EM111 Materials Energy Laboratory Handout

EM111 Materials & Energy Laboratories Dr. J. Stokes

School of Mechanical & Manufacturing Engineering, Dublin City University

1

EM111 Materials & Energy Laboratories ROOM SB14 (Materials) & SB32 (Energy)

Lecturer: Dr. Joseph Stokes

Room S370

School of Mechanical & Manufacturing Engineering

Dublin City University

Dublin

Ireland

e-mail: [email protected]

Web Address: www.mecheng.dcu.ie/staff/JosephStokes.html

Tel: 353-1-700 8720

Fax: 353-1-700 5345

One Report Due For This Module (EM111 Materials & Energy)

Due in (handed on A4 sheet paper) to Dr. Stokes in the

LAST LECTURE OF WEEK 10

READ CAREFULLY BEFORE ATTENDING THE LABORATORY

mailto:[email protected]

http://www.mecheng.dcu.ie/staff/JosephStokes.html



2

SINGLE REPORT FORMAT

The Materials & Energy report will be written based on all Experiments (not as individual descriptions/reports – otherwise

loss of Marks if each experiment is written independently) The Report must be written within the „Number of Lines Guidelines Given‟ (thus it will be Max. 10 pages including drawings/graphs). YOU MUST LAY OUT YOUR REPORT AS FOLLOWS:

Create your FRONT PAGE as follows:

Remainder of the report will go as follows:

1. Describe the COMBINED Aims of the OVERALL Materials & Energy Laboratory in your own words (8 A4 Page Lines

Max. typed or hand written):

2. Tabulate the results and Show any Calculations, Provided any Required Graphs, from Each Laboratory as Indicated

in the Laboratory Details : 2.1 Tensile Test: 2.2 Hardness & Impact Test: 2.3 Label & Present the results of the Second (2

nd) Experiment you conducted in your Energy Laboratory (one of either:

Heat Flow; Air Condition; Refrigeration; OR Heat Pump) 3. Discuss Your Results for Each Experiment described above, as follows: 3.1 Comment on the results obtained for the Tensile test, and the graph given to you (4 A4 Page Lines Max.) 3.2 Comment on the results obtained for the Hardness test. (4 A4 Page Lines Max.) 3.3 Comment on the results obtained for Impact test. (4 A4 Page Lines Max.) 3.4 Compare the results obtained for the Tensile (used the graph, as it describes each of the materials used in the

Hardness/Impact test), Hardness and Impact tests. (8 A4 Page Lines Max.) 3.5 Discuss the Findings from your Second (2

nd) Experiment you conducted in your Energy Laboratory (one of either: Heat

Flow; Air Condition; Refrigeration; OR Heat Pump) as explained in the laboratory session.

4. Conclusions 4.1 Draw conclusion/summary for the Combined Materials and Energy Laboratory. (i.e. can be a summary of the results

found, observations and findings. (5 A4 Page Lines Max.) 4.2 Comment on possible sources of error. (3 A4 Page Lines Max.) 4.3 Describe 2 examples of applications/uses where you would use any of the materials (steel, Al, Brass, nylon) above and 2

examples of applications/uses for the Energy Experiment (your 2nd

Experiment) you have described (6 A4 Page Lines Max.)

5. Bibliography (Detail and Reference the books you sourced to write up your report using the following format;

For example if it was a Book: 1. Callister, W. D. “Material Science & Engineering”, John Wiley, 6

th Edition, (2003), pages 63-64

EM111 Materials & Energy Laboratories For: Dr. J. Stokes


MECHANICAL TESTING LABORATORY

STUDENT NAME: e.g. JOHN SMITH STUDENT NUMBER: e.g. 5000000 PROGRAMME: MMEN 1 Group: Group ?? DATE OF MATERIALS LABORATORY: ………….. DATE OF ENERGY LABORATORY:…….. DATE OF SUBMISSION OF REPORT:…………..(last lecture Week 10) RECEIVED STAMP: RECEIVED GRADE:



3

MATERIALS LABORATORY

DETAILS ROOM SB14



4

MATERIALS: - MECHANICAL TESTING PART (A)

Reference Books: Callister (page 109) Ger. & Timoshenko (page 1 -17) THE TENSILE TEST INTRODUCTION

Many tests can be carried out on a material so as to gain information about how that material will react to different stimuli. e.g. chemical attach, bending forces, tensile forces. etc. The most common mechanical test which can be carried out on a material is the Tensile Test. Tensile tests are carried out on specimens of standard size and shape. This is to ensure repeatability from test to test and to allow for comparisons to be made between different materials. The specimen shape is normally dog-bone shaped as can be seen in figure 1. The large ends of the specimen allow the specimen to be rigidly gripped or held so that the gripping will not damage the gauge length. The gauge length of the specimen is an important dimension because it is used to calculate the engineering strain on the specimen. The gauge length of standard specimens normally ranges from 25mm up to 75mm.

