Experimental Investigation and Numerical Simulation of Energy-Exergy Performance of a Solar Desalination Equipped with a Phase Change Material

Articles in Press

Document Type : Research Article

Authors

H. Samimi Akhijahani ¹

M. S. Barghi Jahromi ²

S. Madhankumar ³

¹ Department of Biosystem Engineering, Faculty of Agriculture, University of Kurdistan, Sanandaj, Iran

² Department of Mechanical Engineering, University of Jiroft, Jiroft, Iran

³ Department of Mechanical Engineering, Dayananda Sagar College of Engineering, Bengaluru, India

10.22067/jam.2026.98203.1484

Abstract

Introduction
Only three percent of the Earth’s water is fresh and usable for drinking. Population growth and climate change have exacerbated water scarcity, implicating many countries, including Iran, in a crisis. Desalination, particularly using solar energy, is considered an effective solution to compensate for the shortage of fresh water resources. Iran, due to its high solar irradiation, has a high capacity for developing solar desalination systems. However, for various reasons, the efficiency of these systems is very low, and solutions are needed to improve their performance. Research has shown that Phase Change Materials (PCMs), by storing latent heat, improve the efficiency of solar collectors and the thermal stability of the system. Furthermore, the CFD (Computational Fluid Dynamics) method is a precise tool for analysing thermal behaviour and determining optimal conditions in desalination systems, and it can impact the improvement of system efficiency. The present study examined a novel combination of a helical tube containing PCM, a spray system, geothermal cooling, and a solar tracker, which leads to increased efficiency and thermal uniformity of the system.
Materials and Methods
Experimental tests were performed under various environmental conditions and at different saline water flow rates. Two system configurations were studied: one with PCM (paraffin mixture) surrounding the collector tubes and another without PCM. Data on temperature, thermal energy input and output, energy and exergy efficiencies, Performance Ratio (PR), and Recovery Ratio (RR) were recorded during the experiments. Additionally, CFD simulations were carried out using appropriate models for two-phase flow (water and air) and heat transfer to analyse the details of velocity, temperature, and phase fraction distribution within the tank and over the heat exchanger.
Results and Discussion
This research evaluates the performance of a novel solar desalination system equipped with a Phase Change Material (PCM) and conducts a Computational Fluid Dynamics (CFD) analysis. The primary objective is to investigate the impact of adding PCM on improving the thermal efficiency and the quality of desalinated water compared to a system without PCM.
Key Findings:
· Thermal Performance: The presence of PCM significantly increased the working fluid temperature in the tank and reduced heat loss. The maximum thermal energy input to the tank with PCM increased by 2.85 MJ, while the total collector output energy reached 38.42 MJ.
· Efficiency: At a flow rate of 4.2 L min^-1, the collector energy efficiency increased from 42.65 to 47.27 percent, while its exergy efficiency was 8.21percent; the desalination unit achieved an energy efficiency of 47.26 percent an exergy efficiency was 7.65 percent. With the addition of PCM, the Performance Ratio (PR) and Recovery Ratio (RR) also rose to 1.32 and 0.129, respectively.
· Velocity Distribution: Velocity contour plots indicated a maximum flow velocity of approximately 1.18 m s^-1 in the central nozzle region. In PCM-equipped systems, the saline water outlet velocity decreased due to more uniform energy distribution and higher evaporation rates.
· Temperature Distribution: The temperature pattern within the tank and on the heat exchanger was analysed. The average saline water temperature was around 54.26°C, with insulation playing a role in reducing temperature loss.
· Phase Fraction Distribution: The water volume fraction was highest at the tank inlet and lowest near the bottom. The inclusion of PCM enhanced the evaporation rate by approximately 6.63%, which reduced the vapour volume fraction from 0.184 (without PCM) to 0.171 (with PCM) at 10.524 seconds, indicating greater vapour generation. However, the average vapour volume fraction throughout the desalination process was 21.05% for the PCM system and 19.74% for the system without PCM.
· Water Production and Quality: The PCM-equipped system produced 987 mL of water, a significant increase compared to 842 mL from the system without PCM. Water quality analysis showed a substantial reduction in Total Dissolved Solids (TDS) with a decrease of at least a 300 mg L^-1, as well as a greater than 30% reduction in sodium and potassium levels relative to tap water, these results confirm the production of high-standard fresh water.
Conclusion
This study demonstrates that incorporating PCM into a solar desalination system significantly enhances its thermal performance and overall efficiency. The increased energy and exergy efficiencies, improved PR and RR, and a notable rise in desalinated water production are the main advantages of using PCM. CFD analysis provided deeper insights into the fluid dynamics and thermal distribution within the system, confirming the positive impact of PCM on evaporation processes. The quality of the produced water also meets the required standards. Total dissolved solids concentration was significantly reduced compared to municipal water (at least 300 mg L^-1). Overall, this system offers a robust and economical solution for water desalination, particularly in regions with limited access to potable water resources.

Keywords

Computational fluid dynamics

Evaporator

Performance ratio

Thermal contour

Thermodynamic analysis

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0)

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