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The artificial roughnesses on absorber plate have been known to enhance the performance of the solar air heater under forced convection. The objective of this paper is to study the effect of conical pin arrangement on the heat transfer enhancement of free convective solar air heater. The conical pins were arranged in-line and in staggered arrangement with the pitch-to-height ratio of eight. The height of the conical pin was fixed at 0.2 cm. The measurement results revealed that the use of conical pin on the surface of absorber plate helped to improve the overall efficiency of the solar air heater. The staggered arrangement of the conical pins performed better compared to the case of the in-line arrangement. The performance of the solar air heater with the staggered arrangement was 42% higher than that of the flat absorber plate with no pins at 435 W/m2 while the in-line arrangement showed an increase of 28%. Hence, the use of the artificial pin roughening technique with the staggered arrangement is recommended in the free convection solar air heater.

The scientific literature extensively mentions the use of a solar air heater (SAH) by utilizing solar energy for heating purposes. The poor heat-transfer rate of an SAH with a flat plate is caused by developing a laminar sub-layer near the heated base plate. The plate temperatures improve significantly, resulting in losses and a decrease in performance. The passive approach entails the placement of fins/turbulators/pouring material/ribs to the surface where the boundary layer forms to disrupt it. Artificially roughened SAH for gathering and efficiently using solar radiations for thermal purposes is extensively described in the literature. This paper includes a thorough literature overview of the history, basics, roughness evolution, forms of SAH, and recent breakthroughs in thermal performance improvement techniques for SAH compiled by several researchers. This paper uses a comparative evaluation of several roughness geometries and kinds of SAH to uncover thermohydraulic performance factors that may be considered in future research to pick the optimal configuration.

To enhance the thermal performance of solar air heaters (SAHs), protrusion ribs on the absorber are considered to be an attractive solution due to their several advantages. These ribs do not cause a significant pressure drop in the SAH duct and help to enhance the heat transfer to flowing air. On the other hand, a degree of roughness of the protrusion rib on the absorber can be produced by pressing the indenting device without adding additional mass. In this paper, the thermo-hydraulic performances of different roughnesses of the conical protrusion rib on the absorber plate have been evaluated by the mutual consideration of thermal as well as hydraulic performance in term of net effective efficiency. Therefore, an analytical technique has been exploited to predict the characteristics of the net effective efficiency under various operating conditions, such as the flow Reynolds number, temperature increase parameter and insolation. The effects of the conical protrusion rib roughness—namely the relative rib pitch (p/e) and relative rib height e/D) in the ranges of 6–12 and 0.200–0.044, respectively—have been evaluated. The highest value of net effective efficiency of 70.92% was achieved at a p/e of 10 and e/D of 0.0289. The optimization of the rib parameters has been carried out in different ranges of temperature increase parameters for the highest values of net effective efficiency. A unique combination of rib parameters—a p/e of 10 and e/D of 0.044—are observed to lead to the best performance when operating a solar air heater with a temperature increase parameter of more than 0.00789 K·m2/W.

To investigate the solar air heater’s (SAH) effectiveness, experiments are conducted using flat plate and artificially roughened plate in terms of inclined and winglet baffles over the collector surface. This proposed system collector plate is made up of inclined and winglet ribs and serves as an artificial roughness generator. Air stream of 0.01, 0.02, and 0.03 kg/s are used in the experiment. To determine the improvement in the proposed work, these experimental results are compared with flat plate SAH. This proposed work offers a greater efficiency, useful energy gain, and lower top heat loss than a conventional SAH. At 0.03 kg/s system efficiency and useful energy gain reach their peak. Experimental day’s average efficiency of a SAH with inclined and winglet baffles is 30.8%, 52.7%, and 72.9%, respectively, for the examined cases, and it is 11%, 13.8%, and 22.2% more effective than a flat surface SAH. For the investigated air flow rates, the proposed system gains 36.2%, 24.2%, and 28.9% more energy than flat plate SAH. Substantial reductions in top losses of up to 8.48%, 7.28%, and 7.27% have been reported at the specified flow rates, respectively. Energy metrics and economic study performed show the payback time, production factor, life cycle conversion efficiency, and economic values of the proposed SAH are optimum.

In this paper, the thermo-hydraulic performance of a solar air heater (SAH) duct roughened with discrete D-shaped ribs is numerically investigated using ANSYS Fluent 2020 R . The numerical investigation is carried out at rib radius to transverse pitch ratio (r/P ) from 0.1 to 0.35 and longitudinal pitch to rib radius ratio (P /r) from 4 to 10 under various operating conditions with Reynolds number (Re) varied from 10,200 to 20,200. The numerical results are validated with previous experimental results for the Nusselt number (Nu) values, and good agreement is found with mean absolute percentage error (MAPE) of 3.6%. Based on the results of the numerical investigation, it was found that the value of Nu and the friction factor (f) decreases with the increase of the value of P /r, while the ratio r/P is kept constant. From the overall analysis, it is concluded that the optimum results are obtained for r/P of 0.25 and P /r = 4, and the maximum thermo-hydraulic performance parameter is 1.12. Further correlations are developed for the value of Nu and f for the whole range of r/P as 0.10-0.35 and P /r as 4-10. According to the developed correlations, the values of Nu are within ± 2% of the results of CFD, while the values of f are within ± 2.7% of the results of CFD.

