What principle describes the method of heat transfer in a recuperative air heater?

The principle that describes the method of heat transfer in a recuperative air heater is the concept of direct heat transfer between mediums. In a recuperative air heater, hot flue gases transfer heat to the incoming combustion air without the two streams mixing. This process occurs through the walls of a heat exchanger, where heat is conducted from the hot gases to the cooler air, raising the air temperature before it enters the combustion chamber. This efficient transfer of heat improves the overall thermal efficiency of the combustion process by using waste heat that would otherwise be lost.

Direct heat transfer is fundamental to how recuperative systems operate because it emphasizes the effectiveness of transferring energy from one fluid to another through a solid boundary, which is the basis for maximizing heat recovery in heating systems. The recuperator’s design allows for a significant temperature change in the incoming air while maintaining the separation between the flue gas and combustion air, thereby optimizing thermal efficiency without mixing the two mediums.