At winter design conditions, a house is projected to lose heat at a rate of 60,000 Btu/h. The internal heat gain from people, lights, and appliances is estimated to be 6000 Btu/h. If this house is to be heated by electric resistance heaters, deter- mine the required rated power of these heaters in kW to main- tain the house at constant temperature.
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- Heat is transferred at a rate of 0.1 kW through glass wool insulation (density=100kg/m3) with a 5-cm thickness and 2-m2 area. If the hot surface is at 70C, determine the temperature of the cooler surface.An automobile engine consumes fuel at a rate of 22 L/h and delivers 55 kW of power to thewheels. If the fuel has a heating value of 44,000 kJ/kg and a density of 0.8 g/cm3, determinethe efficiency of this engine. Hint, Qa= mass of fuel * heating value.The air duct of the heating system of a hall, an electric heater placed inside andIt consists of a 300 W fan. While the air is continuously flowing in the duct with a flow rate of 0.6 kg/stemperature rises by 5°C. Since there is a loss of 400 W 151 from the channel surfaces to the environmentCalculate the power of the electric heater. (The specific heating value of air is - 1.005 kJ/kgK.)
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- Energy can be transferred either by heat or work. Consider a room that is heated as a result of solar radiation coming in through the windows. Is this a heat or work interaction for the room? Why?a. A fan is to accelerate quiescent air to a velocity of 10m/s at a rate of 4 m3/s. Determine the minimum power thatmust be supplied to the fan. Take the density of air to be 1.18kg/m3. b. A classroom that normally contains 40 people is tobe air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed todissipate heat at a rate of about 360 kJ/h. There are 10 lightbulbs in the room, each with a rating of 100 W. The rate ofheat transfer to the classroom through the walls and the windows is estimated to be 15,000 kJ/h. If the room air is to bemaintained at a constant temperature of 21°C, determine thenumber of window air-conditioning units required c. A vertical piston–cylinder device contains water andis being heated on top of a range. During the process, 65 Btu of heat is transferred to the water, and heat losses from theside walls amount to 8 Btu. The piston rises as a result ofevaporation, and 5 Btu of work is done by the vapor.…A heat pump is a device that transfer thermal energy from a lower temperature to a higher temperature place. With the aid of diagram(s), discuss the appropriate integration of heat pumps that could provide substantial energy benefits.
- The Nevada Solar One solar thermal power plant covers a land area of 140 hectares and has an estimated peak output of 64 MW. If the peak solar fl ux reaching the surface of that part of Nevada is about 630 W/m2, what is the net efficiency of the power plant? Compare your answer with some of the higher effi ciencies of semiconductor solar cells.A site is being considered for wind power generation. At this site, the wind blows steadily at 6 m/s for 3,323 hours per year. Assuming the wind velocity is negligible at other times for simplicity, determine the kWh/year that can be produced at the site for a turbine with a mechanical efficiency of 100% and an effective flow area of 5 m2. Use a value of 1.25 kg/m3 for the density of the air. Give your answer in killowatt-hours per year (kWh/year). Hint: I reccomend starting by finding the kinetic energy (kJ/kg) of the wind. Hint 2: Multiply the power generation (kW) by the number of hours of wind per year (h/year) to get kWh/year.A heat machine receives heat from a high-temperature heat source at a temperature of 160 °C andIt delivers heat to a high-temperature heat source at a temperature of 5 °C. In the meantime jobit is claimed that 0.15 kWh of work is done per every 1000 KJ of heat that the machine receivesare made. 1 if the claim is true. and 2. Evaluate according to the law.