Ribbed Surface Research Articles

Multiple Recycling of Wood–Plastic Recycled Composite (WPRC): Developing a Method to Evaluate the Degree of Degradation of Used WPRC

Wood–plastic recycled composite (WPRC) are composites obtained by heating and mixing the main raw material, wood flour, with thermoplastic resin, containing at least 40% by mass of recycled material in the raw material. In order to promote the multiple-recycling of WPRC to reduce greenhouse gas emissions and ensure the sustainability of resources, three types of WPRC decking materials with different exposure conditions (outdoor-exposed product, unexposed product and product stored in the factory for a long time) and samples after accelerated weathering tests (WPRC and recycled plastics from raw materials) were evaluated and compared by a TG-DTA in order to develop a method for evaluating the degree of degradation of used WPRC. Exothermic behavior with weight loss was observed in the temperature range of 30–500 °C for the WPRC product in two temperature ranges. In order to focus on the change in the first exotherm by oxidative degradation, where the rapid weight loss begins, this paper will focus on the exothermic behavior that develops in the temperature range of 150–300 °C on the lower temperature side. The results obtained are as follows. (1) Initial oxidation temperature (IOT) measurement from DTA behavior suggested that it is possible to evaluate the degree of degradation of WPRC. (2) On the exposed surface of WPRC exposed outdoors for more than 9 years and 8 months, significant decreases in the IOT were observed up to 1 mm from the surface, and a slight decrease in the IOT was observed between 1 and 2 mm from the surface. On the other hand, for the indoor long-term storage of 11 years and 6 months, there were almost no changes in the IOT with respect to the depth from the surface. Regarding the outdoor long-term-exposed WPRC, significant decreases in the IOT were observed not only on the exposed surface but also on the hollow and ribbed surfaces up to a depth of 1 mm from the surfaces. (3) A similar decrease in the IOT with increasing accelerated degradation time was observed for the WPRC and raw recycled plastic samples after accelerated weathering tests as for outdoor exposure. Furthermore, FTIR-ATR spectra also revealed that accelerated degradation caused oxidative degradation of the plastic. Therefore, it is thought that the decrease in the IOT can be used as an indicator to evaluate the degree of degradation of the plastic raw material in WPRC.

Spreading of droplet impact on ribbed superhydrophobic surfaces with varying structure height

Hypothesis:Quantifying droplet spreading characteristics on ribbed superhydrophobic surfaces is challenging due to the complex fluid dynamics, limiting the practical applications. Droplet spreading dynamics are significantly influenced by the diameter ratio (rib diameter to droplet diameter) and height ratio (structure height to rib diameter) during impact. Experiment:Ribbed superhydrophobic surfaces with diameter ratios (0.18 to 0.75) and height ratios (0.125 to 0.5) underwent impact experiments with droplets at varied Weber numbers. Through simulations and analysis, we summarized the patterns of the maximum ribwise spreading coefficient, elucidated the droplet spreading mechanism on ribbed superhydrophobic surfaces. Findings:The findings revealed asymmetry in impact dynamics on ribbed superhydrophobic surfaces in the ribwise and radial directions. The maximum ribwise spreading coefficient initially decreases, followed by increase with increasing diameter ratio, decreasing in a slowing down trend with increasing height ratio. These observations indicated that maximum ribwise spreading coefficient can be minimize with critical ratios. Comparatively, the maximum spreading coefficient at critical height ratios is 72.7% to 92.3% of that on flat surfaces. To precisely forecast maximum ribwise spreading coefficient, two models are introduced for diameter ratios below and above critical range when height ratios below the critical range.

