Herringbone Grooves Research Articles

Control of Machining Profiles Based on Material Removal Capabilities in Cylindrical Blasting

Fluid dynamic bearings, which have an advantage in high-accuracy revolutions, are employed for spindle motors of hard disk drive, cooling fans for central processing unit, spindles of machine tool, etc. Micro herring-bone grooves are manufactured on cylindrical surface of the shafts in the bearing units, and they generate dynamic pressure during spins. Although the depth of the herring-bone grooves is generally constant, the shafts of which groove depth decreases from the ends of the groove array to its center improve the performance of bearing. The micro grooves are mainly manufactured by chemical etching, electrochemical machining, cutting and form rolling. However, the chemical etching and the electrochemical machining are difficult to control 3D machining profiles with high accuracy. The cutting and the form rolling have problems in tool lives and manufacturing costs. On the other hand, blasting is expected as one of micro fabrication methods. Therefore, we focused on blasting, and have investigated its material removal capabilities by fundamental tests. The purpose of this study is to control machining profiles in cylindrical blasting. The machining profiles of cylindrical workpieces in blasting were simulated based on the material removal capabilities obtained by the fundamental blasting tests. Then, the simulated profiles agreed well with the experimental ones by blasting under the same experimental condition.

MINIATURE FLUID DYNAMIC BEARING WITH IMPROVED LOAD CAPACITY

In this paper a novel design is proposed to improve the load capacity of fluid dynamic bearing (FDB) for miniature spindle motors and small-form-factor data storage applications. In contrast to conventional miniature FDB with two sets of herringbone grooves on its inner surface, the proposed miniature FDB comprises another one set of herringbone grooves on its outer surface. The proposed miniature FDB is verified numerically utilizing commercial software Advanced Rotating Machinery Dynamics (ARMD). The simulation results show that compared to the conventional miniature FDB, the proposed miniature FDB can obviously improve the load capacity of the bearing system. Overall, the results presented in this study show that the proposed miniature FDB provides another solution for miniature spindle motor applications.

Numerical Analysis of Finger Seal with Grooves on Lifting Pads

Numerical research on lifting and sealing performance of a whole ring finger seal with grooved pad structures is presented in this paper. Different groove structures on the bottom of a lifting pad, such as one and two straight grooves, or two herringbone grooves with different gradients, etc., will be simulated. For discussing interaction between the rotor and finger seal, the vibration trajectory of the rotor is taken into account in the numerical computation. Numerical simulation results indicate that the complete ring model is more suitable than an individual finger model to simulate the fluid–solid interactions of the finger seal. Deformation of the finger seal is changed by vibration of the rotor, and it should adapt the clearance in a uniform way according to the rotor position. The grooved pad structures have effects on the leakage flows and the lifting force on the finger. Analytical data revealed that the self-adaptive performance of the finger seal to rotor vibration is subsistent. The self-adaptive performance will be helpful to make the finger seal processes lower wear and with smaller leakage in a rotor–seal system.

Single- and Two-Phase Thermal Transport in Microchannels With Embedded Staggered Herringbone Mixers

Improving mixing is an effective means to enhance single- and two-phase heat transfer in microchannels. However, it is challenging to induce since the flow in microchannels is laminar in the most working conditions. We report that heat transfer rate and critical heat flux (CHF) on 1-methoxyheptafluoropropane (HFE-7000) can be significantly enhanced by patterning embed- ded micromixers on the bottom walls in a parallel silicon microchannel array, which consists of five parallel channels (height, width, length: 250 µm × 220 µm × 10 mm). Compared with a plain-wall microchannel array at a mass flux range of 1018 to 2206 kg/m 2 · s and a heat flux range of 10 to 198 W/cm 2 ,s ingle- phase heat transfer rate, two-phase heat transfer rate, and CHF are enhanced up to 221%, 160%, and 61% using microscale staggered herringbone mixers in microchannels, respectively. These mixers consist of 7 or 3.5 Hz with 12 staggered herringbone grooves (50 µm in depth and width) with 90° between two asym- metric arms in each cycle. Its asymmetry is defined in accordance with the off center position of the apex of the herringbone groove. Finally, experimental results suggest that the locations and coverage of the micromixers have significant impacts on both single and two-phase heat transfer in microchannels.(2013-0372)

