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The porous absorber in the solar air heater gives considerable temperature increment which is shown by
computational fluid dynamic simulation and verified experimentally. Experimental analysis on porous (wire
screen) and non-porous solar air heaters were carried out to study the heat transfer and friction factor characteristics.
The analysis encomp...
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... center was set to fine. All the simulations then performed with hexahedral fine mesh relevance 100 with 495,157 numbers of elements and 113,280 numbers of nodes. The solution converging criteria for continuity equation is set to 1e−04 and for energy equation it is set to 1e−06. Hexahedral fine mesh structure with relevance 100 is shown in Fig. ...
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... variation in the outlet temperature and temperature difference was studied at different inlet conditions as shown in Fig. 12. On in- creasing the mass flow rate from 0.02 kg/s to 0.05 kg/s, the temperature difference decreases. The temperature increment in porous absorber was more compared to non-porous absorber. The heat transfer rate is more in porous absorber than that of non-porous. Increase in solar radiation increases the outlet temperature. The ...
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... for both the matrix air heaters. The readings were taken for several times and random error was calculated for accuracy of results. It ranged from 15 ± 0.16 Pa to 17 ± 0.28 Pa for WSM-I and from 7 ± 0.28 Pa to 11 ± 0.28 Pa for WSM-II. In the conventional type flat plate air solar heater it ranged from 5 ± 0.20 Pa to 10 ± 0.28 Pa as shown in Fig. 20. Since the pressure drop is insignificant the friction losses may not account to much rise in pumping power. The pressure drop didn't differ much on increasing the mass flow rate. So it can be extracted from the experimental studies that solar air heaters can be operated between 0.02 kg/s and 0.05 kg/s for better thermal performance ...
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... transfer characteristic is presented in terms of colburn J h factor. Colburn J h factor decreased with increasing Reynolds number and increased with increasing pitch to diameter ratio as shown in Fig. 21. It can be explained that at lower p t /d w values, there are vortex created in the wires that restricts the fluid flow circulation. For larger values of p t /d w the vortex sheds and eventually increases the heat transfer ( Prasad et al., 2009). In the packed bed though the friction losses are supposed to be less, investigation on ...
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... and eventually increases the heat transfer ( Prasad et al., 2009). In the packed bed though the friction losses are supposed to be less, investigation on friction factor helps to optimize the geometric parameters. Friction factor is calculated by using the pressure drop across the duct. The effect of Reynolds number on friction factor is shown in Fig. 21. The friction factor decreased with increasing Reynolds number and increased with decreasing pitch to diameter ...
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Solar air heater has shown a huge interest in the past few years trying to make developments to enhance its overall performance. Such systems are being used in many applications such as crop drying and space heating aiming to get the most benefit of solar energy and to reduce pollution in the environment. Performance of solar air heater is measured...
Citations
... Results reveals that a circular constructed hole required less pumping power than slitlike perforations. Rajarajeswari et al. [30] Perforated absorber plates in combination with packed wire mesh layers enhanced the air retaining time and the rate of heat transfer to the air. Found a 20 % increase in thermal efficiency for the highest mass flow rate of 0.055 kg/s and a maximum pressure drop penalty of 17 Pa. ...
... These efficiencies indicate the effectiveness of the SD system in utilizing solar energy for drying purposes. Rajarajeswari et al. [18] investigated the impact of incorporating porous wire mesh with varying porosities along the length of a singlepass SAH. The experimental results revealed that the inclusion of the wire mesh had a positive effect on the thermal efficiency of the SAH thereby leading to an increment in its thermal efficiency by 5 to 20 % when utilizing MFRs ranging from 0.01 to 0.055 kg/s. ...
The shelf life of food products can be increased by reducing their moisture content with the aid of solar dryers. However, the poor efficiency of solar collectors increases the time and energy required for drying the food crops. Hence, the present work aims to overcome the above bottleneck by employing corrugated shot-blasted absorbers in solar air heaters and comparing their performance with flat plate solar air heaters. Subsequently, the drying kinetics of bitter gourd and tapioca cassava were subject to experimental investigation using indirect solar dryers in their natural mode, aiming to assess the dryers' overall performance. The experiments revealed that the average thermal efficiencies of the SAHs equipped with flat plate absorber plates and corrugation with shot-blasted absorber plate treatment displayed variations ranging from 39.05 to 53.12 % while maintaining a constant MFR of 0.02 kg/s. The average exergy efficiency of the FPAP is 1.103 % and the CSB absorber plate is 1.755 % with a constant flow rate of 0.02 kg/s. The research findings indicate that the CSBAP (surface-improved SAH) demonstrates a higher heat-absorbing capacity when compared to the FPAP SAH. The utilization of the CSBAP design along with the incorporation of pebble stone results in a greater ability to efficiently absorb and retain heat when compared to the traditional FPAP design with a shot-blasted surface. The inclusion of pebble stones in the drying process, as observed in Case II for Tapioca cassava, led to a remarkable improvement in drying efficiency by approximately 36 % when compared to Case I. Furthermore, the drying efficiency for bitter gourd in Case IV experienced a notable improvement of around 30 % when pebble stones were integrated into the drying process, in contrast to Case III. Eventually, the experimental results specified that the carbon credits accrued for the CO 2 mitigated by the FPAP and CSBAP systems in the natural convection mode were calculated to be approximately 226.48 and 308.11 Rate $/year, respectively. These alterations synergistically contribute to enhancing the SAH's effectiveness and effectively utilizing solar heat directly contributes to reducing greenhouse gas emissions and, subsequently, the carbon footprint.
