[試題] 100上 楊鏡堂 熱傳學 第一次期中考
課程名稱︰熱傳學
課程性質︰必修
課程教師︰楊鏡堂
開課學院：工
開課系所︰機械系
考試日期（年月日）︰20111102(世界對稱日)
考試時限（分鐘）：2小時
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
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) 書名(2 points) 年份(1 point)
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