Question

-Rome can get pretty hot in the mid-summer! Most of the air conditioning units in the Tiber campus use the working fluid R-134a (1,1,1,2-tetrafluoroethane), which is replaces the less environmentally-friendly R-12 of years ago. a) Illustrate the following air conditioning cycle, indicating material, heat, and work flows, as well as given/known temperatures and pressures: R-134a is pressurized to 10.2 bar in an adiabatic, reversible compressor. This high-pressure, hot refrigerant is condensed outside of the building using ambient air to a saturated liquid state (there is no pressure loss in the condenser). The liquid is then throttled across a well-insulated valve to a pressure of 5.0 bar. Inside the building, saturated vapor of R-134a which is returned to the compressor. b) What are the temperatures (in °C) and specific enthalpies (in kJ/kg) of the streams leaving the condenser and evaporator, respectively? c) What are the specific entropies (in kJ/kg/K) entering and leaving the room air is blown across an evaporator (no pressure loss), producing a compressor, respectively? d)The fluid exiting the compressor will be slightly superheated. What are its temperature (in °C) and specific enthalpy (in kJ/kg), respectively? e) What is the specific heat duty for the condenser (the heat that must be dumped to the outside air), in kJ/kg? f The throttling valve will produce a mixture of liquid and vapor R-134a. What are this stream's specific enthalpy (in kJ/kg) and quality? g) What is the specific heat duty of the evaporator (the heat absorbed from inside the room), in kJ/kg? h) The unit is expected to process about 3 kg/min of air, which enters the evaporator at 27°C and exits at 19°C. Calculate the required heat duty (in kW) if air is approximated as an ideal gas with Cp- 1 J/g.K i) What is the required circulation rate of R-134a, in kg/min?

Answer 1

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