore, a pass ive freezing sy ste mop era ted to produ ce ice wUl be produ ct ive and feas ib le if the system can be ope ratedat a low cost .

Calculat ions showed that an average of 70.4 miUihters of ice was lost in the washings t ep . Th is value was app rox im ately 50 perc ent of the ice formed. Since the ice is notas pure as i t i s in the energy in tensive, indust r ial methods , washing does not have asignificant value in this process.

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Stephan ' s Equat ion Analys i sUsing the s impl i f icat ion of Step han 's equat ion pres ented in Cha pter 3 and the degree-

days of freezing for the winter of 1988-89 in Lubbock, Texas, the amoimt of ice expectedto form is 2.22 inches over a nig ht. Th is value was calcu late d for an S of 7.55 deg reeho ur s, wh ere degrees are in Celsius un its . Th e value of S is for an av erage perio d of 90nights of freezing in Lubbock, Texas. A value of 0.58 was used for a. This value waschosen to malce the economic est imate conservat ive. The value of 2.22 inches is used inthe economic analysis to determine if the facihty is reasonable in cost .

Th e tem pe rat ure used to calculate the am ount of ice th at was expected to form, wastake n f rom NO AA records . This tem pe ratu re was recorded in an ins t ru m ent shel terat an exposed locat ion (sunny dur ing clear-dayt ime condi t ions) and above the ground.The shade provided for the passive cooling ice-maker system would lower the effect ivetem pe ra tur e exper ienced by the pond s dur ing dayt im e hou rs . The d if ference betweenthe r eco rded t empera tu re and the ac tua l t empera tu re near t he g round wou ld a l so causelower tem pe ratu res to be exper ienced by the ponds . Therefore, more ice would formand th is es t imate us ing Stephan 's equat ion i s conservat ive.

When Stephan 's equat ion was apphed to the cont roUed condi t ion tes t s conducted ina freezer u ni t , 3 inches of ice were expec ted to form. In actuaUty, only an average 0.75inches formed. Th e value of S calcu lated from an average tem pe ra tur e in the freezerim it of -15.3 degrees C elsius and a t ime of 7 ho urs , was found to be 4.46 deg ree-da ys.Th ere for e, t he value of a w ould be 0.25 for the freezer un it. T he value of a is lowbecause Stephan's equation only considers heat lost by conduction after the ice sheetis form ed. A no the r factor th at could have affected the value was th at t he soU used forinsulat ion was at room temperature when i t was p laced in the f reezer , and therefore

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exe r ted a coohng capaci ty . Th e smaU diam eter of the freezing uni t s (cups) an d thehigher temperature of the freezer waUs compared to the heat sink of the sky could havealso reduced the value of a.

Economic AnalysisA sche m atic of a pro pos ed passive cooling po nd plan t is shown m Figu re 17. A

prehminary es t imate was used to evaluate the capi tal and operat ional costs in orderto compare th i s method to the energy-mtensive methods exhib i ted by the IFC andV F M P T system s. By com par ing the costs of the three d if ferent system s, the value ofthe pass ive coohng system as a m eth od of pre t rea tm ent can be es t imate d . Table 9 showsthe economics of operat ion .

The design provides a 3.5-foot water depth in the pond. The volume of water inputcan be modi fied to opt imize the a mo unt of ice formed by apply ing Ste phan 's equat ionand using the local weather forecast for the next 24-hour period. Using this method forthe 1988-89 winter period, the average amount of ice formed in Lubbock is 2.22 inchesper night . To prevent the water from freezing sohd and to form ice of a good quahty, adepth of three t imes the depth of ice formed should be used. The 4-foot deep pond wiUprovide for more severe weather .

The design shows that two sides of the concrete pond are sloped. The sloped sidesprov ide a n access for vehicles which wiU remove th e ice. In the m orn ing, the rem ainin gbrin e wiU be d rain ed . Th e ice sheet wiU be broke n an d the ice wiU be mo ved by at ra cto r equippe d wi th a b lade at tac hm ent to the me l t ing pon d. Gr i t p icked up by theice during formation and removal can be set t led out later in a clarif ier .