Figure 1. Example of a tensile test specimen. THEORY

In the context of a materials tensile test:

Engineering Stress = Force divided by Original Cross Sectional Area (Newtons/mm2)

Engineering Strain = Extension divided by Original Gauge Length (mm/mm ) i.e. no units or dimensionless (note: referred to as stress and strain.) Stress and strain are used to describe the effects of an increasing tensile force on a material during a tensile lest. Stress relates the force on a specimen to the cross-sectional area of that specimen. From the formula for stress above we can see that if the area is reduced the stress increases, or if the force goes up the stress increases. Strain relates the elongation of a specimen to the original gauge length of the specimen. OBJECTIVES

To find the tensile characteristics of a material (i.e. how the material reacts when pulled apart). The material properties are normally recorded and calculated as detailed on page 5. (see lecture notes for more information) Normally a Stress V" Strain graph is produced from the tensile test recorded data. Values of "YS" and "UTS" can be taken from this graph "read from the Y axis", Values of Young's modulus are calculated by finding the slope of the straight line section at the start of the graph. Stress and strain values can be calculated from the elongation and force values and a graph of Stress V" Strain can be plotted.

MECHANICAL TESTING (B) Part 1: HARDNESS TEST

Introduction

The hardness of a material is a measure of its resistance to abrasion or indentation. A number of scales are used for hardness, depending on the method that has been used to measure it. The hardness is roughly related to the tensile strength of a material, the tensile strength being roughly proportional to the hardness. Thus the higher the hardness of a material, the higher is likely to be the tensile strength. Objectives

To determine the hardness characteristics of different materials used in engineering. Equipment

OMAG Brevetti Affri hardness tester, model 206 with a diamond V tool and a ball tool

Selection of material blocks

4.5 mm x 1mm section

Gauge length 22 mm



5

Procedure

Record the hardness value for each material (Aluminium, Steel, Brass and Nylon) as per the demonstrator's instructions. Calculations

Determine the Rockwell B hardness values for the chosen engineering materials.

Part 2: THE IMPACT TEST (c) INTRODUCTION

The toughness of a material is a different property to strength. It specifically indicated the material's resistance to fracture. It represents the materials ability to absorb energy up to fracture. Therefore materials which require a lot of energy to fracture are more tough than others which fractures with little use of energy. In the case of dynamic loading an impact test is used to measure toughness. The most common methods are the Charpy and lzod Impact tests. The principle of both is the same: A weighted pendulum hammer is released from a fixed position, and strikes the specimen located as shown in the diagram attached. Some energy is needed to cause the fracture of the specimen. After impact the hammer continues to swing, raising to a maximum height depending on how much energy is left in the system. The difference between the original height, and the final height is a measure of the impact energy used to cause fracture. The difference between the methods is in the way in which the notched specimens are held (see figure in notes). Note: The swinging hammer in this test contain a lot of energy, which would cause serious damage to anyone (or part of anyone) in its path. The guards are for your own safety, and must be respected. NO-ONE is allowed place fingers in the path

of the hammer once it has been raised. PROCEDURE

A load is applied as an impact blow from a pendulum hammer is released from an initial position at a fixed height h.

The specimen (Aluminium, Steel, Brass and Nylon) should be positioned at the base of the apparatus as shown in Fig. 2.1 below.

Figure 2.1

Upon release, a knife-edge mounted on the pendulum strikes and fractures the specimen at the notch, which acts as a point of stress concentration for its high velocity impact blow.

The pendulum continues its swing, rising to a minimum height h', which is lower than h. The energy absorption, computed from the difference between h and h', is a measure of the impact energy.

Procedure

Record the Impact value for each material (Aluminium, Steel, Brass and Nylon) as per the demonstrator's instructions. Calculations

Determine the Impact (J/mm2) values for the

chosen engineering materials.



6

2. Tabulate the results of each test as follows: 2.1 Tensile Test:

Tabulate 1 Sample (Steel or Aluminium or PVC) below and Calculate the following based on the results given; Engineering Stress & Engineering Strain

Force (N) (Measured) Extension (mm) (Measured) Stress (N/m2) (Calculated) Strain (Unit-less)(Calculated)

154 0.1

184 0.2

190 0.3

192 0.4

Show in detail how you calculated one of the Stress and Strain values (include units throughout) above (8 A4 Page Lines Max.):

Calculate the following based on the Sample Results provided:

Yield Strength for 0.2% Strain

Final Gauge Length (mm)

200 N/mm2 30

Young's Modulus of Elasticity (E) = Stress divided by Strain "Within the elastic region, i.e. slope of straight line",

% Elongation at fracture = Elongation at fracture divided by Original gauge length and Indicate if the material is Ductile or Brittle (Provide the graph in your report)

On the graph provided overleaf label the following the 4 lines according to their material types (Metal, Ceramic, Plastic) and suggest an example of a material which would behave in this way (use Steel, Aluminium, Glass/brass, PVC/Nylon, etc.) (Provide the graph in your report)

On the graph provided indicate the following regions/points; Modulus of Elasticity (E), Yield Stress (YS) (The stress at which Yield occurs), Ultimate Tensile Strength (UTS) (The maximum stress recorded), Breaking Point, and which material is Ductile or brittle.

