Groove Width Ratio Research Articles

Effect of droplet size on wetting behavior on laser textured SiC surface

Effect of droplet size on wetting behavior on laser textured SiC surface was studied in this work. The micro-square-convex surface was processed on smooth surface with intrisinc contact angle 101°. Then contact angles were measured on both smooth and textured surface by sessile drop method using deionized water with different droplet volume. It was found that there was significant droplet size effect on wetting behaviors for the textured SiC surface. Contact angles on smooth surface kept stable for different water droplet volume with a variation amplitude 13°. However, contact angles increased significantly from 42.25° to 131.25° with increasing droplet volume from 0.001μL to 1μL, then remained unchanged when the droplet volume exceeds 1μL. The correlation analysis shows that contact angles increase with the increasing ratio of base diameter and groove width, then keep stable when the ratio exceeds 25, which explains the wetting behavior for different droplet volume.

Influences of die structure on constrained groove pressing of commercially pure Ni sheets

Constrained groove pressing (CGP) is an attractive technique for fabricating ultra-fine grained sheet metals through intense plastic deformation. The design of groove dies is of great importance to the evolutions of microstructure and mechanical properties of materials during CGP. Thus, in this work, the effects of groove width and angle on CGP of commercially pure Ni sheets were investigated by experimental and numerical methods. The results show that an optimum combination of mechanical properties for sheet samples with a thickness of 2mm is obtained by a two-pass CGP with a groove width of 2mm and a groove angle of 45°: the yield and tensile strengths are 476.3 and 532.3MPa, respectively, the elongation to failure is 10.6%, and the average hardness is 218.9HV. In this case, numerous elongated subgrains with a mean width of about 500nm are observed and separate grains having clear boundaries and high misorientation angles begin to appear in the microstructure. CGP with a lower groove angle induces more effective passes but a lower process rate, while it enhances the shear intensity with a smaller groove width. Detailed analysis by a simplified model for flattening establishes the process conditions to maintain the stable shear deformation in CGP: an upper limit of the ratio of groove width to sample thickness is 1.25 when the groove angle is 45°, or an upper limit of groove angle is 50.8° when the ratio is 1.0. Once exceeding the limits, the deformation mode may change from pure shear to bending. Numerical and experimental results reveal that, compared with pure shear, the bending deformation is more likely to cause micro-cracks at the sheet surface due to work hardening and stress concentration. In addition, using groove dies with a width of 3mm and an angle of 45°, a rotated cubic texture {100}〈011〉 is developed from the strong cubic texture {100}〈001〉 of the annealed Ni sheets. The forming load of CGP dies shows exponential decrease with groove width but no significant variation with groove angle.

Automated Method for Stereometric Study of Fatigue Failure Mechanisms

Fatigue crack growth micromechanisms are studied in 25Kh1M1F/15Kh13MF bimetal specimens with a side notch with asymmetry cycle R = 0. The main features are established for the geometric ratio of fatigue groove width and depth around the 25Kh1M1F/15Kh13MF bimetal interface.

The role of lubricant feeding conditions on the performance improvement and friction reduction of journal bearings

Most conventional hydrodynamic journal bearing performance tools cannot suitably assess the effect of lubricant feeding conditions on bearing performance, even though these conditions are known to affect important performance parameters such as eccentricity and power loss.A thermohydrodynamic analysis suitable to deal with realistic feeding conditions has been proposed. Special attention was given to the treatment of phenomena taking place within grooves and their vicinity, as well as to the ruptured film region.The effect of lubricant feeding pressure and temperature, groove length ratio, width ratio and number (single/twin) on bearing performance has been analyzed for a broad range of conditions. It was found that a careful tuning of the feeding conditions may indeed improve bearing performance.

Influence of the Groove Width on the Aerostatic Dry Gas Seal

Aerostatic dry gas seal has attracted more and more attention because of its advantages with low friction loss, low heat generation, large opening force and high gas film stiffness at low-speed operation situation. The influence of the radial groove width ratio,Bw, on the performance of the aerostatic dry gas seal has been investigated by an analytical method by solving the N-S equation in order to understand the performance of the seal further more. The results show that the effect of the radial groove width ratio,Bw, on the opening force and on the gas film stiffness is obvious. The opening force decreases with the radial groove width ratio,Bw, increasing at the same gas film thickness. The situation of the gas film stiffness is complex. When the gas film thickness is smaller than a critical value, about 6μm as to the example presented in this paper, the gas film stiffness increases with theBwincreasing, but the gas film stiffness decreases with theBwincreasing when thickness is larger than the critical value. With the increasing ofBw, the leakage to the atmosphere,Q2, increases, but the leakage to the process fluid,Q1, reduces.

