Solid Ribs Research Articles

A Numerical Study on the Novel Composition of Porous and Solid Ribs to Augment the Thermal Performance of a Hybrid Nanofluid-Based Microchannel Heat Sink with External Fins

A Numerical Study on the Novel Composition of Porous and Solid Ribs to Augment the Thermal Performance of a Hybrid Nanofluid-Based Microchannel Heat Sink with External Fins

Structural performance of precast concrete sandwich panels with bolt-steel plate connection subjected to axial loading

A new precast concrete sandwich panel with glass fiber-reinforced polymer connectors was proposed, utilizing bolt-steel plate connections. A compressive experiment was carried out to investigate the performance. The main damage was concrete crushing in the bolt connection region, at the panel bottom, and above the joint. The connector type, solid concrete rib, slenderness ratio, and thickness affected the failure mode and bearing capacity. The use of GFRP connectors and solid concrete ribs enhanced the ultimate bearing capacity and stiffness of the panels while reducing the lateral deflection. Higher slenderness ratios leading to reduced axial bearing capacity and increased lateral deflection. Finally, the results of the existing empirical calculation formulae were compared with experimental ones, and they were overly conservative. A new formula for predicting the bearing capacity was proposed, and the difference percentages between the proposed formula and experimental results were −0.4 %–2.8 %, which was the most accurate prediction formula.

Stability mechanism and countermeasure of the solid coal rib in deep gob-side entry retaining: Insights from theoretical analysis numerical simulation

The stability and integrity of the solid coal rib in deep gob-side entry retaining (GER) can be compromised due to the cyclic loading and unloading caused by mining-induced stress. This can lead to failure of the deep GER during depressurized mining operations. In this study, we focus on a specific case at the 94103 working face in Qishan Coal Mine of Xuzhou Mining Bureau. We establish an engineering model that describes the interaction between the solid coal rib and the main roof in GER, aiming to elucidate the characteristics of main roof failure and instability throughout the entire GER process. this model particularly emphasizes the mechanical properties of the solid coal rib as a contributing factor. Additionally, developed a limit stress state model for evaluating bolt-supported plastic solid coal ribs, which helps determine appropriate support resistance levels to prevent two common forms of failure in these ribs. Furthermore, created a numerical calculation model to investigate different bolt conditions' impact on solid coal rib failure mechanisms. Finally, based on field monitoring data validation, we propose control measures for reinforcing solid coal ribs along with suggestions for roof support design and filling body construction schemes under similar geological conditions. These research findings offer valuable guidance for developing effective reinforcement strategies for filling bodies.

Improved flow boiling characteristics in minichannel with open-cell porous ribs

Porous metal has been proven to exhibit significant heat transfer enhancement in minichannel. Focusing on fully utilizing the advantages of porous metal in heat transfer and reducing pressure penalty, a porous ribs minichannel (PRM) heat sink employing open-cell porous copper as rib was designed and fabricated. PRM heat sink has 19 minichannels that are 1 mm in width and 2 mm in depth. Commercial open-cell porous copper with a porosity of 0.85 and 120 PPI (Pore per Inch, PPI) was selected. Flow boiling experiments were carried out with ethanol as the working fluid. The flow patterns of two heat sinks were recorded with a high speed photograph system and comparative analyzed. High-frequency periodic motion of vapor core boundary in width direction of porous ribs minichannel was recorded. This is considered a fluctuation of density wave along the channel width direction. Cooperating with capillary force, movement of vapor core boundary induces mass transfer between adjacent channels, compensating for uneven flow distribution between channels. The results show that PRM heat sink has better heat transfer performances and flow stability with a slight increment in pressure drop compared with solid ribs minichannel (SRM) heat sink. The porous ribs minichannel heat sink provides a new way to relieve flow insatiability for heat exchangers and thermal management systems.

