Solar Air Heater Research Articles

Modeling of Heat Transfer and Airflow Inside Evacuated Tube Collector With Heat Storage Media: Experimental Validation Powered by Artificial Neural Network

ABSTRACTSolar air heater (SAH) is a widely employed technology for harnessing solar thermal energy in numerous applications. Contemporary research optimizes designs within identical spatial constraints to maximize energy output. However, there is a recognized need to conduct analytical validation to stimulate the experimental setup and formulate an artificial neural network (ANN) model to govern and predict the operation system. This investigation involved developing and assessing an evacuated tube solar air heater (ETSAH) integrated with annulus‐filled heat storage media. Furthermore, this study introduced an ANN model and analytical solution to predict performance parameters, representing a noteworthy contribution. The proposed ANN model achieved its optimal validation performance with a mean square error of 5.4018 × 10−6 after 11 epochs within 31 of training. Also, correlation findings show that the optimal architecture of a feed‐forward backpropagation is achieved when the 5‐40‐40‐40‐2 model architecture is used. In this case, there are five neural nodes in the input layer that represent timing, temperature, radiation, and airflow rate. The power output of the ETSAH device shows a strong correlation with the flow rate, reaching its peak at 0.05 kg/s with a value of 2261 W and dropping to 368 W at 0.006 kg/s. Correspondingly, the greatest energy efficiency was measured at airflow rates of 0.05, 0.01, and 0.006 kg/s, accounting for 48.38%, 27.32%, and 19.65%, respectively.

Investigation of the impact of utilizing PCM into a coil in a single-pass air heater (experimental study)

This study aims to design, build, and assess the SAH's performance with an integrated enhanced phase-change material (PCM) absorber storage system. Using materials found locally, two single-pass solar air heaters were designed and produced for this study. The first solar heater was made without phase change material (Conventional SAH), and the second included PCM by adding paraffin wax to the coil tube (Improved SAH). In February, March, and April of 2024, real - results were carried out on the air heaters in Mosul city, Iraq. At a mass flow rate of 0.0147 kg/s, the experiments were conducted with and without a PCM system. As opposed to the first case without PCM, the study's findings indicated that the air temperature outside of the heater increased significantly in the second case with (the addition of paraffin wax). The highest recorded outlet temperatures in February, March, and April for both cases were (39.5, 50.7 °C), (49.4,58.9°C), and (57.4,70.6°C). To compare the efficiencies of the SAHs for both instances (Conventional and Improved), the efficiency of the improved SAH is higher than the efficiency of conventional SAH, such as (48.1% and 68.32 %), (58.6% and 72.8%), and (67.1% and 86.47%) in February, March, and April.

Research advances in solar dryer technologies integrated with solar air heater: a state-of-the art review on design variations, performance and feasibility assessments

Research advances in solar dryer technologies integrated with solar air heater: a state-of-the art review on design variations, performance and feasibility assessments

Experimental investigation of enhanced thermal performance of solar air collectors through optimized selection of manufacturing materials: Energy, exergy, economic, and environmental analysis

AbstractThe current study aims to experimentally investigate the thermal performance of three identical solar air collectors manufactured from three different metals: aluminum, zinc, and steel. The study conducted environmental and economic analyses of the three proposed solar air collectors over a month. The aluminum solar air collector demonstrated superior performance, achieving a maximum thermal efficiency of 24.46%, while the steel and zinc solar air collectors recorded thermal efficiencies of 21.57% and 18.16%, respectively. The exergy efficiency ranges for aluminum from 0.95% to 13.54%, zinc absorber plate exhibits from 0.63% to 11.89%, and steel from 0.6% to 9.98%. The aluminum solar air collector revealed high monthly cost savings of about $1429.6/month, followed by zinc ($1203.8) and steel ($963.4) solar air collectors. Environmental analysis to showed savings entering the atmosphere per month showed that the aluminum reduced about 19,795 kg CO2/month, Zinc solar air heat 16,668 kg CO2/month, and the steel solar air collector recorded 13,339 kg CO2/month. In this study, the absorber plate made of aluminum was the most efficient material, followed by zinc and steel. That confirms its suitability for designing efficient solar air heating systems in areas with high solar radiation intensity, such as Tunisia, and provides a clear direction for future research and development in manufacturing solar air collectors.

