Solar Air Collector Research Articles

Drying of Nettle Using Concentrated Air Collector and Concentrated Photovoltaic Thermal Supported Drying System and Modeling with Machine Learning

This study examines the performance of a solar assisted drying system in the nettle drying process. The drying process works by using thermal energy obtained from solar air collectors and PV modules. The experimental were carried out in October 2022, and the room temperature, total efficiency and moisture content parameters were investigated. The data obtained from the drying system were modelled using machine learning algorithms such as artificial neural networks (ANN), support vector machines (SVM), and gradient boosting decision trees (GBDT). The average thermal energy transferred to the drying cabin was calculated as 154 W, with 77% of this energy was obtained from the air collector and the remaining 23% from the PV module. The stinging nettle was dried from an initial moisture content of 11.18 g water/g dry matter to a final moisture content of 1.18 g water/g dry matter. The average total efficiency of the drying system was found to be 16.8%. Additionally, the results show that the SVM algorithm exhibits the best performance in estimating important parameters such as chamber temperature, moisture content, and total efficiency. Especially in total efficiency prediction. The SVM algorithm has a significant advantage over other algorithms. As a result, it was concluded that the SVM algorithm can be used effectively utilized in solar energy-supported drying systems and can be a precious choice for the optimization of the drying process.

Improving the performance of a PCM integrated solar air collector by adding porous fins over the bottom side of the absorber: A transient CFD study

In this study, it is aimed to improve the utilization time period of a solar air collector by integrating a PCM unit. In this context, a PCM unit was integrated to a single-pass solar air collector. Additionally, porous fins were added into the PCM unit in order to shorten PCM melting time. Thus, six different solar collectors were designed and numerically analyzed by adding a storage unit and fins to the collector. A collector without storage and five PCM added collectors with different number of porous fins were studied. In other words, the effect of integrating PCM container and adding porous fins inside the PCM container on various parameters such as utilization time period of the collector, outlet temperature, thermal efficiency and exergy efficiency were investigated. The ANSYS Fluent program was used in numerical analyses. As a result, integrating the PCM unit to the analyzed air collector caused to extend utilization time period of the collector. Adding porous fins into the PCM unit has resulted in a significant increase in the overall performance of the system. In addition, increasing the number of porous fins accelerated the melting process of paraffin. Increasing the number of porous fins was significantly improved average energy efficiency. Average thermal efficiency of the tested collectors was obtained between 38.66 and 41.73 %. In general, as a result of numerical analysis of six different systems, the utilization time was increased by adding the PCM unit to the solar air collector. Moreover, placing porous fins inside the PCM unit increased the performance of the system by accelerating the melting of the paraffin.

Design and thermal performance evaluation of the thermal storage layer of a solar air collector with comprehensive consideration of six factors of phase-change materials

The heat storage layer of fully filled phase-change materials (PCM) does not melt completely, and this significantly reduces the heat storage capacity, heat-release time, output temperature difference, collection efficiency, heat peak migration ability, and PCM cost of PCM-based solar air collectors (SACs), thereby affecting the comprehensive heating requirements of building households. To solve these problems and obtain the optimal filling rate for PCM, four PCM filling schemes were designed with comprehensive consideration of the six factors of PCM. (Type I is a SAC filled with 0 % PCM, Type II is the upper portion filled with 25 % PCM, Type III is the upper portion filled with 50 % PCM, and Type IV is filled with 100 % PCM). Four models were constructed for comparative experiments. A comparative analysis of the thermal performance evaluation indices indicated that the phase-change heat storage process of the Type III thermal storage layer only uses 1.25 h to store 1.505 × 106 J of heat energy, thus indicating that Type III possesses a better heat storage capacity. The max-output temperature difference of the Type III collector decreased by 20.1 °C compared to that of Type I. This indicates that Type III collectors can balance the range of output temperatures and increase indoor thermal comfort. After the solar energy ceases, the continuous heat-release time of the Type III collector is 13.75 h, and the ratio of its heat-release time to non-solar time is 94.83 %. This indicates that Type III possesses a better heat release time. The daily average heat collection efficiency of Type III filled was 37.77 %, and this was only 6.72 % higher than that of Type IV, thus indicating that Type III exhibited better heat peak migration ability, PCM utilisation efficiency, and lower PCM cost.