CFD-DEM coupled study of erosion resistance characteristics of ribbed walls

Industrial bulk material transfer systems are exposed to high erosion risk due to prolonged scouring by particle flow. In order to improve the erosion resistance of the system components, this study proposes a wear-resistant improvement scheme by adding square and triangular ribs on the wall surface. A coupled CFD-DEM method was used to analyse the abrasion characteristics of particle flow hitting the flat and ribbed wall surfaces at different particle incidence angles, particle velocities and particle volume fractions. The results show that square ribbed plate is more targeted to reduce the erosion ratio of the groove surface and transfer the risk to the ribs, whereas triangular ribbed plate provides an optimal balance between sacrificial velocity and erosion resistance of the ribbed structure; moreover, square ribbed plate is slightly more capable of transferring the maximum wear to the ribs to reduce the risk of perforation of the wall surface. As the particle velocity increased from 5 m/s to 25 m/s, the triangular ribbed plate reduced the erosion ratio by up to 45 %; both square and triangular ribbed plate groove surfaces reduced the maximum wear rate by about 65 % and 35 %, respectively. With the increase of particle volume fraction from 0.025 % to 0.125 %, the erosion ratios of the square and triangular ribbed plates decreased rapidly by up to 16 % and 73 %, respectively; the groove surface of the square ribbed plate decreased by about 63 % of the maximum wear rate, while the groove surface of the triangular ribbed plate decreased by up to 48 % of the maximum wear rate.

Flow and Heat Transfer Characteristics of Swirling Impinging Micro-Slot Jets by Adopting Circular Ribs in the Wall Jet Region

The flow and heat transfer behaviors of swirling impinging micro-slot jets using circular ribs in the wall jet region have been numerically studied. In this study, the total spiraling length was defined as 290 mm due to the two complete revolutions of the helix generated at a slot nozzle thickness of 1.0 mm. The range of circular rib radius ratios varied from 1 to 4 under the jet-to-target spacing ratio at 2 and 4. Predictions were made using the turbulent kinetic energy-epsilon model at Reynolds numbers ranging from 5000 to 20000. The results showed that the heat transfer enhancement on the target wall depended on the circular rib radius ratios. The jet flow at a low circular rib radius ratio generated recirculating ambient fluid behind the rib zone and a minuscule vortex within a circular rib region. At a high ratio, the jet’s potential flow directly affected the top rib surface and generated secondary flows in the circular rib. The heat transfer rate tended to increase as the Reynolds number increased. The average heat transfer value at a circular rib radius ratio of 3 became the best, up to 18.1% for jet-to-target spacing of 2. Whereas above 14.8% average value at a circular rib radius ratio of 1 in the case of jet-to-target spacing of 4 gained the highest.

Laser ultrasonic testing of defects in milling groove brazed joints of thrust chamber

This paper presented a new approach for noncontact inspection of defects in milling groove brazed joints of thrust chamber with laser ultrasonic testing method and synthetic aperture focusing technique (SAFT). Firstly, laser ultrasonic testing methods for milling groove brazed joints of thrust chamber was studied. Subsequently, numerical models were constructed to analyze the influence of defects on laser-excited signals. The analysis revealed that the brazed defects caused internal waves to reflect on the rib surface, manifesting as defect echo signals preceding the outer wall echo. Through scanning setting, the obtained SAFT images illustrate the presence of the defect directly and clearly. Furthermore, an experimental system was established to detect and image artificial defects with different degrees of weld leakage. The experimental results are consistent with simulation results, validating the capability and effectiveness of the testing and imaging method. In general, the proposed laser ultrasound method offers inherent advantages of non-contact detection with high resolution and precision, and it is easy to achieve fast and automated scanning of large and complex structures like thrust chambers, demonstrating its potential for enhancing the safety and reliability of liquid rocket engines.

Flow Performance Enhancement of a Fluidic Oscillator Through the Integration of Rectangular Ribs on Coanda Surface

Abstract Fluidic oscillators utilize internal flow dynamics to produce oscillatory fluid jets. The Coanda surface in the mixing chamber of a fluidic oscillator plays a critical role by facilitating controlled fluid manipulation through flow attachment and redirection. The mixing chamber pressure drop, jet oscillating frequency, and deflection angles are hence dependent on the geometry of the Coanda surface. In this study, the Coanda surface is modified by using rectangular ribs of different aspect ratios. The effects of ribbed Coanda surface on oscillating jet characteristics are computed numerically through two-dimensional unsteady Favre-averaged Navier–Stokes equations. The aspect ratio (ARribs), the ratio of rib height to rib base, is varied from 0.64 to 1.56 and air is used as a working fluid. An increase in the ARribs increases the jet oscillation frequency. The highest aspect ratio achieves an oscillation frequency of 820 Hz, contrasting with 355 Hz for the smooth case. On the other hand, the jet deflection angles are decreased as the aspect ratio increases. Interestingly the introduction of the ribs on the Coanda surface decreased the pressure drop in the oscillator. A decrease in pressure drop of 22% for an aspect ratio of 1.56 was achieved as compared to the smooth case. These results are attributed to the influence of the ribs on the formation of a separation bubble formed in the mixing chamber. The jet performance parameter, frequency-deflection-pressure ratio, was found to be 43% higher for ARribs of 1.56 as compared to the smooth case.