Experimental analysis of a solar air heater using waste mild steel chips as a sensible heat storage material.

Heat storage materials improve the utility of solar air heaters (SAHs) after sunset. This study investigates an improved solar air heater (SAH) performance with baffles and waste mild steel chips as sensible heat storage (SHS) materials. Comparative experimental natural convection heat transfer studies were performed with four different improved air heater setups under similar solar radiation conditions. These setups consist of a flat collector plate (I), a baffled plate collector (II), a flat plate collector with SHS (III) and a baffled plate collector with SHS (IV) respectively. Setups I, II, III and IV were obtained by modifying the same air heater enclosure and each experiment was replicated for three similar sunny days. During the periods, the solar radiation varied in the range of 556-934 W/m2. The maximum thermal efficiencies found for setups I, II, III and IV were 18.76%, 22.40%, 27.21% and 28.22% respectively under natural convection. The highest average useful energy rate was produced by setup IV, followed by setups III, II and I. After sunset, setups III and IV were able to deliver warm air for an extended period of 1h, 18min and 1h, 42min, respectively. It was found that setups III and IV had sensible thermal energy storage reserves of 0.38kJ and 0.53kJ, respectively. The storage efficiencies found for setups III and IV were 60.25% and 70.89%, respectively. Among the four setups, setup IV boasts the most economical energy cost at 1.39 ₹/kWh and having the least payback period of 1year 4months. As a result, the employment of baffles and waste mild steel chips as SHS in a flat plate SAH not only presents a method for harvesting waste for efficient heat retention, but it also effectively uses solar energy for beneficial uses.

Numerical investigation on the thermohydraulic performance of a solar air heater duct featuring parabolic rib turbulators on the absorber plate

Solar power is a clean and sustainable energy option, widely accessible and capable of driving the creation of more sustainable systems in the future. A specialized device called the Solar Air Heater harnesses solar energy for various applications. In the current study, a novel quadratic shape ribs affixed to the absorber plate in different orientations with a transverse pattern to the flow, and one straight side and one curved side are subjected to a compressive analysis using numerical methods. The two rib orientations are shown individually, with one side being straight and the other quadratic curve. Ansys Fluent is used to examine the impacts of a number of variables on SAH performance, including rib characteristics (pitch and height) and airflow inlet velocity. The range of Reynolds numbers used for the investigation is 3400–20000, with a rib pitch ratio ranging from 6.66 to 20. The contours of pressure, temperature, and velocity are displayed to elucidate the physics of fluid flow and heat transfer. A notable enhancement is achieved, wherein an optimized case with parabolic rib turbulator SAH and rib roughness pitch of 16.66 yields a Thermal Enhancement Ratio (TER) of 2.14.

The optimal design of airflow modes for double-layer solar air heater with perforated baffles

Abstract To further improve the thermal performance of SAH, two mathematical models of the double-layer solar air heater with perforated baffles (DSAH-PB) were established to analyze the optimal airflow modes. In Mode 1, the air flowed parallelly in the upper and lower channels; in Mode 2, the airflow in the upper channel was opposite to the airflow in the lower channel. Validation against reported data showed the models’ accuracy with a maximum relative deviation of less than 10%. Results indicated that Mode 2 achieved a collection efficiency 2.57∼4.28% higher than Mode 1, attributable to a thinner boundary layer and increased turbulence, enhancing the convective heat transfer coefficient. Comparative analysis revealed that the outlet temperatures in Mode 2’s upper and lower channels exceeded those in Mode 1 by 0.37∼ 3.67°C and 1.63∼7.48°C, respectively. Velocity distribution analysis confirmed the superior performance of Mode 2, with a more uniform velocity distribution and lower absorber plate temperature, contributing to improved thermal efficiency. The study underscored the importance of airflow distribution and channel design in optimizing SAH performance.

