Heat Exchanger for Air-Liquid Application with Chaotised Polymeric Hollow Fibres

•Heat exchanger with flexible heat transfer surface.•The overall heat transfer coefficient experimentally determined.•Comparison with the heat exchanger with equally spaced straight fibers.•Proposition of correlation for Nusselt number. Polymeric hollow fibre heat exchangers were presented for the first time in 2004. Nowadays there are not just the shell-and-tube types that there were at the beginning. In this paper, five heat exchangers with a heat transfer surface made from chaotised polymeric hollow fibres were studied. The expression chaotised fiber is used for a hollow fiber with random curvature along it. Each chaotised fiber has a different shape. The heat transfer surfaces presented varied in their fiber diameter, number of fibers (from 180 to 1050) and shape. These heat exchangers were tested as cross-flow heat exchangers in an air tunnel. The cross section of the tested samples was 100 × 100 mm. Water was used as a coolant inside the hollow polymeric fibres. Three different airflow velocities were used. The overall heat transfer coefficients were determined, and the heat transfer coefficients on the air and water sides were derived. A comparison is made between heat exchangers where the heat transfer surface was made from fibers with a regular structure of and those with a chaotic structure. The correlation for the Nusselt number for a heat transfer surface formed by a bundle of chaotised hollow fibers was found.