Analysis of Thermophoretic Effect by Means of Phase Doppler Method

本研究对热泳效应进行了测量方法的建立和测量数据的分析，以积累定性数据，建立充分的理论基础。(1)热泳速度测量方法的建立热泳速度是热泳的特征值之一，建立了热泳速度的测量方法。通过建立温度分布为线性且准稳态的测量场，气体流速与热泳速度相比可以忽略不计，实现了该测量场。测量场是两个平板（90x90mm）之间的封闭空间，水平平行放置在一个狭窄的距离（1mm）内，上面的平板加热形成温度梯度。所产生的对流流的速度与平板距离的3次方成正比，与平板宽度成反比，这对精确测量造成了干扰。由此可知，当距离设置较窄（1mm）时，可以实现100 K/mm左右温度梯度下的精确测量。(2)热泳效应定性数据的积累采用(1)的方法测量了热泳速度，积累了热泳效应的定性数据。在高达90 K/mm的温度梯度下，测量了直径为1 ~ 3mm的SiO2颗粒和直径为5 ~ 30mm的PMMA颗粒的热电泳速度，获得了重复性良好的数据。实测数据比以往研究中提出的数值要大。这一结果指出了以往研究中仅在小温度梯度条件下测量数据的不确定性。热泳速度对温度梯度和颗粒直径的依赖关系也不同于以往的研究。

In this study, establishment of measuring method and analysis of measured data concerning thermophoretic effect have been conducted to accumulate the qualitaive data and establish the adequate theory.(1) Establishment of measuring method of thermophoretic velocityThe measuring method of thermophoretic velocity, which is one of the characteristic values of thermophoresis, has been established. It was realized by setting up the measuring field, in which temperature distribution is linear and quasi steady, and gas flow velocity is negligible compared with thermophoretic velocity. The measuring field was a closed space in two flat plates (90x90mm), which were placed horizontally and parallel to each other in a narrow distance (1mm) with the upper plate heated to form a temperature gradient in between. The velocity of generated convective flow, which disturbs accurate measurements, was found to be proportional to the 3rd power of the plate distance and inverse of the width of plate. By this results, the accurate measurement in the temperature gradient of about 100 K/mm could be realized when the distance was set to be narrow (1mm).(2) Accumulation of qualitative data concerning thermophoretic effectBy means of the method denoted in (1), thermophoretic velocities have been measured to accumulate the qualitative data of thermophoretic effect. Thermophoretic velocities of SiO2 particles of 1-3mm in diameter and PMMA particles of 5-30mm in diameter have been measured under the temperature gradient of up to 90 K/mm, and well reproducible data were obtained. The measured data were found to be larger than the value proposed in previous studies. This result pointed out the uncertainty of the previous studies, in which data were measured in only small temperature gradient condition. Dependence of thermophoretic velocity on temperature gradient and particle diameter was also found to be different from that in the previous studies.