Search Results (113)

Enhancing convective heat transfer in solar air heaters (SAHs) without disproportionate hydraulic penalty remains critical for decentralized low-carbon heating. This study experimentally investigates a serpentine-channel SAH equipped with distributed three-dimensional vortex generators under outdoor winter conditions. The configuration combines curvature-induced secondary motion with distributed vortex generation to intensify absorber–air heat transfer. Experiments were conducted over a mass flow range of 0.012–0.061 kg s⁻¹, corresponding to a Reynolds number range of 2.1 × 10³–1.07 × 10⁴, using a smooth duct as the reference configuration. The enhanced configuration achieved peak thermal efficiencies of 81.6–85.4%, compared with 65.8–67.7% for the smooth collector, while daily averaged efficiency increased from 56–59% to 71–75%. Although pressure drop increased, thermo-hydraulic performance remained superior across the investigated Reynolds number range. Exergy efficiency was consistently higher for the enhanced system and remained within optical limit constraints. Environmental assessment based on grid emission factor displacement indicates approximately 33% greater annual CO₂ mitigation potential, corresponding to about 6.6 tonnes over a 20-year service life. The levelized cost of heating was estimated at 3.1–4.4 ₹ kWh⁻¹. These results indicate that compound curvature–vortex transport intensification can improve thermal efficiency and increase carbon mitigation potential under realistic operating conditions. Full article

This study presents an experimental 3E (energy–exergy–environmental) assessment of a PLC-controlled solar air heater (SAH) equipped with adjustable internal baffles. Unlike conventional passive systems, the proposed design enables active airflow regulation to maintain stable outlet temperatures of 54 °C and 60 °C, achieving rapid stabilization within 3–10 s under outdoor conditions. Experimental results show that increasing the baffle inclination significantly enhances convective heat transfer and thermal efficiency, while the friction factor remains primarily governed by the Reynolds number and exhibits minimal sensitivity to baffle angle. Exergy efficiency values remain relatively low (1.24–2.69%), and the sustainability index stays close to unity, reflecting the inherent thermodynamic limitations of low-temperature solar air heaters rather than deficiencies in system design. A regression-based airflow velocity model is developed to support fan-speed optimization and to clarify the trade-off between thermal enhancement and auxiliary power demand. Long-term projections based on regional solar data indicate that the proposed SAH can deliver approximately 20–22 MWh of useful heat and mitigate nearly 9 tons of CO₂ emissions over a 20-year operational lifetime. Overall, the results demonstrate that PLC-assisted dynamic baffle control provides a flexible and effective approach for improving the performance and operational stability of solar air heaters for low-temperature drying applications. Full article

In this work, three novel optimization algorithms—collectively referred to as the BxR algorithms—and their multi-objective versions, referred to as the MO-BxR algorithms, are applied to diverse heat transfer systems. Five representative case studies are presented: two single-objective problems involving a heat exchanger network and a jet-plate solar air heater; a two-objective optimization of Y-type fins in phase-change thermal energy storage units; and two three-objective problems involving TPMS–fin three-fluid heat exchangers and Tesla-valve evaporative cold plates for LiFePO₄ battery modules. The proposed algorithms are compared with leading evolutionary optimizers, including IUDE, εMAgES, iL-SHADEε, COLSHADE, and EnMODE, as well as NSGA-II, NSGA-III, and NSWOA. The results demonstrated improved convergence characteristics, better Pareto front diversity, and reduced computational burden. A decision-making framework is also incorporated to identify balanced, practically feasible, and engineering-preferred solutions from the Pareto sets. Overall, the results demonstrated that the BxR and MO-BxR algorithms are capable of effectively handling diverse thermal system designs and enhancing heat transfer performance. Full article

Although numerous studies have investigated individual methods to improve the performance of solar air heaters (SAHs), such as flow obstruction barriers, porous media, nanofluids, and thermal energy storage units, the overall integration of these reinforcement strategies into a unified, sustainable system remains to be defined. The current study presents a hybrid solar air heating configuration that combines a solar air collector (SAC) with an electric air heater (EAH) powered by photovoltaic (PV) panels, aiming to stabilize outlet air temperature and enhance overall thermal efficiency. Experimental and numerical approaches were employed to evaluate the influence of barrier geometry (flat, trapezoidal, and V-groove) and airflow rate (53, 158, and 317 L/min) on system performance using three SAC models. Experimental results revealed that lower airflow rate promotes greater temperature rise (ΔT) due to longer air–surface contact, while V-groove barriers achieved the highest ΔT and collector efficiency among all configurations. At higher airflow rates, the absorbed energy factor Fc (τα) increased to approximately 0.73, whereas the heat loss factor FcU decreased, indicating reduced thermal losses and improved energy transfer. Model III demonstrated the most effective heat absorption, confirming its superior thermal design. The integrated SAC–EAH system exhibited improved overall efficiency, with the SAC functioning effectively as a preheating unit and the EAH sustaining thermal stability during variable solar conditions. Numerical results showed that the highest temperature difference occurs at the V-groove barriers at an air flow rate of 53 L/min. In contrast, the difference between inlet and outlet temperatures decreases across the remaining models, with reduced percentages of 11.8% and 12.7% for Model II and Model I, respectively. Numerical simulations ensured the experimental outcomes, showing close agreement with the temperature variation trends and validating the system’s enhanced thermal performance. Full article