Stress V's Strain

0

50

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1

Strain

Str

es

s (

N/m

2)

A B C D



7

Space for Calculations: 2.2 Hardness and Impact Test

Tabulate the hardness and Impact data (Record the data of the energy used to fracture specimen of each material type. Include units in your table, e.g. J/mm

2)

Material Hardness (Rockwell A) Impact (J)

Steel

Aluminium

Brass

Nylon



8

ENERGY LABORATORY

DETAILS ROOM SB32

School of Mechanical and Manuf&during Engineering

E F 'i 7' i , (

Experiment : Turbulent Flow Heat Exchanger

Introduction

Numerous industrial applications require heat transfer from hot to cold fluids and awide variety of Heat Exchangers have been developed for this purpose. Heat istransferred whenever a temperature difference exists and the modes of transfernamely conduction, convection and radiation may operate separately orsimultaneously.

Conduction is the mode of heat transfer through solids and liquids whcre there is nomovement of the fluid in the direction of the heat flow.Convection is the mode in which heat is transferred through a fluid system by themotion of the fluid.Radiation is the mode ofheat transfer by electromagnetic waves. This mode is veryimportant at high temperatures and is considered negligible in small heat exchangers.

Apparatus

The unit consists of a Double Pipe Heat Exchanger with hot water flowing throughthe central tube while cooling water flows through the annular space. Thermocouples, ""are used to sense the stream temperatures at various points throughout the system.Other features include hot and cold water circuits, temperature control and coolingwater control valves. ( See circuit diagram 1 for more details.)

Dimensions and Useful Information

Heat Exchanger: Core Tube Material - CopperExternal DiameterInternal DiameterLength

External Heat Transfer Area,Internal "Mean "Flow area

Outer Tube Material - CopperExternal DiameterInternal DiameterAnnulus flow area,

(dJ =9.5mm(dJ = 7.9mm

= 3 x 350mm

A" = O.031m2

~ = O.0261m2

Am = O.0288m2

Sj = 49 X 10-6 m2

= 12.7mm= 11.1mm

So = 25.9 X 10-6 m2

Specific heat of water

H951 WATER-WATER TURBULENT FLOW HEAT EXCHANGER

~~:4riet -.~CO\.l')ler Currenl

Flow-. -.C()(){i-g ~-. OrenWater Inlet -.

Cool~ WaterFlow Cootrol..-

ConcurrentFlow..-

FIII~ POOl/Cap

Heaters

TemperatLCeIrdcator

I~IT~tLCe

Selector Sw~ch

II @ II

Heath;)ToN<

PressureRelief Valve

Sig'll Glass

t

LowFlowMeIerandCOfilrol

t

Hg,FlowMeter

Hi(tl FlowC;xilralV01ve

HeatExchorgerOran

88

Tori<Drain

Man HealerSw~ch Sw~ch

..-b==============>?=::[]_ Purp

Ie

t5

Healer

+Power

Incfcolor

Oran 019

0

t HoolerCOfilroi

Heal Exchanger

18

t

13

~ CcxfugWaterFlowmeter

MansColdWaler In

t

Start up procedure:

1. Set the Cooling Water Flow Control valves to give either concurrent or counter-current flow asindicated by the arrows on the front panel.

2. Tum on the cooling water supply and open the cooling water flow control valve on the coolingwater flowmeter. Ensure that cooling water flows freely through the flowmeter and heat exchangerto the drain.

3. Supply power to the unit and tum on the main switc:;h. The hot water high and low flowmetersshould indicate a circulating flow.

Close the low flow meter valve and fully open the high flow meter control valve.

4. Tum on the heater supply switch and adjust the heater control.

The heater power indicator will flash, indicating the relative power to the water heaters. When theindicator is on fully, the power supply is at maximum.

~: A certain amount of air will come out of solution as the water is heated, but this will beautomatically vented within the heating tank.)

If this is the fIrst time that the unit has been operated then it may need to run for approximately15 minutes in order to ensure that the majority of dissolved air is released from the hot watercircuit.

5. When the hot water temperature l:l reaches the desired temperature (noi. more than 75 to 80°C)adjust the high or low flow control valves to give the desired hot water flow rate. Adjust the coldwater flow and heater control to obtain stable running conditions so that the system temperaturesremain constant.

6. Alternatively the flows may be set to the desired values and the temperatures adjusted by alterationof the heater control.

7. Note that if the hot water temperature exceeds approximately 90°C then the high temperature cutout will operate and tum off the power to the water heater. The heater power indicator light willbe extinguished under these conditions.

Power will be automatically restored when the water temperature l:l has fallen to approximately70°C.