Machining Characteristics in Cylindrical Blasting of Micro Grooves and Performance of Herring-Bone Bearing

The micro patterning on a cylindrical surface is conventionally carried out by electrochemical machining, chemical etching, cutting and so on. However, there exists some problems in machining dimensional errors and tool lives. On the other hand, blasting is expected as one of micro fabrication methods and progresses to apply for machining of hard and brittle materials. The purpose of this study is to develop the micro blasting technique for patterning of micro herring-bone grooves on spindle surfaces of the fluid dynamic bearings. Then, machining characteristics in blasting of rotating workpieces are experimentally investigated, analyzing stock removals, burr heights and groove shapes. In addition, micro herring-bone grooves are patterned on spindle surfaces by blasting and the performance of herring-bone bearings are evaluated. The herring-bone bearings with micro grooves patterned on a spindle surface by blasting have enough performance, compared with conventional ones.

Geometry optimization for asymmetrical herringbone grooves of miniature hydrodynamic journal bearings by using Taguchi technique

Hydrodynamic bearings (HDBs) have been used for data storage applications because of low friction and shock resistance. However, load capacity of HDB is substantially reduced with a decreasing dimension. Few studies have investigated the behavior of the HDB with its inner diameter smaller than Ø = 2 mm. Therefore, the aim of this study was to efficiently analyze the performance of the miniature journal bearings Ø = 0.6 mm with asymmetrical herringbone grooves. To reduce the number of full-factorial experimental design tests, the Taguchi methodology is used to find out the optimal design parameters of the two-step Herringbone-grooved journal bearings.

Flow-induced voltage generation over monolayer graphene in the presence of herringbone grooves.

While flow-induced voltage over a graphene layer has been reported, its origin remains unclear. In our previous study, we suggested different mechanisms for different experimental configurations: phonon dragging effect for the parallel alignment and an enhanced out-of-plane phonon mode for the perpendicular alignment (Appl. Phys. Lett. 102:063116, 2011). In order to further examine the origin of flow-induced voltage, we introduced a transverse flow component by integrating staggered herringbone grooves in the microchannel. We found that the flow-induced voltage decreased significantly in the presence of herringbone grooves in both parallel and perpendicular alignments. These results support our previous interpretation.

Numerical study on shape optimization of groove micromixers

The performance of a homogeneous T-mixer can be enhanced significantly by the stimulation of secondary/transverse flows in the microchannel. The groove-based micromixers generate helical flows within the microchannel to augment the mixing performance. These micromixers are extensively studied with respect to planar geometric parameters such as groove width, groove spacing, channel height, etc. The effect of groove shape on mixing performance has not been systematically studied. Previous studies have focused on two or three different predefined groove shapes, typically involving slanted grooves, asymmetric herringbone grooves, and their variations. In this computational study, we analyze the effect of groove shape on micromixing performance and search for the optimal groove shape for a pressure-driven flow across the microchannel. The groove shape is parametrically represented by Bezier curves which could take any shape within a constrained plane. The control points of the Bezier curve are chosen as optimization parameters to identify the optimal groove shape which maximizes the mixing for given operating conditions. The optimization is carried out for pressure-driven flow with and without staggered arrangement of grooves. The resulting single groove optimal design improves the mixing efficiency from 0.18 for T-mixer to 0.85 for the same operating conditions (Re ~0.42, Pe ~4,200). Unlike previous studies, axial mixing index profiles are presented for different micromixers which clearly distinguish the effect of flow field on the mixing performance. Various parametric studies are carried out to compare the optimal groove structure with other common groove type (staggered, herringbone, etc.) micromixers for a range of Pe between 400 and 6,200. The improved mixing performance in optimal designs is due to a continuously growing finger-like structure of the interface which enhances the overall mass transfer.

