高通量空气隙膜蒸馏传热研究

RESEARCH FOR HEAT TRANSFER OF HIGH FLUX AIR GAP MEMBRANE DISTILLATION

本文研究了空气隙膜蒸馏的传热过程,给出了其主要的传热计算公式。实验结果表明热腔内进液流量的增加,使传热强化,膜通量增加,但提高膜通量最有效的方式还是提高进液的温度。针对膜蒸馏热腔内切向旋转入流的特点,本文认为采用近似对流外掠平板的经验公式更加合适,并根据实验结果拟合出热腔对流换热的经验公式,计算结果与实验结果吻合较好。空气隙厚度大于3mm后,由于空气隙内自然对流换热的影响,空气隙传递的热量反而增加,并且进液温度越高,自然对流换热对总热流密度的影响越大。根据实验结果给出了水蒸气在冷壁表面凝结换热的表面传热系数计算公式。

The heat transfer of air gap membrane distillation is studied in this paper and main calculation formula is also discussed.The experiment results indicate that heat transfer and membrane permeate flux will be increased with the increase of hot solution flow rate.But the optimal methods to enhance the permeate flux is to increase the hot solution temperature.It is suitable to adopt the empirical relations for flow over flat plate based on the characteristic of rotational and tangential inlet flow in the hot channel of the air gap membrane distillation module. The empirical relation is proposed and the calculation results are good agree with the experiment results.The heat transfer resistance will be increase and total heat transfer rate will be decrease with the increase of air gap width.But the heat transfer rate will be increase when the air gap width is larger than 3 mm because of nature convection in the air gap.And the effect of nature convection on the total heat transfer rate will be more important with the increase of hot solution temperature. At the same time the heat transfer empirical formula for vapor condensation is also proposed.