課程名稱︰熱傳學
課程性質︰機械系大三上必修
課程教師︰陳希立
開課學院：工學院
開課系所︰機械系
考試日期（年月日）︰2007.01.19
考試時限（分鐘）：約140min
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
1. In which mode of heat transfer is the convection heat transfer coefficient
usually higher, natural convection or forced convection? Why?
2. How is the modified Reynolds analogy expressed? What is the value of it?
What are its limitations?
3. Consider laminar flow over a flat plate. Will the friction coefficient
change with distance from the leading edge? How about the heat transfer
coefficient?
4. Consider laminar flow of air across a hot circular cylinder. At what point
on the cylinder will the heat transfer be highest? What would your answer
be if the flow were turbulent?
5. Consider laminar forced convection in a circular tube. Will the heat flux
be higher near the inlet of the tube or near exit? Why?
6. In the fully developed region of flow in a circular tube, will the velocity
profile change in the flow direction? How adout the temperature profile?
7. Physically, what does the Grashof number represent? How does the Grashof
number differ from the Reynolds number?
8. Consider laminar natural convection from a vertical hot plate. Will the
heat flux be higher at the top or at the bottom of the plate? Why?
9. What is the difiference between pool boiling and flow boiling?
10. Draw the boiling curve and identify the different boiling regimes. Also,
explain the characteristics of each regime.
11. Draw the heat transfer coefficient of the different boiling regimes in the
order they occur in a vertical tube during flow poiling.
12. Consider film condensation on a vertical plate. Will the heat flux be
higher at the top or at the bottom of the plate? Why?
13. How does the presence of a noncondensable gas in a vapor influence the
condensation heat transfer?
14. What is a heat pipe? How does it operate? Does it have any moving parts?
15. Does the orientation of a heat pipe affect its performance? Does it matter
if the evaporator end of the heat pipe is up or down? Explain.
16. A 6-mm-diameter electrical transmission line carries an electric current
of 50 A and has a resistance of 0.0002 ohm per meter length. Determine the
surface temperature of the wire during a windy day when the air
temperature is 10度C and the wind is blowing across the transmission line
at 40 km/h.(Fig.1)
17. A 12.1-cm-wide and 18-cm-high vertical hot surface in 25度C air is to be
cooled by a heat sink with equally spaced fins of rectangular profile.
The fins are 0.1 cm thick and 18 cm long in the vertical direction.
Determine the optimum fin height and the rate of heat tranfer by natural
convection from the heat sink if the base temperature is 65度C.(Fig.2)
Wind, 40 km/h Ｗ = 12.1 cm
10度C ├─────────┤
↙↙↙↙↙↙
◢█◢█◢█◢█◢█
◢█████████◤ Ｈ◢█◢█◤█◢█◤██
◢◤ ◢◤ ◢█◢█◤█◢█◤███ Ｌ = 18 cm
◢█████████◤ ████████████
◢◤█ ◢◤█ ████████████
◢█████████◤█ ██████████◤
█ ↑ █ █◤█◤█◤█◤█◤↖
█ ↑ █ ◤ ◤ ◤ ◤ ◤ 65度C
↑
Transmission ├─┤ Ｔ∞ = 25度C
lines Ｓ
Fig.1 Fig.2
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