... In addition, Fudholi et al. [73] examined a hybrid SAC with delta-corrugated plate and achieved SI value as 1.148. Fig. 13 demonstrates a comparison between the efficiency enhancement rates of this work with similar studies available in the literature [14,20,46,69,[74][75][76][77][78][79][80][81][82][83][84][85][86][87]. The ratios given in the figure show how much the thermal efficiency of the new collector design obtained with different modifications has been increased compared to the conventional system. ...
In the current article, it is intended to improve the performance of an unglazed solar air collector using mesh tubes as extended heat transfer surfaces and nano-enhanced black paint as a thermal conductivity booster of the absorber coating material. In this regard, three types of unglazed solar air collectors have been designed, produced and simultaneously tested containing a conventional (unmodified) system, a system with only mesh tube modification and a system with combined usage of mesh tubes and nano-enhanced absorber coating. It should be stated that Fe3O4 nanoparticles have been utilized within the scope of this work. Integrating nanoparticles to the absorber coating material (industrial matt black paint) averagely improved the thermal conductivity as 0.031 W/mK. The experimental process was tested at fixed air flow rate (0.0115 kg/s) in winter climatic conditions. As result of the experimental analysis, average thermal efficiency values were attained between 45.11-63.36%. Combined usage of mesh tubes and nano-enhanced black paint upgraded the mean thermal performance as 40.45% in comparison to the unmodified system. Also, obtained exergetic efficiencies are in the range of 5.49-9.96%. In addition to the energy-exergy analysis, enviro-economic survey was performed within the scope of the current work. Payback periods of the analyzed systems were found between 0.31-0.34 years.
... Fig. 18 presents a comparison of thermal efficiency enhancement in the present work with similar studies available in the literature. The given studies investigate SC systems with different types of configurations such as multi-pass flow channels [77,[79][80][81], grooved/corrugated absorber surfaces [82][83][84][85][86], turbulators [87], fins [88][89][90], baffles [91][92][93], solar tracking systems [94], jet impingement [95,96], packed bed and porous materials [97][98][99], nano-enhanced absorber coating [100] and other types of geometrical configurations [101][102][103][104]. Efficiency was improved in the current study by using a nano-enhanced absorber coating in tests carried out at lower and higher flow rates, respectively, by 16.79% and 11.05%. Additionally, the thermal efficiency was increased by 46% by the use of a nano-enhanced absorber coating in combination with increased flow rates. ...
Solar air heating systems are extensively applied in different applications in order to provide hot air using clean energy. In this study, a spiral type solar collector has been proposed, numerically simulated and manufactured. The main aim of this work is investigating the overall performance of a solar collector with spiral type absorber. In the first stage of this work, CFD approach has been used for simulating unbaffled and baffled spiral solar collector. Numerical findings exhibited better thermal performance of the baffled spiral collector. Therefore, in the following step of this survey, baffled spiral collector has been fabricated and experimentally analyzed at different conditions. In addition, ceria nanoparticles have been used in coating process of spiral-formed absorber plate of the system to upgrade the thermal efficiency. Mean thermal efficiency for spiral collector with and without nano-coating was obtained between 46.15 and 67.39%. Mean efficiency enhancement by using ceria nanoparticle coating in the tests made at 0.009 and 0.014 kg/s are 16.79% and 11.05%, respectively. Also, average exergy efficiency of spiral collector was achieved between 10.28 and 14.46%. Average sustainability index of spiral collector was gained in the range of 1.1151–1.1698. The overall findings of this study indicated successful utilization of the developed spiral type solar collector. Moreover, using ceria nanoparticle coating has significant positive effects on improving thermal efficiency of spiral collector. It can be concluded that the developed spiral type solar collector could be used in building integrated applications for providing fresh and heated air.
... The increasing number of porous blocks can significantly enhance the heat transfer. Rajarajeswari et al. [25] numerically and experimentally investigated the fluid flow in porous and non-porous solar air heaters. A considerable temperature rise generated in a flat-plate solar air heater by using porous media. ...
