Crossflow polymeric hollow fiber heat exchanger: fiber tension effects on heat transfer and airside pressure drop

Abstract

In various applications, a polymeric hollow fber heat exchanger (PHFHE) is a competitive alternative to a conventional heat exchanger (HE). Standard empirical models for predicting the crossfow tube HE characteristics are defned for devices with rigid tubes with relatively large diameters compared to the polymeric hollow fbers with an outer diameter of around 1 mm. This study examines the impact of tension force on airside heat transfer rate and pressure drop in a crossfow PHFHE. The tension force infuences the stifness of the fexible polymeric fbers and their response to applied airfow. Two liquid– gas PHFHEs were designed and manufactured to ensure uniformity of the fbers' arrangement (inline and staggered). An experimental stand enabling the application of defned tension force in the range of 0–9000 N was designed, manufactured and placed into the calorimetric tunnel, where heat transfer rate and pressure drop measurement were performed with varying air velocity between 2 and 8 ms1 (corresponding to Reynolds number of 240–970). Among our key fndings was that the elongation of the fbers due to thermal expansion or stress relaxation has a considerable impact on the fbers' arrangement and resulting fuid fow. Moreover, the application of tension force yielded no substantial change in air pressure drop; however, it led to a notable enhancement in heat transfer rate. Specifcally, under a maximal tension force of 9000 N, the heat transfer rate increased by around 11% compared to the unloaded state.In various applications, a polymeric hollow fber heat exchanger (PHFHE) is a competitive alternative to a conventional heat exchanger (HE). Standard empirical models for predicting the crossfow tube HE characteristics are defned for devices with rigid tubes with relatively large diameters compared to the polymeric hollow fbers with an outer diameter of around 1 mm. This study examines the impact of tension force on airside heat transfer rate and pressure drop in a crossfow PHFHE. The tension force infuences the stifness of the fexible polymeric fbers and their response to applied airfow. Two liquid– gas PHFHEs were designed and manufactured to ensure uniformity of the fbers' arrangement (inline and staggered). An experimental stand enabling the application of defned tension force in the range of 0–9000 N was designed, manufactured and placed into the calorimetric tunnel, where heat transfer rate and pressure drop measurement were performed with varying air velocity between 2 and 8 ms1 (corresponding to Reynolds number of 240–970). Among our key fndings was that the elongation of the fbers due to thermal expansion or stress relaxation has a considerable impact on the fbers' arrangement and resulting fuid fow. Moreover, the application of tension force yielded no substantial change in air pressure drop; however, it led to a notable enhancement in heat transfer rate. Specifcally, under a maximal tension force of 9000 N, the heat transfer rate increased by around 11% compared to the unloaded state.