Rib Inclination Research Articles

Optimizing heat transfer in solar air heater ducts through staggered arrangement of discrete V‐ribs

AbstractThis research paper details an experimental study on airflow dynamics in a solar air heater. The heater's design incorporates unique, discrete V‐shaped ribs with staggered elements to enhance thermal performance. The study investigates the influence of various roughness parameters on flow characteristics. These parameters include a relative coarseness pitch (P/e) ratio of 12, a rib inclination angle (α) of 60°, a relative coarseness height (e/Dh) of 0.043, and a staggered element arrangement with a positioning ratio (p′/P) of 0.65. Additionally, the investigation includes scenarios with three gaps (Ng) between elements and a gap‐to‐rib width (g/e) ratio of 4. The research focuses on how changes to the Reynolds number, ranging from 3000 to 14,000, and alterations to the ratio of staggered element positioning to rib height (r/e), from 2 to 5, impact the flow dynamics. The outcomes indicate a significant boost in heat transfer performance, with the Nusselt number rising to 3.76 compared with a conventional smooth duct. The highest thermal efficiency recorded was 86%, at an r/e ratio of 3.5. These results underscore the potential of using discrete V‐ribs with staggered elements in rectangular ducts to improve heat transfer efficiency.

Experimental studies on bond behaviour of steel rebar with different rib patterns in concrete

The bond between concrete and steel rebar is one of the most crucial parameters in the construction of reinforced concrete structures. The load-bearing capacity and serviceability of these structures depend heavily on bond strength. The rib pattern of the rebar plays a significant role in enhancing bond behaviour. The impact of different rebar patterns on bond studies in the concrete mix is found to be limited. In the study, six concrete mixes were prepared and tested. Three of these mixes incorporated fly ash in varied amounts to partially replace cement, while the other three mixes had no fly ash. Three different rib patterns of steel bars were embedded into these six grades of concrete. The pull-out tests were used to assess the bond strengths of various combinations in accordance with RILEM recommendations. The findings show that the ribs in rebars significantly increase mechanical interlocking whereas the presence of fly ash improves chemical adhesion in bond behaviour. Particularly, pattern 2 rebar (transverse rib thickness, 0.797 mm; transverse rib width, 2.06 mm; rib spacing (inner to inner), 6.428 mm; longitudinal rib thickness, 1.04 mm; longitudinal rib width, 2.312 mm; rib inclination angle, 66.39o; nominal diameter, 16 mm; length of transverse rib, 25 mm) exhibited notably superior bond strength, reaching a maximum of 17.21 MPa in M30 grade concrete in which 95 kg/m³ of fly ash was used as a replacement for cement.

The Secondary Flow Mechanism of Square Ribs with Different Inclination Angles in a Rectangular Channel

It has been confirmed that secondary flow can improve heat transfer, but the current research only stays on experimental research and qualitative analysis. Starting from the mechanism of secondary flow, this paper uses FLUENT software to study the heat transfer characteristics of square ribs with different inclination angles in a rectangular channel and its relationship with the secondary flow. Reynolds number is Re=8, 000–20, 000, relative rib spacing is p/e=6, 9, 12, rib inclination angle varies between 30°−90°, and rib height e and rib width w remain unchanged. The results are as follows: the heat transfer effect is the best when the relative rib spacing (p/e) is 12, and the flow resistance is also the largest. The comprehensive heat transfer effect of the square rib with the rib inclination angle α=45° is the best, and the comprehensive heat transfer effect of the square rib with α=90° is the worst. Setting the ribs inside the channel can generate a significant secondary flow, and the contribution of the longitudinal secondary flow is greater than that of the transverse secondary flow. There is a linear relationship between the secondary flow intensity and Re.

