Absorber Plate Research Articles

Numerical investigation of heat transfer augmentation of solar air heater with attached and detached trapezoidal ribs

The solar air heater has a low heat transfer coefficient due to the development of a laminar sublayer inside the channel of the solar collector. Adding artificial roughness or ribs to the surface of the wall of the absorber plate is an effective and promising method to increase heat transfer by interrupting the laminar sublayer. In this study, a trapezoidal rib was used to enhance the thermal performance of the solar air heater. The characteristics of flow and heat transfer were numerically analyzed using a RNG k-ɛ turbulent model based on the Reynolds number range of 5000, 10000, 15000, 20000, 25000, and 30000. Eight different types of trapezoidal ribs, arranged in shapes that increase in height towards or against the direction of flow, were studied. Four case studies included a solar collector with attached trapezoidal ribs, while another four case studies included a solar collector with detached trapezoidal ribs. The current research involved validation of the results compared to the previously obtained results and showed good acceptable agreement. The results demonstrated that the best thermal performance ratio of the solar collector was achieved when the ribs were attached and detached to the inner surface of a wall, with an increase in the height of the trapezoidal ribs in the opposite direction of the airflow for all ribs. However, these cases resulted in the highest coefficient of friction ratio. On the other hand, the thermal performance was at its lowest level in the cases where the increase in the height of the attached or detached trapezoidal ribs is in the direction of the airflow.

Relationship between midfacial fractures and maxillary sinus pathology.

Midfacial fractures frequently involve the maxillary sinus, leading to maxillary sinus pathology. We aimed to examine the incidence and contributing factors of maxillary sinus pathology in patients who underwent open reduction and internal fixation (ORIF) for midfacial fractures. A retrospective analysis was conducted on patients who underwent ORIF for midfacial fractures at our department over the past 10 years. The incidence of maxillary sinus pathology was identified clinically and/or by computed tomography findings. Factors that significantly influenced the groups with and without maxillary sinus pathology were examined. The incidence of maxillary sinus pathology in patients who underwent ORIF for midfacial fractures was found to be 11.27%, with sinusitis being the most common pathology. Maxillary sinus pathology was significantly associated with the presence of a blowout fracture involving both the medial and the inferior orbital walls. Factors such as sex, age, diabetes mellitus, hypertension, smoking, inflammatory disease, follow-up period, use of absorbable plates, and use of titanium plates did not have a significant impact on the development of maxillary sinus pathology. The incidence of maxillary sinus pathology in patients who underwent ORIF for midfacial fractures was relatively low, and in most cases, it resolved without the need for specific treatment. Consequently, there may not be a significant need for concern regarding postoperative maxillary sinus pathology.

Experimental and transient CFD analysis of parallel-flow solar air collectors with paraffin-filled recyclable aluminum cans as latent heat energy storage unit

In the present study, it is aimed to improve the overall performance of a parallel-flow solar air collector (PSC) using phase change material (PCM)-based latent heat energy storage unit and recyclable materials. In the simulation part of this work, two PSCs including a collector without modification and a collector equipped with PCM filled aluminum cans have been analyzed. The simulation part of the current work is handling the flow of air through the collectors and melting-solidification of PCM material inside the aluminum cans. Considering the simulation study results, three different PSC configurations have been manufactured including an unmodified PSC, a PSC with PCM-filled aluminum cans on the front side of the absorber and a PSC with PCM-filled aluminum cans on both sides (back and front) of the absorber surface. According to the results of the analyses, utilizing PCM-filled aluminum cans in both surfaces of the absorber plate of the PSC improved numerically and experimentally obtained exergetic efficiency values as 61.70% and 74.03%, respectively. Moreover, enviro-economic analysis has been conducted within the scope of this work. The payback periods of the analyzed systems were between 2.17 and 2.43 years. Employing PCM in the both sides of the absorber surface decreased the payback time of the system as 10.69% in comparison to the conventional PSC. Moreover, using PCMs on the single and double side of the absorber plate improved the annual carbon dioxide savings as 22.68% and 35.42%, respectively.

