problem4-75

# problem4-75 - PROBLEM 4.75 KNOWN Electronic device cooled...

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PROBLEM 4.75 KNOWN : Electronic device cooled by conduction to a heat sink. FIND : (a) Beginning with a symmetrical element, find the thermal resistance per unit depth between the device and lower surface of the sink, t,d s R (m K/W) using a coarse (5x5) nodal network, determine ; (b) Using nodal networks with finer grid spacings, determine the effect of grid size on the precision of the thermal resistance calculation; (c) Using a fine nodal network, determine the effect of device width on with w t,d s R t,d s R d /w s = 0.175, 0.275, 0.375 and 0.475 keeping w s and L fixed. SCHEMATIC : ASSUMPTIONS : (1) Steady-state, two-dimensional conduction, (2) Constant properties, and (3) No nternal generation, (4) Top surface not covered by device is insulated. i ANALYSIS : (a) The coarse 5x5 nodal network is shown in the sketch including the nodes adjacent to the symmetry lines and the adiabatic surface. As such, all the finite- difference equations are interior nodes and can be written by inspection directly onto the IHT workspace.

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