Flow Distribution Control and Thermal Homogenization with EHD Conduction Pumping and Experimental Studies in Pool Boiling and Internal Condensation Public
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Electrohydrodynamic (EHD) pumping relies on the interaction between electrical and flow fields in a dielectric fluid medium. Advantages such as simple and robust design as well as negligible vibration and noise during operation make EHD conduction pumping suitable for various applications. This work investigates meso-scale EHD conduction pumping used as an active flow distribution control mechanism for thermal management systems. Two different scenarios are considered for this purpose: alteration of uniform flow distribution and flow maldistribution correction. Its capability of actively controlling the flow distribution is examined in terms of the value of applied potential for initiation of flow divergence or flow equalization and the flow rate difference between each branch. Experimental results confirm that the reverse pumping direction configuration of EHD pumping is more effective than the same pumping direction configuration. A fundamental explanation of the heterocharge layer development is provided for the effect of flow direction on EHD conduction pumping performance. This study also involves a macro-scale EHD conduction pump used as an alternative mechanism of mixing liquid within a storage tank, for example under low-g condition. A numerical analysis of a simplified model of the experimental setup is provided to illustrate the liquid mixing and thermal homogenization process. The experimental and numerical study provide fundamental understanding of liquid mixing and thermal homogenization via EHD conduction pumping. Liquid-vapor phase change phenomena are used as effective mechanisms for heat transfer enhancement and have many applications such as HVAC&R systems. With this in mind, two detailed studies in pool boiling and in-tube flow condensation are carried out. Specifically, nucleate pool boiling on nano-textured surfaces, made of alumina ceramic substrate covered by electrospun nanofiber, is experimentally investigated. Also, the role of surface roughness and orientation in pool boiling is experimentally characterized. The in-tube convective condensation of pure water in mini-channels under sub-atmospheric pressure is also experimentally explored. This study provides valuable information for the design of condensers in a vapor compression cycle of HVAC&R systems using water as the refrigerant, this process has zero global warming potential.
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