11-3 The Ideal Vapor-Compression Refrigeration Cycle (Video Available)

The vapor-compression refrigeration cycle is the ideal model for refrigeration systems. Unlike the reversed Carnot cycle, the refrigerant is vaporized completely before it is compressed and the turbine is replaced with a throttling device.

1-2 Isentropic compression in a compressor
2-3 Constant-pressure heat rejection in a condenser
3-4 Throttling in an expansion device
4-1 Constant-pressure heat absorption in an evaporator

     

Schematic and T-s diagram for the ideal vapor-compression refrigeration cycle.

 

The ideal vapor-compression refrigeration cycle involves an irreversible (throttling) process to make it a more realistic model for the actual systems.

Replacing the expansion valve by a turbine is not practical since the added benefits cannot justify the added cost and complexity.

Steady-flow energy balance  $\left(q_{in}-q_{out}\right)+\left(w_{in}-w_{out}\right)=h_e-h_i$

 

$COP_R=\frac{q_L}{w_{net,in}}=\frac{h_1-h_4}{h_2-h_1}$

$COP_{HP}=\frac{q_H}{w_{net,in}}=\frac{h_2-h_3}{h_2-h_1}$

$h_1=h_{g\:@\:P_1}$    and     $h_3=h_{f\:@\:P_3}$    for the ideal case

                

Figure 11-5 The P-h diagram of an ideal vapor compression refrigeration cycle.

 

 

 

Figure 11-4 An ordinary household refrigerator.

 

 

 

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