Which of the following is NOT a type of heat exchanger?

A heat exchanger is a device used to transfer heat between two or more fluids without mixing them. The question asks for an option that does not represent a recognized type of heat exchanger.

Shell and tube heat exchangers consist of a series of tubes, where one fluid runs through the tubes and another fluid flows outside the tubes within a shell. This is a common design used in many industrial applications due to its efficiency and ability to handle large temperature differences.

Plate heat exchangers consist of multiple thin plates stacked together, creating channels for the fluids to flow. This design increases the surface area for heat transfer and is often used for applications where space is limited.

Air-cooled heat exchangers use ambient air to cool fluids, often by having a fan blow air over finned surfaces to enhance heat transfer. These are commonly used in refrigeration systems and other cooling applications.

In contrast, "rippled" is not a recognized standard term or design for a heat exchanger type in the industrial sector. While various innovations in heat exchanger designs exist, "rippled" does not refer to a widely accepted category or type used in practice, which is why it is identified as the option that does not belong to the group of traditional heat exchanger types.