Anti-fouling rotating polymer-based heat exchanger for zero liquid discharge humidification-dehumidification...

The objective of this investigation is to assess the performance of various heat exchangers for application in a novel solar-powered zero liquid discharge humidification-dehumidification desalination system. In this study four heat exchangers (HX) having two different flow configurations namely counter flow (cf), cross flow (cr) made up of three different materials namely high-density polyethylene (HDPE), aluminum (Al), and Polypropelyne (PP) were compared in terms of their effectiveness and overall heat transfer coefficient under varying salinity levels (up to 10%) and mixing ratios (0.22-0.45). At a mixing ratio of 0.22 and 0% salinity, PP-HX_cr and Al-HX_cf exhibited similar effectiveness (∼85%), surpassing that of HDPE-HX_cf (∼65%). Despite PP-HX_cr's lower thermal conductivity in comparison to Al-HXcf, comparable effectiveness was achieved due to the superior flow distribution in PP-HXcr. Further investigations focused on the impact of salinity on heat exchanger performance. At 3.5% salinity, all heat exchangers experienced a decline in effectiveness and heat transfer coefficient (HTC), with Al-HX_cf experiencing a more pronounced decrease compared to PP-HX_cr. The higher thermal conductivity of Al-HX_cf led to greater salt accumulation, while PP-HX_cr demonstrated minimal fouling. As the experiment progressed, fouling increased for all heat exchangers, with the Al-HX_cf being practically ineffective at 10% salinity with an effectiveness below 10%. To address the issue of fouling, a rotating cross-flow heat exchanger (RPP-HX_cr) was introduced. While the effectiveness of the PP-HX_cr drops from 85% to approximately 60% with increasing salinity from 0% to 10%, the RPP-HX_cr demonstrates only a marginal decline in effectiveness with increasing salinity. For instance, at mixing ratio of 0.22 when the salinity is increased from 0% to 10%, the effectiveness of RPP-HX_cr only drops from 83% to 77%. This exceptional performance was attributed to the continuous contact between the rotating tubes and the incoming feed, effectively preventing fouling and ensuring sustained efficiency. Rotating cross-flow heat exchanger (RPP-HX_cr) is introduced and validated as a potentially reliable solution for mitigating fouling, as it demonstrates sustained efficiency and minimal performance degradation across different salinity conditions.