Rib Pitch Research Articles

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.

On the applicability limits of the structurally orthotropic shell model in problems of calculating the buckling under axial compression of waffle cylindrical shells

The article considers the solution of the buckling problem of a waffle cylindrical shell under axial compression using the Euler (bifurcation) approach. Two models are used: a model based on the numerical integration method and a model based on the finite element method. The first model assumes that the stiffeners are structurally an orthotropic shell obeying the Kirchhoff-Love hypotheses, with the assumption of "smearing". The second model uses a tetrahedron element with ten nodes. The study is based on experimental data from tests of one of the waffle cylindrical shell samples under axial compression. The research results show that with an increase in the waffle shell rib thickness, a discrepancy between the calculation results of the two models is observed. With the optimal value of the k parameter, characterizing the ratio of the rib thickness to the rib pitch, equal to 0.035, such a discrepancy is estimated to be about 5%. At the same time, the calculation using the model of a structurally orthotropic shell leads to an underestimation of the critical load compared to the finite element model. This provides an estimate of the loss of stability of a waffle cylindrical shell with a safety margin. For parameter k between 0.02 and 0.05, the difference between the results from the two computational models for critical loads does not exceed 11%.

Prediction of thermal efficiency of double pass solar air heater having discrete multi V and staggered ribs

AbstractThis manuscript endeavors to elucidate a comprehensive analysis for the assessment of thermal efficiency in double pass solar air collectors augmented with fabricated roughness, instrumental in the generation of heated air for applications in heating and drying. The analytical procedure delineates comparisons between a smooth and a double‐sided, roughened absorber, characterized by discrete, multi V and staggered configurations of roughness. The analysis was performed for different roughness parameters including relative roughness width (W/w) from 4 to 8 and relative staggered rib size (r/e) from 1 to 4 and relative rib pitch (p′/p) from 0.2 to 0.8 while other parameters were kept constant. The research scrutinizes the impact of a constellation of parameters: the temperature rise coefficient (ΔT/I, varying between 0.002 and 0.02 K‐m²/W), Reynolds number (Re, spanning 2000–20,000), solar irradiance (I, ranging from 600 to 1000 W/m²), and the geometric variables of the artificial roughness, on both the thermal efficiency and efficiency enhancement factor of the collector. The study revealed that the roughened collector exhibits higher thermal efficiency compared to smooth collector for a similar condition. The extreme enhancement in thermal efficiency of the collector with roughness has been found to be 56.75% more than nonroughened collector for Re = 2000. A further observation was made that thermal efficiency has increased sharply for lower flow rate (Re < 10,000) whereas for higher flow rates (Re > 10,000), this increase becomes nearly asymptotic. In addition, the efficiency enhancement factor has also been found to increase with an increase in ΔT/I. A peak value of 2.321 has been found to be obtained for the efficiency enhancement factor for ΔT/I = 0.02 K‐m2/W and I = 1000 W/m2 as a result of the studies conducted.

Energy Efficient Downsizing of Ribbed Confinements for Heat Exchange Applications

Abstract Downsizing double-pipe heat exchangers is possible by deploying ribs on the two sides of the heat exchangers. The shape of these ribs, along with two key geometric variables – pitch and height, are crucial in the selection of energy-efficient rib configurations. This is because, the enhancement in heat transfer performance comes at the cost of increased pressure drop. Thus, the goal of this three-dimensional numerical investigation is to identify favourable rib shapes and explore the effect of truncation on triangular ribs, something which is missing from existing literature. Truncation is expected to greatly affect the performance of triangular ribs, either adversely or favorably. To explore this conclusively, an unbiased and exhaustive analysis is carried out by comparing the performance of confinements with modified and regular triangular ribs, keeping plain confinements as the baseline. Furthermore, the effects of two principal design variables – rib height and rib pitch are explored for each shape. Separate results are presented for the inner and outer confinements of the double-pipe heat exchangers (pipes and annuli) to allow for the extrapolation of results for a wide range of applications employing internal flows in pipes and annuli. A phenomenological model is developed to classify the thermo-hydraulic performance of each confinement and identify optimal geometrical configuration and identify best performing design(s). Once optimal rib pitch-height combinations are identified, performance at this optimal combination is evaluated at different Reynolds numbers, spanning from 10,000 to 30,000.