Research on Optimal Arch Rib Inclination of Large Span Highway CFST through Arch Bridge

To investigate the reasonable range of the inclination angle of arch ribs, a spatial finite element method was employed based on a concrete-filled steel tube (CFST) basket-handle through an arch bridge with a span of 360 m. A spatial finite element model was established using Midas/Civil software, which was verified with actual bridge data. The effects of different arch rib inclination angles were investigated under static loads. The structural natural frequencies, linear elastic stability coefficients, internal forces, and displacements were comprehensively considered to determine the reasonable range of the inclination angle. The results show that when the inclination angle ranges between 8° and 10°, the first, third, and sixth natural frequencies of the structure are increased. It effectively improves the lateral and torsional stiffness of the arch ribs while ensuring optimal out-of-plane stability of the arch ribs. Compared with the parallel arch, the stability is improved by 20.2%. The effects of angle variation on displacement and internal force of the arch ribs were not significant. Considering all indicators, the optimal range of the inclination angle for the arch ribs of 300-m-level highway CFST arch bridges is suggested to be 8~10°.

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.

Experimental and theoretical study on bonding performance of FRP bars-Recycled aggregate concrete

Fiber Reinforced Polymer (FRP) bars-Recycled Aggregate Concrete (RAC) can alleviate the environmental damage caused by the massive exploitation of natural aggregates and solve the problem of corrosion of steel bars in concrete structures. However, the bonding performance of FRP bars-RAC determines whether it can replace the original reinforced concrete structure in buildings. In the current study, FRP bars-RAC bond performance factors and bond strength theory have been comprehensively investigated through pull-out tests performed for a large number of FRP bars-RAC. In this context, the effects of Recycled Aggregate (RA) replacement rate (0 %, 25 %, 50 % and 100 %), FRP bar diameter (8 mm, 10 mm and 12 mm) and RAC cover thickness (20 mm, 30 mm, 40 mm and 70 mm) on the bond strength, fracture mode, and bond-slip curve of FRP bars-RAC were investigated. Overall, the findings showed that the inclusion of RA reduces the ductility of concrete. Increasing the recycled aggregate replacement rate resulted in gradual losses in bond strength and ultimate slip of FRP bars. In addition, the increase in the diameter and anchor length of the FRP bars led to a gradual decrease in the bond strength between the FRP bars and the RAC. Nevertheless, through increasing the strength of RAC and the thickness of the concrete protective layer, the bond strength between FRP bars-RAC can be enhanced. Through the analysis of test data, the bond strength model of FRP bars-RAC was established based on the thick-walled cylinder theory. In the model, the diameters of FRP bars, rib inclination angle, rib spacing, RAC strength, and protective layer thickness were taken as variables. While the high degree of agreement between the values calculated from the model and the measured values revealed the success of the established modeling, the ratio of the calculated value of the model to the experimental value was measured as 0.66–1.

Mathematical Model for Energy and Exergy-Based Simulation of Triangular Solar Energy Extractor for Air Heating Applications

In the present work, the thermal and exergy efficiency of the equilateral triangular duct solar air heater is analytically investigated and its performance is improved by attaching an inclined wire rib over the absorber surface. Using triangular ducts improves the operating flow conditions up to the Reynolds number of 35000. The thermal model of solar air heater is solved by using an iterative procedure by code developed in MATLAB. The analysis considers the roughness parameters that roughness pitch (P)-to-height (e) ratio (P/e) of 4 to 16, roughness height (e)-to-hydraulic diameter (Dh) ratio (e/Dh) of 0.021 to 0.043, and rib inclination angle (α) of 30 to 75°. While increasing the Reynolds number from 2000 to 35000, the inclined rib roughened triangular duct solar air heater thermal performance is increased and attains the maximum value of 83.61% and the effective thermal efficiency of 80.26%. The maximum exergy efficiency of 2.62% is obtained at the Reynolds number value of 1864. It improves the thermal performance by 14.2% as compared with the rectangular rib roughened triangular duct solar air heater. The optimum value of roughness parameters is P/e of 12, e/D of 0.042, and α of 75°. The air heater is useable to attain the temperature rise parameter ranges from 0.001 to 0.03 K·m2/W.

