Experimental investigation of wire-mesh equipped U-tube evacuated tube collector integrated with phase change material for hot water generation

This paper presents an experimental investigation of the U-tube evacuated tube collectors (UETCs) integrated with phase change material (PCM). Three distinct experimental test sections were constructed, each comprising three tubes connected by a continuous U-tube configuration. The first setup, designated as Set-A, contained air within the evacuated space of the UETC. The second setup, SetB, involved filling the UETC's evacuated space with a PCM, whereas the third setup, referred as SetC, utilized a combination of wire mesh and PCM. Paraffin wax has been used as the PCM in Set-B and SetC. Liquid water is circulated as a heat transfer fluid (HTF) in all the cases. The comparative performance analysis of these setups was conducted over a span of three days, employing variable mass flow rates of 13 LPH (litres per hour), 7 LPH, and 10 LPH for Day-1, Day-2, and Day-3, respectively. The findings revealed that Set-A exhibited the highest HTF temperature until noon across all considered days. However, beyond this point, Set-C demonstrated superior performance, delivering hot water for extended durations of 108, 82, and 45 min at the respective flow rates of 7 LPH, 10 LPH, and 13 LPH. These durations represent an enhancement of 44.11 %, 41.55 %, and 70.88 % over those observed for Set-B on Days 1, 2, and 3, respectively. A significant observation was the variation in thermal stratification across the setups. Set-A displayed the highest degree of thermal stratification, followed by SetB, with Set-C exhibiting the lowest. Specifically, thermal stratification in Set-C was reduced by 83.41 %, 78.8 %, and 84.48 % relative to Set-A, and by 67.34 %, 78.90 %, and 79.55 % compared to Set-B for Days 1, 2, and 3, respectively. Furthermore, the investigation into daily thermal efficiency across the different setups revealed that Set-C achieved the highest thermal efficiency, followed by Set-A, and then SetB. This enhanced performance of Set-C underscores the effectiveness of integrating a wire mesh and PCM within the UETC, presenting a compelling case for the adoption of such configurations to improve solar collector efficiency.