In the present study, Ultrasonic Falling Film (USFF), as a novel technique has been proposed to increase the evaporation rate of moderate temperature liquid film. It is a proper method for some applications which cannot be performed at high temperature, such as foodstuff industry, due to their sensitivity to high temperatures. Evaporation rate of sodium chloride solution from an USFF on an inclined flat plate compared to that for Falling Film without ultrasonic irradiation (FF) at various temperatures was investigated. The results revealed that produced cavitation bubbles have different effects on evaporation rate at different temperatures. At lower temperatures, size fluctuation and collapse of bubbles and in consequence induced physical effects of cavitation bubbles resulted in more turbulency and evaporation rate enhancement. At higher temperatures, the behavior was different. Numerous created bubbles joined together and cover the plate surface, so not only decreased the ultrasound vibrations but also reduced the evaporation rate in comparison with FF. The highest evaporation rate enhancement of 353% was obtained at 40 °C at the lowest Reynolds number of 250. In addition, the results reveal that at temperature of 40 °C, USFF has the highest efficiency compared to FF.

在本研究中，超声降膜（USFF）作为一种新技术已被提出来提高中温液膜的蒸发速率。对于某些无法在高温下执行的应用（例如食品工业），由于其对高温的敏感性，这是一种合适的方法。研究了在不同温度下，与没有超声辐射（FF）的降膜薄膜相比，在倾斜平板上从USFF上氯化钠溶液的蒸发速率。结果表明，在不同温度下，产生的空化气泡对蒸发速率的影响不同。在较低的温度下，气泡的尺寸波动和破裂以及因此引起的空化气泡的物理效应导致更多的湍流和蒸发速率的提高。在更高的温度下，行为是不同的。与FF相比，大量产生的气泡连接在一起并覆盖了板表面，因此不仅减少了超声波振动，而且降低了蒸发速率。在40℃，最低雷诺数为250的情况下，蒸发率最高提高了353％。此外，结果表明，在40°C的温度下，与FF相比，USFF的效率最高。