Forced air flow through a rectangular channel with 3D turbulence enhancers: fluid-dynamics and thermal analysis by Large Eddy Simulations

Many newer engineering applications, like the cooling of automotive batteries and high-performance CPUs, require heat exchangers (HEs) with large contact areas and very small heights. Performances of this type of HEs can be significantly improved by using surfaces enhanced with optimized 3D structures. The project Mood4hex aims at designing new geometries with optimized morphology, starting from a large database of experimental data on ribbed surfaces. In order to perform an optimization algorithm on such surfaces, analyses are carried out on CFD models with increasing complexity and computational time, to find a fast-running code that preserves the physical meaning. Until recently we used RANS models, and now we began to investigate the use of Large Eddy Simulations (LES) as a higher order validation tool for simpler models. In this paper, we present the results of LES along with experimental data of a forced air flow inside a streamwise periodic rectangular channel of high aspect ratio, i.e., 1:10, equipped with standard transverse ribs (α = 90°). More specifically, the ribs are placed only on the lower wall that is operated at constant heat flux, while air flowing at Re 500 or 1000. Comparison of experimental data vs LES results shows weaknesses and strengths of the model.

Analytical Modeling of Water Droplet Behavior at the Gas Channel Corner for Proton Exchange Membrane Fuel Cells

Abstract Water management is of significant importance to achieving high performance of proton exchange membrane fuel cells. In recent years, droplets emerged from the rib surface and accumulated at the channel corner have been found to be a crucial part of water flooding. In this study, an analytical model is first proposed to quantitatively estimate the variation in the morphology and dynamic behavior of growing droplets with consideration of the channel sidewall interaction. In order to predict the water geometry, the flow channel with compressed gas diffusion layer (GDL) is described mathematically, and water behavior at steady-state and dynamic state are both evaluated through the geometric and force analysis. The model results indicate that the droplet profile transforms from concave to convex when its size grows, in which process contact angles and channel shape play an important role. Compared with the graphite channel, the droplet in the metallic channel is more inclined to be adsorbed on the sidewall and GDL, resulting in a higher adhesion force and a lower gas shear force. The critical gas velocities for the detachment of droplets are quantitatively predicted to avoid water flooding. The model is helpful to understand the droplet behavior in the presence of channel sidewall interaction.

Numerical analysis of jet impingement cooling with elongated nozzle holes on a curved surface roughened with V-shaped ribs

Numerical studies were performed in this study to analyze the effect of dimensionless elongated injection holes (G/d = 0.5, 2.0, 4.0, 8.0) on heat and flow characteristics on rib-roughened surfaces with an array of inclined impingement jets. Experimental and numerical data from existing literature were used to validate the numerical solution procedure’s heat transfer and flow characteristics in the semicircular test section. The turbulence equations were solved using the SST k-ω turbulence model by varying the Reynolds number from 5000 to 25,000. The curvature effect and staggered array pattern created an additional stagnation region between adjacent impinging jets on smooth surfaces, leading to a low heat transfer zone. Rectangular cross-sectional V-shaped ribs (VSR) were placed in regions where the stagnation point occurs to eliminate this disadvantage. The effect of different normalized rib heights (Hr/d = 0, 0.2, 0.3, 0.4) and rib angles (α = 30°, 45°, 60°, 90°) on the curved surface was also investigated to increase convective heat transfer performance and achieve more homogenous heat transfer distribution by relatively reducing the effect of thermal stresses. Flow properties, area-averaged and local Nusselt number variations on smooth and ribbed surfaces, and the thermal performance criterion (TPC) were investigated in detail. The results indicated an increase in overall heat transfer and a more evenly distributed measurement region compared to the conventional (unextended jet and smooth surface) jet impingement configuration. The most significant heat transfer enhancement from combining the elongated jets with VSR was 47.23% at Hr/d = 0.2 by reducing the G/d to 0.5. In addition, the highest TPC was determined as 1.07 on the proposed model with G/d = 2.0 and Hr/d = 0.2 at Re = 25,000.

