A dentist drill is driven by a small, high-speed turbine operating on compressed

Question

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 ?

( ) grams/s

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 ? ( ) kJ

b) What is the coefficient of performance of the refrigerator ? ( )

Please Show Work

Explanation / Answer

ANSWER this will help you Name "G" the required mass flow rate of air through the turbine. [mass/ sec] L = work done by device / mass P = power output P = L * G then G = P/L We haven't L but we know that the process may be assumed adiabatic (Q (heat) = 0) So for the 1

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