課程名稱︰ 熱傳學
課程性質︰ 系必修
課程教師︰ 周賢福 教授
開課學院： 工學院
開課系所︰ 機械系
考試日期（年月日）︰ 2010/01/15
考試時限（分鐘）： 120分鐘+10分鐘延長
是否需發放獎勵金： 是
試題 :
1.(20%) Cooling air of 25度C and 4 m/s is blowing over a flat PCB mounted with
a long module with packed DRAM chips. The length of the DRAM module is 15 cm
and it is dissipating a uniform heat flux at 2 W/cm^2. Determine the surface
temperatures of the DRAM module at the leading edge, the midpoint, and the end
2.(25%) Water flows through a copper tube of 2.5 cm inside diameter and 4 m
long. The water enters the tube at 20度C, and inside surface temperature of
the pipe is kept at 85度C.
(a) What is the outlet temperature of the water?
(b) What is the rate of heat transfer to the water?
(c) What is the total pressure drop through the tube for the following 2 cases
The mass flow rate of the water is 1 kg/s for case 1 and 4 kg/s for case 2
Sketch the bulk temperature change of the water along axis.
3.(20%) On a base area of 5 cm x 5 cm copper block, 26 copper fins of height 4
cm and width 5 cm with negligible thickness are attached on it to cool down a
CPU which is placed underneath the copper block horizontally. If the
temperature of the cooling air is 25度C and the surface temperature of the fins
is 70度C, what will be the total heat transfer rate from the heat sink by
natural convection? Does it dissipate a maximum heat transfer rate from the
copper block? If not so, what kind of configuration should you do to get a
better heat transfer rate?
4.(20%) A flat plate electric radiator of 1.2 m high and 1 m wide is used to
keep the temperature of the classroom warm today. If the room temperature is
20度C and the outer surface temperature of the radiator is 75度C, determine
the rate if heating from the radiator by natural convection and radiation.
5.(15%) A double-pipe heat exchanger is constructed of a copper (k=380W/m-度C)
inner tube of internal diameter 1.2 cm and external diameter 1.6 cm and an
outer tube of diameter 3.0 cm. The convection heat transfer coefficient is
h(i)=700W/m^2-度C on the inner surface of the tube and h(o)=1400W/m^2-度C on
its outer surface. For a fouling factor Ri = 0.0005m^2-度C/W on the tube side
and Ro = 0.0002m^2-度C/W on the shell side, determine
(a) the thermal resistance of the heat exchanger per unit length and
(b) the overall heat transfer coefficients Ui and Uo based on the inner and o
outer surface areas of the tube, respectively.
6.(5% bonus) List the difficulties of dealing with the radiation heat transfer
as compared with the conduction heat transfer and the convection heat transfer.
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老師考試都沒附圖
可是助教會畫在黑板上
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