Refrigerant 22 enters an insulated compressor operating at steady state as satur

Question

Refrigerant 22 enters an insulated compressor operating at steady state as saturated vapor at -16 degree C with a mass flow rate of 1.5 kg's. Refrigerant exits at 7 bar, 70 degree C. Changes in KE and PE from inlet to exit can be ignored. Determine: the volumetric flow rates at the inlet and exit, each in m 3/s the power input to the compressor, in kW A pump is employed to deliver liquid water from a pond to a higher elevation. The pump steadily draws water from the pond at a volumetric flow rate of 192 gal/min through a pipe having a 7 in diameter inlet. The exit diameter of the pipe is 2 in. and the exit is located 42 ft above the pipe inlet. Water enters at 66 degree F, 14.7 lbtf/in2. and exits with no significant change in temperature or pressure. The magnitude of the rate of heat transfer from the pump to the surroundings is 9% of the power input. The acceleration of gravity is 32.2 ft/s2. Determine: the velocity of the water at the inlet and exit, each in ft/s the power required by the pump, in hp. The electronic components of a computer are cooled by air flowing through a fan mounted at the inlet of the electronic enclosure. At steady state, air enters at 18 degree C, 1 atm. For noise control, the velocity of the entering air cannot exceed 0.9 m/s. For temperature control, the temperature of the air at the exit cannot exceed 34 degree C. The electronic components and fan receive, respectively, 68 W and 12 W of electric power. Determine the smallest fan area, in cm2, for which the limits on the entering air velocity and exit air temperature are met.

Explanation / Answer

At 16 deg C and quality = 1 (saturated vapor) we have enthalpy h1 = 256 kJ/kg and specific volume v1 = 0.0291 m^3/kg

At 7 bar and 70 deg C, we get enthalpy h2 = 299 kJ/kg, v2 = 0.0441 m^3/kg

a)

Volumetric flow rate at inlet = m*v1

= 1.5*0.0291

= 0.04365 m^3/s

Volumetric flow rate at outlet = m*v2

= 1.5*0.0441

= 0.06615 m^3/s

b)

Power input to compressor = m*(h2 - h1)

= 1.5*(299 - 256)

= 64.5 kW

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