Investigation on PCM-Based cold storage performance under variable charging temperatures and layout configurations

• Experimental study of PCM layout and charging temperature effects. • Layout 3 achieves 11.5 h cooling and 82.3% effectiveness. • Energy-normalized performance reaches 4.2 h/kWh. • Heat transfer coefficients quantified (h up to 8.7 W/m 2 °C). • Optimized PCM layout improves cooling efficiency significantly. Efficient thermal management in passive refrigeration systems is essential for preserving temperature-sensitive products during transport and storage. Phase Change Materials (PCMs) have emerged as promising candidates for enhancing the thermal buffering capacity of portable cold storage units due to their latent heat storage capabilities. This study investigates the thermal performance of a PCM-based cold storage system using RT4 paraffin wax as the energy storage medium, with a focus on both charging and discharging behavior. The primary objective is to evaluate the influence of PCM layout configurations and charging temperatures (–5 °C, –10 °C, and –15 °C) on system cooling performance under realistic operating conditions. Three different PCM layouts—top (Layout 1), bottom (Layout 2), and all four sides (Layout 3)—were experimentally analyzed inside a temperature-controlled chamber using calibrated thermocouples to monitor PCM and air temperatures throughout the thermal cycles. Experimental results showed that Layout 3 delivered the most uniform and extended cooling during the discharging phase, maintaining cabin air below 8 °C for approximately 6 h at a charging temperature of − 15 °C. Lower charging temperatures significantly improved latent heat utilization, enhanced PCM solidification, and increased the holdover duration by up to 35% compared to − 5 °C. In contrast, Layouts 1 and 2 exhibited directional cooling inefficiencies and quicker temperature rise due to suboptimal heat absorption. The results underscore the importance of PCM spatial configuration and pre-charging conditions in achieving effective thermal management. A combined uncertainty of ± 0.64 °C confirmed the robustness and reliability of the experimental setup and measurements. The results establish a quantitative understanding of the transient thermal response of three PCM layout configurations and uncover the coupled regulation mechanism between charging temperature and PCM placement, demonstrating how buoyancy-driven natural convection governs heat transfer pathways and latent heat utilization in compact PCM-based cold storage systems.