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The capitol cost est imated for the passive coohng pond system includes cost of excavat ion; concrete form-work , pour ing , cur ing , f in i sh ing , and mater ial s ; a p ipe networksystem wi th two low capaci ty pumps per pond, and a smaU t ractor wi th a p low at tac hm en t . As shown in Figure 17 , there is no shade provided for the mel t ing po nd ,so m elt in g wiU be enc oura ged by rad iat io n. Therefore, ene rgy wiU not be need ed formelt ing or freezing processes.

Th e waste water to be t rea ted can be s tored in pond s unt i l processed . Th e onlyenerg y re quir ed wUl be th e fuel for th e ice-removal vehicle and th e electr ici ty for thewa ter pum ps . Th e power used by the pum ps can be minimized by u t ihzing a smaUslope in th e po nd s. Th is slope wiU faciUtate th e drainag e of the brine rem ainin g afterice form ation . Oth er op era t ion al costs include the wage of the ice-remov al vehicle driverand vehicle maintenance costs. This economic analysis shows the cost to add the passivecool ing po nd system to an exis t ing facih ty as a pre t rea tm ent m etho d to remove d issolvedsohds. Therefore, human factors for system operat ion needed are al ready in p lace andwere not considered in the cost analysis.

The final cost per gaUon produced is based on 90 days of freezing weather and anice production amount of 50,000 gaUons per night . These values are based on data forLubbock, Texas. Lubbock experiences an average of approximately 90 days of freezingwe athe r per year according to NO AA records . Th e surface area requi red to produ ce50,000 gaUons of ice (based on an average 2.22 inches forming per night) may be providedby 12 po nd s w hich axe 10 feet wide an d 100 feet lon g.

Th e two freeze technologies exam ined axe the IFC system and the V F M P T system .Ta bles 10 an d 11 show the cost analyses for these processes. T he d at a shown in thesetables is the only data which was avaUable on the costs (6, 11).

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The cost of the IFC system is based on 8000 hours of operat ion per year and a f lowof 300-500 gaUons per minute. The IFC system produces water at a cost of 2 cents pergaUon base d on 1987 doUar values . Th e V F M P T system produces 50 ,000 gaUons perday and the cost per gaUon is 0.31 cents adjusted to 1987 values. The passive coohngice-make r is com parab le to the VF M P T in cost and prod uct ion . Th e cost per gaUonis 0.37 cents based on 1987 doUars for the same water prod uc tion qu anti ty . Th e IF Csyste m produce s ten t imes the am oun t of the o ther systems and costs almost ten t imesmore per gaUon.

T he pa ssive coo hng ice-mak er sy stem wiU not b e as influenced by rising energy costsas the other two systems, since the only energy input is for the ice-removal vehiclean d th e pum ps . T he costs of th e syste m wiU decrease as the sy stem is move d to higherlat i tud es or al t i tudes . More ice can be prod uced na turaUy for the same costs . Therefore,the pass ive coohng system could be a reasonable pret reatment system for the removalof dissolved sohds.

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C H A P T E R 5C O N C L U S I O N

The conclusions of this study axe as fol lows:1. The data gathexed fox the thiee diffexent test concentxat ions show that

impxoved watex quahty can be obtained from ice pxoduced in passive-freezingsystems. In no case did the ice that foxmed contain moxe than 50 pexcentof the ini t ial sohds.

2 . Moxe ice would foxm in axeas highex in lat i tude ox al t i tude thanLubbock , Texas .

3. The quahty of the xesul tant ice is a funct ion of the ini t ial solut ionquah ty .

4. Washing the ice pxoduced outdooxs is nei thex pxact ical nox economical .5. The passive cooling ice-makex system could be an economical method fox

xemoving dissolved sohds from watex in Lubbock, Texas, if enexgy pxices xise.