Parametric optimization of hybrid artificial roughness used in solar air heaters using multiple criteria decision making techniques

Solar air heaters (SAHs) are widely accepted and used for drying and heating purposes. Numerous methodologies are available for augmentation of the performance of a SAH but the application of artificial roughness underside the absorber plate is reported to bean efficient one. This study aims to present the effects of using hybrid artificial roughness combining the transverse ribs along with discrete inclined ribs, on the thermo-hydraulic performance of roughened SAH. The response surface methodology (RSM) is utilized for the design of experiments to investigate the influence of relative roughness height (0.018 ≤ e/ D ≤ 0.036), relative roughness pitch (5 ≤ p/ e ≤ 15), attack angle (45° ≤ α ≤ 75°), and Reynolds number (1,900 ≤ Re ≤ 20,300) as input parameters. The empirical equations are developed for Nusselt number, friction factor, and thermo-hydraulic performance parameter based on the regression analysis. An integrated analytical hierarchy process-based weighted aggregated sum product assessment (AHP-WASPAS) method is used to evaluate an optimal parametric combination ( e/ D = 0.036, p/ e = 15, α = 75°, and Re = 20,300). The results are supported by the corresponding experimental outcomes. Also, the sensitivity analysis and rank reversal tests performed as qualitative assessment procedures for the results obtained from the proposed strategy. The proposed decision framework is reported to be very sensitive to several criteria weight fluctuations with maximum and least deviations of 15.41% and 2.56% for δWjp = +50% and δWjp = −10%, respectively. Further, the obtained results confirm the robustness of aopted decisional scheme with just one rank reversal.

Experimental Thermal Performance of Phase Change Material Embedded Solar Air Heater Employing Impinging Stable Air Jet Array Presenting High Power and Energy Density

Abstract This experimental thermal performance investigation presents that the hot air at a significantly high temperature, and simultaneously at high power density and energy density of phase change material (PCM) can be obtained utilizing a novel design of PCM embedded solar air heater employing impinging stable air jet array. Investigation is carried out following two main objectives, i.e., to obtain (i) instant and (ii) long thermal backups. In the reported design configuration, impinging stable air jets on absorber plate are obtained by reducing the flow path of expelled air from upstream air jets that increased the heat transfer rate to air and consequently instant thermal backup. Although, the use of wavy PCM unit provides instant and long thermal backup by increasing heat transfer area that augments the heat transfer to air and the collection of solar radiations, respectively. Moreover, the present study is extended as follows, (i) the use of shutter on glass cover to increase thermal performance during nocturnal hours, (ii) charging of PCM till the maximum solar radiation hours and use of the stored energy during nocturnal hours, (iii) thermal performance analysis to reveal instant thermal backup, (iv) thermal performance investigation during variable weather conditions, and (v) thermal performance investigation for low ambient air temperature. The obtained results revealed that for the unit collector area, significant thermal backup of about 6 h at a temperature rise of ≥5 °C can be obtained by utilizing the above-mentioned provisions in this research.

Optimisation of thermohydraulic performance of triangular duct solar air heater with alternative dimple shaped protrusion and intrusion on the absorber plate

An innovation is made in solar air heaters to enhance their performance by introducing artificial roughness on absorber plates using alternative dimple intrusions and protrusions. To improve the performance of the air heater, one of the effective techniques is roughness. Roughness is introduced on the heat-absorbing side in the form of ribs. A CFD (computational fluid dynamics) model has been used to simulate the heat augmentation and flow characteristics caused by dimple ribbed through the triangular passaged SAH. The simulations were conducted through modelling and designing the SAH. For a range of Reynolds number (Re) (4000–17700), the analysis considers two roughness parameters, Z/e, Z’/e and X/e by maintaining the height of relative roughness of 3 to 7, respectively. Compared with conventional air heaters, better heat transfer augmentation (1-16-8.27%) is observed in the modified air heater with ribs. Due to the addition of artificial ribs, maximum Nu (38.63 – 96.5%) is observed in the case of Z/e = X/e = 18. Also, the TPP (thermohydraulic performance parameter) has a maximum value of 2.01%.

Performance analysis of a serrated absorber plate solar air heater with paraffin wax storage.

