熱與庫倫力對紊流場之微粒子沉澱的影響

Combined Effect of Thermophoretic and Coulombic Forces on Particle Deposition from a Turbulent Flow

李金紗(Jun-Sha Li)

指導教授 ： 邱明志

國立虎尾科技大學/工程學院/車輛工程系碩士班/碩士(2016年)

摘要

本論文是建立一數學模式，利用拉普拉式運算轉換後探討探討微粒子在紊流場中受到熱泳力作用，與庫倫力作用時對微粒沉澱的影響。當熱泳力及庫倫力的外部電場顯著存在時，將計算微粒沉澱所得偏差數據用曲線圖呈現。觀察到當熱泳力與庫倫力一起作用時對沉澱效率會造成影響，但當粒子夠大擁有足夠慣性時，則不受熱泳力或庫倫力的影響，且同時作用時之沉澱速度並非兩者效應各別相加之總和。

關鍵字

熱泳力 ； 庫倫力 ； 紊流場 ； 溫度梯度

並列摘要

The stedy is in order to further improve the previous results [1], especially for the particles with high values of , the formulating method proposed previously [2] has been modified by introducing the interactions between turbulent transport mechanisms and the persistence of turbulent structures into the present analysis. The close agreement with experimental measurements of the neutral deposition in an isothermal turbulent tube flows over a wide range of particle sizes may regarded as a supporting evidence for the adequacy of the present formulation. The same method has also been extended to further study the significant role of coupling between thermophoretic and turbophoretic interactions, with particular emphasis on the superposition of external applied electric field onto the nonisothermal turbulent flows. The effects of the Coulombic force on the particle mass flux across the viscous sublayer are specified by the number of charges acquired by diffusion, field and combined charging mechanisms of particles at the saturation charge level. The resulting deviations from the curves calculated under isothermal condition become significant with increased thermal intensity gradient and Prandtl number, even when the external electric field is present. The observed trends of is useful in stressing that when both the Coulombic and thermophoretic forces operate together, the total is not the sum of these drift mechanisms considered in isolation, and confirming that the particles with high inertia have sufficient wallward momentum to coast across the boundary layer without being influenced strongly by the thermophoretic or Coulombic force.

並列關鍵字

Thermophoresis ； Turbophoresis ； Coulombic force ； Diffusion charging mechanism ； Field charging mechanism ； Combined diffusion and field charging mechanism

參考文獻

[1] M.C. Chiou, C.H. Chiu, H.S. Chen, Particle deposition with thermal and electrical effects in turbulent flows, Int. J. Thermal Sci. 50 (2011) 1867-1877.

[2] M.C. Chiou, C.H. Chiu, H.S. Chen, Formulation for predicting deposition velocity of particles in turbulence, Int. J. Thermal Sci. 49 (2010) 290-301.

[3] S.L. Goren, Thermophoresis of aerosol particles in laminar boundary layer of a flat plate, J. Colloid Interface Sci. 6 (1977) 77-80.

[4] B. Singh, R.L. Byers, Particle deposition due to thermal force in the transition and near-continuum regimes, Ind. Eng. Chem. Fundam. 11 (1972) 127-133.

[6] R.L. Byers, S. Calvert, Particle deposition from turbulent streams by means of thermal force, Ind. Eng. Chem. Fundam. 8 (1979) 646-655.