Heat transfer and friction factor correlation for rhombus-shaped roughness geometry on the absorber plate of solar air collector

Heat transfer and friction factor correlation for rhombus-shaped roughness geometry on the absorber plate of solar air collector

2D numerical analysis of pentagonal ribbed solar air collector for an indirect solar dryer and the proposal of optimized pitch

The present work aimed to improve the thermo-hydraulic performance of a solar air collector (SAC) by installing pentagonal ribs (as roughness elements) on its absorber surface. Such ribs were not investigated yet hence this study is innovative. A 2D computational analysis was performed using ANSYS Fluent (v 15). The rib roughness height (e) was kept at 10 mm. The Reynolds number, Re (4000–22000), and rib pitch, P (25–200 mm) were the input variables. Nusselt number (Nu), friction factor (f), and thermo-hydraulic parameter (pth ) were the output parameters. RNG k-ε model was picked for turbulence. The peak Nu ratio obtained was 2.49 and it proved that pentagonal ribs enhanced the heat transfer characteristics 2.49 times than the smooth plate. Also, a 60–149% improvement in Nu was noticed with corrugated SAC compared to that of smooth SAC. For a given P, The f value decreased with a rise in the Re value. The maximum pth range (1.533–1.828) was obtained at P/e = 2.5 (continuous pitch). Hence, the optimum P is 25 mm (P/e = 2.5). The numerical results of the pentagonal corrugated absorber plate were compared with the existing literature and were found to be acceptable.

A Comprehensive Review of the Thermohydraulic Improvement Potentials in Solar Air Heaters through an Energy and Exergy Analysis

Supply disruptions, uncertainty, and unprecedented price rises of fossil fuels due to the recent pandemic and war have highlighted the importance of using renewable sources to meet energy demands. Solar air collectors (SACs) are major types of solar energy systems that can be utilized for space and water heating, drying, and thermal energy storage. Although there is sufficient documentation on the thermal analyses of SACs, no comprehensive reviews of the exergetic performance or qualitative insight on heat conversion are available. The primary objective of this article is to provide a comprehensive review on the optimum conditions at which the thermal performance of diverse types of solar air collectors is optimized. The effect of operating parameters such as temperature rise, flow rate, geometric parameters, solar radiation, and the Reynolds number on the thermal performance of SACs in terms of thermal hydraulic performance, energy, and exergy efficiencies has been reviewed adaptively. Beyond the operating parameters, a deep investigation is outlined to monitor fluid dynamics using analytical and computational fluid dynamics (CFDs) methodologies in the technology of SACs. In the third phase, thermodynamic irreversibility due to optical losses, thermal losses between absorber and environment, heat losses due to insulation, edge losses, and entropy generation are reported and discussed, which serve as the fundamental tools for optimization purposes.

Investigative analysis of the influence of diverse fin configurations on the performance of a dual pass solar air collector

This study conducts a thorough investigation into the thermal performance of the double pass solar air collector, with a specific focus on the effects of three distinct fin configurations: parallel, vertical, and opposed. It is significant as it delves into the realm of solar air heating efficiency, a critical component in the broader application of solar energy technologies. Utilizing the geometric details and experimental findings, this study broadens its scope by examining a range of mass flow rates, specifically 0.0036 kg/s, 0.0110 kg/s, 0.0146 kg/s, and 0.0183 kg/s. Such an approach allows for a comprehensive understanding of the double pass solar air collector’s performance across diverse operational scenarios. The methodology is Computational Fluid Dynamics, which facilitates an in-depth analysis of temperature and velocity contours in both XY and YZ planes of the double pass solar air collector. The results of this study indicate that the parallel fin configuration significantly enhances heat transfer, evidenced by notable temperature increases, especially at the lower end of the mass flow rate spectrum. Conversely, while vertical and opposed fins result in greater pressure drops, they do not proportionally increase the temperature in a similar manner to parallel fins. The study concludes with a strong recommendation for the incorporation of parallel fins in future double pass solar air collector designs, particularly in situations where lower mass flow rates are predominant. This study contributes significantly to both the theoretical and practical aspects of solar collector efficiency, offering valuable insights for the development of more effective solar heating solutions.

