Distributed jet array impingement boiling on particle sintered porous surfaces

Abstract

Due to the excellent heat transfer performance and adaptability in dealing with local hot spots, jet array impingement boiling is promising for the high heat flux cooling in a variety of power electrical and electronic devices, such as high-performance CPU, IGBT, and laser diode. A distributed jet array with effusion ports adjacent to jet holes can extract spent flow immediately to avoid the negative crossflow effect in a normal jet array. Consequently, the heat transfer coefficient (HTC) and critical heat flux (CHF) can be both improved greatly. In order to further improve the heat transfer performance of distributed jet array impingement boiling, enhanced boiling surfaces could be used. Particle sintered porous surfaces have been widely investigated in pool boiling and achieved significant enhancement effect owing to the increased nucleation sites and wetting areas. Although several studies on the sintered porous structure have been done for jet impingement boiling, none is for distributed jet array. In this paper, a pumped two-phase loop was built up and three kinds of porous surfaces were experimentally investigated to enhance the distributed jet array impingement boiling of dielectric coolant, HFE7000. The porous structures were sintered with the copper particles of 50, 100 and 200 μm in diameter on a target surface of 11 mm ×20 mm and had a fixed thickness to particle size ratio of 2.0. A distributed jet array with 10 jet holes and 12 effusion holes was used. The diameters of the jet and effusion holes were 1 mm and 2 mm, respectively, while the distances between jet holes or effusion holes were 5 mm. The volume flow rate through the test section was 0.4 L/min, and the liquid inlet temperature and phase change saturation temperature were controlled at 35 and 60  C, respectively. An experimental apparatus was also established up to compare the wickability of the three porous surfaces. The 100 and 200 μm particles sintered surfaces were proved to have the better wickability. The experimental results turn out that the single-phase heat transfer is significantly improved due to the increased heat transfer area and flow turbulence within the porous structures, and the enhancement ratio increases with the increasing of flow rate. The porous surfaces sintered with 100 and 200 μm particles have close heat transfer performances, which are much better than that sintered with 50 μm particles. As for boiling heat transfer regime, the porous structures can provide more nucleation sites but at the same time will increase the flow resistance of effusion vapor. As a trade-off, the best performance is achieved by 100 μm particle, with its largest heat transfer coefficient upon DNB (departure from nucleate boiling) increased by 61% compared with that of the smooth surface. The wickability of porous layer however has no obvious effect on CHF due to the dominant role of distributed jet impingement on liquid feeding as well as the low surface tension of HFE7000. The maximum enhancement of CHF by 17% is acquired using the 100 μm particle sintered porous surface. Nevertheless, the heat flux range between DNB and CHF is greatly extended for the porous surfaces, which is beneficial to practical applications. A number of spots are found to be randomly distributed on the original smooth particle surfaces after many times of boiling experiments, but seem to have little influence on heat transfer performance. The long-term durability of the enhancement surface however needs further investigation.