An experimental and numerical study on effect of longitudinal finned tube eccentric configuration on melting behaviour of lauric acid in a horizontal tube-in-shell storage unit

Abstract

• Enhancing the melting performance of a PCM in a LHTES system through the enrichment of natural convection mode of heat transfer. • Different configurations of triple fin arrangement are simulated and compared for different angles between fins in bottom annulus. • Stephan number and different eccentric arrangement of a longitudinally finned HTF tube are studied for a concentric double pipe heat exchanger. • Temperature variation, melt fraction distribution and heat storage potentiality in PCM are studied for determining the effective heat exchanger having fastest melting rate. • Results indicate that the smaller angle between bottom fins with maximum eccentric distance of HTF tube shows the best melting performance. Melting characteristics of lauric acid in a horizontal shell and finned tube-type storage unit has been studied numerically and experimentally. The low thermal conductive nature of phase change materials (PCMs) have pre-eminently constricted the advantage of such storage systems for various applications hence an attempt has been made to provide the finned tube in the storage container to enhance the heat transfer rate between the heat transfer fluid (HTF) and PCM for three different eccentric position ( e = 12 mm, 18 mm and 24 mm) of a finned HTF tube from the centre of outer tube in concentric configuration ( e = 0 mm). The present work aims on the use of minimum fin length by covering 36% of the annular length of a concentric arrangement for enhancing the melting rate of a phase change material (PCM) particularly to increase the natural convection effects besides sustaining the conduction effects. The melting rate of PCM in an annular is analysed with different angles of 60⁰, 120⁰ and 180⁰ between fins in the bottom annulus of the storage unit at different eccentric positions of the inner tube. The results obtained through numerical calculations are found in agreement with experimental results. The enhancement in the melting rate of PCM has been examined and it has been found that the melting rate is 21% higher at the maximum eccentric annulus as compared to the concentric configuration due to enhanced domination area for natural convection effects which also increases the uniformity in temperature distribution in PCM. The eccentric behaviour for the enhancement of melting performance has been effectively achieved in the fin configuration having an angle of 60º between the fins in the bottom annulus. It has been observed that the increase in Stefan number enhances the melting rate of PCM irrespective of the eccentric position of the inner tube and the heat storage rate in an eccentric annulus is 18.7% higher in comparison to the concentric annulus.