A rigid chamber contains 100 kg of water at 500 kPa, 100 C. A paddle wheel stirs

Question

A rigid chamber contains 100 kg of water at 500 kPa, 100 C. A paddle wheel stirs the water at 1000 rpm with a torque of 100 N-m while an internal electrical resistance heater heats the water, consuming 10 amps of current at 110 Volts. Because of thin insulation, the chamber loses heat to the surroundings at 27C at a rate of 1.0 kW. Determine (a) the rate of shaft work transfer (in kW), (b) the electrical work transfer (in kJ) in 10 s, (c) the rate of heat transfer (in kW). Include the sign in all your answers. (d) Determine the change in stored energy E of the system in 10 s (in kJ). Neglect KE and PE.

Explanation / Answer

a) rate of shaft work transfer = T*w = 100*[(1000*2*pie) / 60] = 10.47 kW b) electrical work transfer = V*I*t = 110*10*10 = 11000 J = 11 kJ c) Q' = Q'in - Q'out Q' = T*w + V*I*t - heat loss Q' = 10.47 + 1.1 - 1 = 10.57 kW d) change in internal energy = Q'*t = 10.57*10 = 105.7 kJ

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