Intensification of heat transfer of polymeric hollow fiber heat exchangers by chaotisation

Abstract

Flexible polymeric hollow fibers are used as heat transfer elements. A potted bundle of several hundred such fibers can be used as a heat exchanger in different ways. The simplest application is a submerged bundle. The fibers studied in this paper have outside diameters below 0.8mm. Such very small-diameter polymer fibers significantly facilitate heat transfer. However, these potted sets of fibers must be designed to guarantee that all fibers are in direct contact with the surrounding stream of fluid. It is possible to use textile technologies to keep fibers strictly parallel and separated. However, a parallel arrangement can be expensive and is not flexible. A low-cost variant utilizes bundle chaotisation, which means that each fiber has a unique shape. The consequence is that their mutual mechanical contacts are point-wise. Several methods of chaotisation are studied in this paper. The best variant is a permanent fiber deformation/chaotisation of fibers using integrated heating/cooling and stretching. The tested CFPFHEs (Chaotised Flexible Polymeric Fiber Heat Exchangers) had an overall heat transfer area of 1m2, and its length was approximately 700mm. It achieved a water/air overall heat transfer coefficient of 100W/m2K with an outside air flow of 2m/s.