Flow and heat transfer for the mist/steam two-phase flow in the U-shaped channel with column-row-ribs and solid ribs

The comparison of flow field and heat transfer characteristics for the new mist/steam working fluid inside the U-shaped internal cooling channel of the gas turbine blades roughed with new V-45 deg. Column-Row-Ribs and V-45 deg. solid ribs are conducted under the limited working conditions in this work. First, the secondary flow vortex and droplets distribution in channels with different turbulators were analyzed. Then, qualitative heat transfer comparison of these two different ribbed channels was conducted. Furthermore, the quantitative analysis of heat transfer enhancement and heat transfer uniformity was presented under the condition of different mist/steam mass ratio (mist/steam) and droplets diameter (D0). Through the analysis, it is seen that the Mainstream Secondary Flow Vortexes in U-shaped channel roughed with 45° V-shaped Column-Row-Ribs has the similar structure as the channel with 45° V-shaped solid ribs. The droplets have a more even distribution in U-shaped channel roughed with 45° V-shaped Column-Row-Ribs than channel with 45° V-shaped solid ribs. And the new Column-Row-Ribs will help to solve the problem that the droplets deposit at the windward side of the solid ribbed channel, which benefits to promote the heat transfer evenness of the heated wall. The results proved that the U-shaped channel with 45° V-shaped Column-Row-Ribs cooled with the mist-steam coolant has better heat transfer characteristics than the 45° V-shaped solid ribs. For the U-shaped channel, there exists a best droplet diameter which can achieve the highest heat transfer enhancement.

Intensification of heat transfer behind the backward-facing step using tabs

The influence of tab size and location on the flow structure, distribution of pressures on the surface, and heat transfer in the separation region behind the backward-facing step at Reynolds number Re = 4000 was experimentally investigated. The effect of tabs on the distribution of the local pressure and heat transfer coefficients in the longitudinal and transversal directions was studied. The presence of tabs significantly intensifies the heat transfer directly behind the separation point and brings the region of maximum heat transfer closer to the step. There is a strong uneven distribution of pressure coefficients and Nusselt numbers in the transverse direction due to the formation of vortical wake. The results of measurements are compared with the case of using two-dimensional obstacles in the form of solid ribs; the features of the development of the flow and heat transfer behind 3D tabs are analyzed. It is shown that the main difference in the installation of two-dimensional and three-dimensional obstacles is observed mainly in the immediate vicinity of the flow separation point at X/H < 6.

Heat transfer and fluid flow analysis of microchannel heat sinks with periodic vertical porous ribs

In this study, a detailed numerical analysis of the fluid flow and heat transfer of a three-dimensional microchannel is performed to evaluate the effect of using periodic vertical porous and solid ribs with various geometrical shapes, including rectangular, elliptical, isosceles triangular, backward triangular and forward triangular on the walls of this microchannel. Darcy-Brinkman-Forchheimer equations are used to model transport through the porous medium. The results for microchannels with solid ribs and with porous ribs are compared to each other. It is found that at the lowest studied inlet velocity (uin=0.25m/s), for the rib heights of Hr=0.025mm,0.05mmand0.07mm, the average Nusselt number of the porous-rib microchannel is 2.16, 2.1 and 1.3 times greater than the solid case, respectively; and, 2.505, 3.62 and 4.01 times greater than the no-ribs microchannel, respectively. It is found that for the same increase in the Nusselt number, the porous ribs induces much less pressure drop compared to the solid cases. Accounting the thermal and hydraulic performance simultaneously, Figure of Merit (FOM) is calculated. The results show that porous ribs lead in much better FOMs compared to the solid ribs case. Effects of the height, porosity and Darcy number of the ribs are also investigated.

Numerical simulation of a separated flow in a ribbed channel by the RANS and LES methods

The results of numerical simulation of a turbulent flow in a flat channel in the presence of vortex generators in the form of periodic solid ribs by the RANS and LES method are presented. The Reynolds number calculated by the rib height and the average flow rate is Re = 12600. The influence of the distance between the ribs on the flow structure is investigated. The boundaries of different types of roughness and their influence on the heat transfer intensity are shown.

