Experimental study on the influence of shell geometry and tube eccentricity on phase change material melting in shell and tube heat exchangers

This study experimentally investigates the combined effect of heat transfer fluid (HTF) tube eccentricity and shell geometry on the thermal performance of latent heat storage (LHS) units. Fifteen transparent shell and tube LHS units were designed and manufactured with circular, horizontal obround, and vertical obround shell geometries and various HTF tube eccentricities. All LHS units have an identical volume and were filled with paraffine as phase change material (PCM). By conducting visualization experiments, the effect of the HTF tube eccentricity (with values of 0, 0.2, 0.4, 0.6, and 0.8) on the thermal performance of LHS units was comprehensively analyzed. The melting process was photographed, and temperatures at predefined locations were recorded to determine the instantaneous liquid fractions and heat transfer characteristics of different systems. The findings revealed that the horizontal obround shell shortens the melting time compared to the traditional circular shell, while the vertical obround shell prolongs the melting time. It was observed that increasing the eccentricity factor from 0 to 0.8 leads to a reduction in melting time by up to 76 %, 72 %, and 60 % for vertical obround, circular, and horizontal obround shells, respectively, along with a substantial improvement of 304 %, 246 %, and 151 % in the time-averaged heat transfer rate. Moreover, the highest time-averaged heat transfer rate enhancements are achieved by the horizontal obround shell, which are 38 %, 77 %, 130 %, and 178 % for the eccentricity factors of 0, 0.2, 0.4, and 0.6, respectively, when compared with the concentric circular shell (base case). It has also been concluded that as the eccentricity factor increases from 0 to 0.8, the impact of the shell geometry on melting performance diminishes. At an eccentricity factor of 0.8, the difference in melting time among different geometries becomes negligible.