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

Exploring the performance of a novel solar water heater by combining three augmentation approaches (nanofluids, absorber roughness, and surface coating)

Three unique approaches were adopted in this research first for the solar water heater (SWH), a surface-modified (resurfacing) absorber plate was manufactured through the steel shot-blasting approach. Furthermore, the naturally acquired activated carbon nanomaterials (ACNMs) have been synthesized and the same was employed as nanofluids (NFDs) and coating material on the absorber plate through the spray painting. Also, ACNMs and water, (DIW) based nanofluids were synthesized using the double-step methodology and applied as heat transfer medium (HTM). In addition, the thermal properties of DIW-ACNM such as ratios of thermal conductivity (TC), specific heat, viscosity, and density were measured experimentally and colloidal stability of NFDs was also ensured through zeta potential and SEM analysis. The temperature difference of the HTM across the SWH was recorded as 7.5, 9.8, 10.6, and 12.04 °C at 0, 0.1, 0.25, and 0.4 vol % of ACNMs loading respectively. The thermal efficiency of modified SWH was increased up to 52.7% with a volume fraction of 0.4% despite a proliferation in pressure drop and pumping power by 23.5 and 22.1% respectively. Overall, combining ACNM as an NFD and coating material along with shot-blasting on the absorber plate had excellent improvement in the SWH performance with a performance augmentation factor of 1.14.

Heat transfer and air flow friction in solar air heaters: A comprehensive computational and experimental investigation with wire-roughened absorber plate

This research focuses on the purpose and importance of studying the impact of physical factors on heat transfer and air flow patterns in a solar air heater (SAH) with wire-shaped roughness on the absorbers rectangle conduit. By understanding these factors, we can enhance the radiation absorption effectiveness of solar collectors. To investigate the effects of artificial roughness arrangement on SAH efficiency, we developed an experimental apparatus. The experiments involved determining the allowable ranges of dimensionless factors such as relative wire roughness height (h/D), relative roughness wire pitch (p/h), and the angle of approach of flow (α). Additionally, we considered the Reynolds number (Re) and the duct width to height ratio (W/H) during the development of computer program code for optimization. By comparing experimental findings with those obtained from a smooth duct under similar flow circumstances, we evaluated the improved heat transfer and friction factor. Notably, for specific parameters such as W/H = 5, h/D = 0.01, p/h = 40, and α = 50◦, the average Stanton number (Stav) was found to be 1.196 times higher than that of a smooth SAH duct. Similarly, the average friction factor (fav) was observed to be 1.044 times higher than that of a smooth SAH duct. At p/h = 40 and h/D = 0.01, the average air friction factor and average Stanton number are the lowest for Reynolds number 3000. These numbers have the best efficiency index, which is 1.148. The research findings have implications for optimizing solar air heaters by incorporating wire-shaped roughness on the absorbers conduit. This enhances heat transfer and overall performance, leading to more efficient solar collectors with positive environmental and economic impacts through increased energy efficiency and reduced reliance on non-renewable energy sources.

Chemical reaction on Unsteady MHD Convection Flow of Second grade fluid over an unbounded perpendicular absorbent plate

ABSTRACT We discuss in this paper the chemical reaction impacts on complimentary convectively flow of the gelatinous secondary graded fluid past a countless vertical porous plate underneath the effects of uniform transversal magnetic field. Time reliant penetrability as well as fluctuating suction are also explored. The prevailing equations are resolved with the regular perturbation method for the small amplitudes of the permeability. The solutions for the velocities, temperature as well as concentrations have been obtained computationally; in addition, behaviour is also explored. The skin fiction, the Nusselts number as well as Sherwood numbers are also found in addition to those behaviour computationally conferred. It is concluded that the velocity is reduced with enhancement in the intensity of the magnetic field and Prandtl number whereas it is enhanced by the ever-increasing thermal Grashofs number. The magnitude of the temperature of the flow field diminished with increase in the Prandtl number, heat source parameter. The concentration of the flow field is reduced by a rise into the Schmidt number and chemical reaction parameters.

