Enhanced flow boiling heat transfer with jet impingement on micro-pin-finned surfaces

Experiments were conducted to study the performance of subcooled flow boiling heat transfer with jet impingement of FC-72 over silicon chips (10 × 10 × 0.5 mm3). Four kinds of micro-pin-fins with dimensions of 30 × 60, 30 × 120, 50 × 60, 50 × 120 μm2 (thickness t× height h) were fabricated on the chip surfaces by using the dry etching technique. The experiments were made at two different liquid subcooling (25 °C and 35 °C), three different crossflow velocities Vc (0.5, 1, 1.5 m/s) and three different jet velocities Vj (0, 1, 2 m/s). A smooth surface was also tested for comparison. The results show that both the microstructure and impingement give a large enhancement on heat transfer. The maximum allowable heat flux increases with the velocity and liquid subcooling. For a fixed Vc, the enhancement degree increases with Vj especially for Vc = 0.5 m/s, Vj = 2 m/s. As Vc increases, the heat transfer enhancement of jet impingement weakens and the increase rate of CHF (the critical heat flux) also decreases. The largest value of qmax (the maximum allowable heat flux) can reach 167 W/cm2 for chip with the fin dimension of 50 × 120 μm2 at the condition of Vc = 1.5 m/s, Vj = 2 m/s and liquid subcooling of 35 °C.