課程名稱︰食品工程學
課程性質︰必修/選修
課程教師︰葉安義教授 蔣丙煌教授
開課系所︰食品科技學程/食品科技研究所
考試時間︰2006.01.13
試題 :(期末考範圍由葉安義教授負責)
★Remember to verify your assumptions★
(1) A room is constructed with a wall having a thickness of 120 mm and
thermal conductivity of 0.25 W/mK. It is known that the outside air
temperature is 90℃ and inside air temperature is 25℃.
The temperatures for the outer and inner surface of the wall are 75
and 40℃, respectively. Please estimate the heat transfer coefficient
(in W/m^2K) for both the outer and inner surface. (20 points)
(2) Water (50℃) flows through a steel pipe (inside diameter of 20 mm and
outside diameter of 28 mm). The water leaves the pipe at 70℃.
Outside the pipe, steam is flowing at 100℃.
The heat transfer coefficient between steam and outer surface of the
pipe is 26200 W/m^2K.
It is known that there are 180 kg/h steam condensed at 100℃ to heat
up the water. The thermal conductivity of the pipe is 45 W/mK.
Calculate the length (in meters) of the pipe. (35 points)
(3) A food material is put on a drying tray
(0.5 m X 0.5 m with a height of 0.05 m) for hot air drying.
Only the upper surface is being contacted with the air.
The air has a dry bulb temperature of 75℃ and wet bulb temperature
of 35℃.
At constant rate period, the total evaporation rate is 1 kg H2O/h.
Please estimate the flow rate (in m/s) of air. (25 points)
(4) a. Please explain the similarity among the rate of momentum transfer,
heat transfer, and mass transfer. (5 points)
b. Please provide the physical meaning of the following dimensionless
group:
1. Reynold's number (5 points)
2. Prandtl number (5 points)
3. Biot number (5 points)
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