Heat transfer enhancement in a solar air heater utilizing novel rotating spiral baffles

Heat transfer enhancement in a solar air heater utilizing novel rotating spiral baffles

Thermal Exploration of Combined Rectangular and Semi-Circular Artificial Ribs in the Flow Regime of Solar Air Heater: A Computational and Experimental Approach

Abstract A roughened solar air heater is developed numerically and experimentally with a novel roughness in the absorber. The roughness incorporated is a combination of rectangular and semi-circular ribs. The analysis is done to improve the thermal characteristics considering two cases. Type A with ribs placed above the absorber and Type B with ribs placed below it. Several operating parameters are investigated including heat flux, Reynolds number (Re), relative obstacle relative height (h/H) ranging from 400 W/m2 to 1000 W/m2, 4000 to 10,000, and 0.4 to 1.0, respectively. The relative pitch is kept constant at 15 mm. The governing equations are simulated employing the renormalization group k–ε turbulence flow model. The results indicated that both Type A and Type B achieved significant improvements over the smooth duct. Type A exhibited a maximum Nusselt number of 4.24, while Type B achieved 3.93 in comparison with smooth duct at Re of 10,000, respectively. The thermal enhancement factor (TEF) ranges from 1.32 to 1.79 for Type A and 1.26 to 1.69 for Type B at a heat flux intensity of 1000 W/m2. Also at a relative height of 1.0, Type A demonstrated the highest TEF of 1.79 at Re = 10,000 and provided a maximum exergy efficiency of 11.2%.

Experimental investigation of heat transfer augmentation of impinging jet solar air heater with stepped transverse ribs

The current experimental investigation analyses the thermal and frictional attributes of an impinging jet solar air heater (IJSAH) with stepped transverse ribs, having varying pitch and size, affixed to the absorber plate. Two ribs of dimension 2 × 4 (R1) and 4 × 6 cm (R2) were tested. The pitch (p) between ribs was 2, 4, and 8 cm, with Reynolds number (Re) varying from 4913 to 13103. The jet hole diameter (Dj) considered were 3, 6 and 9 mm. The maximum Nusselt number (Nu) with the recommended R1 rib having p = 4 cm and Dj = 3 and 6 mm equalled 128.784 and 104.5004 at Re = 13103, respectively, which was 31.22 and 21.76 % higher than that generated by smooth IJSAH. The friction factor (f) generated by the ribbed IJSAH having Dj = 6 mm and p = 4 cm was 57.08 % lower than ribbed IJSAH with Dj = 3 mm. The peak thermohydraulic performance parameter (THPP) achieved was for R1 rib with p = 4 cm and Dj = 6 mm and equalled 1.75, which was 19.49 % higher than smooth IJSAH. The R1 rib with p = 4 cm at Re = 11465 demonstrated better thermal characteristics based on detailed investigation.

Numerical simulation of an innovative design of solar air heater using spiral duct inserts for enhancing thermal efficiency

ABSTRACT An innovative design of solar air heater (SAH) with spiral shape is numerically analyzed in this paper. The spiral-shaped SAH hydro-thermal performance is studied for different air mass flow rates using CFD COMSOL Multiphysics software. The outlet air temperature difference, thermal efficiency, flow structure, thermal field and pressure drop are the main parameters which are considered to estimate the fluid flow and heat transfer behaviors of the SAH. The simulation is realized for 1000 W/m2 of solar heat flux and 25°C of ambient temperature as typical climatic conditions in a middle day. The results show that the maximum outlet temperature difference of the SAH reached 93.08°C with 0.0083 kg/s of air mass flow rate. For the range of 0.0083–0.0332 kg/s, the thermal efficiency is varied from 91.41% to 99.01%. The ambitious percentage of the thermal efficiency of 99.01% was observed for 0.012 kg/s. The proposed design provides high thermal efficiency of SAH compared to other configurations of SAH.