Simulation model of a flat plate air solar collector

Simulation model of a flat plate air solar collector

Drying of the orange slices, and energetic analysis of the drying chamber alimented by a solar air collector for extraction of the water from an orange slice

This study is focused on the extraction of water from sliced oranges through the process of solar drying, while also integrating an energy analysis of the drying chamber, which is powered by a solar air collector for the water extraction process. The experimental investigation encompasses various parameters, including the dimensions of the drying chamber, the solar collector, and the geometry of the orange slices (with a diameter D of 80 mm and thicknesses of ep = 3 mm and 5 mm). The results present the moisture ratio of the orange slices over the drying time and mass flow rate, with three different values (0.019, 0.024, and 0.033 kg/s). Throughout the experiments, the distance between the product support and the drying chamber's heat source was maintained at 140 mm. The report provides an energetic analysis that encompasses the enthalpy of the product, water, vapor, drying chamber, solar collector, and latent heat, all contributing to the control of the drying system. The effects of different mass flow rates (0.019, 0.024, and 0.033 kg/s) on the drying process are also examined in this study, with a focus on the important effects on the moisture ratio and drying velocity. Ultimately, the findings demonstrate that the mass flow rate plays a crucial role in determining the outlet temperature of the solar collector and the inlet temperature of the drying chamber, thereby affecting the kinetics of the drying process and the resulting moisture ratio.

Energy, exergy and economic investigation of novel hybrid dryer, indirect solar dryer and traditional shade drying

By integrating a secondary energy source into solar dryers, more moisture can be removed from food products in the same time period. For this purpose, tomato slices of different thicknesses (7 mm, 15 mm and quarter size) were dried to see the drying, energy, exergy and economic performance of an innovative hybrid dryer consisting of an indirect solar dryer and geothermal heat exchanger unit. The hybrid dryer’s performance was compared simultaneously with indirect solar dryer and traditional shade drying. The analyzes were evaluated according to the feeding of drying air from the solar air collector and geothermal heat exchanger unit. Compared to the other two dryers, the hybrid dryer dried the 7 mm, 15 mm and quarter size samples in the earliest time, with an average of 1380, 2476.3 and 2397.3 min, respectively. The average highest specific moisture extraction rate (0.87 kg/kWh) and dryer efficiency (45.25 %) and the lowest specific energy consumption (4.75 kWh/kg) for hybrid dryer were obtained for the 15 mm. The highest exergy efficiency for the solar air collector and drying chamber of the hybrid dryer was determined at 7 mm with 3.08 % and 38.9 %, respectively. The lowest payback period for the hybrid dryer was found to be 0.37 years for 7 mm. The results showed that the hybrid dryer was superior to the other two dryers by drying continuously day and night. Hybrid dryer can create a successful commercial ecosystem as an important drying alternative for locations where geothermal energy is available.

Numerical analysis of pentagonal ribbed absorber plate of solar air collector in an indirect solar dryer for enhanced performance

ABSTRACT A 2D analysis of the solar air collector of an indirect solar dryer with pentagonal corrugation on the absorber plate was carried out using ANSYS Fluent 16.0 to enhance the performance. SIMPLE algorithm and RNG k-ε model were used for resolving the governing expressions. Corrugation pitch (p), height (e), angle (α) and Reynolds number (Re) were considered as design parameters for the analysis. The p was varied from 50 to 175 mm and an optimized p value was proposed. The Re range used was 1800 15,000. The velocity, velocity vector, and turbulent kinetic energy were presented. Performance characteristics such as Nusselt number (Nu), friction factor (f), Nu ratio, f ratio and thermo-hydraulic performance parameter (T hpp ) were determined and compared for different p and Re. The Nu ratio obtained was 1.81–2.88 and it was proved that corrugation gives a maximum of 2.88 times heat transfer enhancement than a flat plate. Maximum T hpp was found to be 1.748 and was obtained at p = 150 mm and low Re (1800). The proposed optimum pitch was 150 mm (relative roughness pitch, p/e of 15). The outcomes of the present analysis were validated with existing publications and found that the results are comparable.

