What is the superheat at the inlet of a compressor with a suction pressure of 33 PSIG and suction temperature of 34°F?

To determine the superheat at the inlet of a compressor, you must first understand the relationship between temperature and pressure in a refrigeration cycle. Superheat is defined as the difference between the actual temperature of the vapor at the inlet of the compressor and the saturation temperature corresponding to the suction pressure.

In this case, the suction pressure is given as 33 PSIG. To find the saturation temperature, it's essential to convert the pressure from PSIG to PSAT by adding atmospheric pressure (approximately 14.7 PSIA). Thus, the total pressure becomes 33 + 14.7 = 47.7 PSIA.

Using a refrigerant property chart or tables, you can identify the saturation temperature corresponding to a saturation pressure of 47.7 PSIA. For many common refrigerants, this saturation temperature can be around 20°F.

Now that you have the saturation temperature, you can calculate superheat by subtracting the saturation temperature from the actual temperature of the refrigerant vapor. Here, the actual suction temperature is given as 34°F.

Applying the formula:

Superheat = Actual Temperature - Saturation Temperature

Superheat = 34°F - 20°F = 14°F

This calculation confirms the superheat at the