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Unformatted text preview: 1. A pistoncylinder device, with a set of stops on the top, initially contains 3 kg of air at
 200 We and 27 C which supports the piston. Heat is now transferred to the air, and the
piston rises slowly until it hits the stops, at which point the volume is twice the initial
volume. More heat is transferred until the pressure inside the cylinder also doubles.
Determine the work done by the air and the amount of heat transfer for this process
neglecting friction. Also, show the process on a P—v diagram. (36 points). Use formal
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10 k] of heat to the System. The system‘s speciﬁc internal energy increases by
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of temperature from 500 K to 400 K due to heat loss and a decrease of pressure
from 5 bars to 4.5 bars due to ﬁ'iction. What happens to the velocity of the nitrogen? 111)
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’21'09, #3) 3' V9,, , a.) F) a} [:1 T i...— 3. A homeowner has devised a humidiﬁer that is shown below. Water is taken from the faucet
and fed to a reservoir that incorporates an electric resistance heater. The reservoir is shaped
like a nozzle so that a high velocity of vapor will be ejected and distributed to the room.
Water enters the reservoir thmugh a hose having a diameter of 5 mm and has a temperature
of 20 C, a pressure of 100 kPa, and a volume ﬂow rate of 1 liter per hour. Saturated water
vapor at 100 kPa leaves the top of the device through a 20 mm diameter circular opening. a)
Estimate the electrical power input required to operate the device at these conditions
and b) Calculate the ratio of the change in the fluid’s kinetic energy to its change in
enthalpy. On this basis, state whether or not it is reasonable to neglect kinetic energy
differences. You can neglect heat transfer between the reservoir and the room and changes . in potential energy. (36 points). Use formal problem solving procedure or lose points. ' ll '45? «II;I '9 I: ‘ In‘
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 Fall '08
 GAL

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