壓力與電動力對非牛頓流體在微流道中熱流特性之影響

Effects of Pressure and Electrokinetic Forces on Flow and Heat Transfer characteristics of non-Newtonian fluid in microchannel

陳郁融(Yu-Rung Chen)

指導教授 ： 陳建信

國立虎尾科技大學/工程學院/機械與機電工程研究所/碩士(2011年)

摘要

近年來只有極少數的文獻探討以純電滲流方式驅動微流道內非牛頓流體的流動特性，而忽略壓力梯度的作用，然而流場中可能因微幫浦或其他因素而存在有壓力梯度，且因電滲流的流率一般很小，即使很小的壓力梯度仍可能對流體的速度分佈產生明顯的作用，進而影響微流道的熱傳特性；其次現有的研究微流道內流體之熱流特性相關文獻，絕大部分侷限於牛頓流體的流動行為分析，然而許多用於實驗室晶片的生醫流體並不適合視之為牛頓流體，所以非牛頓流體於微流道內的熱流傳輸現象值得更深入的研究。

本文旨在探討壓力與電動力對非牛頓流體在微流道內之流動與熱傳特性，藉由求解電位場、動量及能量方程式以求得電雙層中之電位分佈、速度分佈與溫度分佈、摩擦係數、紐塞爾數等，影響熱流傳輸特性之重要參數包括流動性指數、無因次化壓力梯度比、焦耳熱與表面熱通量之比、無因次化長度尺度比。

從研究結果中可以得知壓力輔助流體流動的值增加時，其速度分佈會隨之增加，而壓力妨礙流體流動時，因流動方向的不同導致其平均溫度趨近於零，使紐塞爾數求解時會發生奇異點。流動性指數的增加會導致速度分佈的減小溫度分佈的增大；在剪切變稀流體時，無因次化長度尺度比的增加使速度分佈增大，但有一極限值，在剪切增稠流體時則趨勢相反。根據不同的焦耳熱與表面熱通量之比，為表面加熱時溫度分佈會隨著無因次化壓力梯度比的增加而增大，表面冷卻時則得相反現象。

關鍵字

微流道 ； 非牛頓流體 ； 電滲 ； 焦耳熱

並列摘要

In the literature only few studies have been conducted on the analysis of non-Newtonian fluid flow through a microchannel. Also, the previous reports were restricted to the case of purely electroosmotic flow, that is, the effects of external pressure gradient were not taken into account. However, the flow rate induced by electroosmotic force is usually small, and therefore even a small pressure gradient applied along a microchannel may cause velocity distributions and corresponding flow rates that deviate from the pure electroosmotic flow. Most of the previous studies pertinent to microchannel flows were concerned with Newtonian fluids. However, microfluidic devices are usually used to analyze biofluids which may not be treated as Newtonian fluids.

The objective of this investigation is to study non-Newtonian fluid flow and heat transfer introduced by the combined effects of electroosmotic and pressure forces in microchannels. The governing system of equations includes the electrical potential field, flow field, and energy equations. Analytical expressions are presented for velocity and temperature profiles, the friction coefficient, and the fully developed Nusselt number. The key parameters governing the problem under consideration include the flow behavior index, dimensionless pressure gradient, the Joule heating parameter (ratio of Joule heating to surface heat flux), and the length scale ratio (ratio of Debye length to half channel height). Typical results of flow and heat transfer parameters are presented for a range of governing parameters.

並列關鍵字

Microchannel ； Non-Newtonian fluids ； Electroosmosis ； Joule Heating

參考文獻

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