R eco m m en d a t i o n sThe xecommendations developed in this study axe as foUows:

1. Study the xelat ionship between xecoxded tempexatuxe and tempexatuxein shaded locat ions at gxound level to impxove the design.

2. Moxe xeseaxch is needed in the outdoox phase to combine empiricaldata wi th Stephan 's equat ion to opt imize the ice-making process .

3. Study the use of metal frames to potent iaUy increase heat loss anddetermine the opt imal number of condensat ion nuclei to increase the amount

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of ice formed.4. Study ice forming effects of variations in dissolved sohds concentration,

especially in the range of 1,000 to 30,000 miUigrams per Uter.

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B I B L I O G R A P H Y

1. A nd erso n , Bru ce and M alcom WeUs. Pass ive So lar Energ y : Th e Hom eown -er^s Guide to Natura l Heat ing and CooHng. Andover , Massachuse t t s : Br ick-h o u se Pu b H sh in g Co . , 19 8 1 .

2 . A sht on , George D. Ed . River and Lake Ice Enginee r ing . L i t t le ton , Colo r ad o : W ate r Reso u rces Pu b l i ca t io n s , 19 8 6 .

3 . Bah ad o r i , Meh d i N . "Pass iv e Co o l in g Sy s tems in I r an ian Arch i t ec tu r e . " InScientif ic Am eric an. F eb rua ry 1978, pp 144-154.

4 . Brad y , Jam es E . an d Jo h n R . Ho lu m. Fu n d am en ta l s of Ch emis t ry . NewYork : J oh n Wiley and Sons , 1981.

5 . Bridge , Richard R. "Vacuum-Freez ing and Vapor-Compress ion fo r Desa l t ingSea wa ter . " Chem ica l Engineer in g . Ju ne 22 , 1964 , pp 114-116 .

6 . Ca ly x e s . "Vac u u m Freeze Mu l t ip l e Ph ase T ran s fo rma t io n . " A lb u q u e rq u e ,New Mexico : Calyxes R and D Corpora t ion .

7. Cowgi l l , U. M. "Sampl ing Waters : The Impact o f Sample Var iab i l i ty onPl an n in g and Conf idence Levels . " In Pr inc ip les of En viron me nta l Sam pl ing .Law rence H. K ei th , ed . 1988 , pp . 171-189 .

8 . Cy win , Al len an d Lewis S . Finch . "Federa l Resea rch and D evelopm entP ro gr am for Sa l ine-W ater Convers ion ." Journ a l of Am er ican W ater W orksAs socia t io n . A ugus t 1960 , pp . 983-996 .

9 . De lyann is , A. and E . -E . Delya nnis . Seawater and Des a l t ing . Vol . I . NewYork : Spr inger -Ver lag , 1980 .

10. Do d g e , Ba rn e t t F . "Fresh W ate r F ro m Sa l in e W ate r : An En g in ee r in g Research Pro b le m ." In Am er ican Scien t i s t . Vol . 48 , No . 4 , Dec emb er , 1960 ,p p . 476-513 .

41

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421 1 . E ng da hl , G. E . and M. Hu sain . "W aste Re duct ion by Freeze Crysta l iza t io n . " P re sen te d a t H azm at -C an a d a . To ro n to , Ca n ad a : CB I Freeze Techno log ies , Inc . , 1987 .

12 . Fle tche r , N. H. Th e Chem ica l Physics of Ice . Cam br idge : Un ivers i ty Pre ss ,1970 . "

13. F yn n , R. Pe ter and Ted H. Sho r t . T he Sal t S tab iHzed Solar Po nd For SpaceH ea t ing -A Pra c t ica l M anua l - . W ooster , Ohio : The Ohio Sta te Univers i tyAg r icu l tu r a l Resea rch an d Dev e lo p men t Cen te r .

