LS2 - Variation in Refrigeration Coefficient of Performance at Various Operating Conditions

Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012

UNIVERSITI TEKNOLOGI MARA FACULTY OF MECHANICAL ENGINEERING ________________________________________________________________________ Program : Bachelor Of Engineering (Hons) Mechanical Course : Thermalfluids Lab Code : MEC 554 ________________________________________________________________________ LAB SHEET NO:

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HEATING, VENTILATION & AIR CONDITIONING LABORATORY SHEET (HVAC) TITLE : Variation In Refrigeration Coefficient Of Performance At Various Operating Conditions. 1. INTRODUCTION 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 it can also be applied as a heat pump for supplying heat to a region of high temperature. 2. OBJECTIVE To investigate the variation of Coefficient of Performance (COPR) of a vapor compression refrigeration system at different cooling load. 3. 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

Wnet

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 = 3517W).

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Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012 3.1

The Vapor Compression Cycle Ideal refrigeration systems follows 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 condition and a throttling process is substituted for the isentropic expansion.

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Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012 The cycle : 1–2 2–3 3–4 4–1

Condensation of the high pressure vapour during which heat is transferred to the high temperature region. Adiabatic throttling of the condensed vapour from the condensing to the evaporating pressure. Evaporation of the low pressure liquid during which heat is absorbed from the low temperature source. Isentropic compression of the vapour, from the evaporating to the condensing pressures.

Energy Transfers Analysis Compressor q4-1 = h4 – h1 + w4-1 If compression is adiabatic, q4-1 = 0, and w4-1 = h1 – h4 = wcomp Power requirement, P = ṁ (h1 – h4), where ṁ is the flow rate of working fluid per unit time. Condenser q1-2 = h2 – h1 + w w = 0, therefore q1-2 = h2 – h1 and rate of heat rejection Q1-2 = ṁ ( h2 – h1 )

Expansion Valve

q2-3 = h3 – h2 + w w = 0, therefore q 2-3 = h2 – h3 and process is assumed adiabatic q  0 therefore h2 = h3

Evaporator

q3–4 = h4 – h3 + w w = 0 therefore q3–4 = h4 – h3 and rate of heat absorbed Q3–4 = ṁ ( h4 – h3 )

Coefficient of Perfomance, COPref:

COPref =

q3 4 h4  h3 = w h1  h4

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Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012 5. EQUIPMENT TH Series Computer Linked Refrigeration Unit (Edibon).

6. PROCEDURES 6a) Condenser-water and evaporator-water a. Select water as a heat source by opening valves AVS-4 and AVS-5.Then click “START” b. Adjust the water flow rate at the condenser to 5 L/m and 3 L/m at the evaporator (evaporator load). c. Then click “COMPRESSOR” d. When the system is stabilized, start recording the data by click “START SAVING” e. Set the sampling rate at 120 second per sample. f. Record the data for six minutes (3 samples @ 360 second). “STOP SAVING” g. Then increase evaporator load to 5 L/m and repeat step (c) to step (f). 6b) Condenser-water and evaporator-air a. Select air as a heat source by opening valves AVS-3 and AVS-5.Then click “START” b. Adjust the water flow rate at the condenser to 5 L/m and adjust the air flow of the evaporator until 50% of the maximal flow (evaporator load). c. Then click “COMPRESSOR” d. When the system is stabilized, start recording the data by click “START SAVING” e. Set the sampling rate at 120 second per sample. f. Record the data for six minutes (3 samples @ 360 second). “STOP SAVING” g. Then increase evaporator load to 100% and repeat step (c) to step (f). 6c) Condenser-air and evaporator-air a. Select air as a heat source by opening valves AVS-3 and AVS-6. Then click “START” b. Adjust the air flow of the condenser to maximum flow (100%) and 50% of the maximal flow at the evaporator (evaporator load). c. Then click “COMPRESSOR” d. When the system is stabilized, start recording the data by click “START SAVING” e. Set the sampling rate at 120 second per sample. f. Record the data for six minutes (3 samples @ 360 second). “STOP SAVING” g. Then increase evaporator load to 100% and repeat step (c) to step (f). 6d) Condenser-air and evaporator-water a. Select water as a heat source by opening valves AVS-4 and AVS-6.Then click “START” b. Adjust the air flow of the condenser to maximum flow (100%) and adjust the water flow rate at the evaporator to 3 L/m (evaporator load). c. Then click “COMPRESSOR” d. When the system is stabilized, start recording the data by click “START SAVING” e. Set the sampling rate at 120 second per sample. f. Record the data for six minutes (3 samples @ 360 second). “STOP SAVING” g. Then increase evaporator load to 5 L/m and repeat step (c) to step (f).

7. DATA AND RESULTS 7.1

By using data obtained from the experiments, show sample calculations of the parameters below and complete the results summary table.

(a)

Refrigerant mass flow rate (kg/s),

(b)

Evaporator cooling load , Qevap

(c)

Coefficient of performance, COPref

(d)

Average COPref

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Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012 Data Summary table

240

360

240

360

Cond - Water Evap - Water

Cond - Water Evap - Air

SC-2 = 5 L/m

Cond - Air Evap - Air

Fan power at condenser = 100%

Cond - Air Evap - Water

Fan power at condenser = 100%

120

SC-2 = 5 L/m

120

d

Time (s)

360

SC-3 = 5 L/m

240

120

SC-3 = 3 L/m

360

120

Fan power at evap. = 100%

240

Fan power at evap. = 50%

360

Fan power at evap. = 100%

240

Fan power at evap. = 50%

360

SC-3 = 5 L/m

240

SC-3 = 3 L/m

360

120

c

Evaporator heat load

240

120

b

Condenser cooling load

360

120 a

Working fluid Exp #

240

120

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SW-1 (W) SC-1 (L/h) SP-2 (bar) SP-1 (bar) ST-4 (oC) ST-3 (oC) ST-2 (oC)

Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012 Results Summary table

Time (s)

Exp #

Vref (m3/s)

v2 (table) (m3/kg)

mref (kg/s) = Vref/v2

h3 (kJ/kg)

h4 (kJ/kg)

Qevap (kW) = mref (h4 h 3)

120 240 360 Average COP a 120 240 360 Average COP 120 240 360 Average COP b 120 240 360 Average COP 120 240 360 Average COP c 120 240 360 Average COP 120 240 360 Average COP d 120 240 360 Average COP

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COP = Qevap/ (SW1/1000)

Thermofluids Lab-MEC 554/ LS 2/ Rev. 02-20012 8. DISCUSSIONS a.

What is the effect on the COPref as the load is increased? Why?

b.

What is the effect of cooling medium on the average refrigeration COP? Why?

c.

What do you understand by the term load? Give examples of actual loads in refrigeration practice in a domestic fridge, in a room, and in a factory.

d.

Conclusion of the experiment.

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