Forced-convection boiling and critical heat flux from a linear array of discrete heat sources

Forced-convection boiling experiments were performed with FC-72, a 3M Fluorinert, at 1.36 bar on a linear array of nine discrete heat sources simulating microelectronic chips, which were flushmounted in a vertical. rectangular channel. The inlet velocity and liquid subcooling were varied from 13 to 400 cm s’ and 3 to 36”C, respectively. Special design of the experimental apparatus allowed each test to continue until all chips had reached critical heat flux (CHF) without damaging the test section. Boiling incipience and CHF were delayed to higher heat fluxes with increasing velocity and/or subcooling. In general, the position of the last chip to reach CHF moved upstream with increasing subcooling. The average bandwidth of CHF values for the multi-chip array, however, was only _+ 12.3%, proving that the discontinuity in wall heat flux between consecutive chips helped to interrupt the growth of the vapor blanket which commonly results in dryout at the downstream edge of long, continuously heated walls. Also, the small CHF bandwidth allows a correlation previously developed for CHF on an isolated chip to be used for an array of chips as well.