Flow Boiling Heat Transfer to a Dielectric Coolant in a Microchannel Heat Sink

This paper presents an experimental study of flow boiling heat transfer in a microchannel heat sink. The dielectric fluid Fluorinert FC-77 is used as the boiling liquid after it is fully degassed. The experiments were performed at three flow rates ranging from 30 to 50 ml/min. The heat transfer coefficients, as well as the critical heat flux, were found to increase with flow rate. Wall temperature measurements at three locations (near the inlet, near the exit, and in the middle of heat sink) reveal that wall dryout first occurs near the exit of the microchannels. The ratio of heat transfer rate under critical heat flux conditions to the limiting evaporation rate was found to decrease with increasing flow rate, asymptotically approaching unity. Predictions from a number of correlations for nucleate boiling heat transfer in the literature are compared against the experimental results to identify those that provide a good match. The results of this work provide guidelines for the thermal design of microchannel heat sinks in two-phase flow.   This paper was also originally published as part of the Proceedings of the ASME 2005 Heat Transfer Summer Conference.