Enhancement of heat transfer utilizing small height twisted tape flat plate solar heat collector: A numerical study

The flat plate solar heat collector captures solar thermal energy for agricultural drying, heating houses and businesses, cooling food, and producing steam. Adding twisted tape inserts to the absorbent surface of a flat plate solar heat collector increases its efficiency. This article describes the absorber plate of twisted tape inserts and discusses the thermal and hydraulic performance achieved by varying the twist pitch and twist height. Computational fluid dynamics is performed for Reynolds numbers ranging from 5000 to 17000, relative twist height (TH/Dh) of 0.011-0.044, relative twisted tape inserts pitch (PTT/TH) of 49.95-73.2 and relative twist pitch (TP/TH) of 8-15. Heat transmission and friction factors owing to twisted tape inserts have been analyzed in depth using computational fluid dynamics, with analysis performed using the k-epsilon model in commercial ANSYS Fluent 19.2 software. A maximum thermal-hydraulic performance value of 2.41 is observed for the many twisted tape parameters, with, TH/Dh of 0.022, PTT/TH of 64.60, and TP/TH of 12.

Enhancing the performance of a solar air heater by employing the broken V-shaped ribs.

This work aims to enhance the performance of a solar air heater (SAH) by introducing broken V-ribs as roughness elements on the absorber plate. The unit with a conventional flat absorber plate is referred to as the "FSAH," while the unit with a broken V-rib-shaped absorber plate is called the "VSAH." The experiment was performed for three air velocities: 25 m/s, 20 m/s, and 15 m/s and the corresponding air flow rates were 0.037 kg/s, 0.031 kg/s, and 0.023 kg/s, respectively. The results showed that the maximum temperature was experienced on the absorber plate, followed by the glass plate for both SAHs. Overall, the average absorber and glass plate temperatures of the VSAH were 0.6-1.4 °C and 0.4-1.9 °C lower than those of the FSAH. Compared to the FSAH, the experimental results showed that the VSAH experienced useful power and thermal efficiency that were 16.6-19.8% and 15.7-20.4% higher, respectively, while the top surface heat losses were found to decrease by 2.1-8.1%. Due to the disrupted air paths in the VSAH, the observed pressure drop was 113.3-133.3% higher than that of the FSAH. More impotently, the thermo-hydraulic performance factor was always higher 1 and the observed values were 1.48, 1.39, and 1.24 at the va (velocity)values of 15, 20, and 25 m/s, respectively. Therefore, the proposed VSAH had an admirable thermal performance as compared to FSAH. Further, optimization through varying the roughness parameters, namely, relative blockage width (W/w), relative pitch ratio (P/e), number of baffles (n), relative blockage height (e/H), and angle of attack (β) could helped to achieve better performance.

Design procedure of stationary compound parabolic concentrator with flat plate absorber for effective year-round performance – Response Surface Methodology and Tracepro as tools

The stationary Compound Parabolic Concentrators (CPC) with a low concentration ratio (C<2) are suitable for pre-heating processes in industrial applications. The reported literature does not analyze the radiation available or the solar angles for whole year towards design of CPC which could provide maximum annual energy. This paper optimizes the design factors of CPC, such as acceptance half-angle (θa) and truncation ratio (TR), to yield maximum energy around the year, maximize optical efficiency and minimize reflector material. Annual irradiation data for the location - Tiruchirappalli, Tamilnadu, India (ϕ- 10°45′36″ N) is considered for the present study. The raw irradiation data is processed to get monthly average daily data, which is used as input for the TracePro v21.1. The experimental design (DOE) is made in response surface methodology (RSM) by considering the factors of θa - 18.5 to 28.5° and TR - 0.5 to 1.0. Nine Geometric models were created using Solidworks based on the combination of parameters given by RSM and simulated using TracePro to estimate the annual energy collection and average optical efficiency. Using the TracePro analysis month wise energy collection is calculated and reported. Further, a model relating θa and TR to the annual energy collected was obtained. According to the results obtained from the multi-objective optimization, the optimum concentration ratio is 2 with the θa of 28.5° without truncation. The results also indicate that the deviation from the average energy collected by the optimized design over the year is less when compared to the other designs.

