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The need to address global warming issues and international policies has placed a greater emphasis on the development of solar energy utilization systems. Intensive study is necessary to expand solar energy applications, as solar energy potential varies widely. This study investigates the thermal and thermohydraulic performance of a modified flat plate solar air heater (FSAH) to assess the effects of using corrugated aluminium duct and sand heat storage elements (HSE) in various combinations. The different arrangements selected for the experimental investigation are the FSAH, FSAH with corrugated aluminium duct (FSAH-C), FSAH with a sand heat storage element (FSAH-S), and FSAH with a combined use of corrugated aluminium duct and a sand heat storage element (FSAH-CS). The materials used for fabrication are low-cost and readily available in the study area. The results indicate that the sand bed enhanced the thermal performance by acting as the thermal heat storage medium, which could also supply heat for a short duration after non-sunny hours, and the corrugated aluminium duct enhanced the surface area and allowed the air to pass twice inside the SAH. We observed that the SAHs with sensible heat storage had a higher top loss compared to the FSAH-S configuration. The average thermal efficiency of the FSAH-CS configuration was 59.17%, which is 8.81%, 5.72%, and 10.95% higher than FSAH-S, FSAH-C, and FSAH, respectively. Furthermore, this configuration achieved an exit temperature of 64.5 °C. The proposed system has a thermohydraulic efficiency of 59.14%, which is not significantly different from the average thermal efficiency. Therefore, the suggested system verifies its ability to function without requiring substantial external power.

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Numerous research studies have found that a double-pass solar air heater (DPSAH) performs better than a single-pass solar air heater (SAH). This suggested study aims to evaluate the performance of a DPSAH setup in Southern Tamil Nadu, India. Several artificial roughness features have been incorporated into the solar black-coated absorber plate for this examination. Broken ribs with semi-circular and semi-polygonal shapes are used and explicitly tested on the absorber plate. Next, the efficiency of these rib designs is contrasted with a typical flat plate DPSAH. These studies also employ three different mass flow rates (0.01 kg/s, 0.02 kg/s, and 0.03 kg/s), enabling a thorough assessment of the DPSAH system's performance at each rate. These studies' findings demonstrate that adding artificial roughness to the solar collector plate has a beneficial effect on the turbulence of fluid flows. As a result, this innovation increases the double-pass solar air heater's (DPSAH) heat transfer rate. It is noteworthy that compared to the DPSAH with flat plates, both rib designs perform better. It is important to remember that the semi-polygonal ribs function better than the semi-circular ones. The average efficiency values for the semi-polygonal rib structure are 17.1%, 18.7%, and 19.1% greater than those seen for flat plates. These efficiency values are additionally 4.4%, 7.4%, and 8.7% higher than those attained with the semi-circular rib topologies at flow rates of 0.01 kg/s, 0.02 kg/s, and 0.03 kg/s, respectively. The study goes into considerable detail on how particular rib patterns can be advantageous economically and environmentally.

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Solar air heaters (SAH) convert solar energy to thermal energy for food processing industries and commercial space heating applications, as solar energy is cost-free. In this experimental study, the thermal performance of the solar air heater has been successively improved using different roughness elements over the absorber. The triangle-shaped wedges in three structures (inline, serpentine, and clustered structure) are investigated in this work. Thermal performance comparison is made with a SAH with a plain absorber. A maximum air temperature rise of 19 °C is observed for the SAH with wedges in a clustered structure. The absorber surface temperature for clustered structured roughness elements is 76.8 °C with an average heat loss coefficient of 4.43 W/m2·K. The useful heat absorption using clustered structure wedges is 33%, 17.9%, and 6.6% higher than the SAH with plain, inline, and serpentine structured wedges. SAH's maximum thermal and exergy efficiency with clustered structured elements is 70.4% and 1.64%. The average thermal efficiency of inline, serpentine, and clustered arrangement is 13.3%, 25.3%, and 35.6% higher than the SAH with a plain absorber. The proposed SAH design shows a sustainability index 1.01, and lower payback periods show economic and environmental viability.

