AET432-Exam-MidTerm2_FA2006

# AET432-Exam-MidTerm2_FA2006 - the pressure decreases at the...

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AET 432 Applied Heat Transfer Fall 2006 Mid Term Examination #2 (Take Home Exam) Due: November 30, 2006 (Thursday) at 9 AM. 1. Aluminum fins (k=240 W/m.K) are added to a 40-cm by 40-cm (40-cm square) surface to improve cooling. The base surface is at 90 o C. There are 50 fins on the surface. Each fin is 20 mm long (base to tip), 3 mm thick and 40 cm wide with a uniform rectangular cross section. The tip of each fin may be assumed to be adiabatic . The surrounding air is at 25 o C with a convection coefficient of 30 W/m 2 .K. Neglecting radiation, calculate the a) amount of heat removal rate by the arrangement b) percent increase in the heat removal rate as a result of adding the fins. c) fin effectiveness (30 pts) 2. Consider the steady, laminar flow of glycerin between two stationary, infinite parallel plates. The plates are 8 mm apart and are at different temperatures. Pressure measurements indicate that
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Unformatted text preview: the pressure decreases at the constant rate of 30 kPa every meter along the flow direction. The top plate is at a uniform temperature of 25 o C while the bottom plate is maintained at 45 o C. Use the mean temperature to evaluate the fluid properties. a) Calculate the velocity and temperature at the location midway between the two plates. b) Calculate the heat fluxes at the two plates. (35 pts) 3. A 6-m long solar collector is made of twelve 50-cm X 3-m flat panels (i.e. the overall dimensions of the collector are 6-m long and 3-m wide). The surface of the collector is maintained at 30 o C. Ambient air at 10 o C flows along the length of the collector at a speed of 2.5 m/sec. Calculate the convective heat transfer rate from the a) first panel b) fifth panel c) tenth panel (35 pts) Note: Q 5 = Q 1-5 – Q 1-4...
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