To cool electronic components that are mounted to a printed circuit board and hermetically sealed from their surroundings, two boards may be joined to form an intermediate channel through which the coolant is passed. Termed a hollow-core PCB, all of the heat generated by the components may be assumed to be transferred to the coolant.

Consider a hollow-core PCB of length L = 300 mm and equivalent width W (normal to the page). Under normal operating conditions, 40 W of power are dissipated on each side of the PCB and a uniform distribution of the attendant heat transfer may be assumed for each of the hollow-core surfaces. If air enters a core of height H = 4 mm at a temperature of Tm,i = 20°C and a flow rate of In = 0.002 kg/s, what is its outlet temperature Tm.o? What are the surface temperatures at the inlet and outlet of the core? What are the foregoing temperatures if the flow rate is increased by a factor of five?

Tmo , - Encapsulated electronic component Air Tmir m