Wetting Behavior and Drainage of Water Droplets on Microgrooved Brass Surfaces

In the present study, contact angle hysteresis and sliding behavior of water droplets on parallel, periodic microgrooved brass surfaces are investigated experimentally for enhancement of water drainage and compared to that on flat baseline surfaces. The surfaces (a total of 17 microgrooved samples, with a range of groove depth of 22 to 109 μm, pillar width of 26 to 190 μm, and groove width of 103 and 127 μm) are fabricated using a mechanical micromachining process. The wetting state and shape/elongation of deposited water droplets, anisotropy of the contact angle hysteresis, and the drainage behavior of water droplets on the microgrooved surfaces are found to be strongly dependent on the topography of the groove geometry, which is analyzed in detail. The wetting state is found to be Wenzel for microgrooved surfaces with very low aspect ratio (<0.2) and narrow pillars (pillar width to groove width ratio of ≈0.2), and also for the two deepest grooved surfaces of two different sample series, all of which exhibit high contact angle hysteresis. Mechanisms of the advancing and receding motions are identified. The critical sliding angle (the angle from horizontal at incipient motion of the advancing confluence) for the microgrooved surfaces is found to be significantly smaller than for flat surfaces. The sliding angle exhibits significant groove geometry dependence and is found to increase with pillar width and decrease with groove depth. The findings of this study may be useful in a broad range of applications where water retention plays an important role.

Effect of gas diffusion layer modulus and land–groove geometry on membrane stresses in proton exchange membrane fuel cells

The electrical functionality of PEM fuel cells is facilitated by minimizing the contact resistances between different materials in the fuel cell, which is achieved via compressive clamping. The effect of the gas diffusion layer (GDL) modulus on the in-plane stress in the membrane after clamping is studied via numerical simulations, including both isotropic and anisotropic GDL properties. Furthermore, the effect of cell width and land–groove width ratio on the in-plane stress in the membrane subjected to a single hygro-thermal cycle is investigated for aligned and alternating gas channel geometries. The results from varying the GDL properties suggest that the in-plane stress in the membrane after clamping is due to a non-linear and coupled interaction of GDL and membrane deformation. The results of the geometric studies indicate that when the gas channels are aligned, the cell width and land–groove width ratio affect the in-plane stress distribution, but do not significantly affect the stress magnitudes. However, when the gas channels are alternating, the cell width and land–groove width ratio have significant effect on the membrane in-plane stresses. The effect of land–groove geometry is qualitatively verified by a series of experimental compression tests.

Analysis and multi-criteria design optimization of geometric characteristics of grooved micromixer

Computational fluids dynamics (CFDs) and numerical optimization techniques are applied in an integrated methodology to explore the effects of different geometric characteristics on fluid mixing in a staggered herringbone micromixer (SHM). To quantify the mixing intensity in the mixer a mixing index is defined on the basis of the intensity of segregation of the mass concentration on a cross-section plane in the mixing channel. Four geometric parameters, i.e., aspect ratio of the mixing channel, ratio of groove depth to channel height, ratio of groove width to groove pitch and the asymmetry factor (offset) of groove, are the design variables initially selected for optimization, then two more parameters, i.e., angle of the groove and number of grooves per channel section, are evaluated. The whole optimization is conducted with a multi-objective approach for which the mixing index at the outlet section and the pressure drop in the mixing channel are the performance criteria used as objective functions. The Pareto front of designs with the optimum trade-off, maximum mixing index with minimum pressure drop, is obtained.

Simulation and Experimental Study on Photoresist Flow and Deforming Behavior in Imprint Lithography Process

Abstract ：It is necessary to understand and predict the photoresist flow and filling behavior in imprint lithography process to obtain high fidelity replication of the template patterns. The finite element model based on viscosity fluid for resist flow and filling is established considering the properties of the resist adopted in this study and the influences of geometric characteristics of template patterns, initial resist film thickness and micro/nano effect on resist rheologic properties are investigated to distinguish different flow driving mechanisms by tracing the resist moving boundary by using volume of fluid (VOF) method. The calculation results show that the resist filling is accomplished in single or dual peak deformation mode. The mode transition point can be predicted from the ratio of characteristic groove width to initial resist film thickness and the transition point is influenced by the surface/interface effects. The required from pressure is minimized when the aspect ratio of the template patterns is approximately 0.8. The optimal initial resist thickness is about twice of the depth of the patterns on the template considering both the pattern transfer quality and residual resist thickness. The numerical simulations are compared with the related experimental results in imprint lithography and it shows that the calculation results are in good agreement with the experimental results, which indicates that the conclusions from simulation analysis are valid and can be used as the process layout rules for the template pattern geometry, initial resist thickness and template surface treatment.

