Thermosyphon cooling modules, to cool multichip modules (MCMs), were designed and tested. The cooling module consists of a cold plate with microfinned channels and a plate-type integrated condenser A separate flow model was employed to predict the mass flux and the pressure drop in the channel of the cold plate. The local and average convective boiling heat transfer coefficients and the corresponding wall superheat were calculated using the Chen's correlation. Experiments were performed to find out how the thermal performance of the cooling module was affected by the condenser size and the amount of charging fluid. Great emphasis was placed on the transient characteristics of the cooling module. For an allowable temperature rise of 58℃ on the surface of the heater the cooling module can handle a heat flux of as much as 2.5 W/cm{sup}2. No boiling retardation was observed inside the cold plate, which resulted in smooth transition from the transient state to the steady one. It was also found that the appropriate size of the condenser and the adequate amount of charging liquid are crucial factors affecting the performance of a closed two-phase thermosyphon device.
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