What type of feed design is used with a shell and tube evaporator when using refrigerant in the shell?

In the context of a shell and tube evaporator that utilizes refrigerant in the shell, a DX (direct expansion) feed design is appropriate. This design allows for the refrigerant to expand and directly absorb heat from the process fluid as it flows through the tubes.

The DX design is characterized by the refrigerant changing from a liquid to vapor as it absorbs heat, which creates an efficient heat transfer process due to the direct interaction between the refrigerant and the medium being cooled. In this way, it maximizes the heat exchange effectiveness while maintaining optimal pressure and temperature conditions for the refrigerant.

Flooded and overfeed designs, while useful in other applications, are not typically used for shell and tube evaporators with refrigerants in the shell. A flooded system keeps the evaporator filled with liquid refrigerant to promote better heat exchange in specific scenarios, and an overfeed design implies that additional refrigerant is supplied to ensure proper cooling, which could complicate operations in this particular type of evaporator setup. Hence, the DX design is the most suitable and efficient method for this specific application.