CHARACTERISTICS OF OIL-LUBRICATED PARTIALLY HERRINGBONE GROOVED JOURNAL BEARING

An experimental investigation of the performance of oil-lubricated partially herringbone- grooved journal bearing (HGJBs) which have a beveled-step groove profile have been carried out. The bearing groove parameters (groove angle α, groove width ratio β , groove depth ratio Γ ) have been optimized for a wide range of bearing operating conditions in search of the best stability characteristics. Hydrodynamic lubrication unit with some accompanying apparatuses are used to measure the pressure distribution, attitude angle, Eccentricity, contact and friction torque. The optimized values are (α = 26.78o , β =0.55, Γ =2.2). The test results are compared to experimental results for the completely grooved bearing which have the same beveled-step groove profile [1] ,and rectangular groove profile . In comparison of the previous work the introduced grooved configurations showed high radial stiffness and load capacity, low friction torque and better stability characteristics.

Experimental and FEM study on sinking of miniature inner grooved copper tube

Miniature inner grooved copper tubes (mIGCT) which have an outer diameter less than 6 mm are in demand for the production of heat pipes. In this work, it is proposed to manufacture such tubes by a multi-stage tube sinking process with an initial mIGCT having an outer diameter of 6 mm. A FEM simulation approach is used to analyze stress, strain and damage distribution for the proposed process. For comparison, a smooth copper tube is also used in the simulation study. Furthermore, experiments are conducted to investigate plastic deformation of the grooves and teeth of the tube. Results show that the maximum stress and strain are occurred at the grooves area, while the maximum damage is located at the top of the teeth. The ratio of groove width to tooth width ( β) is reduced after each drawing pass. Bonding, folding and segmenting, which represent potential flaws, have also been observed in the multi-stage tube sinking process, and are discussed.

Effect of Sessile Drop Volume on the Wetting Anisotropy Observed on Grooved Surfaces

This study reports experimental measurements of the water contact angle (WCA) measured on surfaces with grooves of different widths using drop volumes ranging from 400 pL to 4.5 microL. These measurements were carried out on both relatively hydrophobic and hydrophilic surface chemistry formed using a conformal plasma polymer coating of topographically embossed poly(methyl methacrylate) (PMMA). Anisotropic wetting of the grooved surfaces was found to be more marked for larger drops on both the hydrophilic and hydrophobic surfaces. Above a certain drop base diameter to groove width ratio, topography had no effect on the measured WCA; this ratio was found to be dependent on the water drop volume. The WCA measured from the direction perpendicular to the grooves using submicroliter water drops is found to be a good indicator of the WCA on the flat surface with equivalent wettabilities. To the best of our knowledge, this is the first study on the phenomenon of anisotropic wetting using picoliter water drops.

Evaluation of surrogate models for optimization of herringbone groove micromixer

Surrogate models have been applied to shape optimizations of a micromixer with the aim of assessing the performance of the models. The surrogate models considered include polynomial response surface approximation, Kriging, and radial basis neural network. In addition, a weighted average model based on global error measures is constructed. A mixing index at the exit of the micromixer is used as the objective function. The mixing index is calculated based on Navier-Stokes equations. Two cases of optimization, one with two design variables and the other with three design variables, have been tested. The design variables are selected among the ratio of the groove depth to channel height, the angle of groove, and the ratio of groove width to groove pitch. D-Optimal design generated sampling points are used for sampling. It is found that although the weighted average model does not predict the best optimal point, it does show consistent and reliable performance.

헤링본 미세혼합기의 크리깅 모델을 사용한 최적형상설계

Shape optimization of a staggered herringbone groove micromixer using three-dimensional Navier-Stokes analysis has been carried using Kriging model. The analysis of the degree of mixing is performed by the calculation of spatial data statistics. The calculation of the variance of the mass fraction at various nodes on a plane in the channel is used to quantify mixing. A numerical optimization technique with Kriging model is applied to optimize the shape of the grooves on a single wall of the channel. Three design variables, namely, the ratio of groove width to groove pitch, the ratio of the groove depth to channel height ratio and the angle of the groove, are selected for optimization. A mixing index is used as the objective function. The results of the optimization show that the mixing is very sensitive to the shape of the groove which can be used in controlling mixing in microdevices.

Investigation of characteristics of laterally overgrown GaN on striped sapphire substrates patterned by wet chemical etching

The new developed maskless lateral-epitaxial-overgrowth technique, in which the striped substrates are patterned by wet chemical etching, is systematically investigated using scanning electron microscopy, X-ray diffraction, and atomic force microscopy (AFM). Wing tilt is measured for the GaN films on patterned substrates with a range of “fill factor” (ratio of groove width to stripe period) and for the GaN in different growth time. It is found that changes in these parameters have a significant effect on the extent and distribution of wing tilt in the laterally overgrown regions relative to the GaN directly on the sapphire substrate. Increasing the thickness of GaN films is benefit to reduce wing tilt. The tilt is avoided in the GaN films with 4.5 μm thickness and fill factor for 0.46. The full-width at half-maximum of X-ray rocking curves of the asymmetric diffraction peaks and the image of AFM both show that the threading dislocations in the developed lateral epitaxial overgrowth of GaN films are reduced sharply. The GaN template could be used as an excellent substrate to fabricate high-performance optoelectronic devices.