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In this paper, the thermo-hydraulic performance of a solar air heater (SAH) duct roughened with discrete D-shaped ribs is numerically investigated using ANSYS Fluent 2020 R2. The numerical investigation is carried out at rib radius to transverse pitch ratio (r/Pt) from 0.1 to 0.35 and longitudinal pitch to rib radius ratio (Pl /r) from 4 to 10 under various operating conditions with Reynolds number (Re) varied from 10,200 to 20,200. The numerical results are validated with previous experimental results for the Nusselt number (Nu) values, and good agreement is found with mean absolute percentage error (MAPE) of 3.6%. Based on the results of the numerical investigation, it was found that the value of Nu and the friction factor (f) decreases with the increase of the value of Pl/r, while the ratio r/Pt is kept constant. From the overall analysis, it is concluded that the optimum results are obtained for r/Pt of 0.25 and Pl/r = 4, and the maximum thermo-hydraulic performance parameter is 1.12. Further correlations are developed for the value of Nu and f for the whole range of r/Pt as 0.10-0.35 and Pl/r as 4-10. According to the developed correlations, the values of Nu are within ± 2% of the results of CFD, while the values of f are within ± 2.7% of the results of CFD.

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Solar air heater is widely used for drying and industrial processing application. Different artificial roughened surfaces and coatings over the absorber plates are used to improve their performance of solar air heater by increasing absorption and heat transfer. In this proposed work, the graphene-based nanopaint is prepared by wet chemical and ball milling method and the prepared graphene nanopaint is characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The prepared graphene-based nanopaint is coated on the absorber plate by conventional coating method. The thermal performance of the solar air heater coated with traditional black paint and graphene nanopaint is evaluated and compared. The day's maximum energy gain by the graphene-coated solar air heater is 972.84 W, whereas traditional black paint is only 808.02 W. The average energy gain of graphene nanopaint is 655.85 W, which is 12.9% higher than the traditional black paint. The maximum thermal efficiency for solar air heater coated with graphene nanopaint is 81%. Also the average thermal efficiency of graphene-coated solar air heater is 72.5%, which has a 13.24% higher average thermal efficiency when compared to conventional black paint-coated solar air heater. The average top heat loss for solar air heater coated with graphene nanopaint is 8.48% lower than solar air heater with traditional black paint.

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This study investigated the crisis of energy from which Gaza has been suffering over the past years. It ventured to highlight the growing needs for energy and the urging need to use renewable and sustainable sources of energy such as solar thermal energy. Much specifically, it gave much importance to the solar water heater (SWH) as well as the solar air heater (SAH). These two important tools rely on clean and renewable source of energy, and their use in the Gaza Strip would greatly help in bringing about an environmental conservation and sustainable economy. The result obviously shows that both SWH and SAH systems are very suitable for space heating for buildings. The maximum annual heating energy gained is 20360.7 kWh at an inclination angle of the solar collector of 30° for SWH. While for SAH the best value of heating delivered was 19268.9 kWh at a tilt angle of 45°. Besides, the result exposes that the use of SWH and SAH systems can potentially save up to $3461.3 and $3275.7 respectively of energy cost annually. The payback achieved on the investment in SWH and SAH is 4.4 and 4 years respectively. Additionally, the utilization of SWH and SAH systems can ultimately save energy as well as potentially reduce emission of air pollution. For instance, using SWH and SAH can reduce 17306.6 and 16378.57 kg/year of CO2 emissions respectively.