Numerical investigation on heat transfer performance of matrix cooling channels for turbine trailing edges

The paper investigated numerically the heat transfer and pressure loss characteristics of the converging matrix cooling channels for turbine trailing edges with response surface method. The three selected design factors are scale factor ( SF), rib inclination angle ( α) and channel wedge angle ( β). The discussed range for the design factors, SF, α and β, are 2.5–10; 30°–60° and 1.5°–2.5°. And the investigated Reynolds number range is from 15,000 to 40,000. The turbulence model selected was SST k- ω model. It is newly found that the heat transfer and pressure loss characteristics of the converging matrix cooling channels depend heavily on the scaling effect. The matrix cooling channels with larger scale factor generally present higher heat transfer enhancement, higher pressure loss and lower overall thermal performance. In addition, the converging matrix cooling channels with smaller rib inclination angle and larger channel wedge angle present higher heat transfer enhancement and larger pressure loss. Among all the 13 cases, Case 9 with SF = 2.5, α = 45° and β = 1.5° has the highest averaged thermal performance factor under 6 Reynolds numbers.

Optimization of Rib Shape and Inclination in a Square Duct With Response Surface Methodology

Abstract This article conducts numerical investigation coupled with Reynolds-averaged Navier–Stokes method on detailed flow field and heat transfer characteristics of ribbed channel with symmetric ribs mounted on two walls. The physical domain is modeled by reference to a practical turbine blade internal cooling channel. The effects of three selected geometric factors of ribs, i.e., rib inclination angle, dimensionless rib height, and dimensionless rib pitch, on the flow and heat transfer are investigated by variable-controlled simulations with the Reynolds number ranges from 5000 to 90,000. The parameter ranges are 30 deg ≤ α ≤ 90 deg, 0.5 ≤ e/w ≤ 1.5, and 5 ≤ P/w ≤ 15 with the rib width w fixed at 1 mm. It is newly found that the friction factor does not follow a monotonical trend with respect to the Reynolds number under certain rib configurations. In addition, three-level numerical calculations about three geometric factors as well as the Reynolds number are conducted with the response surface method (RSM). Quadratic regression model for the targeted response, thermal performance factor (TPF), is obtained. The optimal rib shape for the goal of maximizing the channel overall thermal performance turns out to be e/w = 0.5, P/w = 15, and α = 30 deg as Re is fixed at 30,000.

Heat Transfer and Pressure Loss Simulations of Matrix Cooling Channels for Gas Turbine Airfoils

The paper selected 10 geometrical parameter combinations to numerically investigate the dependencies of heat transfer enhancement, flow resistances and overall thermal performance on three geometrical factors including rib inclination angle, channel blockage ratio and subchannel number. The investigated Reynolds number starts at 5,000 and can be as high as 90,000. The turbulence model selected was Transition SST model. The results show that the matrix cooling channels of 30deg rib angle have greater heat transfer enhancement and much higher pressure loss than that of 60deg rib angle. Moreover, matrix cooling channels of higher channel blockage ratio have greater heat transfer enhancement and higher flow friction, while the relationship between the overall thermal performance and the channel blockage ratio depends on the Reynolds number. It was also concluded that the heat transfer performance factor of matrix cooling channel does not change linearly with the subchannel number and the effect of subchannel number on heat transfer performance is less significant than the other two factors. Besides, matrix cooling channels of higher subchannel number have higher pressure loss and poorer overall thermal performance.

Morphological patterns of the rib cage and lung in the healthy and adolescent idiopathic scoliosis.

