Q1: Viscous & heat sensitive liquids are concentrated in __________ evaporators.

ANS:C - agitated film

In an agitated film evaporator, the liquid being processed flows as a thin film over a heat transfer surface while being agitated or stirred continuously. This agitation helps to maintain a uniform distribution of the liquid film, ensuring efficient heat transfer and preventing the formation of hot spots that could lead to product degradation or fouling. The agitation also helps to enhance the renewal of the liquid film, which is crucial for maintaining a high rate of evaporation. By continuously exposing fresh liquid to the heat transfer surface, the evaporator can effectively remove heat from the liquid, causing it to evaporate and leaving behind a concentrated product. Agitated film evaporators are particularly suitable for handling viscous or heat-sensitive liquids because they provide efficient heat transfer without subjecting the liquid to prolonged exposure to high temperatures. Additionally, the agitation helps to prevent the formation of fouling deposits on the heat transfer surface, ensuring consistent performance over extended periods of operation.