Groove Aspect Ratio Research Articles

Enhancing heat transfer in various grooved annular for Taylor-Couette-Poiseuille flow

The present study investigated the impact of various parameters on pressure drop, Nusselt number, and friction factor in grooved annular channels, which have practical applications in cooling electric motors and generators. The parameters studied include the effective Reynolds number, Taylor number, groove aspect ratio, number of grooves, and groove angle. The k-ω SST turbulence model was employed in CFD simulations for various parameter ranges. These ranges include an effective Reynolds number spanning from 4.42 × 103to 1.6 × 104, Taylor number of 0–2.24 ×106, the groove aspect ratio of 0 to 2, the number of grooves ranging from 5 to 20, and the groove angle ranging from 70° to 130°. As the effective Reynolds and Taylor numbers increase within the ranges noted above, the Nusselt number exhibits a corresponding increase of 9.16 % and 1.77 %, respectively. However, the effective Reynolds number plays a more significant role. Various design factors, including the number of grooves, the aspect ratio, and the groove angle, also influenced the heat transfer enhancement. As any of these factors increase within the specified ranges, the corresponding Nusselt number values increase by 2.35 %, 3.62 %, and 6.09 %, respectively.

Jets from shocked metal surfaces with grooves: Missing experiments

Many studies have investigated the mass outflows generated when a planar shock transits an imperfect (“defected”) metal surface, where the defects are symmetric triangular or sinusoidal grooves. Yet a fundamental question remains unanswered: how does the quantity of outflow mass and its maximum velocity vary as a function of the groove cross-sectional aspect ratio? We identify two sets of missing experiments that must be addressed to answer the question. The aspect ratio (groove depth over width) is equivalently represented by θ, the cross-sectional half angle, or by η0k, the amplitude multiplied by an effective wavenumber. Low θ (high η0k) grooves comprise the first set of missing experiments, which are necessary to determine the validity of theoretical predictions of the nonlinear regime (η0k≥1, θ<57.5°). The second set of missing experiments are those in which the volume of the groove (or equivalently, the axial cross-sectional area) has been held constant as θ or η0k are varied. Such experiments are necessary to independently measure the effects of variations in groove volume and groove aspect ratio on the resulting jets.

Experimental study of interfacial adhesion performance of prefabricated UHPC-NC diagonal shear groove

The reinforced lining of the tunnel was carried out using a prefabricated composite structure consisting of Ultra-High Performance Concrete (UHPC) and Normal Concrete (NC), utilizing a semi-post-pouring method. The bond performance between UHPC and NC is crucial for enhancing the overall stability and safety of the tunnel. To investigate the influence of interface construction on the bond performance at the UHPC-NC interface, inclined shear tests were conducted with variations in groove density, groove morphology, groove aspect ratio, and interface angle. The results revealed four different failure modes of the grooved specimens, with over 80% exhibiting failure at the interface between UHPC and NC. The average interface bond strength of the grooved specimens was found to be 5.8 times higher than that of the untreated interface group, indicating a significant improvement in the bond performance of the UHPC-NC interface due to the presence of grooves. When the volume loss ratio was below 0.09, the interface bond strength of the UHPC-NC interface increased with an increase in groove density. The interface bond strength of the 60° trapezoidal grooves was 80% higher than that of the right-angle grooves, while the interface bond strength of the 40° trapezoidal grooves was 28% higher than that of the right-angle grooves. Furthermore, the interface bond strength decreased as the angle between the interface and the horizontal plane increased. The precast inclined shear grooves exhibited a bond-slip curve that consisted of an initial slow-rise stage, an elastic rise stage, a yield stage, and a failure descent stage, with some specimens not exhibiting a distinct yield stage. In this study, a bond-slip model for the precast UHPC-NC inclined shear grooves was proposed, and recommendations for bond stiffness were provided.

Influence of focus positions on underwater femtosecond laser dicing of silicon wafer

This paper investigates the effects of laser-induced bubbles on the surface morphology of silicon wafer at three focus positions: above the focus (positive-defocus), at the focus and below the focus (negative-defocus). Firstly, the behaviors of the bubbles are observed from both the side view and top view of the laser ablation process at the three focus positions. Next, time-resolved shadowgraph images were used to examine evolution of the cavitation bubbles. The experimental results show that laser positive-defocus machining was accompanied by many bubbles, which aggregated to form a large bubbles barrier on the silicon wafer surface and disturbed the subsequent laser beam, and resulted in poor surface morphology of the groove. Compared to the laser machining at focus, laser positive-defocus machining reduced the groove depth by 77.77 %, groove aspect ratio by 80.98 %, cavitation bubbles size by 52.08 %, and cavitation bubbles lifetime by 58.82 %. Laser negative-defocus machining produced few bubbles that moved in the opposite direction of laser scanning. The bubbles did not interfere with the subsequent laser pulses and showed little effect on the surface morphology of the machined groove. Compared to the laser machining at focus, the laser negative-defocus machining increased the groove depth by 88.61 %, groove aspect ratio by 45.65 %, cavitation bubbles size by 65.64 %, and cavitation bubbles lifetime by 80.08 %. The results show that the negative-defocus machining method has application prospects in underwater laser machining.

