壓縮微管流的熱流分析; Thermal fluid analysis of compressible microchannel flow

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Title:	壓縮微管流的熱流分析;Thermal fluid analysis of compressible microchannel flow
Authors:	陳家勇;Chia-Yung Chen
Contributors:	機械工程研究所
Keywords:	壓縮層流;數值模擬;熱對流;微管流;compressible laminar flow;numerical simulation;heat convection;microchannel flow
Date:	2002-07-09
Issue Date:	2009-09-21 11:39:49 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本文以數值模擬探討微管道的壓縮層流之熱流特性，管道水力直徑小於4 m，壁面設定為無滑移流條件。流速範圍有二，一是Main=0.07~0.21，Re=1~10；二是Main=(3~12)×10-4，Re=(1.2~8.9)×10-3。數值解顯示壓縮層流在入口處有速度陡升現象，且不論微管道多長，都不會形成完全發展流；而入口流速愈大，出口流速急遽增加現象愈明顯。非滑移流中的速度剖面類似滑移流，愈靠近出口處愈平坦；且入口流速愈大情況愈明顯。而入口處的速度剖面，因流體在壁面的黏滯性加熱呈現凹陷狀。考慮加熱壁面時，壁溫愈高時，流場的紐索數愈低，且流體需流過較長距離，紐索數才能達到定值。與非壓縮流場比較，壓縮效應使得壓力分佈呈非線性分佈，且在出口處壓力梯度與速度梯度同時達到最大值。且入出口壓力比愈大時，非線性的壓力分佈現象愈明顯。模擬結果顯示在微型流道中，因流道尺寸效應，入口流速雖然極低(Main~10-3)，仍會因為入口流速的些微不同，造成流場差異頗大的壓力分佈。 This numerical study analyzed the thermal-flow characteristics of the compressible laminar flow over the microchannel (dh < 4μm). The channel wall is assumed as non-slip flow condition. Two flow regimes were considered: 1) Ma=0.07~0.21, Re=1~10; 2) Ma=(3~12)×10-4, Re=(1.2~8.9)×10-3. Numerical results show that the compressible laminar flow has abrupt velocity jump near the channel entrance, and the fully developed flow can never be achieved no matter how long the channel is. In addition, further increases inlet velocity, more significant increasing of velocity at the outlet is predicted. The predicted velocity of present non-slip flow has a flat profile, which is similar to the solution of the slip flow simulation, and the velocity distribution is flatter as the flow approaches the outlet. Near the inlet, velocity profiles have a concave shape due to the viscosity heating at wall. For the heating wall case, the Nusselt number is inversely proportional to the wall temperature. When the wall temperature is higher, the flow needs longer channel to reach a constant Nusselt number. Comparing with the incompressible flow, nonlinear pressure distribution is obtained due to the compressibility effect. Both pressure and velocity gradient reach the maximum value at the outlet. Furthermore, enforcing higher pressure ratio (inlet value to outlet value), more significant nonlinear level of pressure distribution is observed. Because of the channel size effect, even the inlet velocity is very low (Main~10-3), numerical results reveal that a slight velocity difference makes a huge dissimilar pressure distribution in microchannel.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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