Optimisation of heat transfer in the absorber tube of a cylindroparabolic trough solar collector

• Elliptical absorber tubes improved heat transfer performance, achieving up to 25 % higher Nusselt numbers and reducing pressure drop by 10 % compared to circular tubes. • Temperature differentials of up to 15 °C were observed, indicating enhanced thermal efficiency, especially beneficial for solar desalination applications. • Among various heat transfer fluids, ethylene glycol yielded the highest Nusselt values (>2200), while water remained the most practical for desalination due to its low cost and availability. • Material analysis showed copper and aluminium offer better thermal performance due to higher conductivity, though steel reached the highest surface temperatures. • The CFD model validation showed high reliability (R² = 0.9784), with low error metrics (e.g., RMSE = 0.3656), confirming the model’s predictive accuracy. This study employs computational fluid dynamics (CFD) to optimise heat transfer in cylindro-parabolic solar collectors (CPCs) by comparing an elliptical absorber tube with a conventional circular design under turbulent flow and uniform heat flux conditions. The CFD simulations are validated against empirical correlations, demonstrating high accuracy with an R² of 0.9784. The elliptical absorber significantly enhances thermal performance, achieving up to 25 % higher Nusselt numbers and temperature differentials of around 15 °C, while also reducing pressure drop by 10 %, leading to improved system efficiency without added energy demand. The study further examines the variation of the Nusselt number using five heat transfer fluids water, molten salt, ethylene glycol, Therminol VP, and Dow Therma showing that ethylene glycol offers the highest Nu (>2200), whereas water maintains steady values (∼500). Despite its moderate convective performance, water is highlighted as the most suitable for solar desalination due to its availability, low cost, and high specific heat capacity. The analysis also includes surface temperature distribution across flow rates ranging from 0.01 to 0.07 kg/s and four absorber materials, demonstrating the influence of material properties on thermal behaviour. Realistic environmental boundary conditions (25 °C ambient temperature, 50 % humidity, 2 m/s wind) from Metronome software are applied to enhance simulation accuracy. The novelty of this research lies in its integrated CFD framework combining absorber geometry optimisation, seasonal thermal stress modelling, and material degradation analysis using real climatic data. This holistic approach offers a major advancement in CPC design, particularly for efficient and durable solar desalination systems.