Conventional Solar Air Heater Research Articles

Heat transfer and flow behavior in solar thermal collector equipped with obstacles

Solar energy, an inherently pure and abundant source of power, is integral to a myriad of daily activities. Among the various solar thermal systems, Solar Air Heaters (SAHs) are often esteemed for their economic viability and practical utility in heating spaces and drying the products.. However, sometimes the conventional SAHs are criticized for their poor performance and capability in heat transfer, making them not well organized in application. The introduction of a new method of improvement in the efficiency of heat transfer in SAHs using carefully designed obstacles with sharp corners is presented in this paper. The obstacles are conceptualized in a Triangular winglet configuration, type-based on the following: Type 1 (Single Triangular winglet), Type 2 (Dual Triangular winglet), Type 3 (Triple Triangular winglet), and Type 4 (Quadruple Triangular winglet). The setups' empirical configurations were processed for the SAH duct where the experiments were executed with a Reynolds number (Re) up to 2000 to 16,000. The obstacle parameters such as the relative transverse pitch (Pt/b), relative obstacle height (e/H), and the relative longitudinal pitch ratio (Pl/e) were clearly maintained at 4, 0.5, and 4, respectively. From the experiments, the Nusselt number was found to be significantly enhanced, up to 3.85 for the Type 3 obstacle configuration. The Thermohydraulic Performance Parameter (η) also showed a strong value for all obstacle configurations that eventually reaches a peak value of 2.29, hence presenting a comprehensive performance for heat transfer efficiency and hydraulic performance within the SAH system.

CFD modeling of a tubular three-pass solar air heater with phase change material: Investigating heat transfer enhancement and energy efficiency

The present study introduces a novel solar air heater design featuring a tubular surface with three passes arranged in a counter-flow configuration, aimed at improving compactness and enhancing heat transfer characteristics. The research involved the development and validation of a computational fluid dynamics (CFD) model, which was utilized to accurately depict the distribution of solar flux through the system components by comparing the model results with experimental data. The study involved conducting a comparative analysis between the tubular three-pass solar air heater with phase change material (TTPSAH_PCM) and conventional flat plate solar air heaters (FPSAH) to ascertain the superior design characteristics. A thorough investigation was carried out, encompassing evaluations of energy, exergy, outlet temperature, convection heat transfer coefficient, and useful heat gain. The findings indicate that the TTPSAH_PCM outperforms alternative geometries. For instance, when operating at a mass flow rate of 0.006 kg/s, the TTPSAH_PCM demonstrates substantial enhancements in several key metrics, including an 11.4 % increase in the system's daily thermal efficiency, a 17 % improvement in exergy efficiency, and a 4 % rise in outlet air temperature. The convection heat transfer coefficient of TTPSAH_PCM exhibited a 155.6 % increase compared to the FPSAH type. Moreover, the system being investigated demonstrates an 8.5 % rise in useful heat gain. The results underscore the enhanced efficacy of the TTPSAH_PCM system in contrast to alternative solar air heater arrangements, and its applicability for both drying operations and indoor heating applications.

Enhancing Solar Air Heater Performance with Quatrefoil Artificial Roughness: An Adaptive Neuro-Fuzzy System Approach

Solar air Collector is used to transform the solar energy into heat energy. Solar heating technologies use only free, renewable and clean energy. More number of previous studies was done. The roughness element is changed to enhance the airflow’s capacity to absorb heat. In this study Experimental investigates the glazed solar air heater with quatrefoil shaped artificial roughness is placed above the absorber plate in the solar air heater. The solar air heaters (SAH) with quatrefoil shaped artificial roughness and conventional solar air heater are tested. The outcome indicates that the maximum temperatures for conventional SAH and purposely roughened SAH are 670C and 470C, respectively. By the increased of heat transfer area and increased the turbulence lead to higher heat recovery rate of quatrefoil shaped artificial roughness is 47% more compared to conventional type. The solar air heater is predicted by using Adaptive Neuro Fuzzy Inference System (ANFIS) and accuracy is measured as 90%.