Topology optimization on fuel tank rib structures for fuel sloshing suppression based on hybrid fluid–solid SPH simulation

In this paper, we propose a topology optimization method for aircraft fuel tank structural design to reduce the fuel sloshing effect, which is beneficial for aircraft fuel gauge accuracy and flight safety. The method is applied to optimize the hole layouts in the tank rib to reduce fuel sloshing time, increase stiffness, and guarantee lightweight requirements. Specifically, we introduce a hybrid fluid–solid particle based simulator by modeling the impact and elastic forces between fluid (fuel) and solid (ribs, tank wall), to analysis violent fuel sloshing inside the complicated internal tanks, caused by large angle maneuvers and accelerations of an aircraft. Meanwhile, an effective optimizer is built for the rib design, in which the explicitly controlled hole layouts are projected onto the modeled solid particles, such that the process of finite element meshing and remeshing is no longer needed during each optimization iteration. In this way, our proposed method is able to work with complicated aircraft fuel tanks under violent fuel sloshing conditions. We then use a real aircraft wing tank as design case to validate the proposed framework. The result shows that by the generated layout of rib holes, the fuel sloshing time is shortened by 46%, the maximal fuel gauge error is reduced by 14%, and the maximal center of gravity (CG) shift is reduced by 0.15 m.

Естественная конвекция в замкнутой полости с реберной структурой при наличии неравномерного температурного профиля на вертикальной стенке

The development of energy instrumentation, electronic industry and energy in general is inextrica-bly linked with the intensification of heat and mass transfer occurring in the base units and aggre-gates of energy systems. One of the approaches to solving this problem is to create an extended heat transfer surface by introducing a rib structure or porous inserts. This work is devoted to math-ematical modeling of natural convection in an enclosure in the presence of a rib structure and non-uniform temperature profile on one of the vertical walls. The governing partial differential equa-tions written using dimensionless non-primitive variables “stream function – vorticity – tempera-ture” based on the Boussinesq approximation, in combination with initial and boundary conditions, have been worked out on the basis of the finite difference method. The developed computational model was varified using the mesh independence test and benchmark problems solved by other au-thors. Numerical investigations of unsteady natural convection of viscous fluid in a cavity with a variable temperature on the left wall under an influence of a rib structure have been carried out for the following values of governing parameters: Pr = 0.71, 103 &lt; Ra &lt; 106, and the number of ribs varied from one to three. Distributions of streamlines and isotherms, as well as the dependences of the average Nusselt number and average cavity temperature, were obtained for a steady mode. As a result of the analysis, it has been found that the addition of solid ribs allows to enhance the heat transfer for low Rayleigh numbers, while for Ra  105 one can find an attenuation of convective heat transfer. A growth of the fins heat conductivity characterizes the heat transfer enhancement.

Preliminary rib support requirements for solid coal ribs using a coal pillar rib rating (CPRR)

Researchers from the National Institute for Occupational Safety and Health (NIOSH) are developing a coal pillar rib rating (CPRR) technique to measure the integrity of coal ribs. The CPRR characterizes the rib composition and evaluates its impact on the inherent stability of the coal ribs. The CPRR utilizes four parameters: rib homogeneity, bedding condition, face cleat orientation with respect to entry direction, and rib height. All these parameters are measurable in the field. A rib data collecting procedure and a simple sheet to calculate the CPRR were developed. The developed CPRR can be used as a rib quality mapping tool in underground coal mines and to determine the potential of local rib instabilities and support requirements associated with overburden depth. CPRR calculations were conducted for 22 surveyed solid coal ribs, mainly composed of coal units. Based on this study, the rib performance was classified into four categories. A preliminary minimum primary rib support density (PRSD) line was obtained from these surveyed cases. Two sample cases are presented that illustrate the data collection form and CPRR calculations.