On the Optimum Groove Geometry for Herringbone Grooved Journal Bearings

Recently, herringbone-grooved journal bearings have had important applications in miniature rotating machines. The scribed grooves, on either the rotating or stationary member of the bearing, can pump the lubricant inward, which generates supporting stiffness and improves the dynamic stability, especially for concentric operation. Most of the previous investigations that dealt with herringbone grooved journal bearings and grooved thrust bearings were theoretical. Few experimental attempts for the investigation of the performance characteristics of herringbone grooved journal bearings (HGJBs) and grooved thrust bearings have been done. All these investigations concentrated on rectangular and circular groove profiles of HGJBs. In order to improve the performance characteristics of HGJBs, a new design of the groove profile, the beveled-step groove profile, is introduced. The introduced groove profile is capable of increasing the pressure recovery at the divergence of the flow over the step. In addition, it increases the amount of oil pumped inward over the circular groove profile. Optimization processes were carried out experimentally, in order to obtain the optimal geometry of the introduced groove profile. The optimum geometrical parameters of the groove (groove angle α, groove width ratio β, and groove depth ratio Γ) are 29deg, 0.5, and 2.0, respectively, which give maximum radial force and maximum radial stiffness of the beveled-step HGJB. In order to check the effectiveness of the introduced beveled-step groove profile, the obtained results were compared with that for rectangular groove profile. The comparison shows that the introduced beveled-step HGJBs have higher radial force, higher load carrying capacity, and lower friction torque than the rectangular HGJBs.

高速スラスト空気軸受の解析と最適設計(G11-1 軸受,歯車,G11 機素潤滑設計部門)

This paper presents the numerical analysis modeling of thrust air bearings and its application to optimum design. In the modeling, the boundary fitted coordinates and divergence formulation method are suitably combined for improving the applicability to the complicated bearing geometry, such as spiral grooved and herring bone bearings. The load capacity, friction torque, spring and damping coefficients are obtained as a function of design variables such as groove depth, groove angle, bearing width ratio and groove width ratio. The calculated results are compared with the experimental results for the verification of validity. Then, using the numerical method, the design variables which optimize the objective function defined as the ratio of friction torque to spring coefficient are determined for a wide range of rotational speeds under various constraints by applying the hybrid optimization technique combining the direct search method and SQP. Some numerical examples are given in the graphical form.

Analysis of a Hydrodynamic Herringbone Grooved Journal Bearing Considering Cavitation

The Reynolds equation, incorporating Elrod’s cavitaton algorithm, is discretized on a rectangular grid in computational space through coordinate mapping in order to accurately analyze a herringbone grooved journal bearing of a spindle motor in a computer hard disk drive. The pressure distribution and cavitation area are determined by using the finite volume method. Predicted results are compared to experimental data of previous researchers. It was found that positive pressure is developed within the converging section of the bearing and that a cavity occurs in the diverging section. Cavitation has been neglected in the previous analyses of the herringbone grooved bearing. Load capacity and bearing torque are increased due to the increase of eccentricity and L/D and the decrease of the groove width ratio. The maximum load capacity was found to occur at a groove angle of 30 degrees while bearing torque remains constant due to the variation of the groove angle. The cavitation region is significantly decreased with the inclusion of herringbone grooves. However, the region increases with the increase of the eccentricity, L/D, groove angle and the rotational speed and the decrease of the groove width ratio. [S0742-4787(00)01401-6]

Drag characteristics of a turbulent boundary layer over a flat plate with transverse square grooves

The effect of transverse square grooves on the drag characteristics of a flat plate has been investigated using direct drag measurements in a tow tank. Two flat plates with 2.5 and 5 mm transverse square grooves, with groove spacing (s) to groove width (w) ratio, s/w=10, 20 and 40, were tested at plate length Reynolds numbers in the range 2–10×106. There is an increase in drag over the “smooth” plate for all s/w configurations.

Stability of Axially-Grooved Self-Acting Gas-Lubricated Journal Bearings.

Both experimental and numerical studies are conducted on half-frequency whirl (HFW) stability of axially-grooved self-acting gas-lubricated journal bearings. The studies demonstrate that 8-grooved bearings are unconditionally unstable with usual bearing clearance and rotational speed. On the other hand, 2 grooved bearings operate stably at relatively low values of bearing number which are obtained with usual clearance and speed. The physics of HFW stability is attributed to the pressure distribution geometry. Further, as a result of extensive numerical simulations, it is found that 3 grooved bearings with groove width ratio to total width of 0.3 through 0.5 give favorable stability performance.