The Effects of Electric Double Layer on Freezing and dehydration in Fine Packed Beds with Liquid Content

研究了双电层传热问题中的两种不同现象；(1)由于液体冻结引起的外来颗粒的捕获和扫掠现象；(2)利用电渗透流对细填料床进行脱水。(1)涉及细颗粒的水溶液冻结时，冻结过程可分为颗粒被困在冻结层和颗粒被扫出冻结层两种情况。颗粒因冻结而被捕获和横扫的现象是与污泥冻结过程、浓缩技术和含外来颗粒金属的凝固有关的一个重要问题。我们研究了两种独立粒子和大量粒子存在于水溶液中的情况下由于冻结引起的这种现象。捕获和扫掠现象在很大程度上取决于冻结速率、颗粒大小和颗粒表面电荷。特别地，我们用不同的粒子和水溶液研究了粒子表面电荷对这一现象的影响。临界冻结速率的计算结果与不同颗粒的实验结果吻合较好。(2)在由细颗粒组成的填充床中，由于颗粒表面附近形成的双电层的作用，外加电场引起电渗透流动。这一现象是污染污泥脱水、微通道电渗透泵和填料床干燥的重要问题。对饱和填料床中的电渗透流动进行了实验研究。结果表明，颗粒的表面电荷、填料床的结构和电导率对流动速率有一定的影响。实验研究了电渗透流对填料床脱水的影响。

We have investigated two different phenomena in heat transfer problems relating to electric double layer ; (1) the trapped and swept phenomenon of foreign particles due to freezing of liquid and (2) the dehydration in fine packed beds using the electro-osmotic flow.(1) When water solution involving fine particles freeze, the freezing process can be divided into two cases whether particles are trapped in the freezing layer or particles are swept out from the freezing layer. The trapped and swept phenomenon of particles due to freezing is widely an important problem related to the freezing process of sludge, the concentration technology and the solidification of metal including foreign particles. We have investigated this phenomenon due to freezing for two cases of independent particles and large number of particles existing in water solution. The trapped and swept phenomenon largely depends on the freezing rate, the size of particle and the surface electric charge of particle. Especially, we focused on the effect of the surface electric charge of particle, on this phenomenon using various particles and water solutions. The calculated results for the critical freezing rate were in agreement with the experimental results using various particles.(2) In packed bed composed of fine particles, an electro-osmotic flow is caused by the addition of external electric fields for the effect of the electric double layer formed near the surface of particles. This phenomenon is an important problem related to the dehydration of contaminated sludge, the electro-osmotic pump in microchannel and the drying in packed beds. The electro-osmotic flow in saturated packed bed has been investigated experimentally. It was found that the flow rate depended on the surface charge of particles, the structure of packed bed and the electrical conductivity. The dehydration of the packed bed using the electro-osmotic flow has been investigated experimentally.