Sustainable Energy
2nd Edition
ISBN: 9781337551663
Author: DUNLAP, Richard A.
Publisher: Cengage,
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Chapter 17, Problem 10P
To determine
Find the average power requirement for the heat pump.
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A closed tank containing hot air has an initial internal energy of 400 kJ. During the next 5 min, the tank loses heat to the surroundings at a rate of 1.5 kW, while an electrical element supplies 1000 W to the air. Find the final internal energy of the air.
A 50-L electrical radiator containing heating oil is placed in a 50-m³ room. Both the room and the oil in the
radiator are initially at 5°C. The radiator with a rating of 3 kW is now turned on. At the same time, heat
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- A refrigerator is to remove heat from the cooled space at a rate of 300.74 kJ/min to maintain its temperature at -8 C. If the air surrounding the refrigerator is at 28.91 C, determine the minimum power input (kW) required for this refrigerator.arrow_forwardCompare the masses and volumes of water, concrete, sand, and wood needed to store 106 Btu of heat if the operating temperatures are Tc = 85F and Th = 180F. In each case, calculate the edge length of a square storage unit with a height of 8 ft.arrow_forwardQ1; If a system has 30J of heat added to it, and the total change in its internal energy is 10J, how much work does it do? a- 70 J b- 0.0 J c- 10J d- 20 J e- 10 Jarrow_forward
- An oil of viscosity 5 poise is used for lubrication between a shaft and sleeve. The diameter of the shaft is 0.5 m and it rotates at 200 r.p.m. Calculate the power lost in oil for a sleeve length of 100 mm. The thickness of oil is 1 mm.arrow_forwardCalculate the power radiated by a woodstove of dimensions 65 cm high by 55 cm deep by 85 cm wide with a surface temperature of 120°C. Assume that heat is radiated from all surfaces of the stove and that the stove has an emissivity of 1. Note that woodstoves are painted black because black surfaces have high absorptance, and objects with high absorptance also have high emissivity.arrow_forward1. An unknown lamp placed 6m from a photometer screen provides the same illuminance as a 90 cd lamp placed 4 m from the screen. What is the candlepower of the unknown lamp? 2. The illuminance of a room 20 ft x 15 ft is being designed. The illuminance required is 50 footcandles. What is the total required lumens output of the lamp assuming room and luminaire efficiency of 42%?arrow_forward
- A PV battery system has an efficiency of 80%. The system is used to run an all-AC load that is run only at night. The charge controller efficiency is 96% and the inverter efficiency is 85%. How much energy will need to be generated by the PV array if the load is 150 watts running for 5 hours per night?arrow_forwardproblem 5.3 Consider a steam power plant that operates on the ideal reheat Rankine cycle. The plant maintains the boiler at 5000 kPa, the reheat section at 1200 kPa, and the condenser at 20 kPa. The mixture quality at the exit of both turbines is 96 percent. Determine the temperature at the inlet of each turbine and the cycle's thermal efficiency. Answers: 327°C, 481°C, 35.0 percent High-P turbine Low-P turbine Reheater Boiler Condenser 2 Pumparrow_forwardA point in a water pipe line, velocity is 3.5m/s, the pressure reading is 20 kPa and the elevation is 20m.What is the energy head in meters at that point assuming that the reference datum is @ elevation 5m. *arrow_forward
- Consider a house that is approximated as a cube that is 8 m on a side and has no windows. The house loses heat from the four walls and the roof. For an inside temperature of 20°C and an outside temperature of –20°C, it is desired to keep the total heat loss less than 5 kW. What is the minimum RSj value that is required for the walls and roof?arrow_forwardWhen the temperature was 3 deg. C, the distance from E to F was measured using a steel tape that has a standard length of 100m at 20 deg. C with a coefficient of thermal expansion of 0.0000116 / deg. C. If the correct distance from E to F is 836.5 m, what is the measured distance in meters?arrow_forwardAn incandescent lamp filament has area 40 mm and operates at a temperature of 1127°C. Assume that all the energy furnished to the bulb is radiated from it. If the filament's emissivity is 0.83, how much power must be furnished to the bulb when it is operating? (b)arrow_forward
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