The solar air heater (SAH) is a simple device manufactured from locally available materials and used to heat air for various purposes, including heating, drying, and industrial applications. Despite its simplicity and low manufacturing cost, it has low thermal performance. Therefore, it has undergone several modifications in an attempt to improve its thermal performance. Among these attempts is the use of roughened air-duct to create turbulent flow of air and then improves heat transfer rates. The challenge was to improve heat transfer rates while simultaneously reducing frictional properties. This review focuses on recent advances in roughened surface used for improving the performance of SAHs. Comparison between different roughened surfaces in in terms of thermohydraulic performance, friction factor (f) is also of great interest in this work. The review results recommended using perforated rectangular fins as the roughened elements as it achieves the highest thermohydraulic performance parameter (THPP = 5.1) among the several roughened surfaces considered in this review. While the highest improvement in Nusselt number was achieved (47.7 times compared to smooth-duct) when punched baffles of delta-shaped winglets were used. The frustum jet impingement roughness showed the highest improvement in f. Based on the previous conclusions, combining perforated fins, punched baffles and frustum jet impingement roughness can result in the best performance of the solar air heaters.

A case study assessing energy-exergy-economic (3E) performance in solar air heaters with different winglet geometries and air flow rates.

Abstract A hybrid numerical–data-driven framework is proposed to evaluate and optimize the thermo-hydraulic performance of a roughened rounded-corner triangular duct solar air heater. High-fidelity flow and heat-transfer data are first generated using a previously validated Computational Fluid Dynamics (CFD) model by systematically varying Reynolds number (5600–21,000), corner radius (0.333h–0.67h), and longitudinal and transverse pitch ratios (z′/e and x/e = 10–18), resulting in a dataset of 60 simulations. This dataset forms the basis for developing surrogate models using multiple supervised machine-learning regressors, including Linear Regression, k-Nearest Neighbour, Random Forest, Decision Tree, Multilayer Perceptron, and Stochastic Gradient Descent Regressor. To ensure robustness and transparency, the ML workflow incorporates feature scaling where appropriate, an 80:20 training–testing split, and five-fold cross-validated hyperparameter tuning. Model performance is assessed using R2 and RMSE metrics, revealing that tree-based and ensemble models are more effective in predicting Nusselt number due to strong nonlinearity in turbulence–geometry interactions, whereas linear models provide stable and accurate predictions of friction factor owing to its quasi-linear dependence on flow parameters. Feature-importance analysis further confirms that Reynolds number primarily governs heat-transfer enhancement, while curvature effects significantly influence hydraulic resistance. A desirability-based multi-objective optimization strategy is subsequently applied to identify optimal operating conditions that balance heat-transfer augmentation and pressure-loss minimization. The optimal configuration predicted by the ML models (z′/e = 10, Rc ≈ 0.34, Re ≈ 21,000) closely matches the CFD-derived optimum, demonstrating strong agreement. Overall, the study establishes a reliable and computationally efficient CFD-ML framework for the design optimization of advanced solar air heaters, reducing dependence on exhaustive numerical simulations while retaining physical fidelity.

Numerical simulation and machine learning modeling of tubular solar air heaters enhanced with twisted tape inserts

Thermo-hydraulic characteristics of solar air heaters designed with semi-capsule-shaped protrusions arranged in a staggered pattern

This study proposes a new and straightforward method to enhance the performance of solar air heaters (SAH) through modified absorber plates. This approach involves altering the absorber plate with several rib packs featuring circular patterns and varying geometric parameters. The study examines the effect of rib geometric parameters, specifically the diameter ratio (d/H), which ranges from 0.1 to 0.3, and the pitch ratio (S/H), which varies between 0.8 and 1.2. Each geometric parameter has been tested with different numbers of rib packs (Np), such as 1, 2, or 3. All calculations are conducted over a wide range of Reynolds numbers, from 4000 to 20,000, through computational fluid dynamics (CFD) analysis. The results obtained are validated against experimental data and existing correlations for a conventional SAH with a smooth absorber plate. The findings indicate that increasing the rib diameter and the number of rib packs enhances the performance of the SAH while expanding the rib pitch adversely affects its performance. A case with the maximum number of rib packs and rib diameter, together with a minimum rib pitch, presents the ideal scenario for the SAH. The findings demonstrate that the proposed method can enhance the thermal performance of the SAH by up to 25.71%. Furthermore, depending on the Reynolds number, the optimal case shows 9.91% to 10.82% greater thermal-hydraulic performance than the conventional SAH.

Enhancing Solar Air Heater Heat Transfer Performance: The Impact of Hexagonal 90° and 120° Inline Ribs with Varying Blockage Ratios in Trapezoidal Ducts

Performance comparison of solar air heaters with heat storage for solar drying in different Moroccan climates

Retraction notice to “Energy storage concentrates on solar air heaters with artificial S-shaped irregularity on the absorber plate” [J. Energy Storage 74 (2023) 109289

Synergistic optimization of mirror-augmented cylindrical obstacles in solar air heaters: A coupled thermal-safety analysis

Augmented heat transfer in the solar air heater having hybrid roughness as continuous and discrete V ribs with dimples: a CFD analysis

Integrating jet impingement and energy storage mechanisms to advance thermohydraulic and exergetic performance in solar air heaters: A comprehensive review

Performance enhancement of solar double-pass air heater by utilizing new turbulators wire: numerical and experimental evaluation

Experimental investigation of double pass solar air heater with sensible heat storage: Effect of sand storage unit number

CFD simulation studies of a solar air heater with double pass configuration using paraffin and metal oxide nano particles as a latent heat storage

Enhancing the performance of solar air heater with innovative fins

Heat transfer and flow analysis of a double-pass solar air heater with sandwich-structured PCM cylinders

Thermal performance enhancement and assessment of a double-pass solar air heater using perforated vertical V-baffles and semi-circular ducts

Deep learning-based prediction of thermal-hydraulic and exergy performance in a novel bidirectional wavy absorber solar air heater

Response surface optimization of perforated solar air heater with novel gong-shaped baffles