Liquid-vapor phase change phenomena for heat exchangers and electronics cooling

Phase change heat transfer is an attractive heat transfer process due to its superior heat transfer coefficients as compared to single phase heat transfer. Among the fluids used as refrigerants, water is of interest for its good thermodynamic properties. It is in addition widely available, inexpensive and of no health hazards. In particular, liquid vapor phase change of water is widely observed. Water vapor condensation is vital to many natural and industrial processes such as building environmental control, power generation, and water desalination. Jumping-droplet condensation of water has recently been shown to have a 10X heat transfer enhancement compared to state-of-the-art filmwise condensation due to the removal of condensate at much smaller length scales (~ 1µm) than what is capable with gravitational shedding (~ 1mm). However, the efficient removal of jumping droplets can be limited by droplet return to the surface due to gravity, entrainment in bulk convective vapor flow, and entrainment in local condensing vapor flow. If used appropriately, convective condensation has the potential to entrain droplets, hence impeding their return to the surface. In addition, obtaining droplet size distributions is critical to determine the heat flux on these surfaces and is still lacking in literature. On the other hand, evaporation of these droplets can provide a cooling mechanism for small electronics components at high flux. Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. In this work, laminar boundary layer theory was used to model the vapor flow and jumping droplet behavior on a plate and inside the tube with condensation modeled as vapor suction. The droplet size distribution for jumping-droplet condensation is also investigated for a stagnant flow. On the other hand, the cooling potential of these droplets is studied for hot spots in electronics, and is compared to a higher heat flux approach of immersion cooling in water