Conjugate heat transfer behavior of an electronic chip module cooled by air

This paper reports on heat transfer and flow measurements in an electronic chip module cooled by air. A standard electronic module package comprising of a single module chip placed on a printed circuit board located in a rectangular plexiglass duct has been designed and manufactured. Three small fans of the type used in laptop computers are located downstream of the electronic module sucking the cooling air over the board. The chip package has a built-in diode for measurement of the chip temperature. The dimensions of the duct are 235 mm long, 200 mm wide, and 10 mm high. The chip package was placed nearly in the center of the duct floor. The module package was 45 mm by 45 mm and was placed on a PCB with dimension of 110 mm by 110 mm. The chip was energized by a DC power supply with a variable voltage ranging from 10 to 23 volts. Both natural convection flow and forced flow were considered by turning the fans on and off and in various combinations. The maximum average air velocity was of the order of 1.5 m/s with all three fans turned on. The maximum power was about 5 watts which resulted a junction temperature of about 70 degrees C above the ambient. The experimental results have been used to develop a correlation for the Nusselt number and the data are compared with existing correlations.