The coefficient of performance of the refrigerator

The coefficient of performance of the refrigerator, COP
R
=
Q
L
W
net
=
Q
L
Q
H
− Q
L
COP
R1
=
0.146 kW
0.027 kW − 0.146 kW
=
|
− 1.22
|
= 1.22
COP
R2
=
0.198 kW
0.0108 kW − 0.198 kW
=
|
− 1.057
|
= 1.057
COP
R3
=
0.219 kW
0.0079 kW − 0.219 kW
=
|
− 1.037
|
= 1.037
COP
R4
=
0.355 kW
0.010 kW − 0.355 kW
=
|
− 1.028
|
= 1.028
COP
R4
=
0.99 kW
0.004 − 0.99 kW
=
|
− 1.0
|
= 1.0

From the above calculation, we can conclude that the value of the coefficient of performance
of the refrigerator (COP
R
) decreases with the increase of the value of the rate of heat transfer in
evaporator, Q
L
. This
COP
R =
Q
L
Q
H
− Q
L
The coefficient of performance (COP) seems to be inversely proportional to the rate of heat transfer in
evaporator Q
L
. From theoretical point of view, (COP) must be directly proportional to the rate of heat
transfer in evaporator. Notice that the value of COP
R
can be greater than unity which is the amount of
heat transfer from refrigerated space can be greater than the work input. This is in contrast to the
thermal efficiency, which can never be greater than1.
A) Heat transfer that occurs in the condenser and evaporator for the five tests.
Based on Graph 1, the temperature versus condenser flow rate, Q
H,
we can see that as the condenser
flow rate increase, the temperature will decrease. This means that, the heat transfer rate is inversely
proportional to the water flow rate. The change in condenser flow rate will affect the temperature of
water which is going through the evaporator and the condenser which is labeled from T1 to T6.
As we can see from the graph, we can interpret that the value of T1, T2 and T4 are almost
constant for every reading even though there is a change in condenser flow rates. For the
temperature T1 and T2, they are almost not influenced by the change of condenser flow rates
because the refrigerant R-141b that enter and leaves the evaporator is at saturated state. For
the value of T3 and T6, they are affected with the changing of condenser flow rates. Their
values are decline as the condenser flow rates increase due to transferring at the condenser.

B) What are the effects of changes in the condenser flow rate of T1-T6, compressor power?
Based on Graph 2, we can conclude that compressor power decrease as the condenser flow
rate increase. Therefore, the compressor power is inversely proportional to the condenser
flow rate. However, compressor power is directly proportional to the specific volume of the
water.