Experimental investigation of effect of different configurations of semi-circular or half-round ribs on heat transfer enhancement in a rectangular duct

This research study investigated the impact of various configurations of semi-circular or half-round ribs on the thermal performance and frictional factor characteristics of a rectangular duct. During this research study, the ribs were provided on the inner surface of the test section’s bottom wall. Six distinct configurations of semi-circular ribs varying from continuous to hybrid arrangement were used. The range of Reynolds number was varied from 13,500 to 34,800; while the ratio of rib pitch to rib height (P/e ratio) was kept constant at 8. The ratio of the height of rib to hydraulic diameter of duct (also known as blockage ratio) was kept at 0.114. The results of experimental investigation showed that the Nusselt number ratio obtained was ranging from 1.36 to 2.74, while the friction factor ratio ranges from 1.70 to 4.51. The overall enhancement ratio for all configurations obtained was in the range of 1.06–1.80 times to that of plain duct. Among all rib configurations, the hybrid rib configuration showed superior ratio of Nusselt number and intermediate increase in ratio of friction factor as compared to all the other rib configurations. Hybrid rib configuration showed overall enhancement ratio values ranging from 1.45 to 1.80 times as compared to that of plain duct (duct without ribs) within the specified range of Reynolds number. The results of study showed that the hybrid configuration of semi-circular ribs exhibited superior overall thermal enhancement as compared to that of remaining tested rib configurations.

Bond strength between ductile carbon/glass hybrid fibers-reinforced polymer bar and concrete through plate-type bond samples

The ductile carbon/glass hybrid fibers-reinforced polymer (C/G-HFRP) bar with excellent corrosion resistance is considered as an outstanding alternative to steel bar in structural concrete. The bond strength of C/G-HFRP bar to concrete plays a dominant contribution to fully realize the prominent properties of C/G-HFRP bar-reinforced concrete structures. In this work, the bond strength between ductile C/G-HFRP bar and concrete was investigated through a plate-type bond sample under direct pullout load. The effects of C/G-HFRP bar diameter, rib pitch, carbon/glass ratio, embedment length, concrete strength, cover thickness, bar type and sample type on the bond strength of C/G-HFRP bar to concrete were considered. The experiment outcomes revealed that the bond strength between C/G-HFRP bar and concrete by plate-type bond samples was 32.4 % lower than that by cube-type ones, resulting from that the influence of reaction frame on the crack propagation of concrete was eliminated during the loading procedure of plate-type bond samples. Also, the bond strength of C/G-HFRP bars to concrete increased with the tensile modulus, while the bond strength between C/G-HFRP bar and concrete was 48.5 % lower than that between steel bar and concrete. The failure mode of bond samples was controlled by the cover thickness of concrete when the compressive strength of concrete was not more than 55 MPa. Furthermore, the bond strength of sample was associated with the failure modes of test samples. The bond strength was decided by the mechanical properties of concrete when the bond sample happened splitting failure, while it was decided by the shear-resistant strength of flange ribs for C/G-HFRP bar when the failure mode of bond sample belonged to pull-out failure. Finally, the bond strength of C/G-HFRP bar to concrete was calculated by the thick-walled cylinder model.

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.

Numerical Study on Flow Field and Heat Transfer Enhancement in a Cooling Channel With Novel Ribs Based on Battery Thermal Management System

Turbulent flow and heat transfer characteristics in a cooling channel with novel ribs have been numerically studied to improve thermal efficiency inside future electric vehicle batteries. In this study, the essential ratios of channel length, rib height, and rib pitch were all set to 6.67, 0.13, and 8.66, respectively. The realizable turbulent kinetic energy - epsilon model was used for the numerical simulation work under the Reynolds number varied from 10,000 to 50,000. The results showed that the heat transfer enhancement on a surface depended on the secondary flows due to the ribs. The enhancement of the wavy-winglet rib was approximately 9.8%−32% compared to other rib cases. Nevertheless, the improved heat transfer came at the expense of a higher pressure penalty. Above 29.7% of the friction factor for the wavy-winglet rib was obtained, compared to orthogonal ribs. In addition, the wavy-winglet rib gave the best thermal-hydraulic performance of the designs explored.

