problem4-21

# problem4-21 - PROBLEM 4.21 KNOWN Platen heated by passage...

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PROBLEM 4.21 KNOWN: Platen heated by passage of hot fluid in poor thermal contact with cover plates xposed to cooler ambient air. e FIND: (a) Heat rate per unit thickness from each channel, i q, (b) Surface temperature of cover plate, T s , (c) if lower surface is perfectly insulated, (d) Effect of changing centerline spacing on i q and T s ′′ S is SCHEMATIC: D=15 mm L o =60 mm L A =30 mm L B =7.5 mm T i =150 ° C h i =1000 W/m 2 K T =25 ° C h o =200 W/m 2 K k A =20 W/m K k B =75 W/m K = 4.25 42 t,c R2 . 0 1 0 m K / W ASSUMPTIONS: (1) Steady-state conditions, (2) Two-dimensional conduction in platen, but one-dimensional in coverplate, (3) Temperature of interfaces between A and B is uniform, 4) Constant properties. ( ANALYSIS: (a) The heat rate per unit thickness from each channel can be determined from the following thermal circuit representing the quarter section shown. The value for the shape factor for the quarter section is S 4.25/ 4 1.06.

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problem4-21 - PROBLEM 4.21 KNOWN Platen heated by passage...

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