LIQUID IMMERSION COOLING OF A SUBSTRATE-MOUNTED PROTRUSION IN A 3-DIMENSIONAL ENCLOSURE - THE EFFECTS OF GEOMETRY AND BOUNDARY-CONDITIONS

A three-dimensional computational study of steady natural convection c ooling of a substrate-mounted protrusion (chip) in a rectangular enclo sure filled with dielectric liquid is described. Energy is generated i n the chip at a uniform rate Q. Conduction within the chip and substra te are accounted for in the, model, as is the coupled natural convecti on in the surrounding liquid. The nondimensional governing equations w ith the appropriate boundary conditions have been solved in the primit ive variable form for Ra = 10(8) using a fully implicit finite volume formulation. Baseline computations have been performed for a cubical e nclosure with a centrally placed silicon chip on a vertical alumina su bstrate, which form's one enclosure wall. The cooling liquid was Fluor inert FC 75 resulting in Pr = 25. The effects of conductive spreading along the substrate were found to be quite pronounced due to the low t hermal conductivity of the liquid. Effects of chip and enclosure sizes on the maximum chip temperatures displayed a strong dependence on the substrate to fluid thermal conductivity ratio, R(S). Conditions for t he validity of two-dimensional approximations were investigated for la rge and small R(S). Two other thermal boundary conditions on the enclo sure walls were also considered, with the smallest chip temperatures f ound for the top and one vertical sidewall cooled condition. For the b aseline boundary conditions a numerical correlation for the maximum ch ip temperature was obtained.