Exploring nusselt number and friction factor correlations for sphere-shaped roughness elements on the absorber to enhance solar air heater efficiency

ABSTRACT This investigation is conducted to analyze the artificial surface roughness influence on the heat flow and friction characteristics within the ducts of solar air heaters (SAHs). This research aims to investigate the consequences of applying spherical-shaped surface roughness to the absorber in a linear and staggered manner with the intention of enhancing the heat transfer efficiency. The utilization of roughness elements in the shape of spheres is aimed at augmenting the heat transfer characteristics; however, it is crucial to acknowledge that this enhancement is concomitant with an elevation in pumping power due to heightened friction. An experimental campaign encom- passes a diverse set of operational and device parameters. These parameters include the Reynolds number (Re), which varies from 3,000 to 8,000. Additionally, the roughness pitch-to-height ratio (p/h) ranges from 10 to 20, while the roughness gap-to-height ratio (w/h) ranges from 4 to 8. Throughout the trials, a constant value of 0.06 is maintained for the roughness height-to-hydraulic diameter ratio (h/D) and an amount of 5 is maintained for the duct width-to-height ratio (W/H). The outcomes of this study indicate a considerable increase in the Nusselt number, ranging from 50.47% to 69.51%, concurrently with a substantial rise in the friction factor, ranging from 27.76% to 144.75%, when compared to designs using a smooth absorber surface in the context of SAHs. By utilizing the experimental data, relationships between the friction factor and the Nusselt number are established based on the artificial roughness parameters and the operating conditions. The current study’s findings significantly advance our knowledge of and ability to improve SAH systems’ heat transfer and friction characteristics. Thus, this investigation improves our understanding of these systems operational behavior in many situations.

Influence of submerged impingement jet designs on solar air collector performance

The present study experimentally investigates the solar air heater performance employing submerged impinging jets (SAHSIJ). The submerged jets produce high flow velocities, leading to significant turbulence aided by shear forces at the heated surface, resulting in increased and evenly distributed heat removal rates. The study explores the impact of geometric parameters viz jet spacing ratio (Sj/Dh) from 0.108 to 0.433, jet angles (α) from 75° to 90° jet diameter ratio (d/Dh) from 0.043 to 0.076, span-wise pitch ratio (Y/Dh) from 0.43 to 1.08 and stream wise pitch (X/Dh) from 0.43 to 1.73 on the Nusselt number and friction performance to enhance the overall efficacy of the system. To evaluate the effectiveness of the new SAHSIJ design in terms of thermal and thermo-hydraulic performance, the results are compared with those from a smooth duct solar air heater. The results show that the novel solar air heater with submerged pipe jet significantly outperforms the smooth duct solar air heater in terms of heat removal from the absorber plate. SAHSIJ achieved a thermal efficiency (ηth) of 75.3 % and a thermo-hydraulic efficiency (ηeff) of 69.2 %, with a thermo-hydraulic performance parameter (η) of 3.19.

A Mini Review of Solar Air Heater Modifications to Improve the Performance

Because solar air heaters are considered one of the most important devices, it may be possible to increase or increase the temperature that can be used in houses and buildings. Solar air heaters are used worldwide. Solar Air heaters are very cheap and easy to fabricate because they require skilled labor. Recently, several researchers have attempted to improve the thermal efficiency of solar air heater, which are presented in this review article. The work, future scope, and problems faced when working on the solar air heater have also been included for the benefit of future researchers. Keywords: Solar air heater; Thermal efficiency; Solar Energy

Impact of collector aspect ratio on the energy and exergy efficiency of a louvered fin solar air heater