Employment of roughened absorber palate and jet nozzles with different hole shapes for performance boost of solar-air-heaters

In this study, roughened absorber plate and jet nozzle are simultaneously employed to enhance the efficiency of a solar based air heater. The impact of jet nozzle hole shape is comprehensively investigated for the mentioned system which have not been investigated before. Three-dimensional steady-state simulations of incompressible turbulent fluid flow and heat transfer are performed using the Reynolds-Averaged Navier-Stokes (RANS) equations to model the jet solar air heater (JSAH). Five different jet hole shapes (circular, triangular, square, hexagonal, and rectangular) are examined and results are compared with conventional structure. The thermal and hydraulic performance of the JSAH is assessed using a variety of geometric and operating parameters, including jet diameter ratio (dj/Dh), jet hole streamwise pitch (Lj/Dh), and Re number (Re). The results show that the ratio of (Nu/Nus) initially increases and then decreases as the hydraulic diameter of the jet holes increases. Circular jet holes consistently outperform other shapes, while rectangular and triangular jet holes perform poorly. The pressure penalty (f/fs) decreases with increasing (dj/Dh), with circular jet holes exhibiting the lowest value. Increasing the Reynolds number enhances heat transfer and pumping power but leads to a decrease in (Nu/Nus) and negatively affects the THPP of the JSAH compared to a conventional smooth solar air heater. The study also reveals that the THPP initially increases with streamwise pitch (Lj/Dh) but then declines, following the trend of (Nu/Nus). The results demonstrate up to 4.5 times higher Nusselt numbers with a jet solar air heater versus a smooth solar heater. A maximum thermal-hydraulic performance parameter of 1.64 indicates the proposed design's efficacy. This research furnishes critical insights into optimizing solar air heater performance by examining jet nozzle hole shape, streamwise pitch, and Reynolds number. It enables enhancing thermal efficiency and thermo-hydraulic performance.

Influence of triangular spoilers on the performance of serpentine solar air heaters

In order to improve the efficiency of the conventional serpentine solar air heaters, this article proposed a serpentine solar air heater containing a triangular spoiler. A 3-D verified mathematical model of serpentine solar air heaters with triangular spoilers was established. The results showed that the arranging triangular spoiler had a positive effect on enhancing the thermal performance of solar air heaters. It could be seen from the velocity and temperature contours that the triangular spoiler could reduce the intensity and area of the vortex zones, and hence decrease the temperature dead zone in the flow channel. The collection efficiency reached its peak value when the angle of triangular spoiler was 64°. Compared with the nontriangular spoiler, the collection efficiency was increased by 4.4% ∼6.2%. In general, the optimal angle of triangular spoiler was determined to be 40° by comprehensive analysis of effective efficiency.

Performance of Finned Absorber Plate Solar Air Heater Having Multiple Triangular Air Flow Passages in Parallel Under Transition to Turbulent Flow Condition

Abstract This paper presents the results of thermal performance study of a solar air heater having absorber plate with inclined fins fitted in equilateral triangular flow passages in parallel using the governing equations under transition to turbulent flow and compares the same with the conventional solar air heater having low aspect ratio rectangular air flow duct at equal pumping power condition. The equal pumping power condition for the equilateral triangular passages of width w and rectangular duct height H has been found to be w = 2.65 H. The finned absorber plate solar air heater has been found to provide 7.3–25.8% better thermal efficiency than the conventional air heater because of the substantial increase in the effective heat transfer surface area due to the fins. The effects of variation of design, ambient, and operating parameters on the performance of the finned solar air heater show that the triangular passage width w must be increased with the increase in the collector length L to satisfy the condition of equal pumping power according to the relation w3/L2.75 = constant. The results of the present study can be utilized for the development of enhanced-performance finned solar air heater with triangular passages.

Effect of jet angle and jet pitch on the Thermo-Hydraulic performance of solar air heater having absorber plate with jet impingement

This numerical investigation focuses on enhancing the heat transfer characteristics and thermo-hydraulic performance of a solar air heater by employing jet impingement over the absorber plate. The study explores the influence of two geometrical parameters, namely jet pitch ratio (P/Dh) and jet angle ratio (α/90), on the heat transfer, frictional losses, and overall performance of the solar air heater with jet impingement (SAHJI) under various flow conditions, represented by Reynolds numbers (Re) ranging from 3500 to 17500. The simulations are conducted using the RNG k-ɛ model with second-order upwind discretization. A comparative analysis is performed between the SAHJI system and a conventional smooth solar air heater (SPSAH) configuration, revealing a significant enhancement in thermal–hydraulic performance with the use of jet impingement. The investigation identifies the maximum thermo-hydraulic performance parameter, reaching a value of 4.12. This peak performance is achieved at specific values of jet pitch ratio (P/Dh) of 1.30 and jet angle ratio (α/90) of 0.094, respectively, at a Reynolds number of 7500. These findings demonstrate the potential of jet impingement as a heat transfer enhancement technique in solar air heaters, contributing to improved overall system efficiency.