Enhancing recuperators performance in supercritical CO2 Brayton cycle of solar power plants through ribbed heat transfer plates

Sixteen diverse combinations of ribbed heat transfer plates (HTPs), comprising continuous and discontinuous rib configurations, are investigated as potential replacements for traditional smooth HTPs in both the low-temperature recuperator (LTR) and high-temperature recuperator (HTR) of supercritical CO2 Brayton cycles. The findings indicate that the impacts of the introduced HTPs are more significant under the operating conditions of the LTR than those of the HTR. Generally, the incorporation of denser ribs at the upstream sections of both the hot and cold flow paths leads to a significant enhancement in j-factor values. On the hot side of the LTR, these increases exceed 60%, while on the cold side, they surpass 40%. It is also observed that variations in rib pitch exert a more substantial influence on thermal performance compared to alterations in rib length. When comparing non-uniform rib patterns, it is found that the use of ribs with variable lengths increases f-factor values, whereas the design of HTPs with variable rib pitches decreases these values. The design of HTPs with a non-uniform arrangement of rib pitch yields the best overall performance in the LTR. The performance index values for the hot-side and cold-side of this model reach 1.39 and 1.26, respectively.

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.

Enhancement of the Thermohydraulic Performance in a Double Passage Square Duct with the Use of Inclined Ribs of 45°: A Comparative Computational Study

The modern gas turbines need to run at very high inlet temperature to promote their power output. Thus, improvements in cooling technologies play a significant role for enhancing the gas turbine blade life. In this paper, thermohydraulic performance (THP) of a two-pass square channel with inclined ribs at 45° was scrutinized employing the k–ε realizable model with enhanced wall treatment in ANSYS Fluent. The calculations were performed for the rib pitch to height ratio (p/e) of 5-10, rib height to hydraulic diameter ratio (e/Dh) of 0.1-0.2, and Reynolds number (Re) of 20,000-40,000. Detailed analysis of the flow structure in a double passage square duct was carried out to understand the interaction of the rib and bend-induced secondary flows and its contribution to heat transfer enhancement for the rib configurations with distinct p/e and e/Dh, which was not available in any other existing numerical or experimental investigations. The results revealed that the ribs with higher e/Dh generated the stronger stream-wise secondary flows which led to the augmentation of the cooling performance with the disadvantage of pressure loss increment. The maximum THP of 26.55% was achieved with the ribbed configuration having p/e=5 and e/Dh=0.1 at Re=20,000. The new correlations were developed from the computational data to predict the normalized Nusselt number and friction factor (Nu/Nu0 and f/f0, where 0 is the correlation), taking the e/Dh and flow Re into consideration.

Parametric optimization of an impingement jet solar air heater for active green heating in buildings using hybrid CRITIC-COPRAS approach

This work aimed to optimize the parameters of discrete multi-arc shaped ribs (DMASRs) in a solar air heating system (SAHS) through multi-criteria decision-making techniques. In the experiment, the roughness parameters of DMASRs were varied to find the best parameter combination for optimal SAHS performance. The relative rib height (Hr/H) was varied from 0.025 to 0.047 , and the relative rib pitch (Pr/H) was varied from 0.58 to 3.1. The results obtained for the Nusselt number and friction factor, which determine the performance of the SAHS system, depend on the geometrical parameters of the roughness. The parameters of DMASRs did not show any discernible trend. Hence, a multi-decision criteria approach that uses criteria importance through inter-criteria correlation (CRITIC) and complex proportional assessment (COPRAS) hybrid techniques was employed to determine the best parameter combination for optimal performance. The novel aspect of this study includes the use of a hybrid method (experimental and analytical) to optimize the performance of SAHS roughened with DMASRs hindrance promoters and predictions of outcomes using a hybrid CRITIC-COPRAS approach. The experimental and analytical examination through the use of the hybrid CRITIC-COPRAS approach is an essential component of this research that contributes to the optimization of the design parameters of such SAHS. The finding demonstrated that when Re = 19000, Pr/H = 1.7, and Hr/H = 0.047 were reached, the SAHS obtained an optimal thermohydraulic performance of 4.1.

Air Bubble Effect on Heat Transfer Enhancement in 90° Ribbed Parallel Channels Based on Photovoltaic-Thermal Collector Cooling

The effect of entrained air bubbles on heat transfer enhancement inside 90° ribbed parallel channels has been experimentally studied to improve electrical efficiency inside future solar panels. In this work, the Reynolds number was measured from 200 to 600. The essential ratios of channel aspect, rib height, and rib pitch were all set to 0.4, 0.18, and 10, respectively. The volumetric flow fraction for all test conditions varied from 0.0 to 0.5. The overall heat transfer distributions on the surface were captured using an infrared thermography camera. The main finding showed that the average heat transfer rate and the thermal performance gained beyond 25–81% and 7–82% compared with the smooth wall. In addition, the volumetric flow fraction of 0.5 at the Reynolds number of 200 became the best.