Solar air heaters have huge applications in renewable energy utilization segments concerning the issues of space heating, drying, and ventilation systems. Performance prediction of such systems largely depends upon the design of the collector itself. The present study has highlighted the influence of various aspect ratios of the collector on the thermal and exergy performance of louvered finned solar or air heaters. In this context, an experimental analysis has been carried out to compare the performance of LFSAH with conventional PSAH. These results show that an increase in aspect ratios enhances thermal efficiencies of heat transfer and the systems. An aspect ratio of 4:1 showed the maximum thermal efficiencies as 81.63 % for LFSAH and 68.13 % for PSAH. On the other hand, at larger mass flow rates, the exergetic efficiency of LFSAH becomes lower owing to the larger friction and exergy losses and sometimes even lower than that of PSAH. The novelties of the present study are in emphasizing the importance of aspect ratio in optimizing solar air heater design and providing relevant insight for better energy use.

Twisted tapes in solar chimney-earth air heat exchangers for equipment downsizing and passive cooling

Harnessing solar and geothermal energy in hot and arid climates is an effective strategy to reduce building energy consumption. This research investigates integrating Twisted Tapes (TT) into Earth Air Heat Exchanger (EAHE) pipes within a Solar Chimney (SC)-EAHE system, aiming to reduce EAHE pipe length while meeting ventilation requirements and decreasing cooling demand. Two key innovations are introduced: first, this study pioneers the integration of TT into a SC-EAHE system; second, it comprehensively explores TT geometry optimization, analyzing the effects of width ratio and rotation rate across 77 configurations. Numerical simulations are conducted in ANSYS Fluent using the k-ε RNG turbulence model to investigate thermal performance and airflow characteristics. Findings reveal that TT integration results in a 153 % increase in Nusselt number. Additionally, it is shown that a 1 m SC diameter achieves ventilation of 4.8 Air Changes per Hour (ACH) using TT with a width ratio and rotation rate of 0.5, while reducing EAHE pipe length by 2.6 %. Increasing the SC diameter to 1.25 m, with a TT width ratio of 0.6 and rotation rate of 1.25, leads to a 13 % (35 m) reduction in EAHE pipe length while meeting a minimum outlet temperature of 290.15 K and ACH requirements. However, the benefit diminishes beyond a 1.25 m SC diameter. This study contributes to understanding of integrating TT into SC-EAHE systems, addressing the critical need for sustainable energy solutions and offering a novel and energy-efficient approach for passive cooling in extreme climates.

Renewable energy as an auxiliary to heat pumps: Performance evaluation of hybrid solar-geothermal-systems

The aim of this study is to combine renewable energy sources with heat pumps so that the usage of electricity needed to operate heat pumps is minimized along with associated fuel combustion. The aforementioned objective leads to reduce the energy consumption, the operational cost and the environmental impact of the heat pump. To minimize the usage of electricity, it is proposed that the heat pump (HP) system is combined by two renewable energy systems, a Solar Air Heater (SAH) and a Geothermal Well Water (G). To enrich this study, five prospective combinations of Heat Pump (HP), Solar Air Heater (SAH) placed Upstream (U) and Downstream (D) of the condenser, and Geothermal Water Well (G) were investigated. Hereafter, these five combinations are referred as HP-G, HP-S-U, HP-S-D, HP-G-S-U and HP-G-S-D. The thermal modeling of the aforementioned combinations in addition to baseline HP were developed and examined using an in-house computational code. To ensure that the input data used in the computational code are reliable, experiments were conducted to validate that the geothermal water temperature is higher than the ambient temperature in winter, in addition to confirming the analytical thermal modeling of the solar air heater. Numerical analyses and associated parametric studies revealed that the combination of Solar Air Heater (SAH) and a Geothermal Well Water (G) can efficiently increase the performance of the system by reducing the power needed to operate the compressor of HP. The gain in COP was found to be 48, 43, 81, 105 and 191 % for HP-G, HP-S-U, HP-S-D, HP-G-S-U and HP-G-S-D respectively. In addition, results revealed that the most efficient system is the (HP-G-S-D) for all simulated conditions and assumptions with a gain in COP that can reach up to 191 % in comparison to the baseline heat pump system.