Prediction of jet impingement solar thermal air collector thermohydraulic performance using soft computing techniques

Solar thermal air collectors are economically efficient for the purpose of heating air in specific applications. This research examines the efficiency of a solar thermal air collector called a jet impingement solar thermal air collector (JISTAC) that is fitted with discrete multi-arc-shaped ribs (DMASRs) utilizing soft computing techniques. Linear Regression (LR), M5P, Gaussian Process (GP), and Random Forest (RF) are used to predict the Nusselt number (Nu), friction factor (f), and thermohydraulic performance (ηthp) of JISTAC. DMASRs absorber plates with different relative rib height (0.025–0.047), relative discrete width (0.32–1.72), arc angle (35°–65°), relative discrete distance (0.27–0.86), and relative rib pitch (0.58–3.1) were used. The tests yielded 245 data sets, with 173 assigned for training and 72 for soft computing testing. The GP surpasses other models in performance owing to its minimum error and maximum correlation coefficient value. The GP model has a MAE of 0.0347, a RMSE of 0.0564, a RAE of 10.88%, a RRSE of 12.77%, and a CC value of 0.9920. Furthermore, it has a model efficiency of 99%, making it the most prominent among the other models. The results indicate that the GP model is quite precise in predicting the ηthp of JISTAC.

Enhancing thermo-hydraulic performance of solar air collectors through three-dimensional airflow using novel artificial roughness designs

BackgroundThe solar air collectors involve exploring their design, efficiency, and performance attributes. Common challenges include addressing issues such as small convective heat transfer coefficients between the air and the absorber, which can result to higher absorber plate temperatures and heightened thermal losses. Through the incorporation of artificial roughness onto the collector plate with a suitable design, it is possible to disrupt the shear layer and improve the convective coefficient. MethodsThis study focuses on hydrodynamic and thermal analyses to identify optimal chicane shapes and arrangements, such as CTPrism, CRRec, and CR, planted on the bottom wall of a solar air collector. Thermo-hydraulic performances are investigated using comprehensive CFD simulations, validated by experimental data and comparing them to smooth ducts. Significant findingsIn this work, a novel hydrodynamic and thermal analysis is introduced, demonstrating that the utilization of (CTPrism) shapes arranged in a staggered configuration leads to a significant enhancement of 68 % in heat transfer and 95 % in turbulent intensity. Consequently, there is an improvement in thermo-hydraulic performance, reaching up to 2.39, while still maintaining moderate friction losses.

An experimental investigation of the thermal performance of solar collectors utilizing finned aluminum can pipes

An innovative experimental study is presented to improve the performance of solar collectors designed for solar drying systems, focusing on the use of recycled aluminum can waste and the development of the air solar collector. The latter’s absorber is made up of 10 cans with a diameter of 65 mm, a length of 160 mm and a thickness of 0.3 mm, forming a cylindrical finned pipe. Several collector configurations under identical weather conditions, including four collectors with different rows of rods (4, 8, 12–14 rows) and a single collector, were analyzed and compared. The thermal performance of this new collector model was assessed on the basis of solar fluxes and collector inlet and outlet temperatures, collected during the month of September 2021. Experimental results revealed that this collector can increase the outlet temperature of air from 32°C up to 130°C, in the case of a 14-row collector. The study also showed that, at low flow rates, the can-equipped collector achieves an efficiency of 54% for the case of a 14-row collector, compared with 34% for the simple case, representing a 20% improvement over the single case. The study also showed that, at low flow rates, the can-equipped collector achieves higher outlet temperatures.

