本文主要探討不同的幾何尺寸及入口速度，水蒸氣是否有回流的現象而影響氣態鋅粒子的形成，在不考慮化學反應條件下觀察兩種高溫氣體混合後的流場與溫度場。 在模型設計上，分別固定反應爐出口直徑與氣體出口直徑、固定反應爐出口直徑與改變氣體出口直徑、改變反應爐出口直徑與固定氣體出口直徑，再藉由改變氣態鋅入口速度，探討其混合區流場與溫度場。 本文結果顯示在低的入口速度，反應爐出口直徑超過16mm，水蒸氣會隨著直徑增加而回流趨勢越明顯；當入口速度為2.192m/s，反應爐出口直徑小於18mm，氣體出口直徑增加或減少，水蒸氣都不有回流現象；若速度增加為4.384m/s，固定反應爐出口直徑或固定氣體出口直徑，都會有大量的水蒸氣往反應爐回流現象，造成產氫效率會大幅降低。 The present thesis tends to investigate the influence of mixing chamber’s geometries, incoming gaseous speeds and the circulations of flow on the forming of the gaseous state Zinc particle. Without the consideration of chemical reaction condition, both high-temperatures gas flow field and temperature field after mixing are investigated in detail. In the numerical simulations, different combinations of furnace exit diameter and gas exit diameter, as well as the gaseous zinc entrance velocity, are taken to see the influence of furnace’s geometry on the thermal and fluid distributions. Results show as the entrance speed is low and the furnace exit diameter is larger than 16mm, the water steam will flow backward into the furnace. The trend will be more obvious as the diameter increases. While the inlet Zinc velocity is 2.192m/s and the furnace exit diameter is smaller than 18mm, no matter what the gas exit diameter is, the water steam will never flow backward into the furnace. If the inlet velocity increases to 4.384m/s, regardless of fixed furnace exit diameter or fixed gas exit diameter, there always has a large amount of steam flows backward into the furnace. The backflow of the steam will surely reduce the efficiency of hydrogen production.