REFRIGERATOR REPORT

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1.0Title

MEC 554-THERMALFLUIDS LAB

THERMODYNAMICS II LAB

VARIATION IN REFRIGERATION

COEFFICIENT OF PERFORMANCE AT

VARIOUS OPERATING

LECTURER: SITI HAJAR BINTI MOHD YUSOP

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2.0Abstract

The potential increase in COP is the greatest in applications where the heat sink

and heat source temperatures are approximately equal and of relatively large magnitude.

The minimum requirements to achieve these performance improvements are the selection

of a mixture that yields the desired temperature change in both heat exchangers, a

counter-flow heat exchanger that takes advantage of the temperature glide of the

refrigerant and minimized degradation of the heat transfer process. The magnitude of the

phase change temperature glide is related to the differences in the normal boiling points

of the mixture constituents.

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Table of Contents

1.0 Title................................................................................................................................. 1

2.0 Abstract .......................................................................................................................... 2

List of Symbols ........................................................................................................................... 4

List of figure ............................................................................................................................ 5

3.0 Inreoduction and Applications .................................................................................... 6

4.0 Objectives ...................................................................................................................... 7

5.0 Theory ............................................................................................................................ 7

6.0 Experimental Procedures ...................................................................................... 11

6.1 Apparatus/Experimental Setup...................................................................... 11

6.2 Procedure .......................................................................................................... 13

7.0 Result ............................................................................................................................ 15

7.1 Data recorded .................................................................................................... 15

8.0 Discussion ..................................................................................................................... 18

9.0 Conclusion .................................................................................................................... 18

10.0 References .................................................................................................................... 19

11.0 Appendices .................................................................................................................. 20

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List of Symbols

A Area over which force (F) acts (m2)

E Elastic modulus (GPa)F Force (N)

() Initial dimension in direction i (mm)

T Specimen thickness (m)

Rate of chart displacement (mm/min)

Rate of sample displacement (mm/min)

w Specimen width (m)

Displacement of chart (mm) Displacement of sample (mm)

Strain

=0 Predicted strain at zero stress

Normal strain in direction i

E Error in the predicted elastic modulus (GPa)

F Error in the force (N)

Change in dimension in direction i (mm)t Error in the specimen thickness (m)

w Error in the width (m)

=0 Error in the predicted strain at zero stress

Error in the predicted intercept of stress-stain data (MPa)

Error in the stress (MPa)

Predicted intercept of stress-strain data (MPa)

Engineering stress (MPa) Yield point (MPa)

Ultimate strength (MPa)

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List of figure

Figure 1: Refrigerator ................................................................................................................. 6

Figure 2: Schematic diagram of refrigeration cycle ................................................................... 8

Figure 3: Computer controlled refrigeration and air conditioning unit [two condenser (water

and air) and two evaporator] / THAR22C ................................................................................ 11

Figure 4: Schematic diagram of computer controlled refrigeration and air conditioning unit

[two condenser (water and air) and two evaporator] ............................................................. 11

Figure 5: The location of valve (AVS3, AVS4, AVS5, AVS 6) ..................................................... 12

Figure 6: Computer system ...................................................................................................... 12

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3.0 Inreoduction and Applications

The age, the seasonal harvesting of snow and ice was a regular practice of most of the

ancient cultures: Chinese, Hebrews, Greeks, Romans, and Persians. Ice and snow were stored

in caves or dugouts lined with straw or other insulating materials. The Persians stored ice in

pits called yakhchals. Rationing of the ice allowed the preservation of foods over the warm

periods. This practice worked well down through the centuries, with icehouses remaining in

use into the twentieth century.

In the 16th century the use of ice to refrigerate and thus preserve food goes back to

prehistoric times. Through, the discovery of chemical refrigeration was one of the first steps

toward artificial means of refrigeration. Sodium nitrate or potassium nitrate, when added to

water, lowered the water temperature and created a sort of refrigeration bath for cooling

substances. In Italy, such a solution was used to chill wine and cakes.

During the first half of the 19th century, ice harvesting became big business in

America. New Englander Frederic Tudor, who became known as the "Ice King", worked on

developing better insulation products for the long distance shipment of ice, especially to the

tropics.

