课程名称︰热传学 课程性质︰ 课程教师︰马小康 开课学院：工学院 开课系所︰机械系 考试日期（年月日）︰2010/10/26 考试时限（分钟）：100 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : (30%)(1) Consider ac ubic block whose side are 5 cm long and a cylindrical block whose height and diameter are also 5 cm. Both blocks are initially at 20℃ and are made of granite (k=2.5 W/m.℃ and α= 1.15*10^(-6) m^2/s). Now both blocks are exposed to hot gases at 500℃ in a furnace on all of their surfaces with a heat transfer coefficient of 40 W/m^2.℃. Determine the center temperature of each geometry after 10, and 60 min. (参考习题4-82) (30%)(2) A 5-mm-diameter spherical ball at 50℃ is covered by a 1-mm thick plastic insulation (k=0.13 W/m.℃). The ball is exposed to a medium at 15℃, with a combined convection and radiation heat transfer coefficient of 20 W/m^2.℃. Please (a) write down the rate of heat transfer and the total thermal resistance Rtotal. (b) determine if the plastic insulation on the ball will help or hurt heat transfer from the ball. (参考习题3-90) (10%)(3) For one-dimensional transient conduction in Cartesian coordinates in a semi-infinite medium, what is the similarity variable η? and why? (30%)(4) A slab insulated on both sides. Assume k and other properties are constant. Please solve T(t,x) by the separation variable method when Initial condition T(0,x)=f(x). Also, the special case when f(x)=T0= constant. │ │ │ k │ │ │ insulated-->│ │<--insulated │<----->│ │ L │ └> x=0 --

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