Capillary Restrictor Research Articles

Combined influence of couple stress lubricant and geometric imperfections of journal on the performance of membrane compensated two-lobe hybrid journal bearing

This paper deals with the comparative performance of the two-lobe and circular hybrid journal bearing systems compensated with membrane restrictor. The combined influence of geometric imperfection of journal and the couple stress behaviour of the lubricant has been taken into the consideration. The non-Newtonian behaviour of the lubricant has been modelled using Stokes couple stress fluid model. The Reynolds equation has been modified to consider the couple stress fluid behaviour and has been solved by the FE Galerkin's approach. The numerically computed results from present study indicates that the couple stress lubricant presents an improved bearing performance in terms of stability (threshold speed), fluid film stiffness and damping coefficients vis-à-vis the corresponding bearing lubricated with Newtonian fluid. Further, the comparative performance of this class of bearings has been evaluated for the capillary, orifice and CFV restrictors.

Combined influence of couple stress lubricant and geometric imperfections of journal on the performance of membrane compensated two-lobe hybrid journal bearing

This paper deals with the comparative performance of the two-lobe and circular hybrid journal bearing systems compensated with membrane restrictor. The combined influence of geometric imperfection of journal and the couple stress behaviour of the lubricant has been taken into the consideration. The non-Newtonian behaviour of the lubricant has been modelled using Stokes couple stress fluid model. The Reynolds equation has been modified to consider the couple stress fluid behaviour and has been solved by the FE Galerkin's approach. The numerically computed results from present study indicates that the couple stress lubricant presents an improved bearing performance in terms of stability (threshold speed), fluid film stiffness and damping coefficients vis-a-vis the corresponding bearing lubricated with Newtonian fluid. Further, the comparative performance of this class of bearings has been evaluated for the capillary, orifice and CFV restrictors.

Research on two methods for improving the axial static and dynamic characteristics of hydrostatic lead screws

This paper researches two methods for improving the axial static and dynamic characteristics of hydrostatic lead screws, i.e. (a) using membrane restrictor instead of capillary restrictor and (b) utilizing the intentional periodic pitch errors in the nut to generate hydrodynamic effect of the lubricating film. The Reynolds’ equation, which is applicable to the lubricating film in hydrostatic lead screws, is deduced based on the equivalent plane of the flank surface of threads. The perturbation technique and the finite difference method are used to obtain the static and dynamic characteristics. The JFO boundary condition is used for capturing the cavitation. The results show that the axial static and dynamic characteristics can gain a marked improvement by combining the two methods.

Combined influence of couple stress lubricant, recess geometry and method of compensation on the performance of hydrostatic circular thrust pad bearing

This study concerns with the theoretical investigation to show the influence of recess geometry and method of compensation on the performance of recessed hydrostatic circular thrust pad bearing operating with couple stress lubricant. Modified Reynolds equation for couple stress lubricant has been derived using Stokes microcontinuum theory. Stokes theory describes the behavior of fluids consisting of long chain polymer additives having sizes comparable to that of the fluid film thickness. Finite element method technique and commercially available software MATLAB 2013 have been used to solve the modified Reynolds equation and, thus, performance characteristics of bearing have been computed. The performance of capillary- and orifice-compensated hydrostatic thrust pad bearings performance have been compared vis-à-vis to different geometric shapes of recess. Each recess shape has identical ratio of bearing pad area to recess area. It has been observed that the couple stress additives have significant positive influence on the static and dynamic performance of the compensated hydrostatic thrust pad bearing provided that restrictors operates with lower values of the restrictor deign parameter[Formula: see text]. Limiting values of 10 and 5 for restrictor design parameter [Formula: see text] have been noticed for capillary and orifice restrictor; beyond these values of [Formula: see text], use of couple stress lubricant on the performance of hydrostatic thrust pad bearing become insignificant.

Active control of multi-input hydraulic journal bearing system

Because of the advantages of high accuracy, high capacity, and low friction, the development of hydrostatic bearing for machine tool receives significant attention in the last decades. The mechanics and mechanical design of hydrostatic journal bearing with capillary restrictors has been discussed in literature. However, pragmatically, the undesired loading effects of cutting force tend to result in resonance and instability of the rotor and damage the shaft during operation. Therefore, multi-input, active flow control using state feedback design is proposed in this paper. To this purpose, the proportional pressure valves are added to the hydraulic system as active control devices, and the linearised models of the bearing and valve are discussed and identified. Simulation and experimental work is conducted to verify the proposed active control and parameter identification techniques. The results show that the unbalance responses of the rotor are reduced by the proposed state feedback controller, which is able to regulate the flow pressure effectively, thus enhancing the stability and accuracy of the hydraulic journal bearing.