Effects of texture patterns on hydrodynamic and mixed lubrication characteristics

Surface texturing effects on the friction characteristics under hydrodynamic and mixed lubrication conditions are investigated experimentally and theoretically. The experiments are conducted by using a ring-on-plate type test rig, where a ring with a flat ring end is rotated against the plate with the engraved texture patterns of longitudinal, transverse and herringbone grooves and of square dimples. It is found that the friction characteristics significantly depend on the texture patterns even though the depth and the groove area ratio are identical in all the texture patterns; among them, the herringbone grooves show the lowest friction coefficients under any lubricating conditions. On the one hand, it is found that the longitudinal grooves and the square dimples effectively reduce the friction; on the other hand, the transverse grooves hardly reduce the friction. The experiments are compared with the calculations and it is found that higher pressure is generated with the herringbone grooves than other patterns, which avoids solid contact and results in friction reduction.

Micro-fabrication of air-bearing grooves onto inner surfaces of fine copper pipes

Applicability of laser-scan lithography onto inner surfaces of small-diameter pipes was investigated by fabricating fine air-bearing grooves. Herring bone patterns with a mean width of [email protected] were precisely formed on inner surfaces of copper pipes with an inner diameter of 2mm using laser direct writing lithography and sequent electrolytic etching. The pipe was cut and machined to a bearing bushing, and a rotor with the air-bearing bushing was fabricated. An aluminum hollow shaft was inserted in it, and the rotor was supported by the air bearing and magnetic thrust bearings placed at the both sides. As a result, the rotor was rotated very smoothly with a high-speed of more than 20,000rpm by blowing air to the rotor. Using conventional machining technology, it is difficult to form precise herring-bone shape grooves onto inner surfaces of such fine pipes. It was demonstrated that the combination of inside lithography and electrolytic etching was very useful for fabricating micro-mechanical components requiring precise patterning on their inside surfaces.

Two Fluid Mixing in a Micromixer with Helical Channels and Grooved Surfaces

The mixing behavior of two fluids in a passive micromixer with a Y-type inlet and helical fluid channels with herringbone grooves etched into the bottom was studied in a numerical simulation and experiments. The mixing of the pure water and acetone solution prepared with different Reynolds numbers and acetone concentrations was investigated. An image inspection method using the variance in contrast of the image gray level as the measurement parameter was adopted to calculate the mixing efficiency distribution. Inspection results show that the mixing efficiency decreased with the increase in the concentration of the acetone solution, although the mixing efficiency around the outlet reached to a value of 90%, even when the Reynolds numbers of the fluids were as low as Re = 1, and the best efficiency achieved for the case of Re = 10 was over 98%. The results show that it should be possible to apply the proposed micromixer in the field of biomedical diagnosis.

Centrifugal Compressor Spiral Dry Gas Seal Simulation Working at Reverse Rotation

Unidirectional dry gas seal may experiences reverse rotation when equipped in a centrifugal compressor. This paper describes how the reverse rotation effects on the spiral unidirectional dry gas seal performance and pressure distribution inside the gas film, also an investigation of using a different herringbone shape grooves configurations has been done using ANSYS FLUENT 14.5 CFD simulation. The influence of decreasing rotational speed to the static condition and rotate in the reverse direction on internal flow and gas seal performance is examined from 10800 to -10380rpm. The results indicate that the internal pressure distribution inside the gas seal in reverse rotation is decreased and the open force consequently decreased by 4%. The modification on the same seal is done to enhance its performance at reverse rotation condition. The herringbone spiral grooves is used with different configuration, the new configurations are examined in the forward and reverse rotation direction. The analysis for the pressure distribution is done and its effect on the seal performance is examined. Seal performance is compared with standard one for all geometrical and operating conditions. At high forward rotational speed 10380rpm, the pressure at the end of the spiral groove is about 11.4% higher than the inlet pressure at the seal outer diameter, while at reverse rotation, the pressure is not increased in radial direction. The open force corresponding to reverse rotation increased with a value 1.5kN for both the 100 overlap and 50% forward overlap seal faces, but using seal face with 50% backward overlap failed to enhance the open force at reversal condition.