Refrigeration is used widely in various applications from industrial to domestic

situations, mainly for the storage and transport of perishable foodstuffs and chemical

substances. It has the prime function to remove heat from a low temperature region, and its

can also be applied as a heat pump for supplying heat to

region of high temperature.

In this experiment we need to investigate the

variation in Coefficient of Performance () of a

vapor compression refrigeration system. The experiment

execute by using THAR22C Computer controlled

refrigeration and air conditioning unit [two condensers

(water and air) and two evaporators].

Figure 1: Refrigerator

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4.0 Objectives

The purpose of this experiment is to:

1.

Investigate the variation in Coefficient of Performance (COPR) of a vapour

compression refrigeration system at different coolong load.

5.0 Theory

A refrigeration cycle works to lower and maintain the temperature of a controlled space by

heat transfer from a low to a high temperature region.

High Temperature Reservoir, TH

QH

E W net

QL

Low Temperature Reservoir, TL

Refrigeration duty is another term for the cooling effect of the refrigeration system,

which is the rate of heat being removed from the low temperature region with specified

evaporation and condensation temperatures. The unit for duty measurements is in Watts

(for 1 ton of refrigeration = 3517 W)

The Vapor Compression Cycle

Ideal refrigeration systems follow the theoretical Reversed Carnot Cycle process. In

practical refrigerators, compression and expansion of a gas and vapor mixture presents

practical problems in the compressor and expander. Therefore, in practical refrigeration,

compression usually takes place in the superheated field and a throttling process is substitutedfor the isentropic expansion.

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Figure 2: Schematic diagram of refrigeration cycle

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The cycle ;

12 Condensation of the high pressure vapor during which heat is transferred to the

high temperature region.

23 Adiabatic throttling of the condensed vapor from the condensing to the

evaporating pressure.

34 Evaporation of the low pressure liquid during which heat is absorbed from the

low temperature source.

41 Isentropic compression of the vapor, from the evaporating to the condensing

pressures.

Energy Transfer Analysis

Compressor

q4-1= h4h1 + w

If compressor is adiabatic, q4-1 = 0 and w = h1h4

Power requirement, P = m (h1h4 ), where m is the flow rate of working fluid per unit time.

Condenser

q1-2 = h2h1+ w

w = 0, therefore q1-2 = h2h1and rate of heat rejection Q1-2 = m ( h2h1 )

Expansion valve

q2-3 = h3h2+ w

w = 0 at the expansion valve, and the process is adiabatic

Therefore h3 = h2

.

.

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Evaporator

q3-4 = h4h3+ w

w = 0, therefore q3-4 = h4h3 and rate of heat absorbed Q3-4 = m ( h4h3 )

Coeffi cient of Performance (COP)

COP ref= q3-4 = h4h3

w h1h4

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6.0 Experimental Procedures

6.1 Apparatus/Experimental Setup

Figure 3: Computer controlled refrigeration and air conditioning unit [two condenser (water and air) and

two evaporator] / THAR22C

Figure 4: Schematic diagram of computer controlled refrigeration and air conditioning unit [two condenser

(water and air) and two evaporator]

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Figure 5: The location of valve (AVS3, AVS4, AVS5, AVS 6)

Figure 6: Computer system

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6.2 Procedure

6a) Condenser-water and evaporator-water

a. Water as a heat source is selected by opening valves AVS-4 and AVS-5and then

click START.

b.

The water flow rate at the condenser to 5 L/m and 3 L/m at the evaporator

(evaporator load) are adjusted.

c. The COMPRESSOR button is click.

d. The data are start recorded when the system is stabilized by click START

SAVING.e. The sampling rate at 120 second per sample is set.

f.

The data for six minutes (3 samples @ 360 second) are recorded by click STOP

SAVING.

g. The evaporator load is increased to 5 L/m and step (c) to step (f) are repeated.

