5.1 An electric oil radiator with a capacity of 30 liters is placed in a room. The volume that the air occupies in the room is 40 m3 . Both the air in the room and the oil in the radiator are initially at 12°C. The radiator has an output of 1.8 kW and is switched on. At the same time, the room begins to emit heat to the outside at an average rate of 0.35 kJ/s. After a certain time, the room temperature is at 21°C and the oil in the radiator is at 60°C. The oil's mass density and specific heat capacity are set to 850 kg/m3 and 2.2 kJ/(kgÿ°C). luft 12°C oljeradiator Calculate how long the radiator has been on. Assume that the room has a constant volume, that it is tight and that no air can leak out or in. You can set the air pressure in the room at the start to 100 kPa. 5.2 Air flows into an adiabatic nozzle at 2.1 MPa, 370°C and 10 m/s. At the outlet of the nozzle, the pressure is 1.7 MPa and the speed 200 m/s. The outlet diameter is 20 cm. Use constant specific heat capacity values at 600 K. 2,1 MPa 370°C 10 m/s luft 1,7 MPa 200 m/s 20 cm a) Calculate the temperature of the air at the outlet of the nozzle in °C. b) Calculate the volume flow in m3 /s at the outlet. c) Calculate the cross-sectional area of the inlet in m2 5.3 Steam flows stationary through an adiabatic turbine. At the inlet, the steam's pressure, temperature and speed are respectively 7 MPa, 600°C and 20 m/s. At the outlet, the pressure is 50 kPa, the steam quality 95% and the speed 70 m/s. The mass flow is 12 kg/s. turbin Calculate a) The change in the kinetic energy of the water vapor in kJ/kg. b) The turbine's power output in kW or MW. c) The cross-sectional area of the turbine inlet in m2- d) The volume flow at the turbine outlet. 5.4 A compressor in stationary operation increases the pressure of CO gas (carbon monoxide) from 100 kPa to 800 kPa. At the inlet to the compressor the gas is at 300 K and at the outlet the gas is at 650 K. The mass flow of CO is 0.4 kg/s and the heat loss to the surroundings is 25 kJ/kg. qut W a) Calculate the volume flows at the inlet and outlet in m3 /s. b) Calculate the required compressor power in kW using constant specific heat capacities at 300 K. c) Calculate the required compressor power in kW using specific heat capacities at the average temperature of this process d) Calculate the required compressor power in kW using values from tab. A-21. Also calculate the deviation between the results from b) and c) and the result id) in %.

5.1 An electric oil radiator with a capacity of 30 liters is placed in a room. The volume that the air occupies in the room is 40 m3 . Both the air in the room and the oil in the radiator are initially at 12°C. The radiator has an output of 1.8 kW and is switched on. At the same time, the room begins to emit heat to the outside at an average rate of 0.35 kJ/s. After a certain time, the room temperature is at 21°C and the oil in the radiator is at 60°C. The oil's mass density and specific heat capacity are set to 850 kg/m3 and 2.2 kJ/(kgÿ°C). luft 12°C oljeradiator Calculate how long the radiator has been on. Assume that the room has a constant volume, that it is tight and that no air can leak out or in. You can set the air pressure in the room at the start to 100 kPa. 5.2 Air flows into an adiabatic nozzle at 2.1 MPa, 370°C and 10 m/s. At the outlet of the nozzle, the pressure is 1.7 MPa and the speed 200 m/s. The outlet diameter is 20 cm. Use constant specific heat capacity values at 600 K. 2,1 MPa 370°C 10 m/s luft 1,7 MPa 200 m/s 20 cm a) Calculate the temperature of the air at the outlet of the nozzle in °C. b) Calculate the volume flow in m3 /s at the outlet. c) Calculate the cross-sectional area of the inlet in m2 5.3 Steam flows stationary through an adiabatic turbine. At the inlet, the steam's pressure, temperature and speed are respectively 7 MPa, 600°C and 20 m/s. At the outlet, the pressure is 50 kPa, the steam quality 95% and the speed 70 m/s. The mass flow is 12 kg/s. turbin Calculate a) The change in the kinetic energy of the water vapor in kJ/kg. b) The turbine's power output in kW or MW. c) The cross-sectional area of the turbine inlet in m2- d) The volume flow at the turbine outlet. 5.4 A compressor in stationary operation increases the pressure of CO gas (carbon monoxide) from 100 kPa to 800 kPa. At the inlet to the compressor the gas is at 300 K and at the outlet the gas is at 650 K. The mass flow of CO is 0.4 kg/s and the heat loss to the surroundings is 25 kJ/kg. qut W a) Calculate the volume flows at the inlet and outlet in m3 /s. b) Calculate the required compressor power in kW using constant specific heat capacities at 300 K. c) Calculate the required compressor power in kW using specific heat capacities at the average temperature of this process d) Calculate the required compressor power in kW using values from tab. A-21. Also calculate the deviation between the results from b) and c) and the result id) in %.

Refrigeration and Air Conditioning Technology (MindTap Course List)

8th Edition

ISBN:9781305578296

Author:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Publisher:John Tomczyk, Eugene Silberstein, Bill Whitman, Bill Johnson

Chapter2: Matter And Energy

Section: Chapter Questions

Problem 27RQ: How many Btu/h would be produced in a 12-kW electricheater?

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