Lattice Boltzmann Simulation of Nucleate Pool Boiling in Saturated Liquid

A thermal lattice Boltzmann method(LBM)for two-phase fluid flows in nucleate pool boiling process is proposed.In the present method,a new function for heat transfer is introduced to the isothermal LBM for two-phase immiscible fluids with large density differences.The calculated temperature is substituted into the pressure tensor,which is used for the calculation of an order parameter representing two phases so that bubbles can be formed by nucleate boiling.By using this method,twodimensional simulations of nucleate pool boiling by a heat source on a solid wall are carried out with the boundary condition for a constant heat flux.The flow characteristics and temperature distribution in the nucleate pool boiling process are obtained.It is seen that a bubble nucleation is formed at first and then the bubble grows and leaves the wall,finally going up with deformation by the buoyant effect.In addition,the effects of the gravity and the surface wettability on the bubble diameter at departure are numerically investigated.The calculated results are in qualitative agreement with other theoretical predictions with available experimental data.

纳米流体强化传热进展综述

伴随电子设备的高速发展,制约其微型化、集成化的热交换设备高传热负荷成为需要解决的首要问题。作为高效、高传热性能的新型能量输运工质,纳米流体可以有效提高工质的导热性能,并改善散热系统的换热性能。因此,对于纳米流体强化传热技术的研究,不仅可以深入探究纳米流体在实际应用中的发展潜力,也有助于热交换设备传热性能的提高,具有广阔的市场应用前景和巨大的潜在经济价值。尽管现今已有大量针对纳米流体强化机理的科学研究,但研究结果的一致性较低,仍存在较大争议。因此,本文将从纳米流体在单相对流传热、池沸腾传热、流动沸腾传热三个方面进行全面的调研分析,针对纳米流体强化的传热机理进行总结和讨论。

板翅式单元液氮中微膜热虹吸浅池沸腾的实验研究

为模拟空气分离装置中冷凝蒸发器的实际运行状况，采用１ｍ长的板翅式单元作冷凝蒸发器的微膜热虹吸沸腾通道，使之部分地沉浸在液氮池中进行浅池沸腾试验，实验结果表明，当板翅式单元露出液面部分从０增加到４０ｃｍ时，在整个试样始终保持相同热流密度的条件下，其沸腾传热温差仅增加０．１９Ｋ；只要热流密度维持在某一最小起始值之上，即使沉浸深度减少４０％，冷凝蒸发器仍将处于高效和安全运行状态。

超声波对池沸腾换热影响

对不同超声强度和辐射距离条件下过冷池沸腾换热特性进行了实验研究。超声波有效强化了沸腾起始段换热,对高热流密度沸腾传热也有一定的强化作用。超声辐射距离越近,强度越大,强化传热效果越好。对单相对流和沸腾起始区传热,超声波强化传热机理为空化作用;高热流密度沸腾时超声波对强化传热的主要机理是声流作用。得到了传热实验关联式。