Heat exchangers are devices that are used to transfer heat from one fluid to another. These are classified on the basis of various factors such as construction, flow arrangement, and the physical state of the fluids being exchanged. One of the most common methods of classification is based on the physical state of the heat exchanging fluids.

Classification of Heat Exchangers Based on Physical State of Heat Exchanging Fluids:

Heat exchangers can be classified into two categories based on the physical state of the heat exchanging fluids:

1. Liquid-to-Liquid Heat Exchangers:

This type of heat exchanger is used when both the fluids are liquids. The heat is transferred from one liquid to another through a heat transfer surface such as a tube or a plate. The two types of liquid-to-liquid heat exchangers are:

i. Double Pipe Heat Exchangers - This type of heat exchanger consists of two pipes, one inside the other. The hot fluid flows through the inner pipe, while the cold fluid flows through the outer pipe. The heat is transferred through the wall of the inner pipe.

ii. Shell and Tube Heat Exchangers - This type of heat exchanger consists of a bundle of tubes enclosed in a shell. One fluid flows through the tubes, while the other fluid flows through the shell. The heat is transferred through the tube walls.

2. Gas-to-Liquid Heat Exchangers:

This type of heat exchanger is used when one fluid is a gas and the other fluid is a liquid. The heat is transferred from the gas to the liquid through a heat transfer surface such as a tube or a plate. The two types of gas-to-liquid heat exchangers are:

i. Plate Heat Exchangers - This type of heat exchanger consists of a series of plates with alternating hot and cold fluids. The plates have channels through which the fluids flow, and the heat is transferred through the plate walls.

ii. Finned Tube Heat Exchangers - This type of heat exchanger consists of tubes with fins attached to the outside. The hot gas flows over the fins, while the cold liquid flows inside the tubes. The heat is transferred through the tube walls and the fins.

Conclusion:

Thus, heat exchangers are classified into two categories based on the physical state of the heat exchanging fluids - liquid-to-liquid heat exchangers and gas-to-liquid heat exchangers. Each type of heat exchanger has its own advantages and disadvantages, and the selection of the appropriate type depends on various factors such as the application, the heat transfer rate required, and the cost.