Analysis of Thermophoretic Effect by Means of Phase Doppler Method

本研究通过建立热泳效应的测量方法和对测量数据的分析，积累了大量的定性数据，建立了相应的理论。(1)热泳速度测量方法的建立建立了热泳特征值之一的热泳速度的测量方法。该方法通过建立温度场为线性准稳态分布，气体流速与热泳速度相比可以忽略不计的测量场来实现。测量场是两个平板（90 X 90 mm）中的封闭空间，这两个平板以窄距离（Imm）水平且彼此平行地放置，其中上板被加热以在其间形成温度梯度。所产生的对流的速度，这干扰了准确的测量，被发现是成比例的板的距离和板的宽度的倒数的3次方。根据该结果，当距离设定为窄（1 mm）时，可以实现约100 K/mm的温度梯度的精确测量。(2)关于热泳效应的定性数据的积累通过（1）中所述的方法，已经测量了热泳速度以积累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- 3 mm的SiO_2颗粒和直径为5- 30 mm的PMMA颗粒的热泳速度，得到了重复性好的数据。测得的数据被认为是大于在以前的研究中提出的值。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性也被发现与以前的研究不同。

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.