Trapezoidal Ribs Research Articles

Numerical investigations of flow around subsea covers at high Reynolds numbers

Two-dimensional (2D) numerical simulations of flow over wall-mounted rectangular and trapezoidal ribs subjected to a turbulent boundary layer flow with the normalized boundary layer thickness of δ/D = 0.73,1.96,2.52 (D is the height of the ribs) have been carried out by using the Reynolds-averaged Navier-Stokes (RANS) equations combined with the k – ω SST (Shear Stress Transport) turbulence model. The angles of the two side slopes of trapezoidal rib varies from 0° to 60°. The Reynolds number based on the free-stream velocity U ∞ and D are 1 × 106 and 2 × 106. The results obtained from the present numerical simulations are in good agreement with the published experimental data. Furthermore, the effects of the angle of the two side slopes of the trapezoidal ribs, the Reynolds number and the boundary layer thickness on the hydrodynamic quantities are discussed.

Numerical simulation study of thermal and hydraulic characteristics of laminar flow in microchannel heat sink with water droplet cavities and different rib columns

Microchannel heat sink is an effective technology to dissipate heat for high flux density devices. However, it is still unknown that what geometric structure form of channel will most effectively improve the overall performance of microchannel heat sinks. Three-dimensional numerical simulations were carried out to investigate the flow and heat transfer characteristics of microchannel heat sinks designed with an innovative combination of water droplet cavities and rib columns. Five different shaped rib columns were considered, including triangular, rectangular, diamond, elliptical and trapezoidal rib columns. A comparative analysis was presented to discuss the performance of these geometric configurations according to average Nusselt number (Nu), friction coefficient (f), entropy production (SΔ) and overall performance factor (η). It was found that the combination of water droplet cavities and rib columns can greatly improve the overall performance of microchannel heat sinks due to the full use of the advantage of rib columns to enhance heat transfer with the strengthened fluid flow disturbance and the advantage of cavities to reduce pressure drop with the enlarged flow area. The rib column shape and geometric parameters have significant effect on hydrothermal performance. Furthermore, the microchannel with water droplet cavities and elliptical rib columns has the best overall performance in all the cases and its overall performance factor achieves up to 1.513 with α = 0.3 and ξ = 0.5 at Re = 331.32.

Thermal performance characteristics of a micro-combustor with swirl rib fueled with premixed hydrogen/air

Outer wall temperature and exergy efficiency of micro-combustor are very essential in determining micro-thermophotovoltaic energy conversion effectiveness. In this study, a swirl rib was designed to improve the thermal efficiency of micro-combustor since a swirl flow can be formed when the hydrogen/air mixture passes through the swirl rib, which increases the residence time and turbulence intensity of the mixture. Effects of position, height, spacing, and shape of the swirl rib on the thermal performance of a cylindrical micro-combustor were investigated numerically. The thermal performance shows different trends with the variation of these geometric parameters, and an optimum mean outer wall temperature of 1260 K is obtained at the distance between the inlet and the rib of 7 mm, the rib height of 1.2 mm and the rib spacing of 0.5 mm, but this optimum setting triggers the large pressure drop that impedes further improvement of the micro-combustor performance. To minimize this effect, three rip shapes including rectangle, trapezoid and inversed trapezoid was designed. The results show that the micro-combustor with trapezoidal rib presents better thermal performance. This study provides theoretical guidance for the optimal design of the hydrogen-fueled micro-combustor.

