Experimental investigation and comparative performance analysis of a compact finned-tube heat exchanger uniformly filled with a phase change material for thermal energy storage

摘要

In the present paper, a latent heat storage system using a heat-transfer enhancement technique has been built and tested. The potential of using a natural phase change material of Moroccan provenance for energy storage was studied by experimental analysis. The enhanced heat transfer surface of the compact finned-tube heat exchanger presents geometric complications. Therefore, a new method based on equivalent circular fin efficiency for the calculation of the effective heat transfer surface area was developed and applied to the system under study. In order to carry out the performance analysis for this innovative system, charging and discharging experiments were conducted for different heat transfer fluid flow rates. It was found that increasing the flow rate from 0.2 to 1 l/min divides melting time by 2.5 and solidification time by four. The average effectiveness was calculated for each flow rate and was proven to decrease during charging from 0.95 for a flow rate of 0.2 l/min to 0.63 for 1 l/min. Likewise, increasing flow rate from 0.2 to 1 l/min for discharging process decreases heat exchanger effectiveness from 0.99 to 0.7. The combination of the effectiveness-number of transfer units method with the procedure that was developed to compute the effective heat transfer area lead to derive an empirical correlation. This equation was used to compare the finned-tube compact storage system with other heat and cold storage units. The comparison showed that the present system displayed satisfactory results. The second use of the correlation was to design, through a case study, a heat storage system suitable for solar domestic hot water production in a residential building.