Energy and exergy analysis of a cross flow solar air heater for thermohydraulic performance augmentation

This study numerically examines the enhancement of thermo-hydraulic efficiency of a cross flow solar air heater (SAH) for Reynolds number ranging from 3000 to 21000. The thermal performance is investigated for various perforation hole diameters of absorber plate and varying number of rows of holes. Discrete Ordinates radiation model is used to simulate the solar radiation heat interactions within the computational domain. Maximum thermo-hydraulic efficiencies of 86.51% and 85.15% are observed for configurations with 3 rows and 4 rows of perforation holes with hole diameter ratio of 0.06 and 0.07 respectively. The maximum exergy efficiency is found to be 5.28%. The system's enviro-economic analysis shows that the CO2 mitigation rate is 1.12 t CO2/annum, whereas the environmental cost is 16.31 $/year. The exergo-economic parameter is computed as 1.18 kWh/$, while the energy cost is calculated as 0.049 $/kWh. Additionally, it is determined that the energy payback period is 5 months while the exergy payback period is 22 years. The heat map for the various configurations shows the economical operating range of the air heater. The envisaged SAH has the advantage of completely decimating the laminar sublayer throughout the absorber plate due to cross flow movement of air through the absorber plate unlike the conventional SAH.

Thermal performance augmentation of solar air heater with curved path

Poor heat convection from absorber to airstream limits the benefits of solar air heater (SAH) utilization. This study aims to maximize the extracted heat from the absorber by increasing air flow mixing rate and boundary layers separation process. Thereby, SAHs with smooth curvilinear paths of radiuses of 5 cm (SAH5), 15 cm (SAH15), and 25 cm (SAH25) are introduced. Moreover, CFD is employed to conduct the present study, and model predictions are found to yield good agreement with respect to well-known correlations from literature. The findings reveal that thermal performance of curved SAH does not vary significantly after path's radius of 15 cm. Additionally, data of Nusselt number of SAH15 are found 3–7%, and 55–83% greater than those of SAH5 and conventional SAH, respectively. Nevertheless, data of friction factor of SAH15 are found 3.2–9.6% lower than those of SAH5. Overall, SAH15 contains smaller stagnant areas, yields better flow distribution, and owns higher overall thermal performance with respect to SAH5.

Improvement of solar air heaters performance with PCM-filled baffles and storage bed

Solar air heaters (SAHs) are popular solar energy collection systems due to their simple design and construction. However, conventional SAHs face limitations, including a small heat transfer surface area, high thermal resistance between the airflow and the heater, and reduced performance during nights or cloudy days. This study proposes a solution by incorporating both a PCM storage bed and optimized PCM-filled baffles in the SAH. Initially, a 3D transient numerical analysis is conducted to investigate the SAH with a storage bed and PCM-filled baffles. The numerical modeling employs the TEDM approach to identify the optimal geometries for the PCM-filled baffles. Subsequently, experimental tests are conducted based on the identified optimal conditions. The results reveal that the height of the baffles is the most influential parameter in determining the daily effective efficiency. The proposed SAH exhibits a daily effective efficiency approximately 57.9% higher than that of a SAH without PCM and 52.6% higher than that of a SAH with a PCM storage bed at Re=5000. Moreover, the proposed SAH outperforms baffles-less SAHs by prolonging the duration during which the outlet air is at least 5° warmer than the inlet by approximately 54%.

Effect of graphene nanopaint on performance of solar air heater attached with inclined and winglet baffles.

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.

Enhancement of thermal efficiency and development of Nusselt number correlation for the solar air heater collector roughened with artificial ribs for thermal applications.

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.

