10.63 A technique for cooling a multichip module involves submerging the module in a saturated fluorocarbon liquid. Vapor generated due to boiling at the module surface is condensed on the outer surface of copper tubing suspended in the vapor space above the liquid. The thin-walled tubing is of diameter D = 10 mm and is coiled in a horizontal plane. It is cooled by water that enters at 285 K and leaves at 315 K. All the heat dissipated by the chips within the module is transferred from a 100-mm X 100-mm boiling surface, at which the flux is 105 W/m2, to the fluorocarbon liquid, which is at Tsat = 57°C. Liquid properties are kl = 0.0537
W/m · K, cp,l = 1100 J/kg · K, h'fg = hƒg = 84,400 J/kg,
pl= 1619.2 kg/m3, pv= 13.4 kg/m3, u = 8.1 X 10-3 N/m, µ,l= 440 X 10-6kg/m · s, and Prl= 9.
Condenser coil
Fluorocarbon vapor and liquid, Tsat
Multichip
module
(a) For the prescribed heat dissipation, what is the required condensation rate (kg/s) and water flow rate (kg/s)?
(b) Assuming fully developed flow throughout the tube, determine the tube surface temperature at the coil inlet and outlet.
(c) Assuming a uniform tube surface temperature of Ts = 53.0°C, determine the required length of the coil.