Numerical analysis is an economically viable method for improving the performance of a thermal system without many trials. The numerical analysis reported in this paper serves to clarify the extent to which a newly designed subducting baffling structure impacts the performance of a solar air heater (SAH). The performance of different baffle shapes is evaluated through a two-dimensional Computational Fluid Dynamics (CFD) simulation in terms of the thermal (Nu), hydraulic (f), and thermo-hydraulic (THP) performances of the SAH. Moreover, the study is performed with different Reynolds numbers (Re) varying from 3000 to 18,000. The study investigates the parameters arm length (k), arm height (l), pitch (p), pitch angle (α), and arm angle (β) within the ranges of 40–60°, 140–160°, 0.03–0.07 m, 0.03–0.05 m, and 0.05–0.15 m, respectively. The results demonstrate that the assistance of a subducting baffle structure is more effective than a smooth arrangement. The SAH shows a maximum Nu and f of 101.23 and 0.97, respectively. The system with the best performance has revealed the highest THP of 0.798. The greatest intensification of heat transfer (Nu/Nu_s) and friction loss (f/f_s) are 2.58 and 87.76, respectively. Full article

This study provides a detailed review of the thermal and thermo-hydraulic performance of solar air heaters (SAHs) enhanced through the application of artificial roughness on the absorber plate. Various roughness geometries, such as wire ribs, V-shaped ribs, arc-shaped ribs, and rib-groove patterns, have been analysed to assess their influence on heat transfer enhancement and frictional behaviour. Findings from previous experimental and numerical studies reveal that the incorporation of artificial roughness can increase the Nusselt number by approximately 1.25 to 6.3 times and improve thermal efficiency by 20–35% when compared to smooth absorber plates. The review further highlights that the most effective performance occurs at a relative roughness height (e/D) between 0.02 and 0.05 and within a Reynolds number range of 10,000 to 18,000. Overall, the analysis confirms that artificial roughness is a simple, economical, and highly effective technique to enhance heat transfer and overall efficiency in solar air heater systems. Full article

This study investigates the performance of a novel, low-cost solar air heater equipped with large V-shaped fins using experiments and numerical simulations. The solar air heater consists of an absorber plate, a glass cover and airflow ducts. Its performance is evaluated under varying fin configurations: finless and (a)symmetric V-shaped fins with four, six, and eight fins. Computational fluid dynamics simulations using the RNG k-epsilon and discrete ordinate models were validated by experimental findings, showing good agreement with minimal discrepancies between both. The experimental setup recorded a maximum air temperature of 55 °C, corresponding to a temperature rise of 33 °C from an inlet temperature of 22 °C, under an inlet air velocity of 2.7 m/s. Results demonstrate that increasing the number of fins significantly enhances heat transfer efficiency, with heat transfer rising from 134.35 W (finless) to 233.29 W (8 fins). The large-scale fins improved thermal performance significantly while still maintaining a low-pressure drop. Moreover, the fins are very low-cost to implement, in contrast to most heat transfer enhancements in solar air heaters, making this design a very budget-friendly solution. This study provides valuable insights into optimizing solar air heater systems, contributing to the advancement of solar heating solutions for a wide range of energy-efficient applications. Full article