Shutting Down

1. Tum the heater control anti-clockwise to its minimum setting and tum off the heater switch.

2. Tum the cooling water flow to a high value, and fully open the hot water flow control valves.

3. When the system has cooled to about 40°C, tum off the mains switch and isolate the unit from themains.

4. Tum off the cold water supply.

Experimental PI'ocedure

1). Write a ONE PAGE description of the apparatus using the enclosed diagram

2). Determination of lIeat Transfer Rate, Log Mean Temperature Difference andOverall Heat Transfer Coefficient.

1). Set cooling water flow control valves for counter current flow.2). Check that the heater tank contains water to the correct level.3). Close the 'Low' flow control valve and fully open the 'High' flow control valve.4). Switch on the mains and the water heater and set the heater control to a highvalue.5). Increase the hot water temperature to approx 70°C and then adjust the hot waterflow rate to a convenient value Eg 5 llmin (80 g/s)6). Adjust the cold water flow until stable operating conditions are reached (approx70°C)

Record results on Sheet 1.

Results

Calculate the following:

1) Hot water mass flowrate

2) Heat transfer from the hot water

3) Heat transfer to the cold water

4) Log mean temperature difference

For counter current flow

1m. =V *p*----

1 I 1000 *60(kg/s)

(watts)

(watts)

5) Overall heat Transfer Coefficient U =~~lJe

6) Plot a graph of Temperature Distribution for counter current flow with Distancefrom Hot Inlet on the X-axis and Temperature on the Y-axis

OBSERVATION SHEET

For relative positions of temperature measurement points please refer to schematic diagram on Page 1.

CONCURRENT FLOW· COUNTER·CURRENT FLOW· *Delete as Requiied

TEST 1 2 3 4 5 6

Metal Wall at inlet tl 1°C 69.8

Metal Wall at exit ~ I °C 57.4

Hot stream at inlet ~ 1°C 71.3

Hot stream 1str../oC 70.4

intennediate

Hot stream 2ndls 1°C 69.2

intennediate

Hot stream at exit ~ 1°C 67.2

Cold stream enay/exit ~ I °C 60.8

Cold stream intennediate fa 1°C 52.0

Cold stream intennediate ~/oC 393

Cold stream enay/exit ro I °C 21.6

Hot water indicated flow ~i 11 min-I 10.0

Hot water actual flow rh; / kg S-I 0.166

Cooling water flow rate rho / kg S·I 0.0175~

Mean hot water ~)/oC69.25

temperature 2

Specific Heat at mean Cp

I kJ kg-I K"l 4.19

Density at inlet to p Ikg m-) 978.0flowmeter ~

Thermal Conductivity atk/Wm-I K-1

mean temperature

Viscosity at mean p IHI N s m-2

temperature

Prandtl No. at meanPrj

temperature

Reynolds No. at meanR<;temperature

hpHimenl ,Air C"odiliooin~Unl,

Inlrod"Ol;OIl

Air oolldWoning m.ay be <l<scribed as lite ,,""Irol of lite a1D'DS!,h,:re so ~lal a desirtdleIop"':"u"" humidily aoo air dislribulion is achieved uruJer "o,"rolled and repealabltcircwm"ances. Applir:a'k"" i"c1ode dnnleS1ic, "ffoces, b",pitals Ilnd buildiJlg uni"IIIlJ D~,er arras wbich "'lllire human comfort. Induslrial application inclode1""",,"luries, food slOJ3gt, manafaclurillg, and pharmaceulical produclion

Appanuo.

l11e unjt C<)II.isl, of a Ilunlocr Dfkey oomponcllts. The.'ie inclade Cans, filt"", healc>:ehangers and homidifiers. We' and dry bulh ,hem",mOlen are os<:d '0 find lhehumidily oflbe air al various pointS Ihroughout II><: rig "loog wi'h " range of Dlheri""nullenialin" fm p"","ure rncasweme,,1 and tlow measuremenl

I) II.", d.. dtn",,,s'ralor give " <l<lailoo i"trOO,"'I;oo aboullhe ')'SIt'" aud lughliglllII><: I:cy oomponenls follJl<l On lhe: rig in 0 <hort ,me page overview oflhe: systom

2) hlilow lhe ;ns!rnc'....... on je,t shed I 10 gene",le lit"", e)'<k evenlS on "Psyd.omclric CIw1. HigJ<iighl lite wet and dry bulb lempe"'lu"" a, c<'IC!I po;1lt ondfind Ihe mois",,,, conlent alld II", specific c"llwlpy "Clhe ai, III "",h poi"l. PreenlIhis da13 in a table for ead c)'<I".

J) Commenl Oil your ""olts

Tos, Sh«' I

I) Tun] on II>c rig and SCI die fM to gi,.., on orifice prt::SStlrt: drop of 401""'.2) To'" On lhe oon'pressor only and record table 2 OIl the "b>crvali"n sltt<:l.3) Tlln, on dIe 1- preheattr and allow lhe: 'ySltm 10 settle for S rni"" I:>efore

""""rding lable J dala.4) Tom on Ih" I~ rebealer all"w "'" sy,le.., '0 ",,,Ie for S min, b<fo.., recording

table 4 dOULS) Ask ,he demon""'I"r I" can-fully mnl 00"" ,he rig.

