Superheated steam is steam heated to a temperature higher than the boiling point of water at a given pressure. It cannot exist in contact with water, nor contain water, and resembles a perfect gas; it is also called surcharged steam, anhydrous steam, and steam gas. Superheated steam can be used as a heating fluid instead of hot air in any direct dryers ( where the heating fluid is indirect contact with the product); for example, in spray drying, in a fluidised bed, in a spouted bed, in drums, etc.
過熱蒸汽的定義：在一定壓力下把蒸汽加熱到比水沸點更高的溫度形成過熱蒸汽。過熱蒸汽不含水分，類似完全氣體。它有好幾個名稱; superheated , surcharged、anhydrous(無水蒸汽)、steam gas(蒸汽氣體)。過熱蒸汽可用來作為烘乾用的流體，取代直接式烘乾機的熱空氣(熱流體與產品不直接接觸)，如噴灑式烘乾、流體床、噴流層乾燥、滾筒式乾燥燈方法。
