This paper presents a three dimensional numerical analysis of a flat plate solar air heater in the presence of pin fin array using the CFD software tool ANSYS Fluent 16.2. The effect of geometric parameters of pin fins as well as the flow Reynolds number (4,000-24,000) on the effective efficiency is evaluated. The longitudinal pitch (P_L) of pin fin array is varied as 30, 40 and 50 mm and the diameter (D_w) is varied as 1.0 mm, 1.6 mm and 2.2 mm. The results show that the presence of pin fins generate considerable enhancement in fluid turbulence as well as heat transfer area to a maximum extent of about 53.8%. The maximum average increase in instantaneous thermal efficiency is found to be about 14.2% higher as compared to the base model for the fin diameter of 2.2 mm and a longitudinal pitch value of 30 mm. In terms of effective efficiency, the pin fin array exhibits significant enhancement, especially at lower flow rate conditions. Finally, the effective efficiency of pin fin array is compared with the previous work of authors involving spherical turbulators and sinewave corrugations on the absorber plate. The results show that the pin fin array exhibits a relatively superior effective efficiency to a maximum extent of about 73% for lower flow rate conditions.

Enhancement of heat transfer for turbulent flow in a circular tube heat exchanger using triangular wing vortex generators (TWVG) is presented using Computational Fluid Dynamics methodology. A detailed parametric analysis is carried out to evaluate the impact of non-dimensional base width (0.059–0.216), non-dimensional height (0.039–0.314) and different flow attack angle of TWVG (α = 22.5°, 45°, 67.5°, 90°, 112.5° and 135°) for Re = 6000–18,000. The results show that the TWVG provides considerable heat transfer improvement through two mechanisms such as flow impingement effect on the upstream side and vortex formation on the downstream side. The heat transfer is found to decrease with increasing flow attack angle. However, the friction factor is found to increase from α = 22.5° to α = 90° and drops for all α > 90° due to increased streamlined orientation of vortex generator to the air stream. Longitudinal vortices are formed for α = 22.5°, whereas transverse vortices are generated for all other flow attack angles used in the analysis which are found to have lower flow mixing effect as well as lower coverage of tube wall region. Greater height and base width of TWVG provides greater heat transfer and friction factor enhancement. The maximum enhancement in Nusselt number and friction factor is in the range of 2.61–2.96 and 6.54–8.1 respectively for b/D = 0.216 and h/D = 0.314. The maximum thermal enhancement factor is produced by the configuration having h/D = 0.235 and b/D = 0.059 and has a range of 1.34–1.63.

Solar air heaters are characterized by poor thermal performance due to limited heat transfer capability of air, thereby necessitating the need for design modifications. Among a different system performance augmentation technique, turbulence promotors are widely used owing to its effectiveness. Based on design parameters such as geometry, size, pitch and arrangement of turbulence promoters, varying levels of heat transfer increment with the pressure drop penalty is achievable. This led to the development of new designs which could offer on optimum thermo-hydraulic performance for a wide range of Reynolds number. Such research invariably requires a thorough insight of data related to various design parameters and optimal thermal–hydraulic performance range. This article provides a detailed overview of various turbulence promotor designs and their optimal thermal–hydraulic performance ranges compiled from a wide spectrum of experimental and numerical studies. Apart from outlining the general flow characteristics of each turbulator design, this study also evaluates different metaheuristic optimization algorithm such as bonobo optimization (BO), particle swarm optimization and teaching–learning-based optimization algorithm for enhancing the thermal–hydraulic performance parameter (THPP). The study shows that the BO algorithm does not exhibit local trapping due to its self-adapting nature of the optimized parameters which makes it a promising choice for THPP optimization studies in air heater applications. The extensive review also shows that the arrangement pattern of rib turbulator plays a key role in thermo-hydraulic performance augmentation. Based on the BO optimization analysis, the range of THPP is determined for the optimized geometry of turbulence promoters. In the pool of rib design, transverse prism rib, multi-V-rib, multi-V-shaped rib with staggered rib, sinewave-shaped rib with gap and S-shaped ribs exhibits an optimal THPP range of 2.05–3.32, 2.43–2.94, 3.00–3.61, 1.58–3.40 and 2.05–3.74, respectively. Other turbulence promotor designs such as winglet vortex generator, dimple protrusion in arc shape and multi-V-baffles exhibits optimal THPP range of 1.95–2.2, 2.44–3.68 and 1.75–2.01, respectively. At the end, the study proposes key research gaps such as the use of combined ribs and vortex generators and discrete fin arrays of different geometry as future scope of research. Graphical abstract

Thermohydraulic performance augmentation using turbulence promotors is a commonly adopted technique in solar air heater (SAH) applications. This article presents the thermohydraulic performance augmentation of triangular duct SAH using semi‐conical vortex generators (SCVG) using computational fluid dynamics and experimental methodology for various flow Reynolds numbers ranging from 6000 to 21,000. An in‐depth parametric analysis is undertaken to establish the influence of flow attack angle, relative longitudinal pitch, relative transverse pitch and cone diameter of SCVG on the thermohydraulic performance as indicated by the thermohydraulic performance parameter (THPP). The results reveal that the SCVG generates longitudinal vortices and introduces flow impingement zones which significantly affects the flow and heat transfer characteristics of air heaters. Correlations for Nusselt number and friction factor are established, which predicts the performance outcomes with an average error of 6.74% and 4.46%, respectively. The optimal THPP is determined to be 1.74 using artificial neural network model and Bonobo Optimization algorithm. The SCVG produces THPP values well above unity for the entire flow Reynolds number range of 6000–21,000.

Enhancement of heat transfer in solar air heater systems using corrugations has the dual benefit of enhanced heat transfer area and enhanced flow turbulence. This work presents two-dimensional computational fluid dynamics (CFD) analysis to evaluate the effect of discrete triangle wave corrugations on the absorber plate for different flow Reynolds numbers of 6000–24000. The geometric parameters of corrugation such as the non-dimensional amplitude (A = 0.025, 0.05 and 0.1) and non-dimensional wavelength (W_L = 0.113, 0.226 and 0.453) are varied to establish the thermo-hydraulic performance. The CFD results reveal that the presence of discrete triangle wave corrugations significantly affect the flow structure near the absorber surface and exhibit enhanced fluid turbulence levels. The highest increase in the Nusselt number is found to be about 2.082 times higher than that of the smooth duct for A = 0.1 and W_L = 0.453 at Re = 6000. The maximum rise in friction factor is about 2.568 times that of the smooth duct at Re = 6000 for the configuration of W_L = 0.113 and A = 0.1. The configuration having A = 0.1 and W_L = 0.453 can be particularly useful for lower flow rate requirements and exhibits the highest thermal enhancement factor (TEF) of about 1.612 at Re = 6000 among all the configurations considered in the present study. However, the configuration having A = 0.05 and W_L = 0.453 provides a relatively steady TEF performance for a wider range of flow rates with a maximum TEF of 1.473 at Re = 12,000.