Unraveling the influence of surface roughness on oil displacement by Janus nanoparticles

Janus nanoparticles (JNPs) possess great potential in recovering the residual oil from reservoirs, however, the fundamental interaction mechanisms among nanoparticles, the oil, and reservoir wall characteristics remain to be elucidated. In this work, models of oil trapping grooves with different geometric features are subjected to molecular dynamics simulations for investigating the influences of roughness parameters on oil displacement dynamics by JNPs. Four key surface geometry parameters and different degrees of surface hydrophobicity are considered. Our results indicate that JNPs hold an outstanding performance in displacing residual oil on weakly to moderately hydrophobic surfaces. Overall, smaller entry and exit angles, the larger aspect ratio of the oil trapping grooves, and a bigger tip length of the rough ridges lead to superior oil recovery. Among the key geometric parameters, the aspect ratio of the oil trapping grooves plays the dominant role. These insights about the interaction of surface properties and JNPs and the resulting trapped oil displacement could serve as a theoretical reference for the application of JNPs for targeted reservoir conditions.

Circumferentially Grooved Seal Flow Field Analysis Based on Effective Film Thickness to Improve Bulk Flow Models

Abstract Bulk flow methods for circumferentially grooved seals use simplified physics models to predict leakage and rotordynamic coefficients efficiently, but uncertainty in empirical quantities like friction factors and loss coefficients leads to limited accuracy. To develop a more fundamental understanding of incompressible grooved seal flow, this study utilizes computational fluid dynamics (CFD) and an effective film thickness, a physical boundary between the jet and recirculating flows, to investigate Reynolds number effects on flow fields and shear stresses. Simulations are run using ansyscfx for a single groove seal model where streamlined analysis produces the effective film thickness. Flow structures, film thicknesses, shear stresses, and net flow expansion into the groove are found to be described completely by the ratio of circumferential to axial Reynolds number and the total resultant Reynolds number. Decreases in leakage with rotor speed are found to be dictated by increased land shear stresses and a decreased role of the groove in inducing pressure drop. An optimal groove aspect ratio between 0.07 and 0.19 is presented based on maximizing expanded film area while retaining a main groove recirculation region. This is the first paper to analyze circumferentially grooved seal flow from an effective film thickness standpoint. The results highlight bulk flow analysis areas where an effective film thickness approach could lead to new, physics-motivated model development and the elimination of particular empirical coefficients, thus providing a foundation on which substantial improvements in bulk flow modeling accuracy can be achieved.

Dewetting regimes of condensation droplets in a microgroove

This paper describes a numerical investigation of the groove-embedded droplet dewetting process, namely the spontaneous transition from the Wenzel state to the Cassie state, using the multiphase lattice Boltzmann method. Numerical simulations are employed to reproduce the dynamic behaviors of extension, squeezing, rupture, and ejection of condensation droplets in a groove, allowing us to examine how the groove geometry and wettability affect the dewetting process. Our results identify three dewetting regimes, namely retention, partial dewetting, and complete dewetting. As the groove aspect ratio and hydrophilicity decrease, the dewetting regime changes from retention to partial dewetting, and then to complete dewetting. The partial dewetting and complete dewetting are two effective ways for droplet removing. In particular, a groove sidewall with enhanced hydrophobicity is desirable to stimulate the dewetting process.

Investigation of convective heat transfer and flow hydrodynamics in rectangular grooved channels

An experimental and numerical investigation is conducted for convective heat transfer and flow characteristics in a channel with rectangular grooved top and bottom walls. The study is performed between 2 × 103and 6.5 × 103 of Reynolds numbers. Heat transfer experiments are conducted by applying constant heat flux to the channel upper and lower walls. The averaged Nusselt number, Nu, is presented as an indicator of heat transfer. In the experiments, 1.9–2.4 times larger Nu values were obtained by using grooved channels instead of straight channels. Pressure measurements show that the corrugated channel causes an increase in pressure loss. The Particle Image Velocimetry, PIV method is employed to reveal the flow hydrodynamics and its relation with convective heat transfer. Using the ability of the PIV method to provide instantaneous flow data, interactions between the recirculation flow bubbles in the grooves and the mainstream are observed. In the numerical part of the study, the k-ε turbulence model is used, and predicted results are found to be consistent with experiments. The validated numerical method is used to investigate the effect of groove aspect ratio on heat transfer and pressure drop.