Experimental Modeling of a Long Orifice-type Restrictor of High Speed Turbine Hybrid Bearing

To overcome the space limit of orifice-type and capillary restrictors in hybrid bearings, a kind of atypical long orifice-type restrictor is proposed and its experimental model is established. Through the analysis of the structure and flow rate of orifice-type restrictor and capillary restrictor, a long orifice-type restrictor and a feasible experimental modeling method are presented by use of orifice plate instead of the whole bearing. The flow rate of water film restrictors are tested under the aspect ratio of 4-10 and the pressure difference of 1.5-5.5MPa and the experimental model of long orifice-type restrictor is established. The result shows that the restrictor of atypical structures needs to be modeled by experiment. The flow discipline of atypical restrictor is approximate to typical orifice-type restrictor and the throttling model is a nearly turbulent model.

Analysis of Noncircular Hole-Entry Capillary-Compensated Hybrid Journal Bearing with Micropolar Lubrication

ABSTRACTThis article presents the analysis of a two-lobe hole-entry hybrid journal bearing operating with micropolar lubrication. The modified Reynolds equation governing the laminar flow of isoviscous, incompressible micropolar lubricant in the clearance space of a journal bearing system has been solved using a finite element model incorporating appropriate boundary conditions. A comparative analysis between circular and noncircular two-lobe hybrid journal bearings with capillary restrictor under Newtonian and micropolar lubrication has been presented. It is concluded that bearing performance characteristics are significantly influenced by micropolar lubrication.

Performance Analysis of a Nonrecessed Hybrid Conical Journal Bearing Compensated With Capillary Restrictors

The present paper deals with the performance analysis of a nonrecessed hole-entry hydrostatic/hybrid conical journal bearing with capillary restrictors. Finite element method has been used for solving the modified Reynolds equation governing the flow of lubricant in the clearance space of journal and bearing. The hole-entry hybrid conical journal bearing performance characteristics have been depicted for a wide range of radial load parameter (W¯r = 0.25–1.5) with uniform distribution of holes at an angle of 30 deg in the circumferential direction. The numerically simulated results have been presented in terms of maximum fluid film pressure, minimum fluid film thickness, lubricant flow rate, direct fluid film stiffness coefficients, direct fluid film damping coefficients, and stability threshold speed. However, the proposed investigation of nonrecess hole-entry hybrid conical journal bearing shows important performance for bearing stiffness and minimum fluid film thickness at variable radial load and at given operating speed.

Numerical Study on the Static Characteristics of Novel Aerostatic Thrust Bearings Possessing Elastomer Capillary Restrictor and Bearing Surface

Numerical Study on the Static Characteristics of Novel Aerostatic Thrust Bearings Possessing Elastomer Capillary Restrictor and Bearing Surface

Floating Ring Balance Analysis of Journal Floating Ring Hybrid Bearing in Turbulent Regime

An externally pressurized deep/shallow pockets hybrid journal floating ring bearing compensated by flat capillary restrictor which can meet the need of high speed rotating machinery is presented in this paper. Bases on turbulent flow theory, the equations governing the flow of inner and outer fluid film in the journal floating ring bearing are established. The control equations together with the pressure boundary condition and the restrictor flow equation are solved by using the Finite Element Method. The balance of floating ring is achieved by adjusting ring-to-shaft speed ratio, inner film radial clearance and inner film eccentricity ratio. It can be seen from simulation results that the ring-to-shaft speed ratio and inner film clearance vary slightly and the floating ring can keep balance under different speed and eccentricity ratio. The variation of static and dynamic performance with eccentricity and rotational speed are calculated and analyzed based on floating ring balance.

