hw6 - 2. Air at 27ºC and 50 kPa enters a smooth tube 0.01...

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ME 322 HW #6 16.04.2008 1. A liquid pharmaceutical in the final stages of production is sterilized by heating it from 25 to 75ºC as it moves at 0.2 m/s through a straight thin-walled stainless steel tube 12.7 mm in diameter. A uniform heat flux is maintained by an electric resistance heater wrapped around the outer surface of the tube. Fluid properties may be approximated as ρ = 1000 kg/m 3 , k = 0.8 W/mºC, p c = 4000 J/kg ºC, µ = 0.002 kg/s m, and Pr = 10. (1) If the tube is 10 m long, what is the required heat flux per unit area? (2) If fluid enters the tube with a fully developed velocity profile and a uniform temperature profile, what is the surface temperature at the tube exit? (3) What about the surface temperature at a distance of 0.5 m from the entrance? (ANSWERS: 12680 W/m 2 ; 152ºC; 69.4ºC)
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Unformatted text preview: 2. Air at 27ºC and 50 kPa enters a smooth tube 0.01 m in (inner) diameter and 0.5 m in length. The mean velocity is measured to be 3.0 m/s. A constant heat flux is imposed and the total heat flux to the tube is 5 W. The outside tube wall is thermally insulated from the atmosphere. (1) Calculate the exit bulk temperature of air. (2) Find the heat transfer coefficient at the exit. (3) Estimate the wall temperature at the exit. (ANSWERS: 63.3ºC; 12.0 W/m 2 K; 89.8ºC) 3. Water flows in a tube of 2 cm in diameter at an average flow velocity of 8 m/s. If the water enters at 20ºC and leaves at 30ºC and the tube length is 10 m, estimate the average wall temperature necessary to effect the required heat transfer. Also find the total heat transfer rate. (ANSWER: 32.2ºC)...
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