6b) Condenser-water and evaporator-air

a. Air as a heat source is selected by opening valves AVS-3 and AVS-5and then

click START

b. The water flow rate at the condenser to 5 L/m and the air flow of the evaporator

are adjusted until 50% of the maximal flow (evaporator load).

c. The COMPRESSOR button is click.

d. The data are start recorded when the system is stabilized by click START

SAVING

e.

The sampling rate at 120 second per sample is set.

f. The data for six minutes (3 samples @ 360 second) are recorded by click STOP

SAVING.

g.

The evaporator load is increased to 100% and step (c) to step (f) are repeated.

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6c) Condenser-air and evaporator-air

a. Air as a heat source is selected by opening valves AVS-3 and AVS-6and then

click START.

b. The air flow of the condenser is adjusted to maximum flow (100%) and 50% of

the maximal flow at the evaporator (evaporator load).

c. The COMPRESSOR button is click.

d. The data are start recorded when the system is stabilized by click START

SAVING

e.

The sampling rate at 120 second per sample is set.

f.

The data for six minutes (3 samples @ 360 second) are recorded by click STOPSAVING.

g. The evaporator load is increased to 100% and step (c) to step (f) are repeated.

6d) Condenser-air and evaporator-water

a. Water as a heat source is selected by opening valves AVS-4 and AVS-6and then

click START.

b.

The air flow of the condenser is adjusted to maximum flow (100%) and the water

flow rate is adjusted at the evaporator to 3 L/m (evaporator load).

c. The COMPRESSOR button is click.

d.

The data are start recorded when the system is stabilized by click START

SAVING

e. The sampling rate at 120 second per sample is set.

f.

The data for six minutes (3 samples @ 360 second) are recorded by click STOP

SAVING.

g. The evaporator load is increased to 5 L/m and step (c) to step (f) are repeated.

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7.0 Result

7.1 Data recorded

Data had been recorded on the provided table of result.(separate sheet)

7.2 Sample calculation

A. Experiment A

Refrigerant mass flow rate, mref (kg/s)

mref = vref / v2

a) vref - change the unit for value SC-1(L/h):

SC-1 = 27.64 L/h

thus vref = 27.64 x (0.001/3600)

= 7.68 x 10-6m3/s

b) v2 taken from table A11 for saturated refrigerant 134-a(provided at

appendices)

At ST-2 = 39.62 oC

=

v2= 0.02017 m3/kg

c) Therefore mref:

mref = vref / v2= (7.68 x 10-6/ 0.02017 )

= 3.808 x 10-4

kg/s

Saturated vapour, vg(m3/kg) Temperature(C)

0.02017 38

v2 39.62

0.019952 40

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Evaporator cooling load, Qevap(kW):

a)

The calculation of h3 refer to table A11 for saturated refrigerant 134-a(provided at appendices):

At ST-3 = 7.54 oC

=

h3= 192.72 kJ/kg

b)

The calculation of h4 refer to table A11 for saturated refrigerant 134-a(provided at appendices):

At ST-4 = 12.06 oC

=

h4 = 189.04 kJ/kg

c) Therefore Qevap:

Qevap = mref (h4-h3) = (3.808 x 10-4

) (189.04 - 192.72)= -1.4 x 10-3kW

hfg(kJ/kG) Temperature(C)

193.94 6

h3 7.54

192.35 8

hfg(kJ/kG) Temperature(C)

189.09 12

h4 12.06

187.42 14

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10.0 References

Websites:

1) http://en.wikipedia.org/wiki/HVAC [Accessed 27/09/14]

2) http://home.howstuffworks.com/refrigerator.htm [Accessed 7/10/14]

3)

http://www.mansfieldct.org/schools/mms/staff/hand/heatrefrig.htm[Accessed 7/10/14]

Books:

4) Eastop & McConkey, Applied Thermodynamics for Engineering Technologists 5 th

Edition, Prentice Hall, 1993.

5)

Yunus A. Cengel, Michael A. Boles,2006, Thermodynamics: An Engineering

Approach 5th Edition, McGraw Hill.

6)

Yunus A. Vengeland Micheal A. Boles, Thermodynamics An Engineering

Approach,7thedition in SI units, 2011 , The McGraw-Hill Companies.

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11.0 Appendices

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