• Energy Research

This study examines the impact of absorber tube geometry on the thermal performance of parabolic trough collectors (PTCs) integrated with phase change materials (PCMs). Addressing a research gap, it compares circular, elliptical, and pear-shaped absorber tubes using solar salt as PCM and water as the heat transfer fluid. The study aims to identify optimal designs for improving thermal efficiency and system scalability in solar energy applications. Results showed that the pear-shaped tube outperformed the circular design, achieving 6–8 °C higher outlet temperatures, a 7 % increase in instantaneous power, and a 15-min longer heat retention time. While the elliptical tube exhibited lower overall performance, its horizontal orientation enhanced power output by 5 % compared to the vertical orientation. These findings underscore the critical role of absorber tube geometry in optimizing PCM-integrated PTCs. The pear-shaped absorber tube, with its superior heat flux concentration and heat transfer efficiency, demonstrated significant potential for enhancing system performance. Its optimized geometry makes it a promising candidate for scalable and efficient solar energy solutions in industrial and domestic applications, offering advancements in sustainable energy utilization.

A numerical analysis was conducted to examine the effect of capsule shape on phase change material (PCM) melting speed. The surface parameters of the irregular capsule shape were amplitude a and the number of sinusoidal undulations n. Case studies were conducted: (1) with the same number of sinusoids but variable amplitude, (2) with the same amplitude but variable number of sinusoids, and (3) same PCM volume, i.e., the same irregular cylindrical capsule perimeter. Unlike observations with a convection-only inside capsule, the amplitude of irregularity in capsule shape a, rather than capsule area, was found to be the dominant factor in heat transfer enhancement. The capsule area was important only during the initial conduction-dominant period. The opposing influences of amplitude a and number of sinusoidal undulations n on the intensity of natural convection was observed. The result shows that only increasing the area does not increase the melting performance, it is the amplitude a which enhance the melting performance.

Thermal energy storage (TES) systems have been verified to be a promising solution for reducing the imbalance between energy supply and demand; however, sensible and latent thermal storage systems have certain limitations. To minimize the issues of rapid drop of temperature in sensible storage and poor heat transfer in latent storage, novel thermal energy storage should be designed. Considering this, combined sensible-latent TES system was developed to mitigate the drawbacks of individual sensible and latent storage. This study aims to investigate experimentally the impact of various volume fractions of phase change material (PCM) in the proposed system on thermal performance and also in terms of economics. The results demonstrated that 60% PCM volume fraction had 50.03% lower capacity cost, 165.4% higher storage capacity, 168.8% higher storage density, and 26.47% efficiency than the sensible TES. Furthermore, 60% volume fraction of PCM had a 13.09% lower installation cost, 4.77% and 11.69% lower charging/discharging time, and 12.64% higher efficiency than the latent storage system. This concludes that under the assumptions of the current study, a 60% volume fraction of PCM is the optimal design parameter for a combined sensible-latent TES system for achieving the best performance in terms of cost and thermal performance.

Abstract Experimental and numerical analyses were conducted to compare the charging and discharging performance of an ice-on-coil latent thermal energy storage tank (LTES). We examined the effect of three parameters: (1) orientation of the tube arrangement (horizontal or vertical), (2) tube diameter (10A or 6A tubes), and (3) tube outlet location (on tank top or tank bottom). Experimental observations had to be confirmed because not only the tube orientation, but also the tube outlet position could have caused a difference in performance. This uncertainty was assessed using numerical analysis. The results show that thermal stratification in molten phase change materials (PCM) plays an important role in charging and discharging performance, and that this performance is different depending on the tube orientation. Thus, the cases when the tube outlet was located on the top of the tank and when the tube orientation was horizontal showed the worst discharging performance. This difference increased with tube diameter.