A novel structure design of porous media-assisted thermal performance enhancement of a flat-plate solar collector (FPSC) is proposed in this study. The thermal performance of FPSC is numerically investigated. The porous substrate with a porous cavity structure is mounted on the upper absorber plate to promote the flow thermal mixing. Meanwhile, the chamfered structure design of porous cavity is proposed and tested for reducing the fluid flow resistance to further intensify the thermal performance of FPSC. The effects of the cavity number (N), cavity depth (HD), inlet mass flow rate (ṁ), Darcy number (Da), and chamfered cavity design on thermal performance of FPSC are compared and analyzed. The ranges of above parameters are N = 1-3, HD = 4-8 mm, ṁ = 0.024-0.072 kg/s, Da = 10-5-10-2, and R = 0.03 m, respectively. Both the Darcy-Brinkman-Forchheimer extended model and the energy equation based on local thermal equilibrium (LTE) model are used to describe the thermo-flow fields in porous media zones. The numerical results show that the more amount of porous cavity can significantly improve the thermal performance of FPSC, especially at a high permeability. PEC increases by a maximum value of 49.57% when the cavity number ranges from 1 to 3. The increment ratio of PEC also markedly ascends with increasing of permeability. Due to the chamfered cavity structure, the global Nusselt number increases, the friction factor reduces, and thus the better PEC value has been achieved. PEC increases by a maximum value of 12.5% compared with non-chamfered designs.
... In addition, Fudholi et al. [73] examined a hybrid SAC with delta-corrugated plate and achieved SI value as 1.148. Fig. 13 demonstrates a comparison between the efficiency enhancement rates of this work with similar studies available in the literature [14,20,46,69,[74][75][76][77][78][79][80][81][82][83][84][85][86][87]. The ratios given in the figure show how much the thermal efficiency of the new collector design obtained with different modifications has been increased compared to the conventional system. ...
... The maximum efficiency in thermal heat was found to be 91.93% with V-coregulated SAH. Rajarajeswari et al. (2018) worked on porous and nonporous SAH, studying the effect of Nusselt number and friction characteristics with two wire screen matrixes (WSM). The increment in efficiency in the thermal domain for WSM type 1 and WSM type 2 were reported between 5 to 17% for the first case and 5 to 20% for the second case, respectively, for the flow of fluid changing from 0.01 kg/s up to 0.055 kg/s. ...
... The present computational methodology using the Rosseland radiation model is validated with the experimental results of Rajarajeswari et al. (2018). To ensure the correctness of the computational methodology, the reference geometry of the smooth duct from Rajarajeswari et al. (2018) is considered for validation. ...
... The present computational methodology using the Rosseland radiation model is validated with the experimental results of Rajarajeswari et al. (2018). To ensure the correctness of the computational methodology, the reference geometry of the smooth duct from Rajarajeswari et al. (2018) is considered for validation. The test duct length of 2000 mm, duct height of 120 mm, and width of 900 mm are used. ...
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.
... Perforated absorber plate with packing wire mesh layers increased the air retention time and improved heat transfer rate. Rajarajeswari et al. [30]] carried out experimental and numerical studies using wire mesh with various pitch values and diameters. For the highest mass flow rate of 0.055 kg/s authors observed 20% higher thermal efficiency with a maximum pressure drop penalty of 17 Pa. ...
In the present work, a rectangular aluminium absorber duct with perforations on the upper surface is placed inside the glazed solar air heater duct. Numerical analysis is carried out to study its influence on thermo-hydraulic performance. The absorber duct insert absorbs the radiation heat by inducing turbulence across the flow path due to the presence of perforations. The upper and lower passages are varied in terms of height ratio so as to create a pressure differential between them which generates a crossflow phenomenon. The perforation hole diameter and number of rows of holes are varied, and the flow physics is analysed. Results indicated that perforated configuration showed significantly higher thermo hydraulic efficiency than the plain configuration. A duct height ratio of 0.667, two row configuration with a hole diameter of 5 mm showed maximum performance with the values of thermal and thermo-hydraulic efficiency being 83.01% and 87.06% respectively.
... The author addressed that the practical solution combines porous supports and PCMs to fabricate shape-stabilized phase change materials. Rajarajeswari et al. (2018) suggested and conducted the experimental analysis on porous and non-porous SAH for the heat transfer and frictional factor characteristics. The result reveals that better performance is achieved at a mass flow rate range of 0.02-0.055 ...
Phase change materials (PCMs) are suitable for various solar energy systems for prolonged heat energy retaining, as solar radiation is sporadic and is unavailable during the nighttime. Though during the non-availability of solar radiation at night time, the PCMs can regain the stored heat energy. This review article focuses on the emerging techniques in PCMs application in various solar energy systems. It discusses the recent areas where PCMs are essential in solar energy systems like solar thermal power plants, solar desalination, solar cooker, solar air heater, and solar water heater. Even though the availability and cost of PCMs are complex and high, the PCMs are used in most solar energy methods due to their significant technical parameters improvisation. Thus, the paper endeavour to impart current innovative methods by the investigators throughout the globe on PCMs applications in renewable solar energy in ideal categorized form. This review's detailed findings paved the way for future recommendations and methods for the investigators to carry work for further system developments
... Modelleme sürecinin önemli aşaması uygun bir radyasyon modeli uygulamaktır. Analiz çalışmasında radyasyon yoğunluğunu hesaplamak, akış ve ısı transferinin çeşitlerini birleştirmek için DO (Discrete Ordinates) radyasyon modeli ve Güneş Işını Takip (Solar Ray Tracing) alt modeli kullanılmıştır [20]. ...
