EVAPORATION

HEAT TRANSFER COEFFICIENTS AND SINGLE EFFECT EVAPORATORS

By T.Shivakumar B.PharmacyShiva.pharmacist@gmail.com

PROCESS DESCRIPTION

• OBJECTIVES– CONCENTRATE SOLUTE– RECOVER SOLVENT– FORM CRYSTALS

• MECHANISM– HEAT EXCHANGE WITH

PHASE CHANGE– BATCH OR CONTINUOUS

http://www.niroinc.com/html/evaporator/rising_film_evaporators.html

DESIGN FACTORS

• SOLUTION FLUID VISCOSITY– HEAT TRANSFER COEFFICIENTS– PRESSURE DROPS

• SOLUTE SOLUBILITY– SUPERSATURATED CONDITION

• MATERIALS (BIO-MATERIALS) MAY BE HEAT SENSITIVE– DEGRADATION TEMPERATURE

• ELEVATED PRESSURE• BOILING POINT ELEVATION

http://www.aai-csi.com/images/evaporator.jpg

EVAPORATION DESIGN FACTORS

• HIGH TEMPERATURE REACTIONS

• FOAMING

• SCALING AND CORROSION

http://www.aquasant-mt.com/Foam.159.0.html?&L=1

http://www.champ-tech.com/images/products/pipe.jpg

OTHER DESIGN FACTORS

• SPECIFIC HEAT

• HEAT OF CONCENTRATION

• FREEZING POINT VS. CONCENTRATION

• GAS LIBERATION

• TOXICITY

• EXPLOSION HAZARDS

• NEED FOR STERILITY

EVAPORATION COMPARED WITH DISTILLATION

• SOLUTE IN EVAPORATION IS GENERALLY NON-VOLATILE, RELATIVE TO SOLVENT

http://www.novasep.com/technologies/img/evaporation-graph2.gif

http://www.schoolscience.co.uk/content/4/chemistry/petroleum/knowl/images/still.jpg

EVAPORATION EQUIPMENT• SUMMARIZED IN FIGURE 8.2-1

http://www.niroinc.com/html/evaporator/esys.html

EVAPORATION EQUIPMENT• FORCED CIRCULATION AND

RECOMPRESSION UNITS

http://www.niroinc.com/html/evaporator/esys.html

EVAPORATOR EQUIPMENT

• PLATE & FRAME - CRYSTALLIZERS

http://www.niroinc.com/html/evaporator/esys.html

OSLO TYPE CRYSTALLIZERS

http://www.niroinc.com/html/evaporator/esys.html

OTHER CRYSTALLIZERS

http://www.niroinc.com/html/evaporator/esys.html

THIN FILM EVAPORATORS

• USED FOR VISCOUS AND THERMALLY SENSITIVE MEDIA

http://www.artisanind.com/documents/pa_lecithin.pdf

INTEGRATED PLANT

http://www.niroinc.com/html/evaporator/flash-ppt/VMPfcopy1.html

EVAPORATOR CONFIGURATION

• SINGLE STAGE EVAPORATORS

• HEAT TRANSFER )12.8()( 1 TTUAq s

MULTI-EFFECT EVAPORATORS• STEAM FROM ONE EFFECT IS THE HEAT SOURCE

FOR THE SECOND EFFECT

http://www.nukem.de/global/downloads/englisch/Evaporation.pdf

MULTI-EFFECT COUNTERFLOW CONFIGURATION

• FIGURE 8.2-3 FEED-FOREWARD– PRESSURE IS REDUCED IN EACH STAGE– FEED & STEAM ENTER THE SAME STAGE

IN THE TRAIN

• FIGURE 8.2-4 – FEED-BACKWARD– PRESSURE IS INCREASED IN EACH STAGE– FEED & STEAM ENTER FROM OPPOSITE

ENDS OF THE TRAIN

PARALLEL FEED• SOLAR EVAPORATION SYSTEM

http://www.rio5.com/proceedings/Solar/da_Silva_et_al_201-206.pdf

EVAPORATOR HEAT TRANSFER

• OVERALL HEAT TRANSFER COEFFICIENTS – SEE TABLE 8.3-1

• NEED TO KNOW RANGE TO REVIEW QUOTED DESIGNS

• NOTE THAT PLATE & FRAME CAN HAVE HIGHER COEFFICIENTS THAN SHELL & TUBE.