14. Geig e r , Rudolf. Scr ip ta Technica , Inc . Trans . The Cl im ate Near the G rou nd .Camb r id g e , Massach u se t t s : Harv a rd Un iv e r s i ty P re ss , 19 6 5 .

15. Gi l l e sp ie , Ro n a ld , Dav id A . Hu mp h rey s , N . Co h n Ba i rd , an d Ed ward A .Ro bins on . Ch em is t ry . Bo ston : Al lyn and Bacon , Inc . , 1986 .

16. H an son , David G. and John I . Yel lo t t . A S tudy of Natu ra l Cool ing ProcessesIn A Hot , Ar id Region . Ph i lade lph ia , Pennsy lvan ia : Univers i ty o f Pennsy l van ia , 1978 .

17 . Ho ule , Jam es F . "Freeze-Desa l t ing of Seawater Goes in to Op era t ion ."Ch em ica l Enginee r ing . J an ua ry 6 , 1964 , pp . 64-66 .

18. Hu tch i nso n , G. Evelyn . A Tres t ice on Limnology . Vol . I . New York : Jo hnWiley and Sons , Inc . , 1957 .

19. "J D O bserve r . " I lHnois : John D eere Com pany , Sum me r 1989 , pp . 5 -20 .

2 0 . Ju m ik i s , Alf red R. Soi l M echanics . Pr in ce ton , New Jersey : D. Van Nos-t r an d Co mp an y , In c . , 19 6 2 .

2 1 . La bin e , R. A. , ed . "M aking Fresh W ater From Sal t W ate r . "Ch em ica l Engine er ing . Ju ne 13 , 1960 , pp . 152-155 .

2 2 . M o n tg o m ery , Jam es M. Co n su l t in g En g in ee r s , In c . W ate r T re a tm en tPr inc ip les and Design . New York : John Wiley and Sons , 1985 .

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432 3 . Pak iz , Geo rg e . "Ou r Pe t ro leu m Pred icam en t . " In F i sh in g Fac t s Mag a z in e .No vem ber , 1975 , pp . 31-50 .

24- Pass ive So lar Design Handbook . New York : Van Nost rand Reinhold Company , 1984 .

2 5 . Po un de r , E l t on R. Th e Physics of Ice . Oxford : P erga mo n Press , 1965 .

2 6 . "Pr ogr ess in SaHne-W ater Convers ion : Task Gro up R ep or t . " Jo urn a l ofAm er ican W ate r W o rk s Asso c ia tio n . Sep tem b er 19 6 1 , p p . 10 9 1-110 4.

2 7 . Re yno lds , WiU iam C. and Hen ry C. Perk ins . Engine er ingTh ermo d y n amics . New Yo rk : McGraw-HiU Bo o k Co mp an y , 197T.

2 8 . "R un do w n on Sal ine W ate r Conve rs ion ." Chem ica l Engine er ing . Ju ly 25 ,1960 , pp . 105-108 .

2 9 . Shoemaker , Morre l l M. The Bui ld ing Est imator ' s Reference Book . lUino is :Frank M. Walker Company , 1980 .

30. Sim pson , Char le s . "Freez ing the Sa lt Out of Sea W ater . " Engin eer ing . Apr i l2 4, 1970 , p . 418 .

3 1 . Snyder , Asa E. "Desalt ing Water by Freezing." In Scientif ic American. Vol.2 06 , No.6 , December 1962, pp . 41-47 .

3 2 . Tay lor , S ter l ing A. Physica l Edap hology : Th e Physics of I r r iga ted an dN on irr i ga ted Soils . Ga ylen L. Ash croft , ed . San Francisc o: W . H. Freeman an d Co mp an y , 19 7 2 .

33 . Tex as So lar Real i t ies , How to Bui ld wi th So lar Power . Texas: Go verno r ' sOff ice of Energy Resources, 1979.

