Question

Identify the evaporator 

• A. Batch-type pan evaporator
• B. Falling-film evaporator
• C. Natural-circulation evaporator
• D. Rising-film evaporator

Hint:

In evaporators with vertical tubes, check the feed direction. Feed at the bottom that travels up with the vapor is a \textbf{rising-film}. Feed at the top that flows down the walls is a \textbf{falling-film}.

Answer 1

The Correct Option is D

Step 1: Analyze the provided diagram. The diagram shows the 'Feed' entering at the bottom of a set of vertical tubes, which are inside a steam chest ('Steam in'). As the liquid is heated, it begins to boil.

Step 2: Observe the flow path. The boiling creates vapor, and the vapor bubbles drag the liquid upwards along the walls of the tubes, forming a thin film. The mixture of 'Product' (concentrated liquid) and 'Vapours' exits from the top.

Step 3: Compare this mechanism with the options. This process, where the liquid and vapor travel upwards together inside the heating tubes, is the defining characteristic of a Rising-film evaporator. In a falling-film evaporator, the feed would be introduced at the top and flow down the tube walls.