Oropharyngeal morphology related to filtration mechanisms in suspension‐feeding American shad (Clupeidae)

To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.

Laser ablation of silicon in water at different temperatures

Underwater laser machining process is an alternative method to cut materials with less thermal damage due to the water cooling of workpiece during the ablation. However, the rapid cooling induced by water can instantly solidify the laser-molten material rather than expel it to form a cut. To understand the roles of processing temperature on ablation performance in water, this paper presents the influences of water temperature on cut width, depth, and surface morphology in the underwater laser grooving of silicon. The effects of laser power, laser traverse speed, and number of laser passes on the groove characteristics were also examined in this work. The results revealed that using high water temperature can increase the groove aspect ratio, particularly when high laser power, slow traverse speed, and multiple laser passes were employed. However, debris deposition and oxides were found on the laser-ablated surface when processing at high water temperature. The implication of this study could enhance the ablation rate for the underwater laser as well as low-power laser cutting systems.

Application of machine learning to predict the product quality and geometry in circular laser grooving process

Micro-grooves have various applications in different industries. Circular laser grooving is a new method for manufacturing micro-grooves on the circumference of cylindrical parts. In this process, the selection of appropriate parameters to reach experimentally the desired groove aspect ratio along with minimum dross formation requires tremendous efforts. Here, the role of a decision-making technique, similarly machine learning is highlighted to evaluate the significance of process inputs and provide the appropriate model for prediction concerning the input parameters. The experiments were conducted with the various inputs such as workpiece rotational speed, laser beam position, duty cycle, power and frequency. The outputs are the groove geometry in terms of width and depth of the circular groove as well as the groove quality considering the dross formation. Then, Random Forest (RF) technique was utilized to derive the most influential inputs on the outputs. The RF analysis revealed that the rotational speed, laser position and duty cycle are the most decisive process parameters in the groove geometry and groove quality. Also, the enhancement of the assist gas pressure does not improve the process outputs according to the results of RF analysis.

Investigation into laser machining of carbon fiber reinforced plastic in a flowing water layer

Over-melting and vaporization of resin matrix are usually found along a cut in the laser machining of carbon fiber reinforced plastic (CFRP). This is considered as the heat-affected zone (HAZ) and it has to be minimized to avoid the delamination of CFRP laminates. This paper presents the use of water flow to cool down the CFRP during the laser machining process. A thin flowing water layer induced by the impingement of low-pressure waterjet was formed on the workpiece surface, where a laser beam performed the ablation underneath the water layer. With this technique, the excessive heat and cut debris can be carried away from the workpiece by water. In this study, the effects of laser traverse speed, orientation of carbon fiber, water flow rate, and flow direction on cut dimensions and HAZ size were experimentally investigated. Using high water flow rate can limit the expansion of HAZ and also assist the material removal. In addition, the water flow directed along the laser traverse direction can increase the cut depth. The groove aspect ratio produced by the presented technique was found to be the same level as the laser ablation in air but the HAZ size was 20% smaller than the dry ablation. A predictive model for cut depth based on energy balance was also developed and analyzed in this study. The experimental findings and theoretical model presented in this work could enable a better understanding of the laser ablation in the flowing water layer and highlight the potential use of this technique for processing CFRP and other similar materials.

Predictions of the effective slip length and drag reduction with a lubricated micro-groove surface in a turbulent channel flow

We perform direct numerical simulations of a turbulent channel flow with a lubricated micro-grooved surface to investigate the effects of this surface on the slip characteristics at the interface and the friction drag. The interface between water and lubricant is assumed to be flat, i.e. the surface-tension effect is neglected. The solid substrate, where a lubricant is infused, is composed of straight longitudinal grooves. The flow rate of water inside the channel is maintained constant, and a lubricant layer under the interface is shear driven by the turbulent water flow above. A turbulent channel flow with a superhydrophobic (i.e. air-lubricated) surface having the same solid substrate configuration is also simulated for comparison. The results show that the drag reduction with the liquid-infused surface highly depends on the lubricant viscosity as well as the groove width and aspect ratio. The amounts of drag reduction with the liquid-infused surfaces are not as good as those with superhydrophobic surfaces, but are still meaningfully large. For instance, the maximum drag reduction by the heptane-infused surface is approximately 13 % for a rectangular groove whose spanwise width and depth in wall units are 12 and 14.4, respectively, whereas a superhydrophobic surface with the same geometry results in a drag reduction of 21 %. The mean slip length normalized by the viscosity ratio and groove depth depends on the groove aspect ratio. The ratio of fluctuating spanwise slip length to the streamwise one is between 0.25 (ideal surface without groove structures) and 1 (i.e. isotropic slip), indicating that the slip is anisotropic. Using the Stokes flow assumption, the effective streamwise and spanwise slip lengths are expressed as a function of groove geometric parameters and lubricant viscosity. We also suggest a predictive model for drag reduction with the heptane-lubricated surface by combining the predicted effective slip lengths with the drag reduction formula used for riblets (Luchini et al., J. Fluid Mech., vol. 228, 1991, pp. 87–109). The predicted drag reductions are in good agreements with those from the present and previous direct numerical simulations.

