What are the different types of heat exchanger?

Heat exchangers can be classified according to flow arrangement and the construction features.

Parallel-flow and counterflow

In the simplest heat exchanger, two fluids (one cold and one hot) move in the same or opposite directions in a concentric tube configuration. When the fluids enter and leave at the same end the arrangement is parallel-flow, whereas in the counterflow configuration, the fluids enter and leave at the opposite end.

Parallel-flow and counter-flow
Parallel-flow and counter-flow heat exchanger

Cross flow

The fluids can also flow in perpendicular directions which is known as cross flow arrangement. The two main types are finned and unfinned tubular. With a finned tubular heat exchanger, both fluids are unmixed, the one between the fins is guided in a direction transverse to the tube flow direction. In the unfinned exchanger heat can be exchanged in all directions, and the fluid can mix.

Cross flow
Finned and Unfinned tubular heat exchanger

Shell-and-tube

The shell-and-tube heat exchanger is composed of a shell containing a large number of tubes. Different types of shell and tube designs are possible.

If the tube is curved, with the shape of a U, it is called a U-tube. The tubes can also be straight, with one or two passes. In a single pass heat exchanger, the fluid goes into one end of a tube and out the other.  In the two pass type the fluid enters and exit on the same side.  Baffles can be installed to guide the flow through the shell sides.

Shell-and-tube
U-tube, single pass straight and two pass straight heat exchanger

Compact heat exchanger

A compact heat exchanger is a device characterized by a high heat transfer area per unit volume (more than 300 m2/m3). There are different types of compact heat exchanger design available.

The plate-and-frame heat exchanger design consists of stacked of corrugated plates which are bonded together. With this configuration the fluid is spread out over the multiple plates.

Plate-and-frame heat exchanger
Plate-and-frame heat exchanger

In the plate-fin heat exchanger, fins are inserted between parallel plates and the fluid flow through these fins. Thus, the heat transfer area is increased. The fins can be triangular, rectangular, wavy or perforated.

Plate-fin heat exchanger
Pate-fin heat exchanger

The shell-and-tube heat exchanger can be adapted in a compact heat exchanger, using polymer tubes. With the reduction of the polymer tube diameter, the shell can accommodate more tubes, hence, increasing heat transfer area density. Polymer materials are light and resist to corrosion but they are limited to ?? temperatures and pressures.

The micro heat exchanger is a device in which the fluid flows in lateral channel with typical dimensions below 1 mm. The diagram below refers to a microchannel heat exchanger.

Microchannel heat exchanger
Microchannel heat exchanger