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

我们研究了与双电层有关的传热问题中的两种不同现象：(1)液体冻结时外来颗粒的捕集和扫掠现象；(2)电渗流在细填充床中的脱水.(1)当含有细颗粒的水溶液冻结时，冻结过程可分为两种情况：颗粒被困在冻结层中或颗粒被从冻结层中带出.颗粒因冻结而产生的捕集和扫掠现象广泛存在于污泥冻结过程、浓缩工艺和含杂质颗粒的金属固化过程中。我们研究了独立粒子和大量粒子存在于水溶液中的两种情况下的冻结现象。捕集和扫掠现象在很大程度上取决于冻结速度、颗粒大小和颗粒表面电荷。特别是利用不同的颗粒和水溶液，重点研究了颗粒表面电荷对这一现象的影响。临界冻结速率的计算结果与采用不同颗粒的实验结果相吻合。(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，在外加电场的作用下产生了电渗流。这一现象与污染污泥的脱水、微通道中的电渗泵以及填充床中的干燥有关。对饱和填充床中的电渗流进行了实验研究。结果表明，流速与颗粒表面电荷、填充床结构和电导率有关。对电渗流脱水填料床进行了实验研究。

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.