Understanding Thermo-Fluidic Characteristics of a Triangular Solar Air Heater Having W-Shaped Rib-Turbulators: A 3D Computational Fluid Dynamics Study

Abstract A solar air heater duct with W-shaped rib-turbulators on the collector plate disrupts the flow that enhances the heat transfer from the hot surface due to turbulence in the flow. In this analysis, a three-dimensional fluid domain of the W-shaped ribbed triangular solar air heater duct is numerically simulated to analyze the impact of roughness and flow parameters on thermo-fluidic performance; also, the turbulence behavior near the rib surfaces is presented. Roughness variables like non-dimensional pitch and non-dimensional height varied from 6.23 to 17.85 and 0.04 to 0.053, respectively. In contrast, the flow parameter, like the Reynolds number, is kept in the range of 4×103 to 18×103. A maximal performance evaluation criterion of 1.51 is attained for the W-shape ribs with a non-dimensional pitch of 7.14 and a non-dimensional height of 0.047 at a Reynolds number of 15×103. For the W-shaped rib-turbulators with a non-dimensional pitch of 7.14 and a non-dimensional height of 0.047 at a Reynolds number of 15×103, the maximum heat transfer is found to be 1.826 times that of a smooth duct. Accordingly, in the parametric range, the maximum friction penalty is 2.63 times that of a smooth duct. Some useful correlations are established considering the computational data.

Novel entropy generation and optimization for hybrid nanofluid flow via ribbed surface parabolic trough collector

This research paper focuses on the optimization of parameters for deformative receiver tubes to achieve prime choice of design for efficient energy absorption. The motivation of the current study lies in addressing the critical need for optimizing parameters of deformative receiver tube to obtain optimal design to enhance energy absorption efficiency in Parabolic Trough Solar Collectors (PTSC). Considering the diverse criteria involved in the design process, the application of a Multi Criteria Decision Making (MCDM) approach proves beneficial. The primary objective of this study is to identify the optimal combination of parameters (Reynolds number (Re), Relative V-rib height (Rh/ Dt), Relative streamwise pitch (PStm/Rh), and Relative spanwise pitch ratio (PSpn/Rh)) of the deformative receiver tube of PTSC) employing the multiobjective optimization based on ratio analysis (MULTIMOORA) method. Additionally, a novel Pythagorean fuzzy sets (PFSs) entropy-based approach is proposed for quantifying the weights of the criteria. The feasibility and practicality of the novel PFSs entropy and MULTIMOORA method are demonstrated through the application of the Technique for Order of Preference by Similarity to Ideal Solution method (TOPSIS), confirming the attainment of Re = 50000, Rh/ Dt=0.0135, Pstm/ Rh=56.67 and Pspn/ Rh=11.11, as optimal alternative parameters. This research offers valuable insights into optimizing deformative receiver tube parameters to improve thermal performance which benefiting researchers in the concerned field.

Correction to: Experimental investigations on the thermal performance of ultrasonic field in pool boiling on rib surfaces

Correction to: Experimental investigations on the thermal performance of ultrasonic field in pool boiling on rib surfaces

Influence of Entrance Geometry and Thermal Boundary Conditions on Heat Transfer in a Rectangular Channel with 45 Deg Angled Ribs on One or Two Principal Walls

