JET IMPINGEMENT BOILING OF A DIELECTRIC COOLANT IN NARROW GAPS

An experimental investigation into the effect of the chip-to-orifice g ap was conducted for jet-impingement boiling of FC-72 at the back surf ace of a 6.5-mm square thermal chip on a 28-mm square ceramic substrat e, Four different types of jets were used, all of them employing a sin gle 0.50-mm diameter orifice, A fixed-position jet impingement pin wit h the orifice centered on a flat face measuring 7.62 mm on an edge was used as a base case, This jet supported a heat flux of about 120 W/cm (2) at a reasonable flowrate. Variable-position jet impingement piston s were shown to perform as well as, but no better than the base case, Additional tests were conducted to investigate performance with variat ion in the chip-to-orifice gap, Thermal performance was found to be in sensitive to the gap at large spacing, but below some specific gap it degraded with decreasing gap, A sudden jump in the chip temperature wa s discovered to occur at a specific gap, This gap length was found to vary with jet flowrate.