本文以直接模擬蒙地卡羅法(Direct SimulationMonte Carlo Method)來模擬三維矩形微管之低流速流場，並改變管口徑大小與比例，來探討流場內部的流場特性與熱傳現象，深入觀察矩形空管內管角於兩壁作用下流場與熱傳的變化情形，而這是在二維模擬無法看的結果，也是真正三維效應所在，更趨近於實際微管流。其次是探討微流場內摩擦係數(C/sub f/)、Poiseuille number(C/sub f/*Re)於管角和管壁面的比較。本文所使用的工作流體為氮氣(N2)，分子模型則採用VHS分子模型。模擬之結果發現，管角於兩壁作用下的變化情形與流體在管壁邊有所差異，矩形微管管角的三維效應最為明顯，即使加大寬高比為5倍時其管中央部份雖然與二維流場99%一致，管角的三維效應還是明顯不同於二維微流場；並發現當流場越稀薄(Kn越大)時，摩擦係數(C/sub f/)會越大，並且在同口徑之微流場(同Kn)時，壓力梯度較大之微管其C/sub f/越大，而Poiseuillenumber則是隨著Kn的增加而降低。對於改變壁溫時，摩擦係數(C/sub f/)、Poiseuille number(C/sub f/*Re)值則隨壁溫的升高(273K~373K)而降低。 The Direct Simulation Monte Carlo (DSMC) method is employed to analyze the heat and fluid flow of low-speed three-dimensional (3-D) rectangular microchannels of various sizes and open cross-section aspect ratios. The VHS model and nitrogen are used in the present study. The distributions of slip velocity and the slip temperature along the wall boundaries and the corners are calculated and discussed. The Fanning friction coefficient and Poisseuille number along the corner and the center of the wall are also investigated. Although in the previous studies showed that when cross-section aspect ratio is 5, both heat and flow fields of 3-D simulations are roughly 99% approaching to that of 2-D case. These agreement only valid in the central part of the the channel. The present results showed that along the two side wall boundaries and the corners of a 3-D channel even at this high aspect ratio, the heat and flow properties still manifest the 3-D effects due to the existence of the two side walls. It is also found that the friction coefficient (C/sub f/) increases when the Knudsen number of the flow increase and the Poissruille number decreases as the Kn number increase. For the same size of the open cross section and the same Kn number, the higher inlet pressure will results in higher C/sub f/ values. When the wall temperature increases that cause decreasing both C/sub f/ and Poissruille number.
2007 CSME CONF中國機械工程學會第24屆全國學術研討會論文集=Proceedings of the 24th National Conference on Mechanical Engineering the Chinese Society of Mechanical Engineers，8頁