Moist air at atmospheric pressure enters a cooling and dehumidifying system at a relative humidity of 80% and a volumetric flow rate of 2.0 m3/s. The air exiting the system is to have a temperature of 20°C and a relative humidity of 50%. Plot the mass flow rate of condensed water, the heat transfer rate through the cooling coil, and the heat transfer rate through the heating element for values of the inlet temperature ranging between 15°C and 35°C. For Problems, assume that the refrigerant exits the evaporator as a saturated vapor and that the refrigerant exits the condenser as a saturated liquid.
Problem 1
A vapor-compression refrigeration cycle is to provide the heat removal mechanism for the cooling coils described in Problem 2. The refrigerant used in the system is R-134a. The evaporator pressure is 210 kPa and the condenser pressure is 1200 kPa. Determine the power required by the compressor of the refrigeration cycle if (a) the compressor is isentropic, and (b) the isentropic efficiency of the compressor is 80%.
Problem 2
Hot, humid air at 30°C and 60% relative humidity enters a cooling and dehumidifying device at a mass flow rate of dry air of 2.5 kg/s. After passing over the cooling coils, the saturated air is heated to 22°C and a relative humidity of 30%. The air pressure is 1 atm. Determine the heat transfer rates through the cooling coils and the heating element, and determine the rate of condensed water leaving the system.
Problem 3
Repeat Problem4 if the refrigerant is ammonia instead of R-134a.
Problem 4
A vapor-compression refrigeration cycle is to provide the heat removal mechanism for the cooling coils described in Problem 5. The refrigerant used in the system is R-134a. The evaporator pressure is 210 kPa and the condenser pressure is 1200 kPa. Determine the power required by the compressor of the refrigeration cycle if (a) the compressor is isentropic, and (b) the isentropic efficiency of the compressor is 80%.
Problem 5
Hot, humid air at 30°C and 60% relative humidity enters a cooling and dehumidifying device at a mass flow rate of dry air of 2.5 kg/s. After passing over the cooling coils, the saturated air is heated to 22°C and a relative humidity of 30%. The air pressure is 1 atm. Determine the heat transfer rates through the cooling coils and the heating element, and determine the rate of condensed water leaving the system.
Problem 6
A vapor-compression refrigeration cycle is to provide the heat removal mechanism for the cooling coils described in Problem. The refrigerant used in the system is R-134a. The evaporator pressure is 20 psia and the condenser pressure is 140 psia. Determine the power required by the compressor of the refrigeration cycle if (a) the compressor is isentropic, and (b) the isentropic efficiency of the compressor is 80%.
Problem 7
Moist air at 90°F and a relative humidity of 40% enters a cooling and dehumidifying system. The air exits the system at 70°F and 40% relative humidity. The air pressure is 1 atm, and the mass flow rate of dry air is 5 lbm/s. Determine (a) the rate at which water is condensed from the air, (b) the heat transfer rate through the cooling coils, and (c) the heat transfer rate through the heating element.
Problem 8
A vapor-compression refrigeration cycle is to provide the heat removal mechanism for the cooling coils described in Problem 9. The refrigerant used in the system is R-134a. The evaporator pressure is 150 kPa and the condenser pressure is 1000 kPa. Plot the power required by the compressor of the refrigeration cycle as a function of the isentropic efficiency of the compressor, with the range of isentropic efficiencies considered to be between 0.40 and 1.0.
Problem 9
Moist air at atmospheric pressure and a volumetric flow rate of 3.5 m3/s enters a cooling and dehumidifying system at 25°C and a relative humidity of 90%. The air exits the system at 20°C with a relative humidity of 25%. Determine (a) the rate at which water is condensed from the air, (b) the heat transfer rate through the cooling coils, and (c) the heat transfer rate through the heating element.
Problem 10
A vapor-compression refrigeration cycle is to provide the heat removal mechanism for the cooling coils described in Problem 11. The refrigerant used in the system is R-134a. The condenser pressure is 1000 kPa. The isentropic efficiency of the compressor is 0.80. Plot the power required by the compressor of the refrigeration cycle for evaporator pressures ranging between 100 kPa and 300 kPa.
Problem 11
Hot, humid air at 30°C and 60% relative humidity enters a cooling and dehumidifying device at a mass flow rate of dry air of 2.5 kg/s. After passing over the cooling coils, the saturated air is heated to 22°C and a relative humidity of 30%. The air pressure is 1 atm. Determine the heat transfer rates through the cooling coils and the heating element, and determine the rate of condensed water leaving the system.
Problem 12
A vapor-compression refrigeration cycle is to provide the heat removal mechanism for the cooling coils described in Problem 13. The refrigerant used in the system is R-134a. The evaporator pressure is 40 psia. The isentropic efficiency of the compressor is 0.80. Plot the power required by the compressor of the refrigeration cycle for condenser pressures ranging between 120 psia and 300 psia.
Problem 13
Moist air at 90°F and a relative humidity of 40% enters a cooling and dehumidifying system. The air exits the system at 70°F and 40% relative humidity. The air pressure is 1 atm, and the mass flow rate of dry air is 5 lbm/s. Determine (a) the rate at which water is condensed from the air, (b) the heat transfer rate through the cooling coils, and (c) the heat transfer rate through the heating element.
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