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The thermal efficiency of conventional solar air heater is very low. This research article concentrates on incorporating V-shaped staggered twisted ribs over absorber surface of solar air heater. Various roughness parameters were tested to determine their effect on the Nusselt number, friction factor, thermo-hydraulic performance index, and thermal efficiency. During experiment, the Reynolds number is varied from 3000 to 21,000; while relative roughness length varied for 4.39 to 10.26 and relative staggered distance for 2 to 6. However, relative roughness pitch, twist length, and angle of attack were kept constant. The Nusselt number and friction factor of the roughened collector enhances to 3.41 and 2.56 times that of the smooth collector, respectively. The thermal efficiency of the roughened solar air heater increases to 73.64% of the roughened plate as it was noticed 42.63% for smooth surface due to breakage of the laminar sublayer. The correlations for Nusselt number and friction factor as function of Reynolds number and roughness parameters are also developed. The maximum thermohydraulic performance gained at the optimum parameters of d/e of 4 and S/e of 6.15 is 2.69. The percentage deviation between the developed correlations and the experimental findings shows very satisfactory outcomes. Therefore, it can be concluded that inclusion of twisted V staggered ribs enhances the thermal performance of solar air heater with the lowest frictional penalty.

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The study aims to examine the thermal performance of solar air heaters employing two different absorber plates under two different configurations. The experiments have been conducted in the summer climatic conditions of Moradabad City, India. A total of about 04 models of solar air heaters have been developed. The experimental investigation has been done using a flat-plate absorber and a serrated geometric absorber (with and without using the tested phase change material) to estimate the thermal performance. Notably, 03 different mass flow rates (i.e., 0.01 kg/s, 0.02 kg/s, and 0.03 kg/s) have been used to investigate the heat transfer coefficient, instantaneous efficiency, and daily efficiencies. Results of the study showed that Model-4 is the best among all the tested models that provide an average exhaust temperature of about 46 °C after sunset. The optimum daily average efficiency has been obtained at about 63% at 0.03 kg/s. The efficiency of a serrated plate-type SAH without using phase change material is about 23% higher than that of a conventional system, while it is about 19% higher than that of a conventional SAH using phase change material. Overall, the modified system is suitable for moderate-temperature applications, like agricultural drying and space heating.

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The objective of this research article is to present a comprehensive review of the work carried out to improve the thermal as well exergetic performance of the conventional smooth absorber plate solar air heater (SAH) duct by the use of the various configurations and arrangements of extended surfaces (fins) for the forced convection. In the SAH duct, these extended surfaces are attached along the air-flow path on the top absorber, on the bottom plate, or on the both plate surfaces. It enhances the performance of the conventional SAH by increasing the surface area and makes flow turbulent by their presence. Several experimental, theoretical, and simulation works, which have been performed by the researchers by utilizing the extended surfaces to improve the thermal efficiency based on first law of thermodynamics, exergy, and entropy generation analysis on the basis of the second law of thermodynamics for SAH ducts, have been included in the present article. Subsequently, an effort has been made to calculate the Nusselt number and friction factor by using the correlations reported by the researchers for comparing the performance of different configurations of fin SAHs. This comprehensive review article will be useful for the investigators and researchers who are working in the area of extended surface SAHs.

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Research dedicated to renewable energies aims at reducing the negative impact of fossil fuels on the ecosystem and particularly to solar applications so to make it more competitive with conventional systems. In this paper, attention is paid to flat plate solar air collector due to their simplicity and immediate use in converting solar energy, and operating at low temperature. A modification has been brought to one of its components to further improve its performance. To meet the needs of thermal energy demand for a given use (heating, drying, etc.), an installation of a field of collectors (solar air collector, solar water heater, etc.) is required to ensure the demanded thermal power. The modification consists in integrating, on the back of the solar air collector, a water tank supplied by solar water collectors, which serves as a heat storage tank for any other use. A simulation is performed using Fluent CFD code, in order to follow the evolution of the heat transfer fluid flow considering the implantation site meteorological data at Bouzaréah (Algeria). Different flow rates were considered for the two heat transfer fluids. A primary heat transfer fluid was represented by air and the second one represented by water. Simulation results show that thermal efficiency of the modified solar air collector is improved compared to the one of the typical solar air heater when we use forced flow. For the different used flow rates, higher efficiency is obtained when the flow rate of the primary heat transfer fluid (air) is increased.