Exergetic efficiency prediction of roughened solar air heater

Energy losses of flowing air through solar air heater (SAH) duct does not consider in the ther-mal performance. Therefore, thermohydraulic performance based on exergetic efficiencies is a tool to assess the performance by considering energy losses in propelling the air simul-taneously to identify the best ribs configuration. This paper presents the thermohydraulic performance of SAHs exploiting various ribs roughness’s. The performance of SAHs is based exergetic evaluation based on IInd law of efficiency is most suitable for design of artificial-ly roughened SAH as it includes both requirement of pumping power and effective energy output. In this paper exergetic evaluation of differently roughened SAH has been done. The exergy efficiency of roughened SAH was calculated analytically with the help of correlations developed by researchers and the results also compared with conventional SAH under same operating parameters. The thermal and exergy efficiency curve as a function of temperature rise parameter (ΔT/I) has been plotted. As a results, hybrid ribs configuration exhibited the highest exergetic efficiencies when temperature rise parameters greater than 0.01 K.m/W, however, smooth duct also showed a significant exergetic efficiency when temperature rise parameters had low values.

An experimental investigation of new roughness patterns (dimples with alternative protrusions) for the performance enhancement of solar air heater

Conventional solar air heater (SAH) has poor performance and in this work, an initiative has been taken to improve their overall performance with the help of a combined roughness pattern over the absorber plate. The experimental setup has been designed and fabricated having a rectangular duct with one heat-absorbing side (with roughness). The combination of dimple and protrusion roughness elements are arranged alternatively over the absorber plate for performance improvement of SAH. The precise placement of these roughness elements over the heat-absorbing side has been ensured with relative roughness pitch (RRP; P/e), print diameter to hydraulic diameter (d/D), and relative roughness height (RRH, e/D) which ranged from 10 to 20, 0.025–0.045, and 0.25 to 0.5, respectively. It is discovered with the experimental results that the thermal performance increases along with the pressure loss in the roughened SAH (rSAH). The heat flow increment is comparatively higher at the trailing and the leading edge of the dimple and the protrusion because of flow separation, reattachment, and flow impingement. The thermal performance is the highest while RRP, RRH, d/D are 10, 0.036, and d/D = 0.35, respectively. The proposed roughness pattern has resulted in a 2.1 and 1.95 times higher thermal augmentation and overall performance of SAH over the conventional.

Numerical analysis of a novel solar air heater design with V-ribs and jet cooling

The application of solar air heaters (SAHs) is an effective method of utilizing abundant solar energy for heating purposes and reducing the consumption of fossil fuels. However, the performance of SAHs is characteristically low owing to a sublayer formation over the heated surface. To address this low performance, numerical examinations on a novel configuration of SAH have been performed in this study. The proposed design encompasses a combined arrangement of both impinging air jets and rectangular sectioned V-ribs on the absorber surface. The effect of varying roughness height, pitch, and angle of attack from 0.016 to 0.024, 0.264 to 0.792, and 30° to 75° respectively is investigated while keeping impingement parameters fixed and varying Re from 3000 to 18000. Nusselt number (Nu) and friction factor (ff) characteristics as functions of roughness parameters are evaluated. The results exhibit a considerable enhancement of 3.36 and 5.31 in Nu and ff respectively in contrast to conventional SAHs under similar boundary conditions. Moreover, the proposed model performs best at Re = 18000 with the highest thermohydraulic performance (ηcombined) of 1.92. The study concludes that the proposed arrangement of jet cooling with rectangular sectioned V-ribs is an efficacious way for improving the performance of SAHs.

Applications of extended surfaces for improvement in the performance of solar air heaters-a detailed systematic review.

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.

Numerical investigation on the performance of a solar air heater using inclined impinging jets on absorber plate with parallel and crossing orientation of nozzles

This work investigates the performance enhancement of a solar air heater using inclined impinging jets on the heater surface. Two main sets of arrangements are considered for the jet nozzles including the parallel and crossing orientation of nozzles in consecutive rows. The RNG k − ɛ model is employed to simulate the turbulent flow in the channel. The influence of different geometrical and operational parameters such as jet diameter ratio (Dj/Dh), inclination angle (α,β), stream wise pitch ratio (L/Dh), span wise pitch ratio (S/Dh), Re number and velocity ratio (Vr) on the hydraulic and thermal behavior of jet solar air heater was studied. Results showed that the proposed jet solar air heater improved the Nu number and thermohydraulic performance parameter compared to the conventional unimproved solar air heater. For the studied range of parameters, up to 4.26 times higher Nu number was obtained using the jet impingement compared to the smooth duct solar air heater. Moreover, it was shown that the amount of velocity ratio (Vr) is a significant factor when comparing the parallel and crossing orientations. Additionally, results indicated that the increment of stream wise and span wise pitch led to the increment of the Nu number while having a minor effect on the friction factor. For example, the increment of L/dh from 0.3 to 0.6 leads to the reduction of f/fs of case 1 and case 4 by 6.5% and 1.09%, respectively Also, the increment of the jet diameter first raises the thermohydraulic performance parameter, and then with a further increment of diameter, the amount of thermohydraulic performance parameter decreases.

