Refrigerating Compressor

a compressor that is a component of a vapor-compression refrigerating machine and is used to draw the refrigerant vapor from the evaporator and deliver it to the condenser. One of the most important characteristics of a refrigerating compressor is the refrigerating capacity of the refrigerating system, which, for a given refrigerant and under given temperature conditions, is proportional to the volumetric refrigerating capacity. Depending on the refrigerants employed, the required volumetric refrigerating capacity, and certain other conditions, the following types of compressors are used in refrigerating engineering: reciprocating, rotary, screw, and centrifugal.

Refrigerating compressors are similar to air and gas compressors in the principle of operation. However, they have a number of features that are associated with the operating conditions of refrigerating machines and with the thermodynamic, physical, and chemical properties of the vapor of the refrigerant used. For example, refrigerating compressors typically operate with superheated vapor. Certain requirements are imposed on refrigerating compressors. These include the feasibility of single-stage compression at substantially higher pressure discharge-to-suction ratios than in air compressors, that is, at pressure ratios of up to 10–12 or—in certain specially designed compressors—up to 25–30; the possibility of controlling the volumetric refrigerating capacity; the reduction of unbalanced forces, overall dimensions, and weight; and low noise levels, especially for the refrigerating compressors used in domestic refrigerators and air-conditioning systems.

In the case of reciprocating compressors, the requirements imposed have led to the development of multicylinder designs within a single hermetically sealed housing, called a monobloc casting, that is pressurized by the refrigerant vapor. Refrigerating compressors of this type are well balanced and can operate at a high piston speed (25–50 sec^–1). When the refrigerants employed are inert with respect to the windings of the electric motor that drives the compressor, the motor is built directly into the compressor housing.

Depending on the extent to which refrigerating compressors are sealed, a distinction is made between semisealed compressors and hermetically sealed compressors. In semisealed compressors, the housing has joints for access to the valves and the driving mechanism; hermetically sealed compressors have a one-piece (welded) housing. Semisealed compressors, which may be of the reciprocating, screw, or centrifugal type, have a wide range of capacities and electric motors with a power output of up to 500 kilowatts. Hermetically sealed compressors, which may be of the reciprocating or rotary type, are used when relatively low (up to several kilowatts) refrigerating capacities are required, for example, in domestic refrigerators and air conditioners and in commercial refrigerating equipment.