This study introduces a climate chamber developed to evaluate the performance of photovoltaic (PV) and solar air heater (SAH) panels based on 12 months of climate data specific to the province of Antalya. In the test environment, the temperature can be controlled between −5 and +50 °C, relative humidity between 10% and 90%, irradiance between 0 and 1500 W/m², and wind speed between 0 and 25 m/s. Experimental data revealed that PV panels achieved the lowest electricity production of 19.21 W in December and the highest of 73.47 W in June, while SAH panels reached an outlet temperature of 31.12 °C in July. As solar radiation increased, panel efficiency rose proportionally; however, an increase in relative humidity negatively impacted efficiency. The panel surface temperature increased from 16.86 °C in January to 39.33 °C in July. The original aspect of this study is the proposal and adaptation of chaos-integrated optimization-based explainable artificial intelligence (XAI) methods instead of classical regression-based models. These models have enabled the development of transparent, understandable, and interpretable rules based on environmental parameters, such as temperature, relative humidity, radiation, and airspeed, that affect panel performance. The methods used in this study make significant contributions to sustainable energy. In particular, the climate control test chamber developed to increase and optimize the efficiency of solar panels enables the investigation of the effects of environmental parameters on panel performance under realistic conditions, thereby facilitating the more effective use of renewable energy sources. Additionally, the use of chaos-integrated optimization-based explainable artificial intelligence (XAI) methods provides reliable, transparent, and understandable decision support models for the design and management of energy systems. This method promotes the adoption of renewable energy technologies, reduces dependence on fossil fuels, lowers carbon emissions, and supports long-term environmental sustainability. Full article

A solar air heater (SAH) converts solar energy into heated air without causing environmental pollution. It features a low initial cost and easy maintenance due to its simple design. However, owing to air’s poor thermal conductivity, its thermal efficiency is relatively low compared to that of other solar systems. To improve its thermal performance, previous studies have aimed at either enlarging the heat transfer surface or increasing the convective heat transfer coefficient. In this study, a novel SAH with fins and sequentially placed obstacles on the fin surface—designed to achieve both surface extension through a finned channel and enhancement of the heat transfer coefficient via the obstacles—was investigated using computational fluid dynamics analysis. The results confirmed that the obstacles enhanced heat transfer performance by up to 2.602 times in the finned channel. However, the obstacles also caused a pressure loss. Therefore, the thermo-hydraulic performance was discussed, and it was concluded that the obstacles with a relative height of 0.12 and a relative pitch of 10 yielded the maximum THP values among the investigated conditions. Additionally, correlations for the Nusselt number and friction factor were derived and predicted the simulation values with good agreement. Full article

This paper reports the improved thermal and drying performance of a solar air heater powered by real solar irradiance and equipped with a tree-like fractal-based cylindrical pin (SAH-TFCP) as a turbulator for drying applications. The main purpose of this work is to demonstrate the SAH-TFCP’s improvement potential based on its thermal and drying performance as compared with a conventional solar air heater based on a flat-plate absorber (SAH-FP). The test was implemented based on solar time from 8:30 to 17:30 under Thailand’s climatic conditions at a latitude angle of 14° and a longitude angle of 100°. Turmeric slices were used to evaluate the SAH’s drying performance. The thermal efficiency, moisture content wet basis (MC_wb), drying rate (DR), and drying efficiency were measured as parameters of interest to assess the improvement potential of the SAH-TFCP over the SAH-FP. The results indicate that the SAH-TFCP provides better thermal and drying performance than the SAH-FP. A higher flow rate yields a higher thermal efficiency and a greater improvement potential. The improvement potential is around 44–85%. The drying efficiency of the SAH-TFCP is always higher than that of the SAH-FP and has an improvement potential of 32–44%, depending on the airflow rate. Full article

In the present study, a numerical simulation and optimization combined approach is applied to investigate the thermal performance of a solar air heater (SAH). Numerical simulation of the solar air heater is performed based on computational fluid dynamics (CFDs) via ANSYS Fluent 2023R1 software. The solar air heater includes a corrugated absorber plate with a Chevron-type design. Present study was conducted in Al-Kharj, Saudi Arabia on August 15. The optimization process is used to enhance the thermal efficiency of the solar system. In the optimization process, several geometric parameters of the solar air heater, including the wave height and pitch length of the corrugated absorber plate and the height of the airflow channel under the absorber plate, have been evaluated. The wave height is between 10 and 20 mm, the pitch length is between 50 and 90 mm, and the channel height is between 70 and 90 mm. Therefore, the design of experiment (DOE) and response surface methodology (RSM) are utilized to estimate temperature rise and thermal efficiency. The thermal analysis shows that increasing the wave height, decreasing the pitch length, and shortening the channel height enhances both the temperature rise coefficient and the thermal efficiency. Full article