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Test Reference: 1 2 3 4

A Air at Fan Inlet Dry

Wet

t1 (oC)

t2 (oC)

B After Pre-Heat or Steam

Injection

Dry

Wet

t3 (oC)

t4 (oC)

C After Cooling /

Dehumidification

Dry

Wet

t5 (oC)

t6 (oC)

D After Re-heating Dry

Wet

t7 (oC)

t8 (oC)

%Saturation (%)

Moisture Content (kg/kg)

Specific Enthalpy e

(kJ/kg)

no ,,, 1)0 '" "0Figure 10

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School of Mechanic:,:! and Manufacturing Engineering

Experiment.: Refrigeration Cycle Demonstration Unit

Introduction

A refrigerator is defined as a machine whose prime function is to remove heat from alow temperature region. Since energy cannot be destroyed, the heat taken in at a lowtemperature plus any other energy input must be dissipated to the surroundings.

The 2nd law of Thermodynamics states that heat will not pass from a cold to a horterregion without the aid of an external agency. Thus a refrigerator will require anexternal source for it to operate. This energy input may be in the fonn of work or aheat transfer at a high temperature. However the most common type of refrigeratoruses a work input and operates on the vapour compression cycle.

Apparatus

The unit consists of a vapour compression cycle utilising a small work input totransfer heat form a Water source evaporator to a cooled condenser. All relevanttemperatures, pressures and flowrates are measured enabling the complete cycle to beinvestigated. (See Fig 1)

Useful data:

Condenser water coil surface area: O.032m2

Evaporator water coil surface area: O.032m2

Specific heat capacity of water Cp: 4.18 kJ/kgK

Refrigerant type:

Experimental Procedure

R141b

1) Have the demonstrator give a detailed introduction to the system and a outline ofhow pumping over into the condenser is achieved.

2) Follow the instructions on test sheet 1 to generate a refrigeration cycle diagram onthe pressure-enthalpy chart. Record one set of results on the observation sheet.

3) Follow the instructions on test sheet 2 to calculate the ow'rail heat transfercoefficient between the refrigerant and water in both the evaporator and thecondenser. Use the same set of results from 2 above in these calculations.

Results

1) Write a ONE PAGE technical description of how the refrigeration unit worksstarting at the compressor.

2) Using the data collected during test 1 plot the refrigeration cycle diagram on thep-H diagram supplied. Comment on the condition of the refrigerant at each pointon the diagram (i.e. liquid, vapour etc,)

3) Using the same data collected during test 1 calculate the overall heat transfercoefficient between the refrigerant and water in both the evaporator and thecondenser.

4) Comment on the results.

Condenser

Evaporator

Compressor

Expansion

Valve

Heat Transfer from

Refrigerated Space (e.g.

food)

Heat Transfer to ambient

air or to cooling water

A Low pressure vapour

B High pressure vapour C High pressure Liq.

D Low pressure

Liq/vapour mix

Work

Refrigeration

ControlValve

EvoporatarWater

Flow Meter

t

t

tJ

ChargingValve

Pressurec====~~v..Relief Valve

EvaporotorPressure

Unit R633

-

SightGloss

--

Oil ReturnCapillary

Compressor

-

Wallmeter (OplionaD

Water Drain +

t

Cycle Demonstration

~I~

Temperalure Indicalor(OptionaD

-

t-

ExpansionValve

Condenser

-

t8(Optional)

PressureSWitcht

tJ

PressureRelief Valve

..VentValve _--H---\t-"

t

Refrigera tion

CondenserPressure

Control 0Valve

MainSwilch

l81

CondenserWoter

Flow Meler

Figure 1 t Water Inlet

2R633 Valve Positions

NORMAL OPERATION

REFRIGERANT PUMP DOWN

OIL RETURN(Only when In Pump Down Condition)

Figure 2

SHUTDOWN

GENERATION OF A REFRIGERATION CYCLE DIAGRAM ON A PRESSUREENTHALPY CHART

Note this procedure can ONLY be undertaken by the following detailed method with the optionaltemperature indicator fitted to the R633 unit as the temperature of the refrigerant liquid in thecondenser is required for one state point on the cycle diagram. However the procedure may bemodified for use with the standard thermometer set. See Page 48.

The fining procedure for the optional temperature Indicator kit, if not already fitted, is given inAppendix A. Details of the kit are available from P.A. Hilton Ltd, or their local representative.

The vapour compression refrigeration cycle is of paramount importance in terms of food and drugpreservation, air conditioning, and heat pumps. In order to analyse the system performance in termsof the thermodynamic cycle it is common for engineers to record system pressures and temperaturesand then to plot the various Slate points on a pressure-enthalpy chart of the working fluid.

