Polymeric hollow fibers are made by extrusion from partially molten material. The fibers used in this experimental study have an outer diameter from 0.8 to 1.3 mm. The thickness of the wall is typically about 0.1 mm. Fibers of this size can withstand boost pressures over 50 bar. From a heat transfer point of view, the thinness of the wall, which eliminates low thermal conductivity, and the fact that liquid flow inside fibers is laminar, which causes a constant Nusselt number, is advantageous. The heat transfer coefficient inside fibers is high because of their small dimensions, and it is velocity independent. The fibers are light, flexible and chemically and corrosion resistant. The smooth polymeric surfaces are fouling resistant both to dust in gas, and to organic and inorganic pollutants in liquids. The paper presents results of laboratory and industrial testing of heat exchangers with hollow fibers.
Shell and tube heat exchangers are typical for liquid / liquid application. Similar units are presented here in steam / water high temperature application with output up to 50 kW.
Smooth polymeric fibers in a vertical configuration are suitable for condensation of liquid from gas. The results of high temperature application of cooling of flue gas with condensation of aggressive liquid are shown.
Recent tests study the use of polymeric heat exchangers in automotive. The case study shows the replacement of the classical aluminum car radiator with a polymeric radiator, and includes vehicle tests. Polymeric radiators require low air flow for equal thermal performance, and this can reduce the aerodynamic drag of the vehicle.