The battery powers the motor that drives a paddle wheel to stir the gas at unifo

Question

The battery powers the motor that drives a paddle wheel to stir the gas at uniform pressure and temperature. The motor is diathermal and the tank containing the gas is also diathermal. The battery is adiabatic. Choose the motor as the system. Show the system from a thermodynamic point of view and the energy (rate) interactions between the system and the surrounding using proper arrows, and label them dearly, e.g., and . Overload the latter with appropriate subscripts. The motor operates at steady state. What is the rate of change of the motor internal energy? The rate of heat transfer from the motor to the surroundings is 20% of the input power to the motor. Find the input power to the motor in kW.

Explanation / Answer

Q in is the energy in..(lable the pipe going in the motor as Q)
W in is the energy out (lable the pipe going out of the motor as W)
U is the change in internal energy of motor (lable the heat going out into surrounding from motor as U)
rate of change of motor internal energy =Qdot -Wdot
input power is 1.2 times the power output... as 20 % energy is wasted

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