The working fluid in the Hilton Refrigeration Cycle Demonstration Unit Series R633 is R141b. Thishas the chemical name 1,1,-Dichloro-l-fluoroethane.

A pressure-enthalpy chart for this substance is shown on Page 55.

A detailed description of the various parameters displayed and obtainable from pressure-enthalpy chartswill be found in most text books on thermodynamics and therefore will not be expanded upon in thismanual.

In order to plot a cycle diagram for the unit the following procedure should be adopted.

Procedure:(i) Start the unit for normal operation as shown on Page 15 and ensure that the unit is air free by

venting air from the condenser as described under air venting on Page 18.

Once air free increase the condenser cooling water flow to a mid range value. The pressure atwhich the condenser stabilises will depend upon the water inlet temperature.

(ii) Set the evaporator water flow to a mid range value and allow the unit to run for approximately15-20 minutes. The time taken to stabilise will depend upon the local ambient conditions and thecooling water inlet temperature.

(iii) Record all the system parameters as illustrated in the table

(iv) In order to demonstrate that the cycle varies for different operating conditions it is recommendedthat the condenser pressure is varied by adjustment of the condenser cooling water flow rate. Theunit should be allowed to stabilise and the system parameters recorded.

The procedure may also be repeated at different evaporating temperatures and the results plottedon a pressure-enthalpy chart as described below.

The results from the following table are shown plotted on Page 50.

The slate points a, b and c on the diagram on Page 50 are located in the following manner:-

(i) Point a is at the intersection of the evaporator chamber pressure Po = 32 kN m,2 absolute and theevaporating temperature ls =4.0°C.

(ii) Point b is at the intersection of the compressor chamber pressure Po = 70 kN m,2 absolute and thecompressor discharge temperature ~ =41.7°C.

Example of Measured Results and Calculations:

Using the Values on the Graph overleaf and information page after the graph, the Rate of Heat Transfer to

Water in Evaporator:

= Cp (t1 – t2) = 20.0 x 10-3

x 4.18 x 103 x (11.2 – 9.7) W = 125.4 W

inlet = (t1 – t5) = (11.2 – 4.0) K = 7.2 K

outlet = (t2 – t5) = (9.7 – 4.0) K = 5.7 K

mean = = = 6.4208 K

U = = = 610.3972 or 610.40 W/m2K

CENTRE D'APPLICATION DE LEYALLOIS

150

60504030

20.-..

15l..~

.0- 10QJl.. 8:::V)V) 6QJl.. 5Q.

QJ 4-::: 3"0V)

.0 2~....... 1.5QJ

:::"0 IV)

.0 0.8et:

c 0.60 0.5'"'" 0.4QJl..~ 0.3

0.2

0.1

200 250 300 350 400 450 550500 600 650 700

Unites I Units P: bar T : 0(' REFERENCES T=O°Ch : kJlkg s : kJ/1.;g.K v : m1 !kg Tb : 32 Pc : 41.8

rrrrmlllITTTrTrlll\T1\"rTrllfTTlII 1mII[rrlllm1mrrrm1"[TTT1lIITTTIV"TTlfTTTlT1[T11T[\,1m,"T]11mtTTTIfrrym]l1TIpm [Tl1 iTm rn IT 11~I~ l11TrmF m1jrnrymrr TIl

h=200kJlkgTc:204.1

'I I ,~T 1]1

s=lkJ/ kg.Kd(25°C) : 1.2(

rrrynrrrn rrrrrmFrprrrym \ I I '\'.

150 200 250 300 350 400 450 500Enthalpie I Enthalpy (kJ/kg)

550 600 650 700

elFatochem~

DETERMINATION OF OVERALL HEAT TRANSFER BETWEEN R141b AND WATERIN THE EVAPORATOR AND CONDENSER

The Overall Heat Transfer Coefficient (U) is the heat transfer rate per unit area of heat transfer surfacewhen a temperature difference of one degree exists between the hot and cold fluids.

In the evaporator, the refrigerant temperature is sensibly constant, but the water temperature falls as itpasses through the coils. In the condenser some degree of superheating may be present when the gasenters the condenser glass chamber. However the quantity of heat delivered due to the superheatingwill be small relative to that attributable to the condensing phase change. Examination of the highpressure line of the cycle diagram generated in Experiment No.9 on Page 47 will confIrm this.

In order to analyse the overall heat transfer coeffIcient a representative temperature difference must bedetermined that represents the driving force for heat transfer between the refrigerant and the water.

The temperature difference to be used in this case is the "Logarithmic Mean" which is given by

where SiDle, = Temperature difference between the two fluids at inlet,and Soudet = Temperature difference between the two fluids at outlet.

A theoretical analysis of the logarithmic mean temperature difference may be found in most text bookson heat transfer and will not therefore be expanded in this manual.

Procedure:(i) Start the unit for normal operation as shown on Page 15 and ensure that the unit is air free by

venting air from the condenser as described under air venting on Page 18.