Enhancement of heat transfer in SAH with polygonal and trapezoidal shape of the rib using CFD

A numerical investigation was carried out in Solar Air Heater (SAH) by implementing an artificial rough absorber plate for higher thermal performances. A polygonal transfer rib, the forward and backward trapezoidal rough ribs were nominated for simulation analysis using ANSYS, Fluent version 13.0. The Renormalization k-ε model was selected to predict the augmentation of Nusselt number (Nu), friction factor (ƒ) characterization and Thermo Hydraulic Performances (THP) for a proposed rib by varying relative roughness pitch P/e = [3.33–20] and relative roughness height e/D = [0.03–0.09]. Dittus Boelter and Blasius correlation were used for validating the smooth surface of Nu and ƒ besides compared with the rough surface to ascertain augmentation of heat transfer. The investigation reported on the performance of Nu and ƒ of the proposed rib at a Reynolds number ranges from 3800 to 18,000. The result reveals that the polygonal rib shape with relative roughness pitch P/e = 3.33 has produced higher Nu and gradual reduction of ƒ at Reynolds number 18000. It was found that THP has achieved a maximum of 1.89 in P/e = 10 & e/D = 0.06 at Reynolds number 15000 in the backward trapezoidal rib.

Optimized Design of Structure of High-Bending-Rigidity Circular Tube

Circular tubes are widely used in daily life and manufacture under bending load. The structural parameters of a circular tube, such as its wall thickness, number and shapes of ribs, and supporting flanges, are closely related to the tube’s bending rigidity. In this study, a tube with eight ribs and a flange was optimized, in order to obtain the lowest weight, through comprehensive structural optimization. We obtained the optimal structural parameters of the tube and the influence of the structural parameters on the tube’s weight. The structural parameters of tubes with different numbers of ribs were optimized. The tube with different number of ribs had the same inner diameter, bending load, and length as the tube with eight ribs. We conducted an experiment to verify the structural optimization simulation. Different tube sizes were subsequently optimized. The optimized tube with four trapezoidal ribs and a flange reduced the weight by more than 73% while maintaining the same deformation. The weight of the optimized tube with a flange reached a stable value after four trapezoidal ribs were added. When the number of ribs was two, the weight was the largest. The analysis results were consistent with the numerical results. A new AWATR (appropriate width and thickness of ribs can improve the bending rigidity of the tubes) formula was proposed, which can effectively improve the bending rigidity of tubes. Different shapes of tubes were optimized and compared. The optimized tube with four trapezoidal ribs and a flange was the lightest and easy to manufacture.

Hydrothermal Investigation of the Performance of Microchannel Heat Sink with Ribs Employed on Side Walls

Abstract In the present study, conjugate heat transfer and fluid flow performance of microchannel heat sink has been investigated using dimensionless parameters. Novel ribs of four different types are introduced on the side walls of channel, which include trapezoidal ribs, rectangular ribs, hydrofoil ribs, and elliptical ribs. The performance evaluation has been conducted by comparing friction factor (f), Nusselt number ( N u Nu ), fluid bulk temperature ( T f {T_{f}} ), wall shear stress (τ), field synergy number ( F c Fc ), irreversible heat loss ( Q d {Q_{d}} ), and Bejan number ( B e Be ) in a Reynolds number, ranging from Re = 100 \mathit{Re}=100 to Re = 1000 \mathit{Re}=1000 . The results revealed that the addition of these novel ribs are helpful in improving the overall thermal and hydraulic performance of microchannel heat sink. From the results of Bejan number, it has been revealed that more than 96 % of losses are because of heat transfer. However, at low Reynolds number, the frictional losses can be neglected, because of very low fluid velocity. Moreover, it has been revealed that synergetic relation between velocity and temperature gradient becomes weaker at higher Reynolds number. Furthermore, it is clear from this study that elliptical ribs performed better in thermal aspects, whereas hydrofoil ribs performed better at hydrodynamic aspects.

Numerical investigation of magnetic field on forced convection heat transfer and entropy generation in a microchannel with trapezoidal ribs

In this study, the effects of adding trapezoidal ribs to microchannel on functionalized multi-walled nano-tubes/water nanofluid heat transfer are examined. The dimensionless slip coefficient (0–0.1), Reynolds number (50–400) and Hartmann number (0–20) are considered as independent variables and the heat transfer along with the entropy generation are considered as the output parameters. The simulation outcomes confirm that the addition of trapezoidal ribs, on the one hand, increases the heat transfer area and, on the other hand, intensifies the possibility of vortex formation. The presence of a vortex decreases the heat transfer potential and thus reduces the performance of the trapezoidal-wall microchannel compared to the base one. With increasing Reynolds number (Re), the probability of vortex formation intensifies, which in turn diminishes the positive effects of using trapezoidal ribs. However, it is found that, with increasing Hartmann number (Ha) and dimensionless slip coefficient , the vortex strength is weakened, and consequently heat transfer is improved. Based on numerical computations, it is found that at Re = 400, Ha = 0 and = 0 and adding trapezoidal ribs to the base microchannel increases heat transfer by 11.12%.