The morphology of the rib cage affects both the biomechanics of the upper body's musculoskeletal structure and the respiratory mechanics. This becomes particularly important when evaluating skeletal deformities, as in adolescent idiopathic scoliosis (AIS). The aim of this study was to identify morphological characteristics of the rib cage in relation to the lung in patients with non‐deformed and scoliotic spines. Computed tomography data of 40 patients without any visible spinal abnormalities (healthy group) and 21 patients with AIS were obtained retrospectively. All bony structures as well as the right and left lung were reconstructed using image segmentation. Morphological parameters were calculated based on the distances between characteristic morphological landmarks. These parameters included the rib position, length, and area, the rib cage depth and width, and the rib inclination angle on either side, as well as the spinal height and length. Furthermore, we determined the left and right lung volumes, and the area of contact between the rib cage and lung. Differences between healthy and scoliotic spines were statistically analysed using the t‐test for unpaired data. The rib cage of the AIS group was significantly deformed in the dorso‐ventral and medio‐lateral directions. The anatomical proximity of the lung to the ribs was nearly symmetrical in the healthy group. By contrast, within the AIS group, the lung covered a significantly greater area on the left side of the rib cage at large thoracic deformities. Within the levels T1–T6, no significant difference in the rib length, depth to width relationship, or area was observed between the healthy and AIS groups. Inferior to the lung (T7–T12), these parameters exhibited greater variability. The ratio between the width of the rib cage at T6 and the thoracic spinal height (T1–T12) was significantly increased within the thoracic AIS group (1.1 ± 0.08) compared with the healthy group (1.0 ± 0.05). No statistical differences were found between the lung volumes among all the groups. While the rib cage was frequently strongly deformed in the AIS group, the lung and its surrounding ribs appeared to be normally developed. The observed rib hump in AIS appeared to be formed particularly by a more ventral position of the ribs on the concave side. Furthermore, the rib cage width to spinal height ratio suggested that the spinal height of the thoracic AIS‐spine is reduced. This indicates that the spine would gain its growth‐related height after correcting the spinal deformity. These are the important aspects to consider in the aetiology research and orthopaedic treatment of AIS.

A Study on the Leakage Characteristics of a Stepped Labyrinth Seal with a Ribbed Casing

A new type of stepped seal with a ribbed casing is proposed to efficiently reduce the leakage at the tips of turbine blades. The leakage characteristics of two different types of labyrinth seals (conventional seal vs. ribbed seal) were compared and analyzed through computational fluid dynamics (CFD) in a wide operating range of pressure ratios and clearances. The analysis showed that the ribbed seal has superior leakage performance to the conventional seal at all clearance sizes. With the same clearance size (S/H = 1.0), the flow function of the ribbed seal was approximately 21.5–42.6% less than that of the conventional seal. Also, different trends of variation in the flow function according to the increase of the clearance were found between the conventional and ribbed seals. The leakage flow inside the labyrinth seal was analyzed to explain the cause of this difference in tendency, and it was confirmed that the added ribs cause collision between the leakage flow and the tooth wall, even with the increase of the clearance. Also, the ribbed seal enables operation at a larger clearance with the same leakage performance when comparing the absolute leakage flow rate of the two seals. In addition, a parametric study on the influence of the rib height and rib inclination angle revealed that the flow function generally decreases as both parameters increase.

Numerical study on heat transfer enhancement using twisted tape with trapezoidal ribs in an internal flow

The enhancement of the heat transfer rate in the heat exchanger is imperative for decreasing the overall cost of its operation. A popular way to increase the performance of these heat exchangers is by use of plain twisted tape, twisted tape with perforation, twisted tape with peripheral cuts, helical inserts, etc. In this paper, a novel twisted tape with trapezoidal ribs has been introduced and numerical investigation has been carried out. The proposed insert created a swirl motion and increased the turbulence intensity in fluid flow in the tube. The CFD simulation has been performed in the turbulent flow regimes with Reynolds number varying from 4000 to 12000. The inclination of ribs has been varied from 30° to 60° and their effects on heat transfer characteristics have been extensively studied. The highest Nusselt number and friction factor are observed with a slant angle of 60° but the thermal performance factor is found highest with a slant angle of 30°. The results are in good agreement with Promvonge model. It is found that the main cause for augmented heat transfer rate observed in twisted tape with trapezoidal ribs is due to higher turbulence intensity induced by trapezoidal ribs.