Wetting Transition from the Cassie-Baxter State to the Wenzel State on Regularly Nanostructured Surfaces Induced by an Electric Field.

When droplets are placed on hydrophobic textured surfaces, different wetting states Cassie-Baxter (CB) state or Wenzel (W) state may occur depending on materials and structures of surfaces, types and sizes of droplets, thermal fluctuations, and external stimuli. The wetting transition from the CB to the W state and the opposite process have attracted a great deal of attention because of their primary importance for designing and fabricating textured surfaces. In this work, molecular dynamics (MD) simulations are employed to understand the mechanism behind the CB-to-W transition for a nanoscale water film placed on a surface decorated with a single nanogroove when an external electric field is applied. The free energy variation during the transition process is computed on the basis of the restrained MD simulations. Water intrusion into the groove is observed by simulation snapshots, which provides direct evidence for the electric field-induced CB-to-W transition. In the previous experiments, however, only a sharp reduction in the apparent contact angle is employed to judge whether the transition takes place. The free energy curves reveal that there are two energy barriers separating the CB and W states (Δ E1) as well as separating the W and CB states (Δ E2). Owing to the presence of Δ E1, although the CB state has a higher free energy than the W state, it cannot spontaneously convert to the W state. When the external energy input exceeds Δ E1, the CB-to-W transition can be triggered, otherwise the transition will stop, and the water film will return to the CB state. Moreover, it is found that the maximum of free energy always occurs after the film touches the groove bottom. Thus, the requirement that the film should touch the groove bottom is responsible for the presence of the energy barrier Δ E1. Finally, the dependence of the two energy barriers on the electric field strength, groove aspect ratio, and intrinsic contact angle of the groove is also discussed.

Experimental study of convective heat transfer in the entrance region of an annulus with an external grooved surface

The aim of this experimental work is to study the effect of grooved surfaces in the entrance region of annular flows on local heat transfer. The outer stationary cylinder is grooved and the inner rotating cylinder is smooth. This configuration is applicable in industrial applications such as rotating heat pipes for cooling of superconducting machines or motors rotor, electrical generators where heat generates in the grooves containing wires, transient heating of axial compressor rotor drams, combustion chamber in turbojets, air-cooled axial-flux permanent-magnet machines. The experimental tests were performed based on aspect ratio of the groove, effective Reynolds number and Taylor number. It is observed that the dimensions of the groove, rotational speed as well as fluid axial velocity have significant effect on heat transfer rate. The present results show that the gradient of the averaged air temperature in the groove zone is larger than that in the gap between the two cylinders and temperature in this zone can be approached to the surface temperature if the channel length is long enough. In addition, a correlation for the local Nusselt number is proposed as a function of the effective Reynolds number, the groove aspect ratio and the local axial position from 270 experimental data. The correlation is capable to predict the local Nusselt number with a maximum error within 11% relative to the experimental data.

Heat transfer enhancement in annular flow with outer grooved cylinder and rotating inner cylinder: Review and experiments

This experimental work is an attempt to identify the most significant parameters influencing heat transfer enhancement in annular flow with outer grooved cylinder and rotating inner cylinder. This type of flow known as Taylor-Couette flow has many industrial applications such as electrical power generators and rotating machineries. A comprehensive review of the previous works on flow regimes, heat transfer and pressure drop in grooved channels is provided. The experiments are conducted based on four different factors including Taylor number, 0<Ta<8.36×106; groove aspect ratio, 0<b/c<2; number of grooves, 0<Ngr<20 and wall temperature, 50<Tw<90°C. Among four different test cases, the average Nusselt number of the model with aspect ratio b/c=2 is higher than the other three cases, i.e., b/c=0,0.5,1. It is found that in the presence of grooves, the thermal entrance length in rotating channel is reduced about 17% due to perturbation and vorticity of the flow inside the channel. Finally, the results are analyzed according to the principle of response surface methodology. It is found that, heat transfer enhances significantly with increasing groove aspect ratio and rotational speed.

