Jet impingement boiling of a dielectric coolant in narrow gaps

An experimental investigation into the effect of the chip-to-orifice gap was conducted for jet-impingement boiling of FC-72 at the back surface of a 6.5-mm square thermal chip on a 28-mm square ceramic substrate. Four different types of jets were used, all of them employing a single 0.50-mm diameter orifice. A fixed-position jet impingement pin with 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/cm² at a reasonable flowrate. Variable-position jet impingement pistons were shown to perform as well as, but no better than the base case. Additional tests were conducted to investigate performance with variation in the chip-to-orifice gap. Thermal performance was found to be insensitive to the gap at large spacing, but below some specific gap it degraded with decreasing gap. A sudden jump in the chip temperature was discovered to occur at a specific gap. This gap length was found to vary with jet flowrate