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A rough rectangular channel of solar-based air heater (SBAH) is made and tested. The work consists of an effort to perceive the proportion of heat discharge and frictional behavior of air passing over a roughened rectangular channel. The absorber surface of SBAH is roughed with discrete V-down rib and staggered element roughness having different values of relative rib pitch (P/e) that ranged from 6 to 14. Fixed parameters such as relative gap size (g/e), relative staggered element pitch (P'/P), numeral of gaps (Ng), relative staggered element size (r/g), and relative rib height (e/D) are considered 4, 0.4, 3,1, and 0.0433, respectively, all throughout the study. The flow Reynolds number (Re) changes from 4000 to 14,000; consequently the Nusselt number (Nu) and friction factor (f) reach up to 2.16 and 2.73 times, respectively, with respect to plane surface. The optimum rise in terms of thermal-hydraulic performance (THP) is gained analogous to a P/e of 10. The correlation for heat transfer function, R(e+), and roughness function, G(e+), is given to anticipate the performance of roughness.

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This study develops reliable and robust machine learning (ML) models to predict the outlet air temperature and humidity and thermal efficiency of a solar air heater (SAH). Also, the application of predictive models for optimal control of the SAH operation is proposed. For this, the work contains three main parts: (a) a vertically-mounted symmetrical SAH was installed outside of a building room and operated throughout the winter of 2022. (b) By conducting experiments for five air mass flow rates, a large dataset with more than 62,500 sample points was collected. (c) Six input features containing time, environmental-related attributes, and SAH variables were applied to develop several state-of-the-art ML algorithms. To figure out the most accurate models for predicting output variables, the dataset was partitioned into three parts. Also, various modeling performance evaluation criteria were calculated and compared on the validation and test sets. Among these models, the gradient boosting machine algorithm based on LightGBM implementation achieved the best degree of generalization in modeling the target variables. The results demonstrated that the developed models obtained the lowest R-squared and the highest mean absolute percentage error of 0.9827 and 2.95%, respectively, on the test set. Moreover, the offline analysis of SAH operation based on the proposed control scheme demonstrated that 350 kWh of thermal energy can be generated during the application in the one-year winter season, 24% more than SAH operation without a model-based control strategy.

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Computational fluid dynamics (CFD) plays a prominent role in the design and development of solar air heaters. The previous investigations have lagged in using a radiation model for the solar heat input; instead, most of the researchers simulated a constant heat flux model. Moreover, an extensive study on the geometrical and boundary conditions like confinement and transition length, suction, and blowing effects has not been studied. The present investigation deals with the aforementioned effects on the flow and heat transfer characteristics of the SAH channel, which is designed for residential space heating. The finite volume-based solver Ansys Fluent is used for finding the field variables. The confinement height is varied from 25 to 150 mm, and the transition length is varied from 250 to 1000 mm. The suction and blowing effect is investigated by changing the flow direction across the channel. Even though the temperature rise is less significant with respect to confinement height and transition length, the effective efficiency increases with decreasing channel height and increasing transition length. In general, blowing of air across the channel gives better performance than suction. When comparing them, the influence is less in temperature rise and more in pressure drop for the channel height of 25 mm, whereas the channel height of 150 mm has better influence in temperature rise and less influence in pressure drop.

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To investigate the solar air heater's (SAH) effectiveness, experiments are conducted using flat plate and artificially roughened plate in terms of inclined and winglet baffles over the collector surface. This proposed system collector plate is made up of inclined and winglet ribs and serves as an artificial roughness generator. Air stream of 0.01, 0.02, and 0.03 kg/s are used in the experiment. To determine the improvement in the proposed work, these experimental results are compared with flat plate SAH. This proposed work offers a greater efficiency, useful energy gain, and lower top heat loss than a conventional SAH. At 0.03 kg/s system efficiency and useful energy gain reach their peak. Experimental day's average efficiency of a SAH with inclined and winglet baffles is 30.8%, 52.7%, and 72.9%, respectively, for the examined cases, and it is 11%, 13.8%, and 22.2% more effective than a flat surface SAH. For the investigated air flow rates, the proposed system gains 36.2%, 24.2%, and 28.9% more energy than flat plate SAH. Substantial reductions in top losses of up to 8.48%, 7.28%, and 7.27% have been reported at the specified flow rates, respectively. Energy metrics and economic study performed show the payback time, production factor, life cycle conversion efficiency, and economic values of the proposed SAH are optimum.

