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

A condenser is actually a type of heat exchanger that is specifically designed to remove heat from a refrigerant or vapor, allowing it to condense into a liquid. It serves a vital function in refrigeration and air conditioning systems, facilitating the transfer of heat from the refrigerant to another medium, typically air or water.

On the other hand, the other options all denote various types of heat exchangers. Shell and tube heat exchangers consist of a series of tubes, one set carrying the hot fluid and the other the cold fluid, making them ideal for many industrial processes. Plate and frame heat exchangers use thin plates to transfer heat between two fluids, providing a compact and efficient solution for heating and cooling tasks. Tube in tube heat exchangers feature one tube housed within another, allowing for effective heat exchange between the fluids circulating through each tube.

Given this understanding, it's clear that the correct choice is the condenser, as it is indeed a recognized category of heat exchanger utilized for specific functions rather than a separate type of heat exchanger itself.