Another type of heat exchanger for high temperature purposes is the regenerator. A regenerator contains heat storage elements which alternately absorb heat from hot products of combustion and preheat the incoming air. Two types of regenerators are in use:

(a) Continuous gas flow, moving element for heat storage and
(b) Intermittent gas flow, stationary heat storage element.

In the continuous gas flow type the two gas streams flow continuously through own compartments and the heat storage elements move from hot stream to cold stream. They are normally constructed of metal and are primarily used for low temperature like boiler.
For high temperature applications, the regenerator contains stationary heat storage elements. It consists of a chamber filled with brick chequework to give a multiple vertical gas passage. The hot products of combustion and cold air flow alternately through the same chamber and same passage in a cyclic fashion.
In all the above types of heat exchangers, the residence of the stream is important for the heat transfer efficiency which is in turn controlled by the flow rate of the stream, cross section area of the vessel and thermal conductivity of the material