The purpose of this paper is to numerically investigate the influence of the entrance geometry and thermal boundary conditions on the local and averaged heat transfer coefficient in a ribbed rectangular channel with an aspect ratio of 5. Ribs, angled at 45°, were periodically deployed on one or two opposite sides, while the remaining walls of the rectangular channel were assumed to be smooth and unheated. The effect of entrance conditions was addressed by considering either a smooth or a ribbed unheated section upstream of the ribbed heated section. The effect of the thermal boundary condition was studied by considering a uniform heat flux imposed at the inter-rib region, or at the inter-rib and the rib baseplate, or at the whole interface between the ribbed surface and the coolant. Results, presented in the form of spatially resolved and spatially averaged Nusselt numbers, show that a ribbed section preceding the heated test section affects the heat transfer coefficient, relative to a smooth entrance section, for several repetitive modules. The influence of the thermal boundary condition was found to be mainly concentrated in the surface regions immediately upstream and downstream of each rib, with small differences, in terms of spatially averaged Nusselt numbers. The presented investigation is meant to point out that heat transfer experiments on ribbed channels, massively provided by the heat transfer community according to the current technical literature, should provide an exhaustive description of the entrance and thermal boundary conditions assumed in the experiments and eventually to discuss how they could potentially affect the results.

Accuracy in evaluating convective heat transfer coefficient by RANS CFD simulations in a rectangular channel with high aspect ratio and 60° tilted staggered ribs

A numerical analysis of heat transfer characteristics of an air flow through a narrow rectangular channel of 1:10 aspect ratio with ribbed surfaces has been carried out, by means of a CFD commercial code, exploiting Reynolds Averaged Navier-Stokes (RANS) equations. The channel is 120 mm wide, 840 mm long, with 60° tilted staggered ribs. Ribs have a square cross section with two different side heights (2 mm and 4 mm) and three different values of dimensionless pitch (10, 20 and 40). The numerical results have been compared with experimental data obtained by the authors inside a ribbed channel both with same geometry and operating conditions as one numerically modelled. Agreement between numerical and experimental data on convective global heat transfer coefficient, i.e., averaged over the whole channel, is discussed for the six different configurations considered. Moreover, performances are presented by considering at the same time both heat transfer enhancement and pressure-drop penalization, highlighting strengths and weaknesses per each configuration. This work is aimed at finding a suitable configuration of a CFD model with RANS that will allow authors to apply it to the range of dimensionless pitches and side heights during early design-phases of parametric studies.

EXPERIMENTAL ANALYSIS OF HEAT TRANSFER AND THERMAL PERFORMANCE OF PARABOLIC TYPE SOLAR COLLECTOR WITH RIBBED SURFACE TEXTURE FOR CLEAN ENERGY EXTRACTION

This paper examines the performance of a parabolic type solar collector (PTSC) that uses both plain tube and ribbed surface textured tube channels for elevating the water temperature used for various applications. The performance of a solar water heater is evaluated experimentally. During the experiment, the solar radiation intensity and the feed water flow rate of 1.0 kg/min to 5.0 kg/min in steps of 1 kg/min are taken into consideration for analyzing the effect of ribbed textured tubes on the thermal effectiveness, frictional factor, convective transfer of heat, Reynolds number, and the Nusselt number of the PTSC. Furthermore, the overall performance of the PTSC is analyzed considering the above thermo-physical parameters. Based on the result of this study, at a flow rate of 3.0 kg/min, the thermal efficiency is found to be enhanced by about 28.25%, the friction factor is augmented by about 0.23%, the convective heat transfer coefficient is improved by 24.22%, and the Nusselt number is increased by about 26.32%. On average, an overall improvement in the performance of 8.25% is observed for the ribbed textured tube than that of the plain tube. The experimental error analysis shows that the standard deviation for both plain and ribbed textured tubes is in the range of 3.2, which is in the acceptable limit.

