Thermo Midterm 2005

Thermo Midterm 2005 - The power input to the compressor is...

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Midterm MAE 221 Thermodynamics Wednesday, 9 November 2005 10:00am – 10:50am FC004 Closed Book Closed Notes Be sure to state all assumptions, and draw and label relevant schematics, processes, etc. 1. A window air conditioner unit consumes 2 kW of electricity and has a coefficient of performance (COP) of 4. a) (5 %) Write down the definition of the COP for an air conditioner. b) (5 %) If the air conditioner is moved to the center of the room and plugged in, what is the rate of heating or cooling the unit will provide to the room air? c) (20 %) Consider a similar air conditioner which operates with Refrigerant 134a. The air conditioner has within it a compressor into which the refrigerant enters at 3.2 bar and 10 ° C, and is compressed at steady state to 10 bar, 70 ° C. The volumetric flow rate of refrigerant entering is 3.0 m 3 /min.
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Unformatted text preview: The power input to the compressor is 55.2 kJ per kg of refrigerant flowing. Neglecting kinetic and potential energy effects, determine the heat transfer rate in kW. 2. (35 %) Steam enters a nozzle operating at steady state at 30 bar, 320C, with a velocity of 100 m/s. The exit pressure and temperature are 10 bar and 200 ° C respectively. The mass flow rate is 2 kg/s. Neglecting heat transfer and potential energy, determine a) the exit velocity in m/s. b) the inlet and exit flow areas, in cm 2 . 3. (35%) Air undergoes a compression in a piston-cylinder assembly from p 1 = 1 atm, T 1 = 70 ° F to p 2 = 5 atm. Using the ideal gas model, find the work and heat transfer per unit mass, BTU/lb, for a) an isothermal process b) a polytropic process with n = 1.3. c) show both processes on a single p-v diagram...
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This note was uploaded on 04/08/2008 for the course MAE 221 taught by Professor Danielm.nosenchuck during the Fall '05 term at Princeton.

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