An array of power transistors, dissipating 6 w of power each, are to be cooled by mounting them on a 25cm ×25cm-square aluminum plate and blowing air at 35°c over the plate with a fan at a velocity of 4 m/s. the average temperature of the plate is not to exceed 65°c. assuming the heat transfer from the back side of the plate to be negligible and disregarding radiation, determine the number of transistors that can be placed on this plate.

Oxygen gas enters well-insulated diffuser at 25 lbf/in.2, 420r, with a velocity of 860 ft/s through a flow area of 1.6 in.^2. at the exit, the flow area is 12 times the inlet area, and the velocity is 19 ft/s. the potential energy change from inlet to exit is negligible. assuming ideal gas behavior for the oxygen and steady-state operation of the diffuser, determine the following: (a) the exit temperature, in r(b) the exit pressure, in lbf/in.^2 (c) the mass flow rate, in lb/s