A dentist drill is driven by a small, high-speed turbine operating on compressed air which produces a shaft power output of 150W . At the inlet to the turbine the air has a pressure of 450kPa and a temperature of 65oC . At the exit of the turbine, the air has a pressure of 150kPa and a temperature of -25oC. Both the inlet and exit velocities may be assumed to be negligable and the process to be adiabatic.
Assume a constant specific heat (at constant pressure) of air, Cpair = 1004 J/kg K
Note, sign convention requires work done by device to be positive
What is the required mass flow rate of air through the turbine to deliver the required power output?
A kitchen refrigerator removes 2.5kJ of energy from the frozen food cabinet using 1kJ of work done by the electrically powered compressor.
a) How much energy is released into the kitchen?
b) What is the coefficient of performance of the refrigerator?