Solar air heating systems offer an effective alternative for reducing greenhouse gas emissions at a profitable cost. This work details the design, construction, and experimental evaluation of a novel double-pass V-trough solar air heater with semicircular receivers, which was built with low-cost materials readily available in the Mexican market. Thermal performance tests were conducted in accordance with the ANSI-ASHRAE 93-2010 standard. The results indicated a peak collector efficiency of 0.4461 and total heat losses of 8.8793 W/(m² °C), with an air mass flow rate of 0.0174 kg/s. The instantaneous thermal efficiency varied between 0.2603 and 0.5633 with different air flow rates and an inlet air temperature close to the ambient temperature. The outlet air temperature reached 70 °C, making it suitable for dehydrating fruits or vegetables at competitive operating costs. Additionally, a second-law analysis was carried out, and the exergy efficiency was between 0.0037 and 0.0407. Finally, a Levelized Cost of Energy analysis was performed, and the result was USD 0.079/kWh, which was 31% lower than that of a conventional electric air heater system. Full article

This study numerically investigates flow and heat transfer in a channel with arc-vane baffles at various radius-to-channel high ratios (r/H = 0.125, 0.25, 0.375, and 0.5) for Reynolds numbers between 6000 and 24,000, focusing on solar air-heater applications. The calculations utilize the finite volume method, and the SIMPLE algorithm is executed with the QUICK scheme. For the analysis of turbulent flow, the finite volume method with the Renormalization Group (RNG) k-ε turbulence model was used. The results show that arc-vane baffles create double vortices along the axial direction, promoting flow reattachment on the heated surface and enhancing heat transfer. Baffles with smaller r/H ratios strengthen flow reattachment, reduce dead zones, and improve fluid contact with the heat transfer surface. The baffles with the smallest r/H ratio achieve a Nusselt number ratio (Nu/Nu_s) of 4.91 at Re = 6000. As r/H increases, the friction factor (f) and friction factor ratio (f/f_s) rise due to increased baffle curvature and surface area. The highest thermal performance factor (TPF) of 2.28 occurs at r/H = 0.125 and Re = 6000, reflecting an optimal balance of heat transfer and friction losses. Arc-vane baffles with a r/H ratio of 0.125 yield a TPF exceeding unity, indicating potential energy savings. These findings provide valuable insights for optimizing baffle designs to enhance thermal performance in practical applications. Full article

This study explores the improvement of building integrated photovoltaic–thermal (BIPV/T) systems and their integration with air source heat pumps (ASHPs). The BIPV/T collector needs a method to effectively extract the heat it collects, while ASHP can boost their efficiency utilizing preheated air from the BIPV/T collectors. Combining these two systems presents a valuable opportunity to enhance their performance. This paper discusses technological improvements and integration through a comprehensive modelling analysis. Two versions of the BIPV/T systems were assessed using a modified version of EnergyPlus V8.0, a building energy simulation program. This study involved sensitivity analysis of the internal channel surface and cover emissivity parameters of the opaque BIPV/T (OBIPV/T), transparent BIPV/T (TBIPV/T), and building-integrated solar air heater collectors (BISAHs). Various arrangements of the collectors were also studied. A BIPV/T-BISAH array design was selected based on the analysis, and its integration with a net-zero energy house. The BIPV/T-BISAH coupled ASHP system decreased space heating electricity consumption by 6.5% for a net-zero house. These modest savings are mainly attributed to the passive design of the houses, which reduced heating loads during sunny hours/days. Full article

A flat-plate unglazed solar water heater (SWH) with a polymer thermal absorber was developed and experimented with. Polymer thermal absorbers could be a viable alternative to metal thermal absorbers for SWH systems. The performance of this polymer SWH system was measured based on inlet and outlet water temperature, water flow rate, ambient air temperature and solar irradiance. The polymer thermal absorbers were hollow Polyvinyl Chloride (PVC) tubes with a 20 mm external diameter and 3 mm thickness and were painted black to enhance radiation absorption. The pipes are arranged in a rectangular spiral inward–outward alternating-flow (RSioaf) pattern. The collector pipes were placed in a 1 m × 1 m enclosure with bottom insulation and a reflective surface for maximized radiation absorption. Water circulated through a closed loop with an uninsulated 16 L storage tank, driven by a pump and controlled by two valves to maintain a mass flow rate of 0.0031 to 0.0034 kg·s⁻¹. The test was conducted under a partially clouded sky from 9 a.m. to 5 p.m., with solar irradiance between 105 and 1003 W·m⁻² and an ambient air temperature of 27–36 °C. This SWH system produced outlet hot water at 65 °C by midday and maintained the storage temperature at 63 °C until the end of the test period. Photothermal energy conversion was recorded, showing a maximum value of 23%. Results indicate that a flat-plate solar water heater with a polymer thermal absorber in an RSioaf design can be an effective alternative to an SWH with a metal thermal absorber. Its performance can be improved with glazing and optimized tube sizing. Full article