Effect of sub-cooling on performance of a multi-jet two phase cooler with multi-scale porous surfaces

An experimental investigation of the heat transfer and fluid flow characteristics of a jet impingement phase change cooler with smooth pin fin and porous coated pin fin target surfaces is presented. In the investigation, a 5 × 5 jet array with orifice diameter of 0.75 mm was used in combination with HFE-7100 as the coolant. Three different types of porous coated pin fin target surfaces, fabricated with varying particle sizes ranging between 10 μm and 177 μm, were tested. The experimental results show that, when compared to a smooth pin fin surface, the porous coated pin fin surfaces significantly increase the achievable heat transfer coefficient with an enhancement of 79% at a heat flux value of 50 W/cm2 for a 75-100 μm particle size surface. The two-phase heat transfer performance was further enhanced 1.8× by reducing the inlet sub-cooling from 10 K to 5.5 K. Additionally, the addition of a porous coating to the pin fin target surface has a relatively small impact on the cooler pressure drop, which was measured as 1.17 kPa for the 75-100 μm particle size surface compared to 1.0 kPa for the smooth pin-fin surface at 10 K sub-cooling. At a reduced sub-cooling of 5.5 K, the pressure drop obtained with the 75-100 μm particle size surface is approximately 3× higher than the pressure drop at 10 K sub-cooling. This study also reports unique trends in pressure drop that are observed with increasing power density, where a sharp decrease in the pressure drop of the cooler is measured with increase in the heat flux.