performance of the ideal compessor
in the ideal compressor, the compression of the gas trapped in the clearance volume are both isentropic. The reexpansion of the trapped gas is the only factor which influences volumetric effiency in the ideal compressor.
in the next few pages the effect of suction pressure on the performance of an ideal compressor will be studied. Figure 11-5 shows the effect of evaporating temperature on clearance volumetric efficiency. The volumetric efficiencies are calculated from Eq. (11-6) and apply to a refrigerant 22 compressor with a clearance of 4.5 percent operaing with a condensing temperature of 35 c. The clearance volumetric efficiency is zero when the evaporating temperature is -61 c, at with temperature the saturation pressure corresponds to p3 in Fig. 11-4. When the suction pressure and discharge pressure are the same (same evaporating and condensing pressure ), the volumetric efficiency is 100 percent.
The mass rate of flow controls the capacity and power requirement more directly than the volume rate of flow. The mass rate of flow, w kg/s, through a compressor is proportional to the displacement rate in liters per second and the volumetric efficiency and inversely proportional to the specific volume of gas entering the compressor.