The Effective Thermal Conductivity of Composite Phase Change Materials with Open-Cellular Metal Foams

Due to their high thermal conductivity, open-cellular metal foams are frequently used to improve the thermal conductivity of phase change materials. In this paper, the effective thermal conductivity of open-cellular foam filled with PCM with cubic units containing 12 solid tubular ribs was determined using an effective medium theory for composites. It was shown that metal foams with a large ratio of the radius of the tubular rib to its length can reach higher thermal conductivity. The case was also analyzed when the surface of the foam ribs was covered with a thin layer of another metal with high thermal conductivity. The results predicted by the proposed model were compared with the theoretical results of other models and with experimental data for some metal foam filled with phase change materials. A good agreement was achieved between present model predictions and experimental data.

Continuous Compaction and Permeability Evolution in Longwall Gob Materials

Understanding the evolution of gob compaction and related gas transport behavior is necessary for the planning and optimization of gas ventilation and control in longwall coal mines. In particular, the detachment of the undermined roof into the gob leaves a loosely compacted perimeter that skirts the longwall panel. This permeable gob perimeter in plan view forms as a result of shear separation from support provided by the solid ribs. This detachment and the resulting rotated and reduced stresses limit compaction, elevate permeability and exert significant control on gas flow during active longwall mining operations. We report gob compaction experiments on in-mine-collected fragmented rock and conduct mechanical compaction on stacked samples that are either uniformly coarsening upwards (case A) or are coarsening upwards, but capped by a segregated upper layer of coarse rock (case B). Observed compaction is linked to a capillary model representing porosity reduction and permeability evolution. As applied uniaxial stress increases from 0 to up to ~ 2000 kPa, the porosity decreases from 0.64 to 0.41(~ 36%) for the uniform stacked material (A) and but only from 0.66 to 0.51 (~ 23%) where the gob is topped with a layer of coarse “roof” rock simulants (B). Particle–particle self-adjustment dominates the compactive behavior at initial low stress and results in significant strain—followed by a linearly elastic region through the remainder of loading. The elastic regime is used to predict the permeability of the loosely compacted gob, considering the redistribution of stresses induced by shear collapse at the rib. Permeability evolution is scaled through the evolving compactive strains and particle size distribution of the fragmented rock, enabling results to be up-scaled to mine scale. These results provide a first rational method for analyzing the interactions between caved gob and the ventilation system towards mitigating gas concentrations and minimizing the hazard.

Effect of Permeable Ribs on Thermal-Flow Characteristics in an Internal Cooling Duct

Abstract This study aims to understand the effect of flow structures within the inter-rib regions of a novel permeable rib configuration in vertical and horizontal streamwise planes upon surface heat transfer parameters. In this investigation, the liquid crystal thermography (LCT) and particle image velocimetry (PIV) are used to extract the local heat transfer and flow-field information, respectively. The effect of slit-converging angle (ϕ = 0 deg, 5 deg, 10 deg, and 15 deg) are examined at a typical Reynolds number of 42,500 and relative rib pitch ratio of 10. Surface- and spanwise-average and overall augmentation Nusselt numbers are obtained along with the pressure drop measurements. Flow-field experiments are performed in both vertical and horizontal streamwise planes, and the results are expressed in terms of mean velocities, stream traces, turbulent statistics, coherent structures, and turbulent kinetic energy budgets. Critical points are also identified on the basis of critical point theory, which provides evidences of the different flow phenomena accountable for enhance mixing between the ribs. The secondary flow coming from the slit shows three-dimensionality in the flow resulting to higher turbulence intensity and rotational motion (say higher turbulent mixing), and thereby leading to high heat transfer just behind the permeable rib. The permeable ribs are also helpful in the reduction of friction factor by 32% with a typical ϕ value of 5 deg, compared to solid ribs, while the thermohydraulic performance increases with increasing ϕ from 0 deg to 15 deg up to 21%. The pentagonal ribs with convergent slit provide comparable or better performance among the permeable rib geometries used in the pertinent literature.