Stability Threshold of Herringbone Grooved Aerodynamic Journal Bearings with External Stiffness and Damping Elements

Stability Threshold of Herringbone Grooved Aerodynamic Journal Bearings with External Stiffness and Damping Elements

The Effects of Trapezoidal Groove on a Self-Acting Fluid-Lubricated Herringbone Grooves Journal Bearing

As a self-acting fluid-lubricated herringbone grooves journal bearing, a trapezoidal cross-sectional shape of grooves is considered. Trapezoidal groove shape effects on its bearing characteristics such as variations of load capacity, attitude, and friction torque for various trapezoidal angle of groove are determined.

Passive mixing of co-flowing slugs in grooved microchannels

The anisotropic grooves in a microchannel induce spiral circulation around the flow axis. The stretch and fold of the streams result in a passive mixing. This article describes the effectiveness of induced crossflow, arising from the grooves, placed at the floor of the microchannel. The results from numerical simulation show the extent of local mixing achieved at various positions around the groove. The emphasis here is to understand the mixing when the two streams enter the channel, and displace air while flowing alongside each other. Microchannels with slanted grooves and staggered herringbone type grooves are considered here. The FLUENT 6.2 software and the Open FOAM software were used for the simulation. The latter was primarily utilized for tracking of the interface when a liquid slug displaced air from the micromixer. At a Reynold’s number of about 1.0, low velocity pockets could be identified near the two ends of the ridges. These pockets did not support crossflow and mixing. The herringbone type micromixer was found to have the best mixing effectiveness, when the advection dominates mixing. This advantage is mostly lost at the higher values of diffusivity, as a crossflow became less important for mixing. These observations were made when one of the streams is 1.5 times more viscous than the other, and the mixture-rule governed the viscosity of the mixed stream. When the liquid front enters the microchannel for the first time, the front had to displace air from the channel. At first, the upper part of the channel was swept. This was immediately followed by the sweeping of the groove-part in the floor. Higher hydraulic resistance in the grooves resulted in this non-uniform movement of the front. The co-flow of streams could either be continuous over the entire length of the channel, or in the form of slugs that maintained an interface with air. At a particular position in the channel, the extents of mixing were compared for the two modes of co-flow. The extent of mixing was found smaller in the slug, next to the interface with air. Lack of axial dispersion with preceding liquid stream seems to be the reason for this trend.

공기동압베어링의 성능 해석 및 가공특성 평가

The need is growing for high-speed spindle because various equipment are becoming more precise, miniaturization and high speed with the development of industries. Air-lubricated dynamic bearings are widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction for the motion of the stage. Air-lubricated dynamic bearing can be used in high-speed, high-precision spindle system and hard disk drive(HDD) because of its advantages such as low frictional loss, low heat generation, averaging effect leading better running accuracy. In the paper, numerical analysis is undertaken to calculate the performance of air-lubricated dynamic bearing with herringbone groove. The static performances of herringbone groove bearings which can be used to support the thrust load are calculated. Electrochemical micro machining(ECμ M) which is non-contact ultra precision machining method has been developed to fabricate the air-lubricated dynamic bearing and optimum parameters which are inter electrode gap size, concentration of electrolyte, machining time are simulated using numerical analysis program.

