Effects of heat transfer medium flow field changes on the heat storage and discharge performance of phase change heat accumulators

Abstract

In this study, a numerical simulation was employed to assess the heat storage and exothermic behaviour of a phase change unit with different heat flow channel configurations, height-to-diameter ratios, inlet flow rates, and addition of different rib structural parameters. Thus, we aimed to explore the heat storage and exothermic behaviour of the phase change accumulator under changes to the heat transfer medium flow field. By analysing the variation in the velocity and temperature fields of the heat transfer medium and using the field synergy principle, the structure of the cylindrical phase change accumulator was optimised, and the liquid fraction, field synergy angle, and Nu number in different structures were compared. The results revealed that the H-type heat exchanger flow channel could effectively improve the heat exchanger field synergy and increase the heat storage rate by 6.3 %. Increasing the inlet flow velocity could accelerate the heat storage rate; however, the flow velocity caused the flow field synergy to fluctuate and the heat storage efficiency to increase gradually. On increasing the height-to-diameter ratio, the heat exchanger field synergy ‘increased first and then decreased’, reaching the optimal heat transfer effect when D = 1.932. Under the heat storage and release condition, the straight rib heat transfer was superior to that for the ring rib. The change in the built-in straight rib length played a dominant role in the heat storage rate. Accordingly, for optimal heat transfer, the rib length was set to >45 mm, rib thickness to 1.5–2 mm, and number of ribs to 10. Meanwhile, the heat release efficiency initially increased as the length of the external straight rib increased and subsequently decreased. For optimal heat transfer, the rib length was set between 15 and 25 mm, rib thickness to >1.5 mm, and the number of ribs to >10 ribs. Therefore, we determined the ranges of structural parameters that would provide appropriate references for this phase change accumulator in fields such as thermal energy storage and waste heat recovery.