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The investment of solar energy in life applications has become mandatory to maintain a clean environment and reduce the use of fossil fuels. This work aimed to improve the performance of solar air heater (SAH) by using evacuated tube solar collectors ETSC integrated with nano-enhancer phase change material (NE-PCM). To achieve this purpose, a system consisting of 5 linked collecting panels was designed, fabricated, and experimentally investigated. Each panel included a glass-evacuated tube with two concentric aluminum pipes installed inside. NE-PCM was placed between the inlet and outlet air paths inside the evacuated tube to enhance the heat transfer rate. The performance was investigated with and without NE-PCM at five mass flow rates (0.006, 0.008, 0.01, 0.03, and 0.05 kg/s). Experimental results revealed that the highest temperature was 116, 108, 102, 95, and 93 °C, respectively, for the above mass flow rates without adding NE-PCM. The outlet temperature was decreased by 6-15 °C when using NE-PCM. The SAH efficiency was increased by 29.62% compared to the system without NE-PCM at 0.05 kg/s. The maximum thermal efficiency for the system with NE-PCM was 62.66% at 0.05 kg/s, and the pressure drop was 6.79 kPa under the same conditions. As well known, the hot air is used for a variety of purposes including space heating, food processing, drying of fruit, vegetables, dairy, and solar cooking.

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Artificial roughness on the absorber of the solar air heater (SAH) is considered to be the best passive technology for performance improvement. The roughened SAHs perform better in comparison to conventional SAHs under the same operational conditions, with some penalty of higher pumping power requirements. Thermo-hydraulic performance, based on effective efficiency, is much more appropriate to design roughened SAH, as it considers both the requirement of pumping power and useful heat gain. The shape, size, and arrangement of artificial roughness are the most important factors for the performance optimization of SAHs. The parameters of artificial roughness and operating parameters, such as the Reynolds number (Re), temperature rise parameter (ΔT/I) and insolation (I) show a combined effect on the performance of SAH. In this case study, various performance parameters of SAH have been evaluated to show the effect of distinct artificial roughness, investigated previously. Therefore, thermal efficiency, thermal efficiency improvement factor (TEIF) and the effective efficiency of various roughened absorbers of SAH have been predicted. As a result, thermal and effective efficiencies strongly depend on the roughness parameter, Re and ΔT/I. Staggered, broken arc hybrid-rib roughness shows a higher value of TEIF, thermal and effective efficiencies consistently among all other distinct roughness geometries for the ascending values of ΔT/I. This roughness shows the maximum value of effective efficiency equals 74.63% at a ΔT/I = 0.01 K·m2/W. The unique combination of parameters p/e = 10, e/Dh = 0.043 and α = 60° are observed for best performance at a ΔT/I higher than 0.00789 K·m2/W.

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Solar air heater (SAH) is simple and the greatest effective approach to utilize and convert solar energy into thermal energy for heating utilizations. The employment of artificial roughness under side of the observer surface is the key technique for augmenting heat transfer with minimal friction factor penalty. Current paper summarized different kinds of artificial roughness used in SAH, which augments its performance. In this review article, 96 research papers are cited, which provide detailed information about the effect of different geometrical parameters on heat transfer and friction factor. This paper also brings the information about the optimum roughness parameters and heat transfer and friction factor correlation developed by different investigators in tabular form. Optimum roughness parameters and empirical correlations are used for comparative analysis of heat transfer, friction factor, and thermo-hydraulic performance parameter (THPP) of different roughness geometries. The best performing roughness geometry is reported on the basis of comparative analysis. Mathematical model is developed for predicting the thermal efficiency (ηth) of roughened SAH duct.