Process Simulation–Assisted Fabricating Micro-Herringbone Grooves for a Hydrodynamic Bearing in Electrochemical Micromachining

This study presents the process simulation of fabricating a herringbone groove in a hydrodynamic bearing by electrochemical micromachining (EMM) process. The finite element simulation involved the multiphysics of a chemical reaction, a static electrical field, and electric current density. A dedicated EMM system was established for this study. The groove pattern on the cathode tool was transferred to the internal side of the bearing (anode) by anodic dissolution. The width of the microgroove was selected as a quality index to explore the effects of the process parameters, such as cathode tool, interelectrode gap, voltage intensity, and the pulse rate of the applied voltage, on the electric field distribution and groove fabrication. The experimental results show that the proposed micromachining system has an electrochemical processing rate of k = 1 × 10−11 m3/C, and could complete the micro-herringbone groove fabrication of 11 µm depth in 0.85 seconds. The simulation results were comparable to those of the experiment. The numerical simulation can be used to design the cathode tool and the parametric selection for the microgroove fabrication of hydrodynamic bearings.

Microstructure-based intensification of a falling film microreactor through optimal film setting with realistic profiles and in-channel induced mixing

The high liquid based specific interfacial area, up to ∼20,000 m 2/m 3, of falling film microreactors renders them to be ideally suited to carry out fast exothermic and mass transfer limited reactions. To understand the role of and control this interfacial area, it is important to account for realistic liquid film profiles. Here, we vary the liquid film profile or its velocity profile by two different means – through the (external) shape of a plain microchannel and through in-channel structures within the microchannel (staggered herringbone grooves (SHG) on the microchannel bottom). The variations in the liquid films are evaluated via two computational fluid dynamic (CFD) models. First is the pseudo 3-D which explicitly accounts for the liquid film thicknesses, flow velocities, species transport and reactions. Here, the pseudo 3-D model is used to investigate (1) the effects of five microchannel shapes and (2) three microchannel cross section dimensions; to account for a scale-out through both numbering-up and smart increase in dimensions. The model reaction used is the absorption of CO 2 in aqueous NaOH solution. It is found that the mass transfer into the liquid and the reaction conversion depend on the velocity profile and flow pattern. Second CFD model is the full 3-D which is used to evaluate the liquid film in the presence of SHG. The simulations from the full 3-D model indicate that: (1) residence time distribution is narrowed by five times compared to plain microchannels and (2) the penetration depths of particles seeded at the gas/liquid interface are 1.7 times larger in the presence of SHG. Furthermore the effect of SHG on penetration depth is more pronounced at higher flow rates. This is experimentally exploited by increasing the liquid throughput by more than a factor of two while keeping the same reaction conversion, using the SHG microchannels.

헤링본 그루브 공기 스러스트 베어링의 해석

*School of Mechanical Engineering, Yeungnam University*Graduate school of Mechanical Engineering, Yeungnam University(Received May 4, 2011; Revised August 10, 2011; Accepted August 20, 2011)Abstract − In this study, the characteristics of herringbone grooved air thrust berings are studied. It is shown thata generalized coordinate transformation method which was developed for handling complex geometry such asherring bone groove journal bearings is well applied to herringbone grooved air thrust bearings. The load car-rying capacity and stiffness and damping coefficients are calculated according to the design parameters likegroove depth or the number of grooves and compared to that of plain air journal bearings.Keywords − herringbone groove(헤링본 그루브), air thrust bearing(공기 스러스트 베어링), analyses(해석), generalized coordinates(일반좌표계)

Numerical Analysis of Static Characteristics of Herringbone Grooved Hydrodynamic Journal Bearing

By means of the finite differential method, the Reynolds equation is solved and the static characteristics of herringbone grooved hydrodynamic journal bearing are numerically analyzed by presenting the circumferential and axial pressures. The influences of parameters such as the eccentricity, width-diameter ratio of bearing, spiral angle, depth and number of grooves, on the static characteristics of herringbone grooved bearing are discussed. The results indicate that the normal pressure of oil film and the load carrying capacity as well, of herringbone grooved bearing will decrease with the increase of groove number and depth. On the other hand, as the pressure distributes in wider area in the circumferential direction, the stability of bearing can be improved. In consideration of these two aspects, the optimal groove number is 8-12, and the selection of depth and screw angle of grooves should also be chosen carefully to obtain the significant performance of herringbone grooved bearing.