Computational and experimental studies on the development of an energy-efficient drier using ribbed triangular duct solar air heater

Triangular duct cross-section is introduced for solar air heater (SAH) of an indirect type of solar dryer (ITSD). Using computational study, the thermo-hydraulic performance of triangular duct SAH with inclined ribs for varying rib inclination (30° <α < 75°) in the turbulent flow regime (5000 < Re < 17500) is studied. With the rib configuration providing maximum thermos-hydraulic performance, a ribbed rectangular duct SAH is designed, and the performance of the same is compared to the former for similar heat input. Results show that the ribbed (α = 45°) triangular duct has 17% higher effectiveness compared to the latter and 79% when compared to smooth SAH. Ribs in triangular duct solar air heater facilitate the increase in temperature even in the core of the duct, delivering the air at 6 K additional temperature relative to a rectangular ribbed duct for same heat input and flow Re. The superiority of the ribbed triangular SAH is further confirmed by studying the drying characteristics of Okra and two variants of banana, namely Nendran and Robusta for the maximum temperature obtained at the outlet of the respective SAH. Various thin layer drying models available in the literature were analyzed, and Modified page model represented the drying behaviour with R2 = 0.99. For ITSD, ribbed triangular duct SAH exhibits a maximum of 60.3% reduction in moisture ratio with a maximum increase of 97.9% increase in average values of diffusivity coefficient confirming that it is an energy-efficient design for an ITSD.

Enhanced thermo-hydraulic performance in a V-ribbed triangular duct solar air heater: CFD and exergy analysis

Computational fluid dynamics (CFD) and exergy analysis are conducted to investigate the impact of secondary flow produced by V-ribs on the overall performance of a triangular solar air heater (SAH) duct. For a fixed relative rib pitch (Rp = 10) and relative rib height (Rh = 0.05), the effect of rib inclination (α) is studied using CFD technique for varying Reynolds number (5000 ≤ Re ≤ 20000). Based on the CFD simulation results, empirical correlations capable of predicting Nu and f with an absolute variance of 8.7%, and 4.7%, respectively, are developed. Employing these correlations, exergetic performance analysis is carried out. Maximum effectiveness parameter (ε) of 2.01 is obtained for α = 45° at Re = 7500. The exergy analysis reveals that the entropy generated is lower for the ribbed triangular duct compared to the smooth duct with maximum enhancement in exergetic efficiency (ηex) as 23% for α = 45°. The study is extended for the rectangular duct to compare the performance with the ribbed triangular duct SAH (α = 45°). Results show that ribbed triangular duct SAH (α = 45°) is superior over various configurations of the ribbed rectangular duct SAH at higher mass flow rates.

Strategies to improve the structural integrity of tied-arch bridges affected by instability phenomena

A numerical study is proposed to investigate the nonlinear behavior of steel tied-arch bridges, whose arch ribs are inclined inwardly. The main aim of the paper is to assess if the arch rib inclination may be an effective strategy to enhance the structural integrity of the bridge structure against out-of-plane buckling mechanisms. The nonlinear behavior of the structure is investigated throughout an advanced 3D finite element model, which accurately reproduces nonlinear sources involved in the cable system and structural elements. An analysis that combines results obtained by traditional elastic buckling analysis and incremental nonlinear elastic analysis is employed to properly evaluate the maximum capacity of the structure. Comparisons between bridge structures with inclined and vertical ribs configurations are proposed focusing attention on both structural and economic aspects. Results show that rib inclination provides several structural benefits to the bridge while reducing overall construction costs.