Design, fabrication and investigations of natural convection step serrated fin plate integrated trough array low-cost collector for solar air heating: An application to agricultural crop drying

This paper establishes the design modification procedure for flat plate solar thermal collector and investigates the performance by incorporating a specially designed low-cost Step Serrated Fin Plate Integrated Trough Array (SSFPT) on the sun-facing side of the collector. The idea of integrating trough profile on the step serration is for concentrating heat radiations with a latent heat storing copper pipe at its focal point filled with phase change material, giving tremendous improvements and high thermal and exergy efficiencies. Also, the step serrated fins increase air stagnation and heat acquisition. The performance of the SSFPT collector solar air heater is experimentally investigated and compared with the conventional Flat Plate Collector Solar Air Heater (FPC SAH) of the same collector area by natural convection. The average outlet temperature of SSFPT collector SAH and FPC SAH varies from 44.5 to 74.5 °C and 38.0–48.2 °C and the average stagnation temperature lies between 43.1 and 74.4 °C and 38.5–48.5 °C. The maximum thermal and exergy efficiency of SSFPT SAH is 66.32 % and 23.06 %. This proposed collector achieves a maximum Nusselt number of ∼ 7.11 at Rayleigh number ∼ 441.5 × 103 and a better augmenting effect with a thermo-hydraulic performance factor of 1.4 after 4 h of operational time. The thorough economic analysis yields cost per kWh of the SSFPT collector is 0.10$ which is 0.18$ lesser than conventional FPC SAH.

The Experimental Investigation of Double -Pass Solar Air Heater with V-Corrugated Plate, Phase -Change Material and Baffles Under Recycling Operation

The current paper presents an experimental work that had been implemented to observe the performance of an improved solar air heater and compared it with that of a conventional double-pass flat plate solar air heater. Improvements that have been added include the use of a V-shaped corrugated plate at an angle of 60 degrees, the addition of wood baffles in the lower pass and the use of phase-changing materials PCM as well as air recycling conditions. The heater was designed and tested under the weather conditions prevailing in the Duhok Governorate (latitude 36° 52' 1.52" N and longitude 42° 59' 18.42" E) in the Kurdistan Region of Iraq. The phase-changing material PCM is paraffin wax. The gathered results showed that the improvements that were added to the solar air heater significantly improved the performance at different mass flow values (0.037, 0.057, 0.077 kg/sec). For example, the maximum values of useful heat transfer at mass flow rates (0.037, 0.057, and 0.077kg/s) are 1.68, 1.86, and 2.34 kW, respectively, and the daily efficiency for improving and conventional heater value at mass flow rate 0.037kg/s for 15,16, and 17 of February on 2022 was (84% and 45%), (86% and 46%), and (91% and 60%), respectively.

Performance analysis of single‐pass solar air heater thermal collector with adding porous media and finned plate

AbstractThe recent study encompasses a practical inspect on adding porous material above absorber flat plate having fins to improve the effectiveness of solar air heater (SAH) collector along with forced air circulation process. The efficiency of the altered model and conventional SAH system is compared at the same time to display the impacts of adding porous material. The model that used porous material is called Model‐2, whereas the conventional SAH is called Model‐1. The measuring data is collected in January 2021 in Iraq (Mosul city). Outcomes emphasize that the effectiveness of altered model is better than traditional model by 7% for all air mass flow rates values. The highest efficiency is obtained equal 67% for Model‐2 and 60% for Model‐1 for mass flow rate 0.02 kg/s. For all mass flow rate values, a substantially change in temperature is observed in altered system as compared to traditional system, where the exhaust temperature of Model‐2 is higher than Model‐1. The improvement in the effectiveness of Model‐2 demonstrates that the employ of porous material has an extreme action on the heat exchange and subsequently heat transfer rate.