34. U .S . D ep a r tm en t of Hea l th , Ed u ca t io n , an d W el fa re . Su m ma ry Re p o r t Th eAd v an ced W a s te T rea tm en t Resea rch Pro g ram . Cin c in n a t i , Oh io : Pu b l i ca t io ns Off ice, R ob er t A. Taft San itar y Enginee ring Cen ter , 1964.

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35. U. S. Environmental Protection Agency. Method 300.7. Cham paign, Illinois: Environmental Monitoring and Support Laboratory, March 1986.

36. "Vacuum-Freezing and Vapor-Compression For Desalting Seawater."Chemical Engineering. June 22, 1964, pp.114-116.

37. Viessman, Warren, Jr. and Claire Welty. Water Management Technology andInstitutions. New York: Harper and Row Publishers, 1985.

38. Watanabe, Masatalca, Donald R. F. Harleman, and Jerome J. Connor.Finite Element Model for Transient Two-Layer Cooling Pond Behavior. Re-port No. 202. Boston, Massachusetts: Ralph M. Parsons Laboratory forWater Resources and Hydrodynamics, July 1975.

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ProcessLong- tube-ver t ical evaporat ionMult istage f lash dist iUationElect rodialys i sForced-ci rculat ion-vapor-compress ionFreeze evaporat ionDirect refrigerant coohng

Locat ionFreepor t , TXSan Diego, CAWebster , SDRosweU, NMWrightsviUe Beach, NCSt . Pe t e r sbu rg , FL

Figure 1. OSW ProjectsSource: 28

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FREcZINGCHAMBERMELTINGUNIT

HEAT EXCHANGER

r^CCMING S t A WATER FRESH WATERBPfNE RETURN

Figure 2. Freeze-evaporation ProcessSource: (31)

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WATER VAPOR VACU UM

l 4COMIN6 SEA WATERBRINE RETURN FRESH WATER

Figures 3. Direct-refrigerant FVeeze ProcessSource: (31)

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0 0.01Temperature

Figure 4. Water Phase DiagramSource: (4)

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Figure 5. franian Ice-makerSource: (3)

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a. View perpendicularto the c-axis. b. View along the c-axis.

Figure 6. Ice CrystalSource: (2)

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SEA-WATER SALINITY^

oc 31 4^-"ZUIo 5UJUu. *o c

,Z& 9O

1 2 3 4SAUNITY (PER CENT)

Figure 7. Natural Arctic IceSource: (17)

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First VacuumProcessing ZonaFed 4

Second VacuumProcessing ZoneConcentrattf

FlrwtVapor

[^-^Vacuum^'i^r'aezing"

-+-J'! ^

Two StageFirstVopor .

Uquafoctfon

SecondVapor

Uqutd Second,. Va po r -:Gen oration

Slurry(Cryotala and Ue(hr Liquor)

S e c o n d , . .Vapor .-Generation

1CrystalWashingSoeondVapor T

PurlflodOryolafi

UqutdCrystal Melting

Purified Solvent Purlfled SolventF i g ur e 8 . V F M P T P r o c e s sSource: (6)

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Figure 9. VFMPT Phase DiagramSource: (6)

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Table 1Sodium Chloride in Solution

Sodium (mg/L)

5001,0001,5004,50030,000

35,000

NaCl (g/L)

1.272.543.8111.4476.2688.97

Significance

used in experiment (lower saline threshold)upper saline thresholdused in experimentused in experimentlower sea-water thresholdupper sea-water threshold

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^ *

> oFigure 11. Test Unit

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Table 2

1988-89 Winter Nights with Freezing Weatherin Lubbock, Texcis

(with Average Temperature Below FVeezingin degrees Fahrenheit)