Once air free increase the condenser cooling water flow to a mid range value. The pressure atwhich the condenser stabilises will depend upon the water inlet temperature.

(ii) Set the evaporator water flow to a mid range value and allow the unit to run for approximately15-20 minutes. The time taken to stabilise will depend upon the local ambient conditions and thecooling water inlet temperature.

(iii) Record all the system parameters as illustrated

OBSERVAnONS

Local Aunospheric Pressure:

Test No. 1 2 3 4 5

Evaporator Gauge Pressure p. / leN m-2

Absolute Evaporator Pressure p. / leN m-2

Evaporator Temperature k, / °C

Evaporator Water Flow Rate rile / gm S-1

Evaporator Water Inlet Temp. tl / °C

Evaporator Water Outlet Temp. ~ / °C

Condensed Liquid Temp. ~ / °C

Condenser Gauge Pressure Pc / leN m-2

Absolute Condenser Pressure Pc / leN m-2

Compressor Discharge Temp. t-, / °C

Condenser Temperature ~ / °C

Condenser Water Flow Rate rilc / gm S-l

Condenser Water Inlet Temp. ~ / °C

Condenser Water Outlet Temp. ~ / °C

Compressor Power Input W / Watts

CENTRE D'APPLICATION DE LEVALLOIS

150 200 250 300 350 400 450 500 550 600 650 700

Unites / Units P: bar T : 0(' REFERENCES T=O°C h=200kJ/kg s= 1kJ/ kg.Kh : kJ/kg s : k.Jlkg.K v : m3 /kg 10 : 32 Pe : 41.8 Te : 204.1 d(25°C) : l.2C

rmmmnmmmrrn nnmmmrrnmmTtmmmnnmnmm rmmmnnrmmn mmTmHnnmTmr!tnmTT 1111111111111111 mmrrmmmmnnImmmmTTTT11TT1TT1 TTITl1mnlTTmnmnrnrrTTlmm TIm H1TTT~T1InTTTllrrmr,nrrTT1rrrt

150 200 250 300 350 400 450 500Enthalpie / Enthalpy (kJ/kg)

550 600 650 700 , .

elf atocheln~

School of Mechanical and M~nufacturingEngineering

_~ "_~;""'.v.,-~_";",, .. ~_;., ~,_ .";.,.""",,I= ~'"~ ~

~ =~ : &""'t~ ~~ ~ ,,:"'''' " - ~ ..

Experiment : Heat Pump Cycle

Introduction

The vapour compression refrigeration cycle finds applications in countless industriesand domestic situations. The emphasis is upon maintaining a product or air stream ata low temperature whilst rejecting heat extracted at a high temperature usually toatmosphere.

However the vapour compression refrigeration cycle cycle may equally be used toupgrade heat from a low grade ( such as a river, atmosphere, soil) so that it may bedischarged at a more useful higher temperature for some other application e.g. spaceor water heating.

For Example large dairy fanns require chilled water for cooling milk and hot waterfor cleaning pipework. A heat pump can provide energy savings in this situationassuming the scale and utilisation factors justify the increased capital costs.

ApparatusThe air and water heat pump apparatus is a vapour compression cycle utilising asmall work input to transfer heat form either a Air or Water source evaporator to acooled condenser. AU relevant temperatures, pressures and power inputs aremeasured enabling the complete cycle to be investigated. (See Fig 1)

Analysis

A machine whose prime function is to deliver heat to a high temperature region (usually above ambient) is called a Heat Pump. For such a system the importantquantity is the heat rejectedfrom the system.

A machine whose prime function is to remove heat from a low temperature region(usually below ambient) is called a Refrigerator. For such a system the importantquantity is the heat supplied (taken in )to the system from the surroundings.

The main running cost of both these systems is the power input 'W'.

Experimental Procedure

Test 1:I) Turn on the water supply to the unit and turn on the main switch.

2) Select the water evaporator by pressing the evaporator change over switch.

3) Set the condenser gauge pressure to between 700 and 11 OOkN/m2 by adjusting thecondenser cooling water tlowrate.

4) Allow the unit time to reach a stable condition.

5) Record results on test sheet 1 and test sheet 2

Results

1) Plot the vapour compression cycle on the P-H diagram supplied.

2) Comment on the condition of the refrigerant (liquid/vapour) at each point.

3) Determine the specific enthalpy at each point from the graph. (Four points)

4) Carry out an energy balance for each of the following processes

.Evaporator:

Heat transfer from water source

Heat transfer to HFC 134a

Condenser:

Heat transfer to water

Heat transfer from HFC134a

Compressor:

Heat transfer to water

TEST SHEET J<>

Specimen

HFC134a Gauge Pressure ~\\ r;ompressorPI 1 leN m-2

145suction

HFCl34a Absolute" Pressure at compressorPI 1 leN m·2 250suction

HFCl34a Gauge Pressure at compressorPI/kN m·2 651discharge

HFC134a Absolute" Pressure atP2/kN m·2 756compressor discharge

HFC134a Temperature at compressortl/OC 2.4suction

HFC134a Temperature at compressorlz 1°C 64.2discharge

HFC134a Temperature of condensed liquid t) 1°C 27.2

HFC134a Temperature at expansion valve 41°C -4.1outlet

*Absolute pressures, Le. gauge pressure + atmospheric pressure.

