Heat exchangers have been utilized in the past as chemical reactors in several different applications, including heterogeneous catalytic incineration in a number of unusual venues such as aircraft, automobiles, hospitals, laboratories, and underground mines, as well as for the homogeneous combustion of low-heating-value fuels. In general, the same considerations that favor compact exchangers in conventional applications, namely the minimization of the volume of the equipment, the minimization of heat losses to the surroundings, and the improvement of the energy efficiency, are operative in the combined function. However, the constraints on the design of the exchanger may differ greatly, not only when the chemical reactions and heat exchange occur in the same space, but also when the process of reaction influences the geometric configuration, the regime of flow, and/or the materials of construction. A recent development is the fabrication and use of reactor/heat exchangers with characteristic dimensions of less than a millimeter. Such micro-reactors have the potential for many new applications both in the laboratory and in manufacturing.
Rather than reviewing past combinations of reaction and heat exchange in compact devices exhaustively, a number of specific examples are chosen to illustrate the consequences of carrying out chemical conversions in or in close conjunction with a heat exchanger. These consequences include the enhancement of heat transfer directly or indirectly by the chemical reaction and vice versa.