Heat Exchangers:

Plate and frame heat exchangers:
A plate heat exchanger is a type of heat exchanger that uses metal plates to transfer heat between two fluids. This has a major advantage over a conventional heat exchanger in that the fluids are exposed to a much larger surface area because the fluids spread out over the plates. This facilitates the transfer of heat, and greatly increases the speed of the temperature change.

Plate heat exchangers are now common and very small brazed versions are used in the hot-water sections of millions of combination boilers. The high heat transfer efficiency for such a small physical size has increased the domestic hot water (DHW) flowrate of combination boilers.

The small plate heat exchanger has made a great impact in domestic heating and hot-water.

Shell and tube heat exchangers:
A shell and tube heat exchanger is a class of heat exchanger designs.[1][2] It is the most common type of heat exchanger in oil refineries and other large chemical processes, and is suited for higher-pressure applications.

As its name implies, this type of heat exchanger consists of a shell (a large pressure vessel) with a bundle of tubes inside it.

One fluid runs through the tubes, and another fluid flows over the tubes (through the shell) to transfer heat between the two fluids. The set of tubes is called a tube bundle, and may be composed of several types of tubes: plain, longitudinally finned, etc.