Experimental and numerical investigation of a bar-and-plate heat exchanger for enhanced latent thermal energy storage

Latent thermal energy storage (LTES) employing phase change materials (PCMs) offers a promising solution for thermal management in various applications, compensating for the intermittent and unstable characteristics of several thermal energy sources, such as solar energy. However, the inherently low thermal conductivity of PCMs hinders their heat transfer efficiency, resulting in extended charging and discharging times. This limitation can be addressed either by enhancing the thermal conductivity of the PCM or by optimizing the storage system geometry. In this study, two LTES configurations, finned and finless units based on bar-and-plate technology, were tested under different conditions of mass flow rate (100, 150, 200 kg h⁻¹) and heat transfer fluid (HTF) inlet temperature (46, 49 , 52 °C), corresponding to temperature difference (∆Tthermal) of 3, 6 and 9 °C. To the best of the authors' knowledge, the bar-and-plate technology has been only marginally addressed in the context of LTES systems, and no comprehensive experimental investigations are currently available in the literature. The PCM employed, a paraffin wax (RT42), has a melting temperature range between 38.2 °C and 42.5 °C. Results demonstrated that the finned unit reduced the melting time by up to 84 % compared to the finless configuration. At ∆Tthermal = 9 °C and a mass flow rate of 200 kg h⁻¹, the charging process was completed within 2 hours for the finned unit versus about 8 hours for the finless unit. Moreover, for the finned unit, increasing ∆Tthermal from 3 °C to 9 °C resulted in a 28–50 % decrease in melting time, while an increase in the mass flow rate from 100 to 200 kg h⁻¹ shortened melting time by about 35 %. As a further step, the experimental data were used to validate a resistance-capacitance numerical model of the LTES unit, providing a valuable tool for LTES optimization and design according to specific application requirements. Unlike other available calculation methods, the developed model accounts for the explicit incorporation of fin geometry and PCM material in equivalent conductivities (PCM-fin composite) to capture the directional heat transfer pathways. Moreover, a parametric study was carried out to analyze the effect of fin parameters on melting time and energy storage.