课程名称︰热传学 课程性质︰必修 课程教师︰杨镜堂 开课学院：工 开课系所︰机械系 考试日期（年月日）︰20111102(世界对称日) 考试时限（分钟）：2小时 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 1.For which solid is the lumped system analysis more likely to be applicable: actual apple or a golden of the same size? Why? Please suggest a scientific criterion for judging similar cases. (5 points) 2.What is the driving force for (a) heat transfer, (b)electric current flow, and (c)fluid flow? (6 points) 3.On a hot summer day, a student turns his fan on whe he leaves his room in the morning. When he returns in the evening,will his room warmer or cooler than the neighboring rooms? Why? Assume all the doors and windows are kept closed. (4 points) 4.Consider a hot baked potato on a plate. The temperature of the potato is observed to drop by 4。C? Why? (5 points) 5.A thin metal plate is insulated on the back and exposed to solar radiation on the front surface. The exposed surface of the plate has an absorptivity of 0.8 for solar radiation. If solar radiation is incident on the plate at a rate of 500W/m^2 and the surrounding air temperature is 10。C,determine the surface temperature of the plate when it remains constant. Take the convective heat transfer coefficient to be 25W/m^2．K and disregard any heat loss by radiation. (20 points) 6.A spherical metal ball of radius r0 is heated in an oven to temperature Ti throughout and is then taken out of the oven and dropped into a large body of water at T∞ where it is cooled by convection with an average convection heat transfer coefficient of h. Assuming constant thermal conductivity and transient one-dimensional heat transfer,express the mathematical formulation of this heat conduction problem. Do not solve. If the thermal conductivity varies with the temperature ,derive the mathematical formulation? (20 points) 7.A 12-m-long and 5-m-high wall is constructed of two layers of 1-cm-thick sheetrock (k=0.17W/m．K) spaced 16 cm by wood studs (k=0.11W/m．K) whose cross section is 16 cm X 5 cm. The stud are placed vertically 60 cm apart,and the space between them is filled with fiberglass insulation (k=0.034W/m．K). The house is maintained at 20。C and the ambient temperature outside is -9。C. Taking the transfer coefficients at the inner and outer surface of the house to be 8.3 and 34W/m^2．K,representative , determine (a) the thermal resistance of the wall considering a representative sectionof it and (b) the rate of heat transfer through the wall. (20 points) 8.A 2.2-mm-diameter and 14-m-long electric wire is tightly wrapped with a 1-mm-thick plastic cover whose thermal conductivity is k=0.15W/m．K. Electrical measurement indicate that a current of 13A passes through the wire and there is a voltage drop of 8V along the wire. If the insulated wire is exposed to a medium at T∞=30。C with a heat transfer coefficient of h=24W/m^2K,determine the temperature at the interface of the wire and the plastic cover in steady operation. (20 points) 9.Bonus. (5 points) 作者(2 points) 书名(2 points) 年份(1 point) --

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