Performance investigation of a novel flat-plate solar air collector with L-shaped dual micro heat pipe arrays

To improve the thermal performance of solar air collectors by reducing heat leakage and fully transporting the heat absorbed in the evaporation section, this paper proposes a structural innovation based on previous research, that is, L-shaped dual micro heat pipe arrays integrated with a flat-plate solar air collector with a double glazing cover. Experiments are conducted to investigate the thermal performance of the proposed collector. The effects of solar irradiation, ambient temperature, and air flow rate on thermal performance are reported. Thermal resistance is analyzed theoretically. The application performance of the collector is evaluated based on a typical rural building heating model. The results show that the average heat collection efficiency is 49.72 %, 55.69 %, 59.37 %, and 61.48 % for air flow rates of 80, 120, 160, and 200 m3/h, respectively. The evaporation section temperature is reduced by a maximum of 25.28 °C under flow rates of 200 m3/h. The performance of the solar collector is more significantly influenced by solar irradiance than by ambient temperature. The average thermal efficiency is linearly related to the normalized temperature difference. The CO2 reduction over the lifetime of the device is 15040.09, 19287.80, and 5662.95 kg compared with the use of conventional bulk coal, electricity, and natural gas, respectively.

Development of an optimal mechanism for a solar-air collector for drying thermolabile products

The article presents theoretical and experimental studies about the alternative construction of energy-efficient solar air collector that generates heat based on alternative energy sources for the drying process of agricultural products. In particular, the geographical latitude of the place (φ), the angle of elevation of the sun to the horizon (h°), the angle of deviation of the sun (δ), and τ the interrelationships between the sun’s hour angles (τ) were studied. The patterns of changes in the wet air and dry air parameters entering the solar air collector were analyzed. The mechanism of efficient use of the heat generated in the solar air collector was developed. The kinetics of the process of drying spices at low temperature was studied.B NNBB. 1

Investigation of a Photovoltaic–Thermal Solar Dryer System with Double-Pass Solar Air Collectors and Absorber Surfaces Enhanced with Graphene Nanoparticles

As a result of increasing energy demand, seeking eco-friendly and sustainable energy resources increases the interest in renewable energy, specifically solar energy. In this study, a novel photovoltaic–thermal solar dryer system with double-pass solar air collectors and nano-enhanced absorber surface was developed, and its performance was experimentally investigated. Initially, a double-pass solar dryer (DPSD) with an absorber surface of flexible aluminum ducts coated with black matte paint was produced. Then, a double-pass solar dryer (NDPSD) consisting of flexible aluminum ducts coated with graphene and black paint was designed. These two systems were experimentally and simultaneously examined, and parameters such as energy and exergy efficiency, drying rate, and moisture ratio, which are the performance indicators of solar air collectors and the drying process, were analyzed. The sustainability parameters were also considered as a part of the analysis. The mean thermal efficiency of the solar air collectors for DPSD and NDPSD was calculated as 57.23 and 73.36%, respectively, where the airflow rates were measured as 0.024 and 0.017 kg/s. Furthermore, under the same airflow rate conditions, while the mean exergy efficiency of the collector was 27.77% for NDPSD, it was calculated as 16.64% for DPSD. Moreover, exergy efficiencies of the drying chamber varied between 27.35% and 82.20% for NDPSD and between 21.03 and 81.25% for DPSD, under the airflow rates of 0.012–0.016 kg/s conditions, respectively.

A MATLAB simulation-based analytical study of energy, exergy, and cost benefits in jet-impinged protrusion-roughened double pass solar air collector.