In this present work, an exergetic efficiency of the solar air heater (SAH) with jet impingement on multiple arc protrusion roughened absorber plate is analytically studied. It is examined out for roughness parameters of relative width ratio ( W P / W AP ) of 1–5, relative height ratio ( e P / d P ) of 0.5–2, relative pitch ratio ( P P / e P ) of 8–12 and angle of arc ( α a ) of 35°–75°. Performance of SAH based on the second law has been effectively assessed by enumerating the useful exergy gain, irreversibility and losses occurred due to the inefficiency of the system components. Results indicate that the exergetic efficiency has been enhanced by 56.8%. Effects of roughness parameters on exergetic efficiency have been presented based on Reynolds number and temperature rise parameter. The optimized values of roughness parameters are identified, and the maximum exergetic efficiency is found to be 10.5%. Maximum exergetic destruction caused due to temperature difference between absorber plate and Sun is 65.2% at optimized conditions. In order to identify the optimum values of roughness parameters to attain the required temperature rise with maximum exergetic efficiency, design plots have been developed.

In this work, the thermal performance of single-pass double-duct jet plate solar air heater with various designs of artificial roughness is analyzed by developing a mathematical model. The influence of artificial roughness designs on the performance of the solar air heater is analyzed based on energy and exergy basis, and the results are compared with single-pass single-duct jet plate solar air heater. Further, year-around enviro-economic analysis is carried out for artificial roughness design providing the better performance. The results show that single-pass double-duct jet plate solar air heater with arc-shaped rib roughness produces highest energetic and exergetic efficiency. The results are compared with single-pass single-duct jet plate solar air heater in the form of energetic and exergetic efficiency enhancement ratios, annual overall energy and exergy gain and amount of carbon credit earned. The mathematical model has been validated with analytical and experimental results available in the literature with acceptable deviation. On the basis of numerical calculations, it has been concluded that single-pass double-duct jet plate solar air heater improves annual usual energy and exergy gain by 111.7% and 185.6%, respectively. Further, it reduces 2.11 times of production of CO 2 mitigation per year and enhances the revenue of annual carbon credit by 2.85 times.

An exhaustive experimental investigation was carried out for the thermal performance of artificially roughened solar air heaters (SAHs) under the actual outdoor conditions. Circular shape wire ribs have been arranged to form an arc-shape geometry on top of the absorber plates, and it has been tested for two configurations of SAHs named as arc-shape apex-downstream flow and arc-shape apex-upstream flow SAH. Roughness parameters have been taken as relative roughness pitch (P/e) in the range of 8–15 (three values), angle of attack (α) 45°–75° (three values) for fixed relative roughness height (e/D) of 0.0454, and duct width-to-duct height ratio (W/H) = 11. The range of mass flow rate (m) and Reynolds number (Re) covered during experimentation was 0.0100–0.0471 kg s−1 and 2983–13,955, respectively. Based on the experimental results, it was found that arc-shape wire with apex-upstream flow SAH is having a higher value of thermal efficiency ( ηth ), heat removal factor (FR), collector efficiency factor (F′) and duct pressure drop (ΔPD) as compared to arc-shape wire with apex-downstream flow SAH and smooth absorber plate SAH. In the range of the operating parameters investigated, the maximum ηth , FR, F′ and ΔPD have been found for e/D = 0.0454, α = 60° and P/e = 8 for m = 0.0471 kg s−1. At these conditions, apex-upstream and apex-downstream configurations enhance the thermal performance by 71.6% and 55.8% when compared with the conventional plane solar air heater.

The flow being discharged from the culvert during flood events leads to significant alterations in the topographical features of the downstream bed. These modifications, manifested as scouring, have the potential to compromise the structural integrity of the culvert. It is therefore greatly important to investigate the factors affecting the extent and the form of scouring downstream. One effective approach to minimizing flow energy, thereby mitigating downstream scour, is the implementation of artificial roughness within the culvert structure. This study examined influences of a box culvert’s longitudinal gradient on the topographical variations of the bed downstream in relation to the artificial roughness. Moreover, the outcomes derived from various slope configurations were analyzed in conjunction with scenarios where the culvert was integrated with artificial roughness components and positioned horizontally with a zero slope. A key finding of this research was that the maximum slope examined had a more significant effect on diminishing the maximum scour depth downstream of culvert than the other slopes analyzed did. By inclining the culvert bed, the maximum sedimentation height in the downstream areas was enhanced in comparison to the horizontal culvert configuration. Furthermore, the configurations incorporating an artificial roughness with a height equivalent to 0.13 times the height of the culvert opening demonstrated a significantly advantageous impact toward mitigation of the maximum scour depth. The sedimentation volume and area downstream were observed to undergo reductions in instances where the longitudinal slope of the culvert was greater, in comparison to scenarios with other slopes.

A solar air heater (SAH) is investigated experimentally by employing multi-geometry arrangements over the absorber plate. In the current work, the absorber plate is designed with rectangular ribs, slits, and cylinders. For the proposed system, this multi-geometry arrangement serves as an artificial roughness (baffles). Different airflow rates of 0.01, 0.02, 0.03, and 0.04 kg/s are used in the experiment. The results of this experiment are compared to those of a conventional SAH to assess the improvement. Compared to a conventional SAH, the proposed system has higher thermal efficiency, energy gain, and minimal top loss. The highest thermal efficiency and energy gain are observed at a mass flow rate of 0.04 kg/s. Increasing the mass flow rate increases the system’s performance. For the analyzed flow rates, the average thermal efficiency of a SAH with multi-geometry baffle is 40.8%, 58.2%, 68.2%, and 77.4%. For the same flow rates, it is 12.8%, 10.2%, 12.3%, and 13.5% higher than a conventional SAH. For the same examined air flow rates, the suggested air heater gains 31.9%, 21%, 19.2%, and 20.8% more energy than conventional SAH. Significant decreases in top losses are reported up to 8.1%, 7.3%, 7.2%, and 6.5%, respectively for the specified flow rates.