CFD-Based Simulation and Analysis of Hydrothermal Aspects in Solar Channel Heat Exchangers with Various Designed Vortex Generators

The hydrothermal behavior of air inside a solar channel heat exchanger equipped with various shaped ribs is analyzed numerically. The bottom wall of the exchanger is kept adiabatic, while a constant value of the temperature is set at the upper wall. The duct is equipped with a flat rectangular fin on the upper wall and an upstream V-shaped baffle on the lower wall. Furthermore, five hot wall-attached rib shapes are considered: trapezoidal, square, triangular pointing upstream (type I), triangular pointing downstream (type II), and equilateral-triangular (type III) cross sections. Effects of the flow rates are also inspected for various Reynolds numbers in the turbulent regime (1.2 × 104–3.2 × 104). The highest performance (η) value is given for the II-triangular rib case in all Re values, while the square-shaped ribs show a significant decrease in the η along the achieved Re range. The η value at Remax is 2.567 for the II-triangular roughness case. Compared with the other simulated cases, this performance is decreased by about 3.768% in the case of I-triangular ribs, 15.249% in the case of III-triangular ribs, 20.802% in the case of trapezoidal ribs, while 27.541% in the case of square ribs, at the same Remax. Also, a comparison is made with air-heat exchangers that have non-rough walls and contain cross-shaped VGs presented previously, in order to highlight the effectiveness of the rough surface presence in the baffled and finned channels. The obtained results indicated that the triangular-shaped rib (type II) has the most significant hydrothermal behavior than the other cases. This indicates the necessity of roughness heat transfer surfaces for finned and baffled channels to improve significantly the performance of the air-heat exchangers they contain.

Experimental and CFD Analysis of Two-Phase Forced Convection Flow in Channels of Various Rib Shapes

This paper investigates numerically and experimentally heat transfer forced convective two-phase flow (i.e. air and water) over a rectangular ribbed channel with a vertical orientation. Three distinct rib–groove shapes have been examined. Ribs - groove shapes are; Triangle, Trapezoid, and Semi-Trapezoid ribs-groove. The present study has been performed with continuous heat flux through range of water and air superficial inlet velocity values between 0.105 – 0.316m/s, and 0.263 – 1.320 m/s, respectively. Continuity, momentum and energy calculations have been formulated using the Finite Volume Approach (FVM). Results indicate that the triangle rib-groove has the high heat transfer coefficient and lower temperature difference than other cases against a different number of Reynolds. The experimental data has been compared to numerical results for ribs –grooved channel with deviation of about 1.0% - 7.5%. The channel fitted with triangle ribs shows the highest heat transfer, which is about 59% higher than the smooth channel; 56% for trapezoidal rib, and 44% for channel fitted by semi-trapezoidal rib. Finally, the triangle rib-groove gives a better heat transfer improvement value in comparison with trapezoidal and semi trapezoidal rib-groove channel at constant pumping power.

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.