Three-Dimensional Visualization of Flow Characteristics Using a Magnetic Resonance Imaging in a Lattice Cooling Channel

Flow structures in lattice cooling channels are investigated experimentally by measuring three-dimensional (3D) velocity components over entire duct. The lattice cooling structure is formed by crossing two sets of parallel inclined ribs. Heat transfer is enhanced when coolant flows through the narrow subchannels between the ribs. According to the past literature, longitudinal vortex structures are formed inside the subchannels due to interactions between crossing flows. In this study, 3D velocity field measurement is performed using magnetic resonance imaging (MRI) scanner to clarify the flow mechanism. The rib inclination angle is varied from 30 to 60 deg. Reynolds number is set at approximately 8000 based on the whole duct inlet hydraulic diameter and bulk velocity. Working fluid is 0.015 mol/L copper sulfate aqueous solution. Measured results show that coolants in the upper and lower subchannels interact not only at the both ends of the duct, but also at diamond-shaped openings formed by opposite subchannels. The exchange of momentum between the upper and lower subchannels occurs at the openings, leading to sustained longitudinal vortex in each subchannel as mentioned in the literature. When the ribs are arranged with obtuse angle, a large vortex spreads across the contact surface, while the vortex structure independently stays in each subchannel for acute rib angle. The measured velocity fields are compared with numerically-simulated ones using a Reynolds-averaged Navier-Stokes (RANS) solver. Overall flow pattern is captured, but flow interaction between the upper and lower subchannels is underestimated.

Thermo-hydraulic performance of solar air heater having twisted rib over the absorber plate

Researchers are working to enhance the performance of the solar air heater through infusing various turbulators of different geometry and size over the absorber plate. The present work studied the effect of twisted rib over the absorber plate of solar air heater. Experimentations are performed varying roughness parameters such as relative roughness pitch (P/e) values of 6–10, rib inclination angle (α) in the range of 30°–90°, twist ratio (y/e) of 3–7 and Reynolds number in the range of 3500–21000, to acquire its influences on heat propagation rate and flow friction. The heat transfer and flow friction characteristic with this roughness are compared with a smooth surface for similar flowing conditions. The maximum enhancement for heat propagation characteristic and friction factor had been noticed to be 2.58 and 1.78 times that of smooth surface respectively. The thermo-hydraulic performance had been evaluated for the optimum range of roughness geometric parameters.

Nusselt number and friction factor correlation of solar air heater having twisted-rib roughness on absorber plate

A study is carried out providing integrated roughness over absorber plate of solar air heater to improve its potential for heat transfer augmentation. A number of experiments are conducted with twisted roughness to pursuit test results for heat transfer augmentation along with friction factor phenomena. The experiments stand with a relevant range of flow parameters as Reynolds number from 3500 to 21000, and geometric parameters such as relative roughness pitch from 6 to 10, rib inclination angle domain from 30° to 90° and twist ratio from 3 to 7. Finally, the correlations are developed for the Nusselt number and the friction factor in terms of flow parameter and roughness geometries and compared with experimental results which are reasonable and eventually satisfactory. The enhancement of heat transfer as well as friction factor are obtained and compared with smooth conventional duct for the same flow circumstances. The results are analyzed to pursuit optimum condition of roughness parameters to achieve the best performance.

Nusselt number-friction characteristic for a twisted rib roughened rectangular duct using liquid crystal thermography

Liquid crystal thermography technique is applied over a wide wall of a rectangular channel having twisted rib roughness to evaluate heat transfer distribution. The temperature distribution can be easily visualized easily as color pattern obtained by a CCD camera. The captured color pattern is digitized and converted to HIS (Hue, Saturation and Intensity) from RGB (red, Green and Blue). In this study the effect of different roughness parameters such as relative roughness pitch, twist ratio and rib inclination angle on heat transfer coefficient and friction factor are investigated. The range of Reynolds number and aspect ratio of the duct is selected those are most suitable for solar air heater. It is observed that relative roughness pitch of 8 shows the maximum heat transfer while friction factor decreases with increase in relative roughness pitch. The effect of twist ratio is to create the jet formation on the downstream side of the ribs, which creates vigorous mixing to increase in heat transfer. The increase in twist ratio decreases the number of jets formed and the Nusselt number, while friction factor increases. The rib inclination to the main flow generates secondary flow, increases turbulence level as well as Nusselt number. The secondary flow increases with increase in inclination angle to create maxima in Nusselt number at an angle of 60°. The friction factor increases with increase in rib inclination angle.