REFRIGERATING ENGINEERING In reality,additional work is required to compensate for mechanical friction,fluid friction,and other losses in the compressor.Let us define a total isentropic compression efficiency as mk =Edl ak or ak=Edl mk 3.08c where a is the actual work that must be supplied to the shaft of the compressor. Hence the actual compressor power is 民=i/Tk 3.08d The efficiency nk often is in the range 0,6-0,8,and with an adequate knowledge of the magnitude in an actual case,the outlet state c from the compressor can be established when the inlet state b is known. It is often of interest to calculate the outlet conditions from the compressor.If the compressor operates adiabatically,i.e.without any heat transfer to or from the sur- roundings,we have hik=hak +a or hik=h2k+&m 3.08e where hik is the enthalpy of the refrigerant at the true outlet state from the compressor. Combining this with Equation 3.08a we can also write hik =h2k +(hik.is -h2k)/m 3.08f If the compressor is non-adiabatic,i.e.some heat transfer occurs,the Equations 3.08c-f must be modified according to Equation 3.05b. The discharge line,or the hot gas line,delivers the high pressure,high temperature vapor from the compressor to the condenser. 3.09 The condenser might be air cooled or water cooled or a combination thereof.The refrigerant condenses in the condenser.The pressure of the vapor will be so high that the available cooling medium can be used to bring the vapor to condensation.To enable this heat transfer,from the refrigerant to the cooling medium,the condensing temperature must be higher than the temperature of the cooling medium.With the relation between saturated vapor pressure and temperature,Figure 3.03,it is possible to determine the necessary condensing pressure. For example if the condensing temperature is supposed to be +30C,using ammonia as the refrigerant,the compressor has to maintain a pressure equal to 11,7 bar in the condenser. 3:8