Heat transfer surface area enlargement by usage of metal textile structures - development, potential and evaluation

In order to transfer heat from one fluid to another without mixing them, the fluids are separated by impermeable walls. An increased heat transfer rate can be achieved by extending these walls with fins and thereby enlarging the contact surface area between fluid and separation material. Generally the fins are manufactured by metal sheets and connected to the walls by a metal-joining process. However the possible surface area enlargement is in the range of the surface area of the underlying metal sheets. In order to increase the surface area further on, without using more material, a metal textile structure can be used as base material for fins instead of metal sheets. In addition fluid flow along textile structures experiences a very high heat transfer coefficient due to the repeating interruptions. New textile developments enable the fabrication of adapted structures with non-regular grid sizes purpose-built for gas-to-liquid heat exchanger application. A variety of textile structure heat exchanger samples has been designed and manufactured. In this paper some design ideas and applications shall be presented. For performance evaluation the design ideas for gas-to-liquid heat exchangers are modelled within computational fluid dynamic software in order to get heat transfer coefficients and gas side pressure drop information. Thereby the velocity, pressure and temperature field within the textile structure is calculated. Samples are tested for performance on a heat exchanger test facility, by using temperature controlled air on the gas side. The results are then used to compare textile structure heat exchangers with finned heat exchangers available on the market. The comparison involves thermodynamic and hydraulic performance as well as material quantity used for manufacturing.