A 1200 kW water-cooled chiller has a centrifugal compressor with refrigerant R134a as the working fluid. The compressor runs at 9600 rev/min and has a slip factor of 0.95 and an overall isentropic efficiency of 90%. The impeller tip speed is not to exceed 160m/s. The evaporating and condensing temperatures are 2°C and 40°C respectively. Assuming that there is no superheating and sub-cooling, a) sketch the refrigration cycle on a P-h diagram (please indicate the pressures and specific enthalpies of all points in the cycle); b) determine the mass flow rate of the refrigerant R134a; c) determine the coefficient of performance of the chilled water plant; and discuss the possible measures to uplift the plant COP d) determine the number of stages and the impeller tip diameters, assuming that all stages would share same work input and each stage compression would have the same impeller tip diameter. e) Please also comment how the slip factor can affect the energy performance of the centrifugal compressor.
A 1200 kW water-cooled chiller has a centrifugal compressor with refrigerant R134a as the working fluid. The compressor runs at 9600 rev/min and has a slip factor of 0.95 and an overall isentropic efficiency of 90%. The impeller tip speed is not to exceed 160m/s. The evaporating and condensing temperatures are 2°C and 40°C respectively. Assuming that there is no superheating and sub-cooling,
a) sketch the refrigration cycle on a P-h diagram (please indicate the pressures and specific enthalpies of all points in the cycle);
b) determine the mass flow rate of the refrigerant R134a;
c) determine the coefficient of performance of the chilled water plant; and discuss the possible measures to uplift the plant COP
d) determine the number of stages and the impeller tip diameters, assuming that all stages would share same work input and each stage compression would have the same impeller tip diameter.
e) Please also comment how the slip factor can affect the energy performance of the centrifugal compressor.
Use the online software http://www.peacesoftware.de/einigewerte/r134a_e.html or property table and p-h diagram for R134a where necessary.
Step by step
Solved in 2 steps with 3 images
