A square isothermal chip is of width w 5 mm on a side and is mounted in a substrate such that its side and back surfaces are well insulated; the front surface is exposed to the flow of a coolant at T 15 C. From reliability considerations, the chip temperature must not exceed T 85 C. If the coolant is air and the corresponding convection coefficient is h 200 W/m2 K, what is the maximum allowable chip power

Solution :

All of the electrical power dissipated in the chip is transferred by the convection to the coolant.

So P = q

and from the Newton's law of cooling,

And in air,

         = 0.35 W

In the dielectric liquid,

         = 5.25 W

Relative to the liquids, the air is considered a poor heat transfer agent. So, in the air the chip are able to dissipate far less of energy than in the dielectric liquid.

oil flow is a highly convective flow compared to water flow at normal temperature and pressure.

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