TABLE OF CONTENTS Waste heat must occasionally be removed from a process at below-ambient temperatures. This is normally accomplished by evaporating a light fluid called a refrigerant. Common industrial refrigerants are
Ammonia
Propane
Freon
Your home central air-conditioning system is a good example of a simple refrigeration loop. Figure 26.1 illustrates the basic components:
Refrigerant motor-driven compressor
Refrigerant condenser
Refrigerant letdown valve
Evaporator
Refrigerant receiver
The basic process flow of the refrigerant system is
The compressed refrigerant vapor is discharged from the compressor. This vapor is superheated, meaning that it is above its dew-point temperature.
The vapor is next cooled and condensed in the refrigerant condenser. Typically, 75 to 80 percent of the condenser heat duty is the latent heat of condensation of the refrigerant. The remaining heat duty is sensible-heat removal. The sensible heat removed is a combination of desuperheating the vapor and subcooling the condensed liquid refrigerant.
Figure 26.1: Refrigeration system.
The subcooled refrigerant next flows into the refrigerant receiver. Subcooled means that the refrigerant temperature is below its boiling point or bubble-point temperature. The liquid refrigerant loses a small amount of pressure as it enters the receiver. The pressure loss is due to friction in the piping and an increase in the elevation of the refrigerant as it enters the receiver.
The condensed liquid refrigerant next flows through the letdown valve. In Fig. 26.1, this letdown valve is not controlling the receiver liquid level. The receiver level is allowed to vary as the total refrigerant...