Heat Dissipation and Thermal Stress-Strain Characteristics of an Impinging Jet Strengthened Rib Surface under a Laser Heat Source

Heat Dissipation and Thermal Stress-Strain Characteristics of an Impinging Jet Strengthened Rib Surface under a Laser Heat Source

Computational study of heat transfer and fluid flow in a solar trough collector with a ribbed surface and an MWCNT—Al2O3/water-based hybrid nanofluid

The parabolic trough solar collector (PTSC) is renowned for its impressive ability to harness solar energy effectively. Nevertheless, it does suffer from a low thermal efficiency [Formula: see text], which presents an exciting opportunity for its performance enhancement using novel coolant hybrid nanofluids (NFs) and reconfigured receiver tubes. This study performs computational simulations to analyze the thermal and hydraulic performance of PTSC equipped with a V-ribbed receiver tube for MWCNT—[Formula: see text]/water hybrid. All turbulent flow simulations are performed for different values of parameters (relative rib height [Formula: see text], relative streamwise pitch ratio [Formula: see text] and relative spanwise pitch ratio [Formula: see text] of V-ribbed receiver tube with different Reynolds number [Formula: see text] (10,000–50,000). Various performance indicators (Nusselt number [Formula: see text], friction factor [Formula: see text], and performance evaluation criterion) had been investigated to assess the collector's performance. The results indicate that the highest Nu achieved of 760 with [Formula: see text]. Additionally, the maximum [Formula: see text] of 0.29 was observed at [Formula: see text] with [Formula: see text] and [Formula: see text]. Furthermore, the peak enhanced [Formula: see text] of 1.9 was attained with [Formula: see text], specifically at [Formula: see text] of 50,000. The findings indicate that using a V-ribbed receiver tube augments the heat transfer of the solar collector by 134.57% at Re of 50,000 with hybrid NF.

Effect of jet-impingement and surface roughness on performance of solar air heater: Experimental study and its optimization

The performance of solar air heaters can be improved by either active or passive techniques. In this research manuscript, both active and passive technique is used to enhance the thermal characteristics of the solar air heater. The proposed solar air heater consists of an innovative approach in which an impinging air stream and wired ribs (arranged in the multiple V-pattern over the absorber plate) are used for performance improvement. The impinging air stream is synchronized in such a way that it strikes the ribs to promote local turbulence. The investigation has been performed considering various design parameters like relative width ratio, relative roughness height/pitch, the angle of attack, the stream-wise jet pitch, the span-wise jet-wise pitch, and the jet diameter ratio. The results have shown that the presence of the ribs opposite to the impinging air stream promotes local turbulence over the ribbed surface which ultimately enhances the thermal characteristics of the solar air heater. The proposed design is also been optimized using the surface response methodology and the significance of the various roughness parameters on the thermal characteristics has also been predicted. Additionally, the best performance observed is 3.12 at a relative width ratio of 5, relative roughness height/pitch of 0.043/10, angle of attack of 60˚, stream-wise jet pitch of 0.4, span-wise jet-wise pitch of 0.84, and jet diameter ratio of 0.064.

Experimental investigations on the thermal performance of ultrasonic field in pool boiling on rib surfaces

Experimental investigations on the thermal performance of ultrasonic field in pool boiling on rib surfaces

Effects of Ribbed Surfaces on Profile Losses of Low-Pressure Turbine Blades

Abstract In this work, streamwise oriented riblets were installed on a flat plate exposed to an adverse pressure gradient typical of low-pressure turbine (LPT) blade and, successively, on the suction side of an LPT cascade operating under unsteady flow. Different riblet dimensions and positions have been tested to quantify their effects on the boundary layer transition and on losses. The flat plate experiments allowed the detailed description of the riblet effects on the coherent structures affecting transition, thus providing a rationale for the identification of the optimal riblet geometry once scaled in wall-units. For riblet heights equal to about 20 wall-units, a maximum loss reduction of 8% was observed. Otherwise, for larger riblet dimensions, earlier transition occurs due to enhanced boundary layer instability and losses increase. Interestingly, the streamwise extension of the ribbed surfaces with respect to the transition region was found to play a minor role compared with the riblet dimension. The riblet configurations providing the highest reduction of viscous losses were then tested in the LPT blade cascade for different Reynolds numbers and with impinging upstream wakes. An overall profile loss reduction comparable to that observed in the flat plate case has been confirmed also in the unsteady operation of the turbine cascade. Low sensitivity of the profile losses to the riblet streamwise extension was also observed in the cascade application. This confirms that positive effects in terms of loss reduction can be obtained even when the exact transition position is not known a priori.