A Critical Review of All Mathematical Models Developed for Solar Air Heater Analysis

In this paper, three mathematical models to predict the air collector temperature are reviewed and analyzed. These three models were drawn from 30 publications between 1980 and 2022. The models include lumped model (model 1), a one-dimensional (1D) steady model (model 2), and 1D unsteady model (model 3). The models are established based on the energy balance of the heat exchanger surfaces and the airflow. Solution techniques for models are presented using a system of linear equations, numerical integral, and finite difference method. The results of the sensitivity analysis of the models indicate that the temperatures of the air exiting the collector are similar. Model 3 considers the thickness of the glass cover, absorber plate, and bottom plate thus having the effect of thermal inertia in the morning and afternoon. The maximum difference of outlet air temperature between models 1 and 2 is 0.18 K. The highest outlet air temperature deviation of 0.77 K between models 1 and 3 occurred at 8 AM. When the thicknesses are negligible, the temperature distribution along the air collector of models 2 and 3 is the same. In other words, model 3 should be used when there is the presence of the thickness of the plates and the glass cover.

Hybrid thermal and optical modeling of a solar air heater with a non-flat plate absorber

In this study, we developed a model based on a SAH. We can enhance air turbulence by creating a non-flat plate on a SAH absorber using a ratio of (e/H = 6), thereby increasing the solar collector’s convective heat transfer coefficient, Nusselt number, and thermal performance. A validation experiment was conducted to determine the accuracy of the developed model. Ray tracing and FEM simulation techniques were used to analyze the optical and thermal properties of the system simultaneously. Various operational and structural conditions were applied to analyze the system’s thermal performance under inhomogeneous heat flux on the absorber’s surface. The data demonstrate that non-flat plate surfaces contribute to wall-induced turbulence, which affects air temperatures. Outcomes demonstrate that mass flow rate excessively affects thermal efficiency, useful energy, and outlet temperatures. Thus, when the inlet air flow rate increases from 0.02 to 0.06 kg/s, the average hot air temperature at the SAC outlet during the daytime reduces from 55.6 to 47.82 °C, applicable heat energy increase from 646.5 to 970 W, and the average thermal efficiency increased from 28.8 to 54.7 %. Instantaneous non-flat absorber plates increased average thermal efficiency and heat transfer coefficient (h) to 9.10 and 27.24 % compared with flat plate absorbers (e/H = 1) at the same mass flow rate (0.05 kg/s). The highest Nusselt number increase observed during the day is 141.5% for non-flat plate compared to flat plates.

Investigation of Thermo-Hydraulic Performances of Artificial Ribs Mounted in a Rectangular Duct

This research investigates the fluid flow characterization and thermohydraulic performances (THP) of rib surfaces, using computational and experimental methods. ANSYS computational fluid dynamics (CFD) software was used to predict and validate the findings in the experimental setup. Artificial rib surfaces, including polygonal and forward trapezoidal-shaped ribs, were placed in the absorber plate at different relative pitch distances (p/e) = 6.7, 10, 13.4 and relative height (e/d) = 20, and the mass flow rate of air (working fluid) varied at Reynolds numbers ranging from 2000 to 20,000. According to the validation results, the RNG renormalization k-ε model was selected for the investigation. The results show that strong turbulence occured closer to the wall surface and behind the rib surface, enhancing thermal performances due to the sharp edge shape of the rib. A polygonal rib with a pitch distance of p/e = 6.7 achieved a higher Nusselt number (Nu) and thermohydraulic performance of 2.95 at Re 4000. An empirical correlation between the Nusselt number (Nu) and friction factor (f) was developed using linear regression analysis and was compared with the predicted values. The comparison results show a close range of ±8% between the experimental and predicted values.