Reprint of: Flow and Heat Transfer Characteristics of the Mist/Steam Two-Phase Flow Cooling the Rectangular Channel with Column-Row-Ribs

Using mist/steam two-phase flow by mixing a small amount of fine water droplets into steam as the working fluid for the internal cooling passages of blades and vanes is a promising cooling technology for future gas turbines. We proposed a new cooling channel roughed with the column-row-ribs to achieve higher cooling efficiency and better heat transfer uniformity. The heat transfer experiment was conducted to validate the effectiveness of our numerical method. Flow and heat transfer performance of mist/steam two-phase flow was investigated in channels of different gap ratios and in a column-row-ribbed channel with gap ratios of ε = 0.177 under different working conditions. Comparing to the solid ribbed channel, the column-row-ribbed channels sacrifice the heat transfer performance to achieve better heat transfer uniformity. As ε larger than 0.264, the column-row-ribs have better thermal enhancement performance than the solid ribs. For the column-row-ribbed channel with gap ratio ε = 0.177, the heat transfer effect increases with the Re number. But the thermal uniformity and the thermal enhancement of the channel decreases obviously. As the wall heat flux q rises from 3000W/m2 to 40000W/m2, the thermal enhancement factor F gradually increases. But the wall heat transfer becomes less even. Continuously increasing the mist/steam mass ratio will help to increase the heat transfer effect of the heated walls, so does the heat-transfer non-uniformity. Simply increasing the droplets diameter will decrease the thermal enhancement factor and increase the heat transfer non-uniformity at the same time.

Heat transfer and flow characteristics of microchannels with solid and porous ribs

The microchannel cooling technology is an effective method to solve heat dissipation problems caused by high power electronic devices. In this work, the heat transfer and flow characteristics of microchannels with solid and porous ribs are comprehensively investigated using numerical approaches. It is reported that the thermal performance of microchannels with solid and porous ribs are significantly better than those without any ribs. The field synergy principle is adopted to analyze the thermal performance, which proves that microchannels with porous ribs show a better synergy effect compared to those with solid ribs. On the other hand, the pressure drops and friction factors for all microchannels with solid ribs are larger than those with porous ribs. When solid ribs are replaced by porous ribs, the pressure drops reduce about 67%, 57% and 12% for the middle, symmetrical and staggered rib configurations, respectively. It can be found that vortices and recirculation flow come into being behind solid ribs. The thermal boundary layers are disrupted and redeveloped due to the intensified fluid mixing in porous regions, which facilitates the convective heat transfer. Finally, the comprehensive thermal and hydraulic performance is evaluated, and microchannels with symmetrical and staggered porous ribs exhibit the best comprehensive thermal and hydraulic performance.

Flow and Heat Transfer Characteristics of the Mist/Steam Two-Phase Flow Cooling the Rectangular Channel with Column-Row-Ribs

Using mist/steam two-phase flow by mixing a small amount of fine water droplets into steam as the working fluid for the internal cooling passages of blades and vanes is a promising cooling technology for future gas turbines. We proposed a new cooling channel roughed with the column-row-ribs to achieve higher cooling efficiency and better heat transfer uniformity. The heat transfer experiment was conducted to validate the effectiveness of our numerical method. Flow and heat transfer performance of mist/steam two-phase flow was investigated in channels of different gap ratios and in a column-row-ribbed channel with gap ratios of ε=0.177 under different working conditions. Comparing to the solid ribbed channel, the column-row-ribbed channels sacrifice the heat transfer performance to achieve better heat transfer uniformity. As ε larger than 0.264, the column-row-ribs have better thermal enhancement performance than the solid ribs. For the column-row-ribbed channel with gap ratio ε=0.177, the heat transfer effect increases with the Re number. But the thermal uniformity and the thermal enhancement of the channel decreases obviously. As the wall heat flux q rises from 3000W/m2 to 40000W/m2, the thermal enhancement factor F gradually increases. But the wall heat transfer becomes less even. Continuously increasing the mist/steam mass ratio will help to increase the heat transfer effect of the heated walls, so does the heat-transfer non-uniformity. Simply increasing the droplets diameter will decrease the thermal enhancement factor and increase the heat transfer non-uniformity at the same time.

