Thermal Power Engineering Answers

Two large parallel planes having emissivities of 0.4 and 0.6 are maintained at temperatures of 846 K and 288 K, respectively. A radiation shield having an emissivity of 0.2 on both sides is placed between the two planes. Calculate (a) the heat-transfer rate per unit area if the shield were not present, (b) the heat-transfer rate per unit area with the shield present. If the emissivity of the shield is increased by 50%, how many shields are needed for the heat transfer rate per unit area as compared with the obtained results from (b)?

A piston–cylinder device contains 1.2 kg of nitrogen gas at 120 kPa and 27°C. The gas is now compressed slowly in a polytropic process during which PV1.3 = constant. The process ends when the volume is reduced by one-half. Determine the entropy change of nitrogen during this process.

The radiator of a steam heating system has a volume of 20 L and is filled with superheated vapor at 200 kPa and 150°C. At this moment both the inlet and exit valves to the radiator are closed. After a while the temperature of the steam drops 40C as a result of heat transfer to the room air. Determine the entropy change of the steam during this process.

An air-conditioning system operating on the reversed Carnot cycle is

required to transfer heat from a house at a rate of 750 kJ/min to

maintain its temperature at 24°C. If the outdoor air temperature is

35°C, determine the power required to operate this air-conditioning

system.

An inventor claims to have developed a heat engine that receives 700 kJ of heat from a source at 500 K and produces 300 I of net work. while rejecting the waste heat to a sink at 290 K. Is this reasonable claim?

Determine the COP of a heat pump that supplies energy to a house at a rate of 8000 kJ/h for each kW of electric power it draws. Also, determine the rate of energy absorption from the outdoor air.

An air conditioner removes heat steadily from a house at a rate of 750 kJ/min while drawing electric power at a rate of 6 kW. Determine (a) the COP of this air conditioner and (b) the rate of heat transfer to the outside air.

As team power plant receives heat from a furnace at a rate of 280 GJ/h. Heat losses to the surrounding air from the steam as it passes through the pipes and other components are estimated to be about 8 GJ/h. If the waste heat is transferred to the cooling water at a rate of 145 GJ/h, determine (a) whethupoometoutput and (b) the thermal efficiency of this power plant.

1. A 600 MW steam power plant, which is cooled by a river, has a thermal efficiency of 40 percent. Determine the rate of heat transfer to the river water. Will the actual heat transfer rate be higher or lower than this value? Why?

A turbine operating under steady flow conditions receives steam at the

following state : pressure 13.8 bar ; specific volume 0.143 m3/kg ;

internal energy 2590 kJ/kg ; velocity 30 m/s. The state of the steam

leaving the turbine is : pressure 0.35 bar ; specific volume 4.37 m3/kg

; internal energy 2360

kJ/kg ; velocity 90 m/s. Heat is lost to the surroundings at the rate of

0.25 kJ/s. If the rate of steam flow is 0.38 kg/s, what is the power

developed by the turbine ?