Practice exam 2

# Practice exam 2 - 1 A reversible cyclic device does work...

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1. A reversible cyclic device does work while exchanging heat with three constant temperature reservoirs as illustrated in the figure. The three reservoirs 1, 2, and 3 are at temperatures of 1000 K, 300 K, and 500 K respectively. It is known that 400 kJ of heat are transferred from reservoir 1 to the device, and the total work done by the cyclic device is 100 kJ. Determine both the magnitude and direction of the heat transfer with the other two reservoirs. [40] 100 = Q 2 + Q 3 + 400 (Q 2 , Q 3 : heat from the device) Since the equation has two unknowns, a second equation must be obtained. From the second law S = (dQ/T) rev = 0 or Q 1 /T 1 + Q 2 /T 2 + Q 3 /T 3 = 0 Substituting, 400/1000 + Q2/300 +Q3/500 =0 0.4 + Q2/300 + Q3/500 = 0 Solving gives 0.4 + (-300-Q 3 )/300 + Q 3 /500 = 0, Q 3 = -450 kJ Q 2 = 150 kJ Therefore, 150 kJ of heat is transferred from reservoir 2 to the device and 450 kJ of heat are rejected to reservoir 3.

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2. Water at 15 kPa, 40°C enters a pump and leaves after the pressure has been raised to 5
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Practice exam 2 - 1 A reversible cyclic device does work...

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