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# HW 1 - What is the allowable power dissipation from the top...

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MAE 412 Homework 01 1. You want to investigate the heat transfer from a submarine shell when it is moving through 17 o C water at 10 m/s. You have a water tunnel available to you with atmospheric water at 27 o C. The submarine is modeled with a 1/10-scale model. Find: (a) the desired model water velocity, (b) the ratio of the model heat transfer coefficient to the submarine heat transfer coefficient, if Nu L ,avg ~ Re L 1/2 Pr 1/3 , and (c) the ratio of the model total heat transfer to the submarine total heat transfer, for a specified temperature difference between the surface and free stream temperatures. Assume the surface area varies with the square of the length. 2. A circuit board surface covered by IC chips, which has dimensions of 150 mm by 150 mm on a side, is cooled by atmospheric air blowing across it (parallel to one side) with a velocity of 2 m/s. Wind tunnel tests with the same flow conditions produced a shear stress on the top surface of 0.080 N/m 2 .
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Unformatted text preview: . What is the allowable power dissipation from the top surface of the assembly of IC chips if the average surface temperature of the IC chips must not exceed the ambient temperature by more than 25 o C? Evaluate the properties of air at a film temperature of 300 K. (You need to apply the Chilton-Colburn Analogy, Sec. 6.7.3) 3. A 100 W light bulb may be modeled as a cylinder 80 mm in diameter and 100 mm in height. (yeah, I know, it's a poor model) The room air blows across the bulb at 1.5 m/s and 27 o C. Ignore the top and bottom surfaces of the model of the bulb. (a) Assuming that all of the heat transfer occurs through convection, find the approximate surface temperature of the bulb (T s ). 4. Engine oil initially at 47 o C enters a drilled passage 5 mm diameter x 100 mm long in an engine block that is at 177 o C. The velocity of the oil is 0.1 m/s. Use 330 K for the properties of the oil. What is the outlet temperature of the oil?...
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