,., " "'~' "...

0 0 q <> 0 0 0 g 0 0 0~ ~

0 0 0~

0 0 :." 0 '" '" "- '" '" ~ ci N

~ g ~ R g :i: 'OJ ~ 0 ~ " '" .,; ..; N 0 0 0 0 0 0 0 0

9S>l:Jnuo NOlSS3Ud (uva) 3unSS3Ud

0

'"~:;

~illQ~

C

(-)

20

~,~

~

uU

~

~

~

0><>M

0~

M

0

'"M

0g

g'"

0

~

~0;

N 2->-s

0<i-

N i"N Z

UJ

8N

~

§ .,"::"t'

0 [~ "t

~

E0

..,~ ~

c,0

§G.G'

<>¥

'" E:;

0~

><> 0"-~

u

~ !.u

Q

0 <-N

~.

~u

0

TEST SHEET 2..

OBSERVAnONS Date:

Atmospheric pressure:

Atmospheric temperature:

l.05 Bar = 105 leN m-2 Heat Source: Aj.f

Water(delete)

Test I 2 3 4 5 6

ElectrlcdElectrical input to

W / Watls 470compressor

Mass flow rate Ill, I g sol 5.5

Compressor suctionp. I kN m-2 148

gauge pressure

Compressor suction p.1 kN m-2 253absolute pressure

Condenser gaugeP21 kN m-2 1180

pressure

Condenser absoluteP2/ kN m-2 1285

HFCl34a pressure

Compressor suctiontt / DC -1.4

temperature

Compressor delivery~ I DC 80.0

temperature

Condensed liquid~ / DC 44.8

temperature

'.

Evaporator inlet~ I DC -4.2

temperature

Mass flow rate rh,,1 g sol 7.0Water

Compressor Inlet temperature ~ / DC 13.0

CoolingOutlet temperature t"fC 16.4

Mass flow rate rh,,1 g S·I 7.0

WaterInlet temperature t"fC 16.4

CondenserCoollng

Condenser outlctLtI"C 49.8

temperature

Mass flow rate rh.1 g S-I 11.5WaterSource Inlet temperature . ~ I DC 13.0

EvaporatorOutlet temperature 101 DC -1.2

Solenoid

ValveThermostatleExpansionValve

-RefrigerantFlowmetero AIr

~Evaporator

'0 Watero Wate1 Flowmeter

EvaporatorChangeoverSwitch g

Pawer Hetero118 Solenold

Valve

••IF"-'-'-'-'-'-'-'-'-'-'"'-'-'-~..:J

Non-Return ~---.Valve ~~

~_=Zt4~"Z"Z'~'~"*'Z'Z"D"~'="Z'*"~"Z"Z'D"~"~··Z·D·D··~··Z··Z·D··D··~··z··a·D··~·=··=·a··D··D·r=~z-a.rD..~..=..z.a..D..D··=··=·:·:··_I=··_5=·_·Z._.Z.:..:..:.•._.a.•..:..:._.Z.:.•..:..•.•.Z·_·~~······:~_a~·_~a:·::e:t_lJ(·~n:~t__~ ~;~~

Air and Water Heat Pump R831Condenser EvaporatorPresslXe Temperature Pressure

HgtI Pressure 0Indicator

Cut-Out

~lsolaHog ValveNormal!y Open

CondensedLiquidReceJver

Compressor I 6COolingCoil

Waste WaterDrain

WaterFilter(InternaD

Cooling WaterInlet

Fig 1 below shows the main components ofa standard vapour compression cycle. Thechanges in thermodynamic propertie::: of the refrigerant and the cycle ofevents aredetailed below

-Qcooo.to ,oem

Expansion valveor .

capillary tube

Qevap from coldrefrigerated space

Figure 1.

Process 1-2. Compression - dry saturated vapour enters the compressor where it iscompressed increasing its pressure and temperature

Process 2-3. Condensation - cooling of hot vapours at constant pressure. Heatrejected by the refrigerant

Process 3-4. Expansion - Simple throttle valve expansion form high to lowpressure. Constant enthalpy process

Process 4-1. Evaporation - Heating of liquid at constant pressure. Heat suppliedfrom cold sources

These processes and the corresponding thermodynamic properties are shown on thefollowing P-h diagram Fig 2.

Enthalpy I( kJ Ikg)

Figure 2

p

Under-

~

rl-----t......;2

hj = h.

r=fh, ~h·)I~1

(hl-h,)

h

EM111 Materials Energy Laboratory Handout

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