Turbulence characteristics over k-type rib roughened porous walls

To understand the permeability effects on turbulent rib-roughened porous channel flows, particle image velocimetry measurements are performed at the bulk Reynolds number of 5000–20000. Solid impermeable and porous ribs are considered for the rib-roughness whose geometry is categorised in the k-type roughness whose pitch/rib-height is 10. Three isotropic porous media with nearly the same porosity: 0.8, and different permeabilities (0.004, 0.020, 0.033 mm2) are applied. It is observed that the recirculation between the ribs becomes weak and the recirculation vortex submerges into the porous wall as the wall permeability and Reynolds number increase for both solid and porous rib cases while the recirculation vanishes in high permeable cases. These phenomena result in characteristic difference in turbulence quantities. By fitting the mean velocity profiles to the log-law form, the permeability effects of both rib and bottom wall on the log-law parameters and the equivalent sand-grain roughness are discussed. It is concluded that the zero-plane displacement increases while the von Kármán constant and the equivalent sand-grain roughness decrease as the wall and rib permeability increases.

Parametric study on flow characteristics and heat transfer in rectangular channels with strip slits in ribs on one wall

Augmentation of heat transfer must always be judged against an additional pressure loss. To this context, this paper explores slitted ribs on the turbulent flow and heat transfer characteristics in rectangular cooling channels with an aspect ratio of 4:1. A verified v2f turbulence model is applied in the present numerical simulations in the Reynolds number range from 20,000 to 80,000. The flow and thermal performance of various geometrical structures for the ratios of slit-length-to-rib-length (Rl = 0, 0.20, 0.35 and 0.50) and the rib heights (e = 10 mm, 15 mm and 20 mm) are comprehensively compared and evaluated. Special thermal behaviors are carefully observed and analyzed with slits on ribs of different height. It is found that strip slits in low-height ribs provide both lower Nusselt number and friction factors than the corresponding solid ribs, while an opposite effect is captured for strip slits on high-height ribs. The present results suggest that introducing a short-length strip slit in ribs could be a beneficial way to enhance heat transfer of cooling channels with high-height ribs.

Reverse Modeling and Topological Optimization for Lightweight Design of Automobile Wheel Hubs with Hollow Ribs

Lightweight of wheel hubs is the linchpin for reducing the unsprung mass and improving the vehicle dynamic and braking performance of vehicles, thus, sustaining stability and comfortability. Current experience-based lightweight designs of wheel hubs have been argued to render uneven distribution of materials. This work develops a novel method to combine the reverse modeling technique with the topological optimization method to derive lightweight wheel hubs based on the principles of mechanics. A reverse modeling technique is first adopted to scan and reproduce the prototype 3D geometry of the wheel hub with solid ribs. The finite element method (FEM) is then applied to perform stress analysis to identify the maximum stress and its location of wheel hub under variable potential physical conditions. The finite element model is then divided into optimization region and nonoptimized region: the former is the interior portion of spoke and the latter is the outer surface of the spoke. A topology optimization is then conducted to remove the optimization region which is interior material of the spokes. The hollow wheel hub is then reconstructed with constant wall thickness about 5[Formula: see text]mm via a reverse modeling technique. The results show that the reconstructed model can reduce the mass of 12.7% compared to the pre-optimized model. The present method of this paper can guarantee the optimal distribution of wheel hub material based on mechanics principle. It can be implemented automatically to shorten the time interval for optimal lightweight designs. It is especially preferable for many existing structures and components as it maintains the structural appearance of optimization object.