Parametric Analysis Of Condensation Heat Transfer Characteristics Of AMTEC Wick Condenser

Alkali Metal Thermal to Electric Converter(AMTEC) is a device which can convert thermal energy to electricity directly. This device is composed of evaporator, BASE tube, condenser, liquid return channel and high/low pressure chambers. As one of the main components, the condenser has great importance for the efficient circulation of working medium. i.e., sodium in the AMTEC. The efficient condensation of sodium vapor in the porous condenser not only guarantees the circulation of working medium, but also is a potential measurement to control the total mass of AMTEC. Searching for the parameters which affect the condensation performance of AMTEC wick condenser and investigating how these parameters influence the condensation characteristics may have great significance and value for the development and application of AMTEC. In addition, this work may enrich the theoretical research on condensation in porous medium.Based on some reasonable assumptions, a physical and mathematical model has been established to simulate the flow and heat transfer characteristics in porous condenser. Further, the condensate film thickness δ and local Nusselt number Nu were determine by means of theoretical derivation and numerical calculation. The heat and mass transfer features of sodium vapor condensation in AMTEC wick condenser were revealed. The effects of radiation, inertia force and wettability on the flow and heat transfer characteristics were analyzed. Meanwhile, the impacts of structure parameters(the distance from the top of liquid return channel to the condenser H, the inner and outer diameters 2r1, 2r2), the operating parameters( the temperature of BASE TB, heat conduction temperature difference ΔT), thermophsical properties such as the effective conductivity λe, the type of working fluid(sodium Na or potassium K) have been carried out.The results reveal that the condensate film thickness δ appears thin in the centre and thick outward when not taking account of the wetting effect. While, the the condensate film presnts meniscus shape when the wetting effect is taken into consideration. It is found that the radiation can reduce the film thickness and increase the Nusselt number. Under some situations, the difference in the thickness and average Nusselt number would exceed 10% between the condition of considering or not considering radiation effect. Increasing the temperature of BASE TB or decreasing the magnitudes of the folling parameters i.e, the effective thermal conductivity λe, temperature difference of heat conduction ΔT, the distance from the top of liquid return channel to the condenser H and the inner and outer diameters 2r1, 2r2 can reduce the condensate film thickness and increase the average Nusselt number at different levels. It is demonstrated that the influence of the inertia force is so small that can be ignored. Also it is shown that with the increasing of wetting angle θ, the film thickness decreases and average Nusselt number increases. Besides, the variation is almost not affected by effective thermal conductivity λe. In the end, the comparisons of the flow and heat transfer characteristics of the AMTEC wick condenser using sodium Na or potassium K have been conducted. Under the same condition, the film thickness of K is larger than that of Na, while the average nusselt number is lower. This phenomenon is attributed to the physical properties of the different work fluids.