Regenerative heat exchanger

The simplest Stirling engines, including most models, use the walls of the cylinder and displacer as a rudimentary regenerator, which is simpler and cheaper to construct but far less efficient.

The heat storage medium can be a relatively fine-grained set of metal plates or wire mesh, made of some resistant alloy or coated to resist chemical attack by the process fluids, or made of ceramics in high temperature applications.

A large amount of heat transfer area can be provided in each unit volume of the rotary regenerator, compared to a shell-and-tube heat exchanger - up to 1000 square feet of surface can be contained in each cubic foot of regenerator matrix, compared to about 30 square feet in each cubic foot of a shell-and-tube exchanger.

In another configuration, the fluid is ducted through valves to different matrices in alternate operating periods resulting in outlet temperatures that vary with time.

The hot gas from the furnace is ducted through the brickwork for some interval, say one hour, until the brick reaches a high temperature.

Valves then operate and switch the cold intake air through the brick, recovering the heat for use in the furnace.

This type has a fixed matrix in a disk shape, and streams of fluid are ducted through rotating hoods.

[citation needed] The nose and throat work as regenerative heat exchangers during breathing.

Some animals, including humans, have curled sheets of bone inside the nose called nasal turbinates to increase the surface area for heat exchange.

[citation needed] The design of inlet and outlet headers used to distribute hot and cold fluids in the matrix is much simpler in counter flow regenerators than recuperators.

Finally properties such as small surface density and counter-flow arrangement of regenerators make it ideal for gas-gas heat exchange applications requiring effectiveness exceeding 85%.

[citation needed] The major disadvantage of rotary and fixed-matrix regenerators is that there is always some mixing of the fluid streams, and they can not be completely separated.