Today most industry evaporation is done as falling film evaporation or as rising film evaporation. Falling film evaporation is typical for shell and tube heat exchanger technology and rising film technology is typical for plate heat exchanger technology. Rising film evaporators may suffer from fouling of the heat transfer plates, which may lower the heat transfer capacity of the evaporator. The degree of fouling may be the highest at the inlet area of the heat transfer plates where the vapor ratio is low and the fluid flow is laminar. In this zone of the evaporator, the fluid velocities are relatively low, which causes uneven fluid distribution across the heat transfer plates and relatively long fluid retention time. As result, this zone of the evaporator is more prone to the formation of deposits than other zones of the evaporator where full rising film flow is developed, and fluid velocity is much higher.
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