Which heat exchanger is described as occasionally used in power plants, a replacement for shell and tube when thermal duty increases, with counterflow types and plates instead of tubes to transfer heat?

• A. Plate and Frame
• B. Shell and Tube
• C. Direct Contact
• D. Indirect Contact

Answer: (A)

The main idea here is how heat exchangers are built to handle different heat-transfer duties. Plate heat exchangers, often called plate-and-frame, use a stack of thin, corrugated plates that create many small channels. This setup gives a very high heat-transfer coefficient per unit area, so you can transfer more heat in a compact space than with a traditional shell-and-tube unit. Because of that compactness and the strong driving force in a counterflow arrangement, they’re a natural choice when the thermal duty increases but you still want to keep the footprint reasonable.

They transfer heat indirectly (no mixing of the two streams) through the metal plates, which can be easily disassembled for cleaning or reconfiguration. In power plant contexts, they’re used occasionally as a replacement for shell-and-tube when the duty is high or space, maintenance, or fouling considerations favor a plate design. The description—counterflow operation with heat transfer across plates instead of tubes—fits this type precisely.

Direct contact exchangers, where streams mix, don’t fit this scenario, and shell-and-tube units use tubes rather than plates, so they don’t match the described arrangement.