Date

NOV 1617192027282931

DEC 147-9111214151620242728293031

JAN 789

ATBF

2.50.55.00.51.35.65.04.31.01.03.42.01.01.77.03.81.00.37.85.84.03.01.01.810.40.3

Duration

4 h r2.514.5669.510

72435

9.85.8516.5106515

15.58.57.54.810.510.51.5

Date

JAN 91112-1314151617

18192025

FEB 2-5789

11131522Mar 3-4567

2021

APR 10

ATBF

0.32.06.52.05.61.703.00.33.30.3

18.28.38.30.32.00.70.73.012.79.83.50.54.41.70

Duration

1.5 hr837.5312507.5383

9316

15.55.5276.593815.593176.50

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Table 3Winter Data Collection Problems

Date

Feb 234567891622

Mar 14567

202122

Significance

Frozen soUdFroze too fast/ too coldFroze too fast/ too coldFroze too fast/ too coldSalt Concentration too high for volumeSalt Concentration too high for volume

Salt Concentration too high for volumeSalt Concentration too high for volume

Skim iceSkim iceCollected and testedCollected and testedCollected and testedCollected and tested

Human ErrorInterference from snowInterference from snowInterference from snow

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Table 4Winter Results

Date

Mar 1456

NaCl in Influent Water

10000100001000010000

Residual in Ice

4218329.54358110.8

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Table 6Results of 500 mg/1 Test

Sample1234567891011121314151617

AverageStandard DeviationMaximumMinimumCoefficient of Variation

Ice Concentration (mo/I)40.5387.5950.6150.6153.9787.5977.5053.9774.1443.8957.3360.7080.8760.7080.87106.0365.8866.6318.03106.0340.5327.06 1

Residual Concentration Cma/1)617.08500.27580.57540.42503.92522.17503.92609.78591.52

562.32511.22598.82628.03562.32624.38573.27595.17566.19440.90628.03500.277.93

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Table 7Results of 1500 mg/1 Test

Sample1I.34567891011121314151617181920

AverageStandard DeviationMaximumMinimumCoefficient of Yoriotion

Ice Concentration (mq/l)464.09309.45427.11359.88487.62541.40343.07423.75393.49373.32470.81504.43443.92544.77638.89975.05477.53538.04576.92606.12494.98143.61975.05309.4524.63

Residual Concentration (mq/l)1785.171639.161675.661449.341697.561617.261540.601726.771686.611898.331825.331781.521792.471828.982146.552237.811770.572007.841777.872131.951800.87201.572237.811449.3410.01

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Table 8Results of 4500 mg/1 Test

Sample1234567891011121314151617181920

AverageStandard DeviationMaximumMinimumCoefficient of Variation

Ice Concentration 4500 (mq/l)1311.211243.98941.44891.012084.381580.141546.521731.411966.721580.141657.461563.331630.561731.412689.472151.611512.911865.881630.561983.531664.68409.962689.47891.0111.19

Residual Concentration (mq/l)5037.594782.073778.243102.937191.275220.105366.125147.106515.965731.153471.615785.906059.675731.157519.796132.685512.136424.706077.926023.175530.561126.097519.793102.9320.36

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800 T I Ice Concentration (mg/L)Q Residual Concen tration (mg/L)

6 0 0 - ^aEcococoo

4 0 0 -

2 0 0 -

PI ^ ' m n* V - ' . . ' ' . ' '* ' f / ,

k , V N V \' ' ' X /k^ N \ . \^ ' X > ,k N \ \

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3000-1H Ice Concentratk>n (mg/L)Q Residual Concentraion (mg/L)

01EcococoOo

2 0 0 0 -

1000

m m^ t^> ^- ' > . - '

r 0 " \ .' 'v . ' ; .' "> .- * \ ^' '' . / . /* "k N S, ' J y' ^ \ \* ' J yy \ \ \r i f\ \ \ \* s. 'I 'k I> Ik I N I'k \ >k ^ ^vk ^H ^B ^ ^B^ ^BH.' H'' H' H.' H''

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

S a m p l e

Figure 13. Results from 1500 mg/1 Test Run

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8000 -II Ice Concentration (mg/L)CZ] Residual Concentraion (mg/L)

6