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A solar air heater (SAH) is investigated experimentally by employing multi-geometry arrangements over the absorber plate. In the current work, the absorber plate is designed with rectangular ribs, slits, and cylinders. For the proposed system, this multi-geometry arrangement serves as an artificial roughness (baffles). Different airflow rates of 0.01, 0.02, 0.03, and 0.04 kg/s are used in the experiment. The results of this experiment are compared to those of a conventional SAH to assess the improvement. Compared to a conventional SAH, the proposed system has higher thermal efficiency, energy gain, and minimal top loss. The highest thermal efficiency and energy gain are observed at a mass flow rate of 0.04 kg/s. Increasing the mass flow rate increases the system's performance. For the analyzed flow rates, the average thermal efficiency of a SAH with multi-geometry baffle is 40.8%, 58.2%, 68.2%, and 77.4%. For the same flow rates, it is 12.8%, 10.2%, 12.3%, and 13.5% higher than a conventional SAH. For the same examined air flow rates, the suggested air heater gains 31.9%, 21%, 19.2%, and 20.8% more energy than conventional SAH. Significant decreases in top losses are reported up to 8.1%, 7.3%, 7.2%, and 6.5%, respectively for the specified flow rates.

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Flat plate solar collector is one of the main solar collectors that has a simple structure, reliable operation, large heat preoccupation area, and low cost. Its drawback is the low heat transfer between the working air and the absorber plate. A solar air heater of V-shaped transverse finned absorber having new designed absorber plate of lateral gaps and central holes to enhance its performance is investigated experimentally at single-pass and double-pass airflow conditions. Moreover, the energy and exergy assessment of its performance was studied and compared with traditional longitudinal finned heater having the same fin surface area and construction except for the absorber plate design. The study is investigated at air mass flow rates of 0.025, 0.05, and 0.075 kg/s. Findings show that the new heater achieves maximum outlet temperature rising of 28.2 °C at 0.025 kg/s and double-pass flow. Moreover, it has an average daily energy efficiency of 88.5%, 81.88%, and 61.3% at mass flow rates of 0.075, 0.05, and 0.025 kg/s with increments of 9.4%, 13.3%, and 9.66%, respectively, compared to the longitudinal finned heater. Additionally, it achieves exergy efficiencies of 2.5%, 2.1%, and 1.7% at mass flow rates of 0.025, 0.05, and 0.075 kg/s with increments 18%, 25.7%, and 18.2%, respectively, relative to longitudinal finned heater. Furthermore, the new heater design possesses greater energy efficiency comparing to former studied SAH designs.

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Among all renewable energy sources, solar power is one of the major sources which contributes for pollution control and protection of environment. For a number of decades, technologies for utilizing the solar power have been the area of research and development. In the current research, thermal performance parameters of multi-gap V-roughness with staggered elements of a solar air heater (SAH) are experimentally investigated. The artificial neural network (ANN) is also utilized for predicting the thermal performance parameters of SAH. Experiments were executed in a rectangular channel with one roughened side at the top exposed to a uniform heat flux. A significant rise in thermal efficiency performance was reported under a predefined range of Reynolds number (Re) from 3000 to 14000 with an optimized value of relative roughness pitch ratio (P/e) and relative staggered rib length (w/g) as 12 and 1, respectively. The maximum thermal efficiency was attained in the range from 42.15 to 87.02% under considered Reynolds numbers for optimum value of P/e as 12 and w/g as 1. A multilayered perceptron (MLP) feed-forward ANN trained by the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm was utilized to predict the thermal efficiency (ηth), friction (f), and Nusselt number (Nu). The thermal performance parameters such as P/e, w/g, Re, and temperature at the inlet, outlet, and plate were the critical input parameters/signals used in the ANN method. The optimum ANN arrangement/structure to predict the Nu, f, and ηth demonstrate higher accurateness in assessing the performance characteristics of SAH by attaining the root mean squared error (RMSE) in prediction and the Pearson coefficient of association (R2) of 1.591 and 0.994; 0.0012 and 0.851; and 0.025 and 0.981, respectively. The prediction profile plots of the ANN demonstrate the influence of various input parameters on the thermal performance parameters.