Future study

Thermophoretic particle deposition efficiency is investigated at 1 atm in this study. There are practical applications in the high-tech industry to prevent particle deposition in tube flow in vacuum. Thus, it is of great interest to investigate further the thermophoretic particle deposition in vacuum in the future.

There have been some developments in the filterless removal of combustion aerosol particles, such as diesel soots, by thermophoretic precipitator. Messerer et al.

(2004) developed a miniature pipe bundle heat exchanger to enhance the particle collection efficiency. The experimental results show that collection efficiency is not high enough, and the deposited soot particles lead to enhanced isothermal deposition and reduced thermophoreic deposition after the long-term operation, a typical soiling effect. In the future, it is worthwhile to develop a highly efficient thermophoretic precipitator and investigate the effect of soiling on the thermophoretic particle deposition efficiency.

This study has shown that the present theories under-predict particle deposition efficiency by image force for particles in Boltzmann charge equilibrium. In the presence of external electric field, the deposition of charged particle can be enhanced further. Fan and Ahmadi (1993) investigated the particle deposition in turbulent flow numerically and develop an empirical equation for the non-dimensional deposition velocity enhanced by electrostatic. The numerical results show that the deposition

rate of particles < 10 µm increases significantly as the electric field intensity increases.

However, experimental validation of the empirical equation is not yet available.

Further experimental study in the electrostatic effect on particle deposition is therefore necessary and warranted.

Appendix A: Derivation of equation for the combined fully developed case

Assuming steady, laminar fluid flow in a circular tube, thermophoretic velocity Vth(r, z) in the radial direction is a function of r and z, and the particle equations of motion, Eqs. (2.8) and (2.9), can be simplified as

)

The critical particle trajectory can be calculated by

∫

∫

The temperature gradient in the radial direction can be found by the energy equation as

The mixing-cup temperature distribution is a function of z only and is given by Incropera and De Witt (1996) as

⎟⎟

where

Combing Eq. (A.5) and the invariant fully developed temperature profile, Eq.

(2.4), Eq. (A.4) can be solved analytically to obtain the temperature gradient, and the corresponding thermophoretic velocity can be obtained as the product of two functions: g(r) and h(z), where g(r) depends on r while h(z) depends on z only.

Taking separation of variable of equation (A.3) results in the following dimensionless analytical equation which can be solved to obtain the dimensionless critical radial position, Rc,

= rc/r0 is the dimensionless critical radial position. Once Rc is obtained, thermophoretic particle deposition efficiency can be calculated.

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VITA

Name: Jyh-Shyan Lin

Date of Birth: October 12, 1976

Place of Birth: I-Lan Country, Taiwan, Republic of China

Education: 2000-2004 National Chiao Tung University, Ph. D. program in Institute of Environmental Engineering.

1998-2000 National Central University, M. S. program in Institute of Mechanical Engineering

1994-1998 National Central University, B. S. program in Department of Mechanical Engineering

簡歷

作者：林智賢

出生地：台灣省宜蘭縣

出生日期：1976 年 10 月 12 日

學歷：2000-2004 國立交通大學環境工程研究所博士班 1998-2000 國立中央大機械工程研究所碩士班 1994-1998 國立中央大機械工程學系

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