This study analyzes the performance and cost-effectiveness of a protrusion-roughened jet-impinged double-pass solar air collector (PRJDPSAC) within a Reynolds number (Re) range of 2500 to 22,500. Examining jet slot parameters, i.e., the jet height ratio (Hjp/Dhd = 0.11-0.44), stream-wise pitch ratio (Xjp/Dhd = 0.44-1.32), and span-wise pitch ratio (Yjp/Dhd = 0.44-1.32), the model demonstrates enhanced energy conversion, minimizes losses, improves efficiency, and brings positive economic impact, making it a promising solution for diverse applications including drying processes, livestock facilities, remote accommodations, and HVAC system pre-heating. The examination incorporates advanced MATLAB simulations to assess energy-exergy performance and cost viability. At lower Re values, both energy ([Formula: see text]) and exergy ([Formula: see text]) efficiencies increase uniformly; however, stabilization and decline occur at higher Re values. The maximum [Formula: see text] for the PRJDPSAC is 4.38% under a temperature rise parameter of 60 × 10-3 Km2/W for obtaining optimum values of Xjp/Dhd = 1.32, Hjp/Dhd = 0.22, and Yjp/Dhd = 1.32, which is 31% higher than that of the smooth double-pass solar air collector (DPSAC). Economic benefits are significant for PRJDPSAC within mair (0.01-0.07kg/s), but above 0.07kg/s, the DPSAC becomes more cost-effective. Integrating simulation and experimental data, the study highlights MATLAB's effectiveness for solar energy system analysis and optimization, reinforcing the practicality of the proposed collector design.

Development of a novel solar dryer with an incorporated heat exchanger

This study analyzes the thermal performance of an indirect-type solar dryer incorporated with a heat exchanger to recover heat from the exhaust. Data were recorded for 8 h from 9:00 to 17:00 from November to January to determine the drying rate for varying airflows from 2 l/s to 12 l/s under the weather conditions of Nepal and Bhutan. The air temperatures in multiple locations in the dryer were recorded and logged for 30-second intervals. The results indicated that incorporating a simple heat exchanger can achieve 78 % and 81 % effectiveness for the lowest tested airflow of 2.5 l/s and 2 l/s in Nepal and Bhutan. The heat transfer effectiveness increases with decreasing flow, resulting in a higher cold side outlet temperature of the heat exchanger for lower airflows. The solar air collector demonstrated efficient performance, achieving 80 % and 90 % efficiencies for the highest tested airflows of 12 l/s and 10 l/s in Nepal and Bhutan, respectively. Due to an increased heat transfer coefficient, the incoming air can effectively remove the accumulated heat from the absorber plate for higher airflows. The drying rates were observed to be the highest for 12 l/s, with a value of 85 g/(h × m2) for apples and 10 l/s, with a value of 56 g/(h × m2) for gingers in Nepal and Bhutan, respectively. From both cases, it can be concluded that the highest tested airflows provide higher air circulation for effective heat and mass transfer from the product to the surrounding air for drying.

Thermal and effective assessment of solar thermal air collector with roughened absorber surface: an analytical examination

Abstract The current work analyses the thermal (ηth) and effective efficiency (${\eta}_{\mathrm{eff}}$) of a solar thermal air collector (STAC) that has an arc-shaped dimple as a roughness geometry on the absorber plate. Nusselt number (Nu) and friction factor (ff) were computed for roughness geometry during the testing, which was done on STAC. Additionally, for different roughness values, the correlations for Nu and ff were developed and further used in this study. The temperature rise parameter and a parametric design are used to assess these efficiencies. The influence of design variables on STAC performance is analyzed using a numerical model based on thermal and effective evaluations. During the investigation, parameters such as relative roughness height (e/Dh) varied from 0.021 to 0.036, relative roughness pitch (p/e) from 10 to 20, arc angle (α) from 45 to 60°, temperature rise parameter from 0.003 to 0.02 and Reynolds number (Re) from 3000 to 48 000 at a constant solar intensity (I = 1000 W/m2). The ηth and ${\eta}_{\mathrm{eff}}$ are observed to be 85% and 78%, respectively, at the optimum values of roughness parameters, i.e. e/Dh = 0.036, p/e = 10, and α = 60°. The curves have been plotted between each of the roughness parameters and Re in order to evaluate the best ηth and ${\eta}_{\mathrm{eff}}$ . The research emphasizes the usefulness of MATLAB for STAC analysis and optimization, roughness parameters of the suggested collector design, by integrating simulation and experimental data.