Consider a Carnot heat pump cycle executed in a steady-flow system in the saturated mixture region using R-134a flowing at a rate of 0.264 kg/s. The maximum absolute temperature in the cycle is 1.15 times the minimum absolute temperature, and the net power input to the cycle is 5 kW. If the refrigerant changes from saturated vapor to saturated liquid during the heat rejection process, determine the ratio of the maximum to minimum pressures in the cycle.

7.15

Explanation:

Firstly, the COP of such heat pump must be measured that is,

Therefore, the temperature relationship,

Then, we should apply the values in the COP.

The number of heat rejected by the heat pump must then be calculated.

We must then calculate the refrigerant mass flow rate.

The value is 145.27 and therefore the hot reservoir temperature is 64° C.

The pressure at 64 ° C is thus 1849.36 kPa by interpolation.

And, the lowest reservoir temperature must be calculated.

the lowest reservoir temperature = 258.703  kpa                    

So, the pressure ratio should be = 7.15