Design and evaluation of a modified basin-type stepped solar- still under Malaysia climate conditions

ABSTRACT Distillation represents one of the earliest methods of treating water, and it remains as such in many parts of the world. A basin-type stepped solar-still remains the simplest desalination technology. It is simple, easy to construct, requires minimal maintenance, and is cost-effective. The objectives of this study were to design, fabricate and evaluate the performance of a modified stepped solar-still. The theoretical analysis was conducted to determine the optimum design of the still. The productivity and solar-still efficiency were obtained by solving the energy balance equations for the absorber plate, saline water, and glass cover, the temperature difference between saline water and the glass cover, and evaporation, convective, and radiative heat transfer coefficients under the climate of Malaysia. The experimental setup was constructed, and experiments were conducted at the Universiti Kebangsaan Malaysia (UKM), Selangor (Latitude 2°56‘22“North and Longitude 101°47’16” East). The basin area of the stepped solar-still was 1.m2 (0.5 m × 2.0 m). The basin of the still was constructed from a black-painted galvanized steel sheet to increase the absorptivity. The cover of the still was made up of glass. The absorber plate of the stepped still consisted of 5 steps (0.1 m × 2 m). The stepped solar-still has been modified to include external and internal reflectors, fins, and an external condenser. The performance of the modified stepped solar-still design has been investigated and compared with the unmodified stepped solar-still. The theoretical results show a significant improvement in the performance of the modified stepped solar-still. The productivity was higher than that for stepped solar-still before modification by approximately 29% under the same climate conditions. The experimental results have shown that the maximum temperature of saline water and glass cover were 62.1°C and 56.2°C, respectively. The maximum distillate water in the still was 6.10 kg/m2. The daily efficiency of the modified stepped solar-still was approximately 52.3%. Based on the experimental and theoretical results, the proposed design significantly enhanced the stepped solar-still thermal performance. A statistical t-test was conducted to establish the significance of the difference in the stepped solar-still experimental. It was found that there was a significant improvement in the stepped solar-still performance after modification. The techno-economic analysis showed that the product cost would be around USD0.07 per liter of distillate.

Control of Mandibular Width With 3D Printed Occlusal Splint in Children With Multiple Mandibular Fractures.

The fracture of mandibular symphysis combined with bilateral condylar fractures often leads to changes in the width of the mandible, which significantly widens the face of the child. Therefore, it is necessary to reposition the mandible through accurate adduction. To ensure that the mandible can be accurately repositioned, a 3D printed occlusal splint was used. Bilateral maxillomandibular fixation screws were implanted. The 3D printed occlusal splint was located on the maxillary dentition and fixed to the maxillomandibular fixation screws with wire loops. The reference basis for adduction is to make the mandibular dentition located in the occlusal splint. The absorbable plate was contoured according to the restored model and fixed at the fracture site. The 3D printed occlusal splint was retained in the maxillary dentition for two months. Postoperative computed tomography showed that the mandible had been adducted according to the preoperative design. Two months of follow-up showed that the child's facial development, mouth opening type, occlusion, and range of motion were good. It is especially suitable for children with mandibular symphyseal fractures accompanied by bilateral condylar fractures.

Performance prediction of aluminum and polycarbonate solar stills with air cavity using an optimized neural network model by golden jackal optimizer

Solar stills (SS) are simple eco-friendly desalination devices that exploit solar energy to obtain freshwater from seawater. In this study, a hybrid artificial intelligence model is proposed to predict the thermal behavior of two designs of SSs. Two SSs with a basin and absorber plate made of aluminum for the first SS (ALSS)and polycarbonate for the second SS (PCSS) were established and tested. Both SSs have a modified absorber plate with an air cavity. The hybrid model was composed of an optimized Artificial Neural Network (ANN) model by Golden Jackal Optimizer (GJO). To prove the capability of the proposed model to predict the SSs performance, it was compared with the conventional ANN model as well as two other optimized models with Genetic Algorithm (GA) or Particle Swarm Optimizer (PSO). The results showed that ANN-GJO had better accuracy than ANN, ANN-GA, and ANN-PSO to predict overall heat transfer coefficient, energy efficiency, exergy efficiency, and distillate output. Moreover, ALSS showed better thermal performance compared with PCSS regarding water productivity, exergy efficiency, and energy efficiency. The average exergy efficiency and energy efficiency of PCSS and ALSS were 2.30%, 42.40%, and 3.44%, 48.80%, respectively. The maximum distillate output for PCSS and ALSS were 3.40 l/m2/day and 3.80 l/m2/day, respectively.

A comparative experimental performance evaluation of solar air collector having absorber plate with convex oval-trench dimple

A comparative experimental performance evaluation of solar air collector having absorber plate with convex oval-trench dimple