PROBLEM 4.81KNOWN:Upper surface of a platen heated by hot fluid through the flow channels is used to heat a rocess fluid. pFIND:(a) The maximum allowable spacing, W, between channel centerlines that will provide a uniform temperature requirement of 5°C on the upper surface of the platen, and (b) Heat rate per unit ength from the flow channel for this condition. lSCHEMATIC:ASSUMPTIONS:(1) Steady-state, two-dimensional conduction with constant properties, and (2) ower surface of platen is adiabatic. LANALYSIS:As shown in the schematic above for a symmetrical section of the platen-flow channel arrangement, the temperature uniformity requirement will be met when T1– T2= 5°C. The maximum temperature, T1, will occur directly over the flow channel centerline, while the minimum surface temperature, T2, will occur at the mid-span between channel centerlines. We chose to use FEHT to obtain the temperature distribution and heat rate for guessed values of the channel centerline spacing, W.
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