Applications of polymeric materials for condensing heat exchangers

Abstract

AbstractManufacturers have begun to investigate the use of plastic materials for use in condensing heat exchangers attached to high‐efficiency gas‐fired furnaces. However, a number of technical problems have slowed the use of polymers in this application. While a low thermal conductivity relative to metals is one limitation, a more significant problem relates to the unknown performance of polymers in the harsh chemical environment of a condensing heat exchanger. Recent years have seen some major developments in the use of coatings and plastics for hightemperature service in heat exchangers. In these studies, commercially available acid‐resistant and heat‐resistant polymers were tested, primarily as protective coatings on metal heat exchanger elements, in both experimental‐ and prototypecondensing heat exchangers. These studies indicated that the effectiveness of polymers as coatings was sensitive to the presence of pinholes, and thus, the coating thicknesses had to exceed 0.25 mm to insure adequate protection. The use of a covering, rather than a coating, was found to be one method of insuring pinhole‐free coatings. In this study several all‐plastic heat exchanger elements were found to perform satisfactorily as heat exchanger elements in a gas‐fired condensing heat exchanger. This investigation identified several promising polymeric materials that survived 10,000 cycles in a highly acidic condensing heat exchanger. The polymers that successfully survived this evaluation included fluorinated ethylene propylene, poly(phenylene sulfide), polysulfone, poly(ether imide), and poly(tetrafiuoroethylene).