Chapter 4 - Compact and micro-heat exchangers

Abstract

The chapter discusses the current status of intensified heat exchangers, ranging from compact to microsized heat exchangers. Compact heat exchangers, while accounting for perhaps 10% of the worldwide market for heat exchangers, have in recent years seen their sales increase by about 10% per annum, compared to 1% for all heat exchangers. There are a variety of compact heat exchangers that can be used in the process industries of interest to designers and users of intensified plant; these include the plate heat exchangers of Alfa Laval (and a range of other manufacturers), the printed circuit heat exchanger (PCHE) of Heatric, the Chart-flo unit of chart heat exchangers, and the polymer film heat exchanger. Plate heat exchangers (PHEs) are the most common form of compact heat exchanger, but their area densities are inferior to other types. Microheat exchangers are generally defined as having area densities well in excess of the best values achieved with compact heat exchangers. Microheat exchangers with area densities in excess of 15,000 m2/m3 are available. The microheat exchanger concept has been driven in the past by the increased cooling requirements of microelectronics systems. The principal applications include microsensors, micromachines, and the “chemical plant-on-a-chip.” Metal meshes (woven as textiles) have also been tested as heat exchangers. Chemically reacting operations in heat transfer processes (which may include chemical reactions, dissolution, absorption, adsorption, and desorption) have several advantages over conventional heat exchangers/heat transfer systems—a heat transfer capacity larger than that compared to sensible or latent heat, the reversibility of the reactor operation, the lack of need to involve mechanical operations, and the possibility of silent operation. Furthermore, the chapter examines the use of chemical reactions as a means of improving or enhancing heat transfer.