CHANGE OF PHASE HEAT TRANSFER

• SECTION 4.8 FOR SUMMARY OF MECHANISMS

• FIGURE 4.8-1– CONVECTION– NUCLEATE– TRANSITION– FILM http://www.scielo.br/img/revistas/jbsmse/

v27n1/25372f10.gif

HEAT TRANSFER COEFFICIENTS

• BASED ON ΔTNUCLEATE BOILING

CONFIGURATION EQUATION RANGE REFERENCE HORIZONTAL 3/1

2)(1043 KT

Km

Wh

q/A, kW/m2 < 16 (4.8-1)

HORIZONTAL 32

)(56.5 KTKm

Wh

16 < q/A, kW/m2

< 240 (4.8-2)

VERTICAL 7/12

)(537 KTKm

Wh

q/A, kW/m2 < 3 (4.8-3)

VERTICAL 32

)(95.7 KTKm

Wh

3 < q/A, kW/m2 < 63

(4.8-4)

FORCED CONVECTION IN TUBES

155132

)(55.2sysP

eKTKm

Wh

Psys = kPa (4.8-5)

FILM BOILING HORIZONTAL TUBE

4/13

2

4.0()(62.0

TD

Tchgk

Km

Wh

vtube

Pvvapvlvv

(4.8-6)

OTHER CORRELATIONS• FOR EACH

CONFIGURATION• PERRY’S PAGE 5-22• HANDBOOK

– http://www.wlv.com/products/databook/ch5_3.pdf

• CONVECTIVE BOILING IN COILED TUBES– http://www.graham-

mfg.com/downloads/12.pdf• BASED ON SURFACE

– http://www.energy.kth.se/index.asp?pnr=10&ID=125&lang=0

SINGLE STAGE MODELS• MASS AND ENERGY BALANCES

STEAMCONDENSATE

FEED SOLUTIONPRODUCT VAPOR

PRODUCT LIQUID

F, TF,xF,hF V,TBP,yV,HV

L, TBP,xL,hL

S,TS,HSC,TC,hC

CSVLF

MASS & ENERGY BALANCES

• COMPONENT MASS BALANCE

• SYSTEM HEAT BALANCE

VAPORINSOLUTENOLxFx LF

)84.8(

)74.8(

)64.8(

Sq

HVHLhSFh

ShVHLhSHFh

vapVLF

SVLSF

OTHER DESIGN FACTORS

• LOWER EVAPORATION PRESSURE– WILL INCREASE EFFECTIVE ΔT– LOWER EVAPORATOR AREA– INCREASED SOLVENT CONDENSER AREA– HIGHER VELOCITIES MIST ELIMINATION

• BOILING POINT ELEVATION– REDUCES EFFECTIVE ΔT WITH

INCREASING CONCENTRATION

BOILING POINT ELEVATION

• DÜRING’S RULE – SOLUTION BOILING POINT IS LINEARLY RELATED TO PURE WATER NBPt AT PSYS

• FIGURE 8.4-2

http://www.nzifst.org.nz/unitoperations/unopsassets/fig8-3.gif

ENTHALPY-CONCENTRATION

• HEAT OF MIXING EFFECTS

• NON-IDEAL

Dharmendira Kumar, M.; Ashok Kumar, P.; Rajendran, M., Salt Effect on the Enthalpy of Mixing of 1,4-Dioxane + Acetic Acid at 303.15 K , J. Chem. Eng. Data; (Article); 2003; 48(6); 1422-1424.