Thermal and hydraulic characteristics of TiO2/water nanofluid flow in tubes possessing internal trapezoidal and triangular rib shapes

Configuration improvements are greatly important in heat transfer enhancement. In this study, TiO2/water nanofluid was used in combination with ribbed tubes for this purpose. Namely, this article presents a numerical investigation on the effect of rib geometries (trapezoidal and triangular rib shapes), number of ribs (4, 6, and 8 ribs) on heat transfer using TiO2 nanofluid in turbulent flow with Reynolds numbers of 5000–40,000. The thermal and hydraulic behavior of nanofluids was simulated utilizing single-phase approach with the assumption that the fluid properties are constant with temperature, and the flow is under uniform heat flux. The average size of the nanoparticles used in this work was 50 nm, and the nanofluid was considered at concentrations of 0.25–1.0%. The investigations were performed with the aim of establishing the impact of rib numbers and shapes on friction factor and heat transfer employing TiO2/water nanofluid as the working fluid. The results show that the helical-ribbed tube significantly improves heat transfer compared to the plain tube taking into account the shape and number of ribs. Further, by means of performance evaluation criteria, the tubes with trapezoidal ribs provide better thermal performance followed by the ones with triangular ribs compared to the plain tubes. Ultimately, the nonlinear models of Nusselt number and friction factor in the foregoing configurations were proposed with maximum deviations of ± 7.0% and ± 5.0%, respectively.

Bionic microstructure on titanium alloy blade with belt grinding and its drag reduction performance

Researches show that surface with bionic structure plays an important role in improving the aerodynamic performance on aero engine parts. Belt grinding, a popular method to process titanium alloy parts such as aero-engine blade, is also found that it can be used to obtain bionic microstructure through special grinding method and parameters. In order to explore the performance of bionic microstructure processed by belt grinding and its effects on airflow dynamics, several groups of simulation and an experiment are carried out in this paper. Firstly, the mechanism of drag reduction of bionic microstructure is discussed. It shows that the effect of drag reduction of bionic microstructure is related to protrusion height, which is related to the shape and size of the bionic microstructure. Then, three groups of typical belt grinding bionic microstructure are set up. In addition, the drag reduction values are calculated in CFD simulation. The results are analyzed and discussed. Further, to verify the airflow dynamics of drag reduction of belt grinding bionic microstructure, an experiment of aero-engine blade is carried out. Finally, the effects of airflow dynamic performance of blade with belt grinding bionic microstructure are obtained in CFD simulation. In general, the shape of wave ribs, compared to V-ribs and trapezoidal ribs, has the best performance in drag reduction. To a certain extent, the improvement of airflow dynamic performance is higher with the increasing of the size of bionic microstructure, which suggests lower feed rate and higher grinding pressure for bionic structure.

Thermo-hydraulic performance of nanofluids flow in various internally corrugated tubes

This study examines the impact of corrugation configuration on the thermal, hydraulic, and overall energy performances of nanofluid flows in corrugated tubes. Different fluids (distilled water “DW”, GNP-SDBS/DW, Al2O3/DW, and SiO2/DW) and tube geometries (rectangular, triangular, trapezoidal, and curved ribs) are investigated using a carefully validated computational fluids dynamics (CFD) model. Compared to DW flow in a smooth tube, the maximum overall performance improvement (∼37 %) was found in the case of GNP-SDBS/DW nanofluid flow in a curvedly ribbed tube at Re of 10,000. For all fluids and tube geometries, the overall performance enhancement was found to decrease at Reynolds numbers higher than 10,000. Curvedly ribbed tubes have better performances at medium and high flow rates, regardless of the fluid type. However, at low flow rates or when the pumping power consumption is not a major concern, trapezoidal ribs can be used to achieve higher heat transfer rates. Overall, using corrugated tubes (maximum performance improvement of ∼20 %) was found a more energy-efficient technique than using nanofluids (up to ∼11 %). Combining both techniques achieves enhances the performance by up to ∼37 %. These findings can be used as a guide for determining the most suitable technique based on an overall techno-economic evaluation.