Performance improvement of solar air heater duct-employing rib roughness on absorber: an experimental study

ABSTRACT Solar energy is a pure and plentiful source of power for daily activities. Out of many solar thermal system, Solar air heaters (SAHs) are frequently regarded as the most economical and practical method of heating and drying indoor spaces. Due to its poor performance and minimal heat transfer capacity, its applicability in certain circumstances is quite limited. In this paper, an effort has been made to improve the heat transfer efficiency of SAH by utilizing hybrid ribs. Hybrid rib roughnesses are designed to integrate V-shaped ribs downstream of arc-shaped ribs and were experimentally tested in the SAH duct at Reynolds numbers (RN) between 2000 and 16,000. The various roughness pattern i.e. arc angle (α), relative V ribs position (d/w), relative rib pitch (p/e) and relative rib height (e/Dh) have been exploited in the range of 30º-75º, 0.2–0.8, 8–14 and 0.036–0.056, respectively. As a result, maximum enhancement in NuNu has been found as 3.75 at α = 45º, d/w = 0.5, p/e = 12, e/D = 0.056. Thermohydraulic Performance (TP) parameters have also been evaluated for all set of parameters and it was found to be maximum 2.49 at α = 45º, d/w = 0.5, p/e = 12, and e/Dh = 0.036.

Thermohydraulic performance of hybrid ribs pattern combining V and arc shape ribs in solar air heater

ABSTRACT Solar energy is a limitless and ecological-friendly renewable energy source, which can be utilized for varieties of application ranging from heating/cooling, power generation, drying, and in heat-processing industries. Solar air heaters (SAHs) are among the best options for harnessing solar energy for thermal purposes like heating and drying. However, the performance of SAH is not sufficient to take into practical applications. Low performance of SAH is due to its low convective heat transfer capability because of smooth absorber plate. In this regard, an attempt has been made to enhance the heat transfer capability of SAH exploiting hybrid ribs in this paper. Hybrid rib roughness pattern incorporating to V shape ribs and arc shape ribs has been designed and tested experimentally in the SAH duct under the following range of Reynolds number (Re) from 2000 to 16,000. The various roughness patterns, i.e., arc angle (α), angle of attack (β), relative V ribs position (d/w), relative rib pitch (p/e), and relative rib height (e/D), have been exploited in the range of 30º-75º, 30º-75º, 0.2–0.10, 8–10, and 0.023–0.043, respectively. As a result, Nusselt number (Nu) and friction factor (f) have been enhanced significantly. Maximum enhancement in Nu has been found as 3.08 at α = 45º, β = 60º, d/w = 0.65, p/e = 10, and e/D = 0.043. Thermohydraulic performance (TP) parameters have also been evaluated for all set of parameters of hybrid ribs pattern and it found to be maximum 2.18 at α = 30º, β = 60º, d/w = 1.0, p/e = 10, and e/D = 0.043.

Performance of supercritical carbon dioxide heat transfer in several enhanced tubes under external high-temperature airflow

A precooler is installed in the Synergetic Air-Breathing Rocket Engine to ensure the compressor operates properly at high Mach numbers. To better fit the actual precooler scenario, the present study simulated the flow and heat transfer fields of supercritical carbon dioxide (sCO2) in a horizontal tube in which hot air counterflows outside. In the coolant channel, two types of ribs were selected and added, including rectangular ribs as well as isosceles triangular ribs. The geometry parameters of the rib and its configuration on the flow and heat transfer characteristics of sCO2 were examined in detail. Results show that six out of eight cases revealed an increase in Nut over 100% in the triangular rib, making it the optimal enhanced structure. Compared to rectangular ribbed tubes, triangular ribbed tubes display a different variation trend in Nut with rib height due to the combined effects of fluid disturbance and recirculation zone. Both types of ribs increase their Nut first and then decrease it with the rise of rib pitch, which may be due to the fact that high turbulence zones require several distances to develop. This research can provide theoretical foundations and data support for the design of high-efficiency air-precoolers in the future.

