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Unformatted text preview: 1. A heat pump uses R134a as a working fluid. The evaporator pressure is 165 kPa and the condenser pressure is 1.6 MPa. The R134a enters the compressor as a saturated vapor and leaves the condenser as a saturated liquid. The compressor is adiabatic and has an isentropic efficiency of c = 0 . 85. The power input to the compressor is W c = 5 kW. Determine a) The mass flow rate of the R134a b) The rate of heat transfer from the condenser c) The coefficient of performance of the cycle. Advice: the heat from the condenser could be obtained from q H = ( h 3- h 2 ), where 2 and 3 are the compressor exit and condenser exit, or it could also be obtained from q H = q L + w net = h 4- h 1 + w net , where w net = h 1- h 2 = ( h 1- h 2 s ) / C is the compressor work and h 4 = h 3 across the throttle. The latter approach bypasses the need to calculate the actual enthalpy at state 2 (although this would not be too difficult). Here are some numbers via the latter method; w c = w s / c = 55 . 9 kJ / kg , h 2 = h 1 + w c = 297 kJ / kg m = W/w c = 0 . 0894 kg / s 2. An ideal vaporcompression refrigeration cycle that uses R-134a maintains the condenser at 1 MPa and the evaporator at 4 C. Determine the system COP and the amount of power required to serviceC....
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- Spring '11