Problem 2: The refrigerator in the diagram below uses R-134a as its working fluid and operates with $P_1 = 140$ kPa and $x_1 = 1$ at the outlet of the evaporator, and $P_3 = 800$ kPa and $x_3 = 0$ at the outlet of the condenser. Complete a thermodynamic analysis of the system assuming ideal operation of the compressor by finding (A) the pressure, temperature, enthalpy, and entropy at each state, (B) the required power into the compressor and the heat exchanged in the condenser and evaporator, and (C) the coefficient of performance of the system. Compare the coefficient of performance for the vapor compression system with that of the Carnot system where $T_H = 25$ °C and $T_L = -10$ °C.
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Calculate the pressure, temperature, enthalpy, and entropy at each state: A = 800 kPa, T = 25 C, H = -287 J/Kg, S = -273 J/Kg Show more…
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Problem 2 Air enters a compressor at a pressure of 1.0 bar and exits at 8.5 bar. The compressor inlet temperature is 37 °C. The compressor is not insulated. Kinetic and potential energy effects can be neglected. The compressor outlet temperature is 650 K and the power input to the compressor is 500 kW. The compressor is operating at steady-state, and the air can be modeled as an ideal gas. The air mass flow rate through the compressor is 1.8 kg/s. a. Determine the direction and rate of heat transfer, in kJ/kg. b. Determine the compressor isentropic efficiency. c. Draw the process on a T-s diagram (clearly indicate the direction of the process and label the states). d. Determine the entropy generation rate, in kJ/kg/K, assuming the boundary temperature is 100 °C, and state the nature of the process (reversible, irreversible, or impossible). Summarize you results in the table below a. heat transfer, kJ/kg (include direction, so in or out?) b. isentropic efficiency d. entropy generation rate, in kJ/kg/K, and is it reversible, irreversible, or impossible?
Madhur L.
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