Numerical Study of the Impact of Transverse Ribs on the Energy Potential of Air-Based BIPV/T Envelope Systems

Overheating in BIPV/T applications is a concern due to its negative impacts on the electrical conversion efficiency of the solar cells. Forced air cooling can be an effective thermal management strategy. However, its effectiveness is limited by the thermal resistance associated with the boundary layer formation on the walls of the air channel. The heat transfer effectiveness can be improved by appending transverse ribs to the BIPV/T air channel. This study numerically investigates the energy improvements associated with appending transverse ribs to a BIPV/T air channel using CFD. The impact of the varying the transverse rib roughness shape, pitch and height on the thermo-hydraulic performance parameter, electrical efficiency of the BIPV and building heating/cooling load is quantified. With the optimized transverse rib geometry, the heat removal rate is 2.73 times greater than with the smooth channel. This translated to a 30.5% reduction in the PV surface temperature and an increase in the electrical efficiency by 11.3% compared with the smooth channel under peak summer conditions for a mild oceanic climate. The wall heat gain during summer is also reduced by 45.2%.

Invoking Pre-Rotation Induced Flow to Improve the Performance of Gas Turbine Film Cooling

The present study proposes a novel method to improve the performance of film cooling. In this type of cooling, due to the presence of counter-rotating vortex pairs downstream of the injection hole, the formed film on the surface tends to detach from the surface. A new geometry is proposed to overcome this vortex pair. In this geometry, the injection passage is equipped with one or more helical ribs. These ribs induce rotation in the injected cooling fluid flow which prevents the separation of the coolant film from the surface. Analysis and optimization of the effective parameters are done including the injection angle, the height, thickness, number, and pitch of the ribs. The results show that by exceeding the injection angle from an optimum value, the mixing tendency of the injected fluid and main flow increases, and the cold fluid film liftoff occurs faster. On the other hand, as this angle decreases, the pressure drop rises. Considering both the heat transfer and pressure drop effects, the best performance is observed at the injection angle of 20°. Moreover, the best performance is achieved for the ribbed passage (of D diameter) with two ribs of 0.025D ​​thickness, 0.1D height, and 0.33D rib pitch.

Effect of discrete inclined ribs on flow and heat transfer of supercritical R134a in a horizontal tube

In this work, discrete double inclined ribs (DDIR) are introduced into the horizontal flow of supercritical R134a to improve the thermal performance of vapor generators in the trans-critical Organic Ranke Cycle. Effects of operating and geometric parameters are investigated after model validation against experimental data. Results show that DDIR are adaptable to changes in operating conditions because spiral flow maintains the dominant position of forced convection heat transfer. DDIR enhance the PEC of horizontal ST by at least 70% and reduce circumferential thermal non-uniformity by up to 90%. Rib pitch has the most significant effect on heat transfer, followed by rib height and inclination angle. The optimal values for the three geometric parameters are 20 mm, 0.8 mm, and 60°. Finally, the mechanism of rib-induced enhancement is analyzed. Average heat transfer is improved by the strengthened mixing between bulk and near-wall fluid instead of suppressing the buoyancy effect. DDIR-induced enhancement is superior to subcritical cases owing to the integral effect of sharp variations in specific heat at supercritical conditions.

Apex-up discrete-arc rib roughened solar air heater- energy and exergy based experimental study

An artificial roughened plate is the most efficient way to disturb the viscous layer and enhance the turbulent intensity near the absorber plate to augment the heat transfer performance of the solar air heater. The present study is carried out by varying the Reynolds number from 3000 to 14000 for novel apex up-flow discrete-arc-rib roughen and smooth absorber plates to examine the exergy-based performance of Sol-Ah. Further, the parameters arc rib angle (α) of 30°, 45° and 60° are investigated with relative gap width (g/e) of 4, relative rib height (e/Dh) of 0.045 and a relative rib pitch (p/e) of 10. The results are compared with recently investigated best exergy-based Sol-Ah systems to justify the superiority of the present roughens plate geometry. It found that exergy destruction due to absorption of irradiance by the absorber (ELA) is 70–80% of total exergy losses. The maximum thermal & exergetic efficiency reported is 82.2 % & 4.14 %, respectively, reported at ΔT/I of 0.0377 m2K/W. The pressure drop increases due to the discrete arc rib absorber plate; nonetheless, this increment is nominal to influence the net useful energy. Additionally, the proposed apex-up discrete arc rib is more effective compared to a smooth plate and previously designed Sol-ah system. Finally, the performance of the present rib roughened Sol-ah is optimized for α = 30°, g/e = 4 and p/e = 10.