Numerical and experimental investigation of heat transfer of longitudinal fin with varying pitch length in flat plate solar air heater

Solar energy is a promising clean energy alternative, and consequently, the novel and innovative applications of solar energy in day-to-day life are expected to rise in the near future. The reason for limited applications of solar air heaters is their low thermal efficiency. This is due to inadequate heat transfer from the absorber plate to the air (working fluid). It has done various experiments with different pitch lengths and recorded the efficiencies corresponding to various pitch lengths. Numerical and Experimental Investigation of heat transfer of longitudinal fin with varying number of pitch length (1–5) in a flat plate solar air heater to improve the rate of heat transmission, thin and lengthy fins have been put underneath the absorber plate. The fin was intended to be square. The investigation included two different fluid masses at rates of 0.0252 and 0.10 kg/s with two distinct Reynolds numbers, 627.46 and 26585.55. The goal of the present study is to get an understanding of the effects of variations in air flow rate on the outlet temperature, heat transfer through the solar collector's thickness, and overall thermal efficiency. It has done a CFD simulation on Ansys to verify the experimental results with the simulation results.

Experimental study on thermal performance of reverse flow solar collector for dual heating applications

AbstractThe present study investigated the performance of dual function reverse flow solar collector (RFSC). The impact of the mass flow rate of air and water on outlet temperature, thermal performance, and overall performance of dual‐function solar air heater (SAH) has also been investigated. An experimental investigation of three different working models namely, Model‐A: SAH, Model‐B: solar water heater (SWH), and Model‐C: integrated solar air‐water heater (SAWH) for dual heating applications was performed to analyze the actual performance of these models. The investigation of the impact of time intervals on the water inlet and outlet temperatures at various mass flow rates of water is conducted to analyze the time‐varying efficiency of SWH systems. Furthermore, the effect of solar intensity on the performance of the dual‐function heating system has also been explained. The result reveals that the maximum thermal efficiency of Models: A and B can be achieved at about 78.8% and 67.9%, at a mass flow rate of 0.0644 and 0.10 kg/s, respectively, according to the experimental findings. The maximum temperature rise of air and water reaches about 52.4 and 55.58°C for Models A and B, respectively. The total efficiency of Model C reaches 81.69%, exceeding that obtained in Models A and B individually. The efficiency, outlet temperature of the fluid, and heat transfer effectiveness of the system strongly depend on the mass flow rate. The increase in heat removal factor is negligible for a higher flow rate (more than 0.10 kg/s).

Heat transfer and fluid flow analysis of a solar air heater using conical jet impingement with sine-wave corrugation on absorber plate

In the pursuit of renewable energy solutions, solar air heaters emerge as a promising technology to efficiently harness solar thermal energy for diverse applications such as space heating, agricultural drying and industrial process heating. However, the system’s efficiency is often limited by the low heat transfer capability of air and the formation of laminar sub-layer over the absorber plate. This study addresses the issue by investigating the innovative use of conical jet impingement combined with sine wave corrugations on the absorber plate to enhance heat transfer in solar air heaters. The design parameters include wave amplitude ratio (0.079–0.314), throat jet diameter ratio (0.063–0.141), base jet diameter ratio (0.126–0.251), and Reynolds number (3200–19200) as the operational parameter. The computational fluid dynamics simulations are employed to solve the Reynolds-Averaged Navier-Stokes equations coupled with RNG k-ɛ turbulence model to assess the heat transfer and frictional characteristics, followed by experimental validation. The findings demonstrate a significant improvement in the system’s heat transfer rate with the Nusselt number increase by a factor of 6.71 times compared to a smooth solar air heater, while the friction factor increase by 13.87 times. Furthermore, the highest thermo-hydraulic performance parameter is found to be 2.79 corresponding to Reynolds number of 3200, wave amplitude ratio of 0.079, throat and base jet diameter ratios of 0.126 and 0.220, respectively. The proposed geometry will be helpful for academic researchers and can be adopted by the industries for various applications.