Rib shape and nanoparticle diameter effects on natural convection heat transfer at low turbulence two-phase flow of AL2O3-water nanofluid inside a square cavity: Based on Buongiorno’s two-phase model

In this study, the effects of the rib shape with constant height, width and pitch and nanoparticle diameter on natural convection heat transfer of low turbulence flow of AL2O3-water nanofluid inside a square cavity is numerically simulated based on Buongiorno’s model. Two rib-ed vertical walls are with different constant temperatures (Th>Tc), while the top and bottom walls are insulated. Heat transfer of nanofluid in rib-ed square cavity is investigated at Rayleigh numbers107, 108 and 109 for various Prandtl numbers 7.0659, 7.3593 and 7.8353. The CFD simulation of AL2O3-water nanofluid is studied for 1–3% volume fractions ranges. Also, the effect of the various diameters of nanoparticle 50, 100 and 150 nm on natural convection heat transfer performance is analyzed. The comparison of present numerical and experimental results shows that due to the thermophoresis and the Brownian motion effects, obtained numerical results are acceptable. Results indicate that at high Rayleigh number, low volume fraction has better performance and trapezoidal rib is the best. Also, by reducing nanoparticle diameter, nanofluid heat transfer and NBT increase considerably. However, by increasing nanoparticle diameter, convection heat transfer decreases greatly and even gets less than base fluid and smooth walls.

Flow field investigation behind a trapezoidal rib and the effect of the synthetic jet

The motive of the present work is to investigate the combined effect of synthetic jet and chamfer angle (15°, 18° and 21°) of a trapezoidal rib on flow phenomena. However, detailed study is restricted to 21° chamfer angle, which is the optimum angle from the heat transfer perspective. The rib has an obstruction of 5% of the tunnel for an aspect ratio of 30. Emphasis has been given to identifying the optimal location of the synthetic jet at which the recirculation zone behind the rib turbulator becomes a minimum. Experiments are performed on a low-velocity subsonic wind tunnel by particle image velocimetry (PIV) and hotwire anemometry (HWA). Flow field has been characterized in terms of time-averaged velocity magnitude, vorticity, streamlines, turbulence quantities such as turbulence intensity, Reynolds stress and root mean square (rms) velocities as well as instantaneous flow field. The data are presented at Reynolds number 32,000, based on the hydraulic diameter of the test section. Along with the large primary recirculation, a secondary recirculation bubble is visible at the leeward corner predominantly for the angles 18° and 21°. The secondary bubble is considered to be responsible for maximum heat transfer from the near rib surface. The synthetic jet is placed at different upstream and downstream locations to see the effect on flow parameters. With the synthetic jet, the primary recirculation bubble moves closer to the rib, which ultimately reduces the recirculation length. A greater mixing is observed in the near wake of the obstacle, and the secondary recirculation zone near the surface diminishes. Out of six different synthetic jet locations studied, the maximum reduction of the recirculation bubble is observed when the synthetic jet is placed 0.5D upstream and 1.5D downstream from the rib front face. A comparison has been made between with and without synthetic jet for these flow parameters.

Heat transfer and flow field features between surface mounted trapezoidal-ribs

Present work is an experimental study of flow over array of trapezoidal-ribs transversely placed on the wider bottom surface of the rectangular passage. It is intended to study the profound impact of taper angle variation (0 to 20°) on the flow mechanism, and subsequently on heat transfer improvement. The local and augmentation heat transfer patterns have been investigated using liquid crystal thermography (LCT). Further, the aerodynamic characteristics, in a module between seventh and eight ribs, have been obtained using particle image velocimetry (PIV) for understanding the flow physics. Existence of large- and small-scale coherent structures within the detached shear layer zone have been confirmed and further explained by means of critical points. As compared to square rib, trapezoidal rib provides higher heat transfer rate just downstream of the rib, which is observed to be in line with the fluid flow results.

Enhanced heat transfer in a labyrinth channels with ribs of different shape

Purpose The purpose of this study is to enhance the thermal performance in the labyrinth channel by different ribs shape. The labyrinth channel is a relatively new cooling structure to decrease the temperature near the trailing region of gas turbine. Design/methodology/approach Based on the geometric similarity, a simplified geometric model is used. The k − ω turbulence model is used to close the Navier–Stokes equations. Five rib shapes (one rectangular rib, two arched ribs and two trapezoid ribs) and five Reynolds numbers (10,000 to 50,000) are considered. The Nusselt number, flow structure and friction factor are analyzed. Findings Nusselt number is tightly related to the rib shape in the labyrinth channel. The different shapes of the ribs result in different horseshoe vortex and wake region. In general, the arched rib brings the highest Nusselt number and friction factor. The Nusselt number is increased by 15.8 per cent compared to that of trapezoidal ribs. High Nusselt number is accompanied by the high friction factor in a labyrinth channels. The friction factor is increased by 64.6 per cent compared to rectangular ribs. However, the rib shape has a minor effect on the overall thermal performance. Practical implications This study is useful to protect the trailing region of advanced gas turbine. Originality/value This paper presents the flow structure and heat transfer characteristics in a labyrinth channel with different rib shapes.

