Question: In a refrigeration cycle, how is the pressure at the compressor outlet determined?

The outlet pressure of the compressor is related to the condensing pressure; the outlet pressure of the compressor cannot be too low, otherwise the compressor cannot operate properly.

If the outlet pressure of the compressor is too low, it will result in a low evaporation pressure, which in turn poses a risk of the evaporator freezing.

This post was last edited by 47238789 on 2010-7-14 at 13:56. Reply to 1#: It makes no sense. The exhaust pressure is related to the condensation pressure, and the condensation pressure is related to the condensation temperature. The condensation temperature affects the energy consumption and efficiency of refrigeration; the lower the condensation pressure, the lower the required condensation temperature. There is a limit point at which, when the condensation temperature equals the refrigeration temperature, refrigeration becomes meaningless. That’s why normal-temperature air or water is often used to facilitate the condensation of the refrigerant. Additionally, the condensation pressure must be higher than the evaporation pressure; otherwise, how can the refrigerant flow, and how can it be throttled to reduce pressure and lower temperature? Using an economizer can improve energy efficiency; the condensed refrigerant flows through both the tube side and the shell side of the economizer, with the evaporation of refrigerant in one side lowering the temperature of the refrigerant in the other side

In fact, the exhaust pressure is influenced by various factors such as the compressor’s performance, operating conditions, and condensation conditions. The exhaust temperature of a compressor generally falls within a certain range; temperatures that are too low or too high are not acceptable. If the temperature is too low, the cooling capacity cannot be utilized effectively, while if it is too high, the power consumption increases and the compressor ratio rises. Therefore, an appropriate exhaust temperature is necessary

The compression outlet pressure is related to the condensation pressure, which in turn relates to the condensation temperature. The condensation temperature is influenced by the cooling capacity of the condenser, as well as the temperature of the cooling water and the ambient temperature; it is necessary to ensure that the refrigerant can be condensed. As can be seen from the graph, the pressure is low as well; consequently, the difference between the evaporation temperature and the condensation temperature is small. Given the work that the compressor has to perform, the coefficient of performance for cooling must be high.

With the suction pressure remaining constant, an appropriate increase in the discharge pressure can enhance the cooling capacity; of course, the work done by the compressor also increases.

This pressure is the theoretical condensation pressure, and the condensation pressure is related to the condensation temperature – the higher the pressure, the higher the temperature. In order to enhance the condensation effect, it is desirable for the condensation pressure to be low, but it must remain within a certain range; too low a pressure is not acceptable.

This post was last edited by li*ch1968 on 2011-1-4 at 19:11. I took a look, and no one got it right; aside from the person who replied on the 5th floor. First of all, what the original poster said is correct: the lower the outlet pressure, the greater the cooling capacity will be. This pressure corresponds to the condensing pressure (slightly higher). The expansion valve needs the pressure difference between the condensing pressure and the evaporating pressure in order to function properly (it is necessary to ensure an adequate supply of refrigerant to the evaporator). If the condensing pressure is too low, a sufficient pressure difference cannot be established, and only part of the refrigerant will reach the evaporator, which will result in abnormal cooling performance. According to our design requirements, this pressure must be 11 kg (the minimum value); if it’s lower, things will not work properly. Another important reason is that the oil also requires this pressure difference in order to return properly; otherwise, the compressor will suffer severe wear or even get damaged (due to insufficient oil)