Optimization of the heat transfer coefficient and pressure drop of Taylor-Couette-Poiseuille flows between an inner rotating cylinder and an outer grooved stationary cylinder

The aim of this study is to find optimum values of design parameters of annular flow with outer grooved cylinder and rotating inner cylinder in the presence of axial flow by using Response surface Method (RSM). This configuration is popular in cooling of electric generators and rotating machineries. Groove aspect ratio (0<b/c<1.5), number of grooves (0<Ng<20), Taylor number (0<Ta<2.24×106) and axial Reynolds number (4437<Rea<14,297) are selected as design parameters while the Nusselt number (Nu) and pressure drop (ΔP) are selected as responses. Firstly, the effect of b/c and Ng on pressure drop, friction factor and heat transfer enhancement inside grooved channel is investigated. In the next step, RSM has been employed to construct correlations required in optimization. The accuracy of correlations is proved experimentally. Finally optimization based on heat transfer to pressure drop ratio has been employed to determine optimum values of design parameters to maximize heat transfer and minimize pressure drop of Couette-Taylor-Poiseuille flow inside the grooved channels. Heat transfer to pressure drop ratio is maximum at b/c=1.42 and Ng=19. This optimization gives a lot of freedom to designers to choose the optimal geometric parameters of electric motors.

Improving Surface Hydrophobicity by Microrolling-Based Texturing

A two-pass microrolling-based texturing (μRT) process was utilized to improve the hydrophobicity of aluminum surfaces. Square micropillars were fabricated on aluminum sheets by two mutually orthogonal forming passes by a roller pretextured with microgrooves. Subsequently, the droplet contact angle was measured to evaluate the hydrophobicity of the surface. Results show that surfaces with μRT-imprinted textures have higher contact angles than nontextured surfaces indicating improved hydrophobicity. Furthermore, the process has led to the creation of hierarchical valleylike features on top of each of the micropillars caused by the pile-up effect during the forming process. It was hypothesized that such hierarchical features positively contribute to the improved hydrophobicity of the surface. This hypothesis was validated by testing surfaces with a similar hierarchical textured pattern produced by laser-induced plasma micromachining (LIPMM). The effects of various aspects of texture geometry including surface area-to-volume ratio and groove aspect ratio on the surface contact angle and the anisotropy of the contact angles were investigated.

Around the corner: Colloidal assembly and wiring in groovy nematic cells.

We study colloids suspended in nematic liquid crystal in grooves with homeotropic anchoring. We observe "eyelashes", topological dipole chains that follow the local, curved director field. These beget wires that connect the groove corners to topographical features on the cell lid to yield oriented, curvilinear colloidal wires spanning the cell, formed in a nonsingular director field. As the groove aspect ratio changes, we find different ground states and corroborate our observation with numerics. Our results rely upon on the scale of topographical features, the sharpness of edges, and the colloid-sourced distortions; all these elements can be exploited to guide the formation of reconfigurable structures in nematics.

Influence of Changing Casing Groove Parameters on the Performance of Centrifugal Compressors Near Stall Condition

The casing treatment is an effective method for increasing the stall margin of compressors and enhancing the flow distribution at the blades tip. The present numerical study focuses on making an optimization of the casing groove parameters which can enhance the centrifugal compressor performance during stall. The casing grooves parameters considered are the groove cross section aspect ratio (the groove height to width ratio), groove location, and the number of grooves. Five groove aspect ratios were considered ranging from 0.2 to 1.8. Three groove locations were studied: at full blades leading edge, at splitter blades leading edge, and after the splitter blades leading edge by a distance equals to the distance between the first and second groove locations. Comparisons were made among different cases with number of grooves starting from one up to seven grooves located at the most effective locations and have the optimum cross section dimensions as deduced from the results of the groove aspect ratio and groove location optimization. Results showed that by using groove aspect ratio less than one, the reinjected groove flow is relatively weak but when the aspect ratio is equal to one, there is enough space inside the groove for the flow to circulate and generate the reinjected groove flow with higher velocities. When the groove aspect ratio was increased to be more than one, the reinjected flow velocity was increased slightly and its effective area was increased in the circumferential direction. Results also indicated that the best location for the groove is at the full blades leading edge because the stall area can be minimized and controlled in a better way comparing with the other groove locations. Results showed that by increasing the number of grooves, the surge margin (SM) increases and the isentropic efficiency decreases, but the stall area at the shroud surface decreases in size and its location is shifted toward the blades trailing edge.