本文以直接模擬蒙地卡羅法(Direct Simulation Monte Carlo Method)來模擬研究三維微結構物理模型對流場現象與熱傳作分析與探討。本文使用直接模擬蒙地卡羅法在低速時出入口邊界的隱性條件來修正。 在低速管流的模擬中，紐森數的範圍設定在0.08到1.8之間且微結構溫度分別設定為273 K ，323 K 和373 K。在模擬中，比較三維模擬結果與二微模擬結果之差異性。就結果而言，可以觀察出在三維模擬的例子中，兩側壁的效應影響了熱傳與流場性質且在三維的流場模擬中，壁的熱傳量也隨著紐森數的增加而減少。而在三維的模擬中，也模擬加大長寬比1，3和5倍，其結果顯現在三維的模擬中，長寬比小於3的時候，兩邊壁的效應對熱傳與流場的影響就相當顯著，隨著長寬比的增加，此時流場的性質與熱傳表現是接近二維模擬時的結果。當長寬比大於5的時候，發現二維模擬的結果是合理的。 The Direct Simulation Monte Carlo (DSMC)  method is employed to analyze the heat transfer and the fluid dynamics characteristics of a 3-D microstructure. An implicit treatment for low-speed inflow and outflow boundaries for the DSMC of microchannel flows is used. The microchannel flows are simulated with Knudsen numbers ranging between 0.08 and 1.8 and with three different temperatures 273k, 323k and 373k of microstructure. The calculated flow properties in the 3-D case are compared with those in the 2-D case. It shows that the two extra side walls in the 3-D case have significant effects on the heat transfer. The wall heat transfer in the calculated microchannel flow decreases with an increase in Knudsen number. The 3-D microchannel flows is also simulated with the cross aspect ratio in the range of 1, 3 and 5. It shows that when the aspect ratio < 3, the two extra side walls in the 3-D case have significant effects on the heat transfer and flow properties. When the aspect ratio increases, the flow pattern and heat transfer characteristics tend to approach that of 2-D results. The 2-D simplification is found to be reasonable only when the cross aspect ratio is larger than 5.