Electronic components mouted on a flat plate are cooled by convection to the sur

Question

Electronic components mouted on a flat plate are cooled by convection to the surroundings and by liquied water circulating through a U-tube bonded to the plate. At steady state, water enters the tube at 20 degree C and a velocity of 0.4m/s and exits at 24 degree C with a negligible change in pressure. The electrical components receive 0.5kW of electrical power. the rate of energy transfer by convection from the plate-mounted electronics is estimated to be 0.08 kW. Kinetic and potential engerfy effects can be ignored. Determine the tube diameter, in cm.

Explanation / Answer

Heat transfer to cooling water = 0.5 kW - 0.08 kW = 0.42 kW. Let mdot be the flow rate of water, cp its specific heat, then 0.42 kW = mdot * cp * (24 C - 20 C). If cp is assumed (or read from a table of water properties), then mdot is obtained. Finally, mdot = rho * V * (pi *d^2/4), where rho is density of water (assume 1000 kg/m^3 or read a value from a table) V is water velocity = 0.4 m/s d = diameter of tube.

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