95 psia the condenser consists of 144 horizontal

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Unformatted text preview: 0-cm-long cylindrical heat pipe having a diameter of 0.5 cm is dissipating heat at a rate of 150 W, with a temperature difference of 4°C across the heat pipe. If we were to use a 40-cm-long copper rod (k 386 W/m · °C and 8950 kg/m3) instead to remove heat at the same rate, determine the diameter and the mass of the copper rod that needs to be installed. 10–70 Repeat Problem 10–69 for an aluminum rod instead of copper. 10–71E A plate that supports 10 power transistors, each dissipating 35 W, is to be cooled with 1-ft-long heat pipes having a diameter of 1 in. Using Table 10–6, determine how many 4 pipes need to be attached to this plate. Answer: 2 Heat sink Heat pipe 10–75E The condenser of a steam power plant operates at a pressure of 0.95 psia. The condenser consists of 144 horizontal tubes arranged in a 12 12 square array. The tubes are 15 ft long and have an outer diameter of 1.2 in. If the outer surfaces of the tubes are maintained at 80°F, determine (a) the rate of heat transfer from the steam to the cooling water and (b) the rate of condensation of steam in the condenser. 10–76E Repeat Problem 10–75E for a tube diameter of 2 in. 10–77 Water is boiled at 100°C electrically by a 80-cm-long, 2-mm-diameter horizontal resistance wire made of chemically etched stainless steel. Determine (a) the rate of heat transfer to the water and the rate of evaporation of water if the temperature of the wire is 115°C and (b) the maximum rate of evaporation in the nucleate boiling regime. Answers: (a) 2387 W, 3.81 kg/h, (b) 1280 kW/m2 Transistor Steam Water 100°C FIGURE P10–71E 115°C Review Problems 10–72 Steam at 40°C condenses on the outside of a 3-cm diameter thin horizontal copper tube by cooling water that enters the tube at 25°C at an average velocity of 2 m/s and leaves at 35°C. Determine the rate of condensation of steam, the average overall heat transfer coefficient between the steam and the cooling water, and the tube length. Steam 40°C Cooling water 35°C 25°C FIGURE P10–72 10–73 Saturated ammonia vapor at 25°C condenses on the...
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This note was uploaded on 01/28/2010 for the course HEAT ENG taught by Professor Ghaz during the Spring '10 term at University of Guelph.

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