點解蒸餾法既冷凝器既入水位置是下面，不是上面？

如果冷凝器既入水位置在上方, 當水注入時就會立即從下方留走, 在冷凝器內既停留時間太短, 不足以把需要冷卻物體的熱量迅速帶走. 相反, 從冷凝器下方入水, 水在冷凝器內注滿後從上方流走, 有足够時間把熱量帶走, 冷卻效果好.

答案很好,為什麼只值2星??

This is a fair answer. The answer contains the main essential point. However, it should be farther expanded to meet the need of the questioner and, at least make him understand, Haha.

are u talking about the Liebig condenser?
it you are,入水位in 下面because water can go in the condenser and condense the vapour in the most effective way.
It is because when the vapour enter the condenser,it makes the water in the condenser less cool,and at this time ,the less cool water leave form the exit and then cooler water replace it, so the water near the entrance of the condenser is always cool,so the vapour can be cooled down immediately and condense gradually through the condeser because the water in the condenser is always cool.

令冷卻效果更佳。

因為可以注滿成支冷凝器
如果起上面,好快就因地心吸力而離開冷凝器
起下面GE話,水會慢慢注滿成支冷凝器從而整冷D水蒸汽
又省水又更易整冷D水蒸汽
SO會起下面