Comparative study on heat transfer enhancement of nanofluids flow in ribs tube using CFD simulation

AbstractThis study presents, a numerical investigation of two‐dimensional turbulent nanofluids flow in different ribs tube configurations on heat transfer, friction, and thermal performance coefficients using ANSYS‐FLUENT software version‐16. Governing equations of mass, momentum, and energy have been solved by means of a finite volume method (FVM). Four types of nanoparticles namely; Al2O3, CuO, SiO2, and ZnO with volume fraction range (1%‐4%) and different size of nanoparticles (dp = 30 nm, 40 nm, 50 nm, and 60 nm) with various Reynolds number (10 000‐30 000) in a constant heat flux tube with rectangular, triangular, and trapezoidal ribs were conducted for simulation. The results exhibit that Nusselt number for all cases enhanced with Reynolds number and nanofluid volume fraction increases. Likewise, the results also reveal that SiO2 with volume fractions of 4% and diameters of nanoparticles of 30 nm in triangular ribs offered the highest Nusselt number at Reynolds number of Re = 30 000. In addition, the higher value of thermal performance factor was obtained at Reynolds number of Re = 10 000.

Turbulent forced convection flow inside inward‐outward rib corrugated tubes with different rib‐shapes

AbstractThe thermal and hydrodynamic behaviors of forced convection turbulent flow inside the corrugated tube are investigated numerically. The ribs of corrugated tube are distributed in inward‐outward arrangement simultaneously and alternately (referred as IOCT). Three roughness shapes of the corrugated tube are examined; rectangular, semicircular, and trapezoidal ribs. The computational model is validated through comparison with the predicted results with correlated and experimental ones of related works. The performance of IOCT is compared thermally and hydrodynamically with that of the inward‐rib corrugated tube (ICT), outward‐rib corrugated tube (OCT) and smooth tubes. The results reveal that the heat is exchanged effectively by employing IOCT than utilizing OCT but with extra pumping power losses. At the maximum Re, it is found that the heat transfer of IOCT is 17.7% higher than that of OCT, and utilizing IOCT instead of ICT results in a reduction of friction factor by about 27.2%. Also, IOCT exhibits a lower friction factor and pressure drop penalty than that imposed by ICT. Also, roughness shapes have an insignificant effect on the thermal and hydrodynamic performances of IOCT for the same rib geometrical parameters. Furthermore, the influence of variation pitch‐to‐diameter ratio is also examined for various rib shapes of IOCT.

Numerical investigation and performance analyses of rectangular mini channel with different types of ribs and their arrangements

An investigation of a three-dimensional rectangular minichannel with different types of longitudinal vortex generators, (rectangular and trapezoidal) which are considered as ribs along the channel, is carried out. Five different models with different angles of attack and height of ribs have been designed and studied numerically for analyzing the heat transfer and overall performance of the channel in single-phase laminar flow. The results indicate that the configurations with the attack angles of 60° have the best heat transfer performance. An augmentation for heat transfer performance improves with the increase of rib's height and the Reynolds number in the channel, however, flow resistance increases in return. Minichannels with both rectangular and trapezoidal ribs have better results for heat transfer and flow performance in comparison to a minichannel with rectangular ribs only. The model with all trapezoidal ribs leads to best overall performance due to its better flow performance, which is a crucial factor in the overall efficiency. The overall performance of the minichannel enhanced by 52.7% for the case “M3” in comparison with the smooth channel.