Recuperator, optimum efficiency for heat conduction..!
There are two main types of heat exchangers: a recuperator and a regenerator. A recuperator operates by means of a direct heat exchange, a regenerator on the basis of an intermediate storage.
In a regenerator, heat from the primary medium is first stored in a thermal mass and later (in the next cycle) regenerated from that mass by the secondary medium. The thermal mass can be the wall material of the flow ducts or a porous medium, through which alternating the primary and the secondary flow is led. The regenerator has a serious disadvantage as the heat has to diffuse in and out of the intermediate storage material. It will lose energy here as the heat front in the flow direction is flattened and not all heat can be regenerated.
In a recuperator both mediums are separated by a wall through which heat is transferred directly. The only fundamental loss hereby is the heat conduction through the wall in the flow direction. However, this can be reduced to less than a per mille by using materials with low heat conductivity, such as plastics.
In order to obtain the required efficiency, only a recuperator can be used.