Influence of wear on the performance of hole-entry hybrid misaligned journal bearing in turbulent regime

Purpose – The present work aimed to study analytically the influence of wear on the performance of a capillary-compensated hole-entry hybrid misaligned journal bearing system operating in a turbulent regime. The numerically simulated results are presented for the chosen values of restrictor design parameter, Reynolds numbers, wear depth and misalignment parameters. Design/methodology/approach – The wear caused on the bearing surface due to start/stop operations is modeled using the Dufrane’s abrasive wear model. The modified Reynolds equation based on Constantinescu’s lubrication theory is solved using finite element method together with capillary restrictor flow equation. Findings – It is found that the value of minimum fluid-film thickness increases significantly for a constant value of restrictor design parameter when unworn aligned bearing operates in turbulent regime vis-à-vis laminar regime. Further, it has also been observed that when a worn bearing operates in laminar/turbulent regimes, the reduction in the value of minimum fluid-film thickness is more due to journal misalignment as compared to the aligned bearing operates in laminar regime. Originality/value – The present work is original concerning the performance of worn hole-entry hybrid misaligned journal bearing system operating in turbulent regime. The results are expected to be quite useful for the bearing designer.

Fritting techniques in chromatography

It is surprising that there has been no devoted review article for frits and relevant studies so far despite the long history of packed columns and the use of frits in them. This review was activated for such a reason. Both separate frits and in situ permanent frits have been covered since the appearance of primitive frits. The in situ fritting methods such as the formation of organic monoliths, sol-gel technology, sintering, fritless techniques such as tapered tip and capillary restrictors, and miscellaneous fritting techniques including magnetically trapped frits and single particle frits are introduced and discussed. In addition, frit-related studies and patents are also introduced. Finally, some conclusive comments on the choice of fritting technique in different situations and future perspectives are given.

Study on Throttle Methods for Hydrostatic Bearing

In hydrostatic bearing, the applied load is carried through the compensatory effect of restrictors. Different throttle methods will bring different oil film rigidity and carrying capacity. There are mainly four types restrictors such as capillary,orifice,slide valve and film feedback restrictors. The mathematical models of carrying capacity and oil film rigidity of the hydrostatic bearings throttled by the restrictors mentioned above were presented. The oil film rigidity of hydrostatic bearings throttled by different restrictors were analyzed. Reynolds equation was provided and the numerical solution model was constructed. The pressure fields show the static performances of hydrostatic bearing with different restrictors.

A Comparative Elastohydrostatic Analysis of CFV- and Capillary-Compensated Multirecess Hydrostatic/Hybrid Journal Bearing Operating with Micropolar Lubricant

A comparative study on the performance characteristics of the flexible multirecess hydrostatic journal bearing system with constant flow valve and capillary restrictors has been presented considering the effect of micropolar parameters. The modified Reynolds equation for the flow of micropolar lubricant through the bearing has been solved using finite element method, and the resulting elastic deformation in the bearing shell has been determined iteratively. The results indicate that the micropolar parameters of the lubricant affect the performance of the flexible multirecess hydrostatic journal bearing system quite significantly.

A study of misaligned hole‐entry worn journal bearing operating in turbulent regime

PurposeThe purpose of this paper is to study theoretically the combined influence of journal misalignment and wear on the performance of a hole‐entry hybrid journal bearing system. The bearing is assumed to be operating in a turbulent regime.Design/methodology/approachThe modified Reynolds equation based on Constantinescu lubrication theory has been solved by using finite element method together with orifice and capillary restrictors flow equations as a constrain together with appropriate boundary conditions.FindingsIt has been observed that for a symmetric hole‐entry journal bearing configuration the value of h¯min is more for the bearing compensated by orifice restrictor as compared to capillary restrictor when bearing operates in turbulent regime under worn/unworn conditions. From the point of view of stability threshold speed ω¯th, the reduction in the value of ω¯th for capillary compensated bearing is around −3.89 percent whereas for orifice compensated bearing it is −7.85 percent when misaligned worn bearing is operating in turbulent regime.Originality/valueThe present work is original of its kind, in case of misaligned hole‐entry worn journal bearing. The results are quite useful for the bearing designer.

Study on the Oil Film Static Performance of Sliding Bearings with Different Throttling Methods

The restrictors of fluid lubricated sliding bearings play vital role in oil film rigidity and carrying capacity of bearings. The mathematical models for solution of the oil film static performance of the bearings with four different restrictors were presented and the numerical solution methods were analyzed. The solutions for oil film static characteristics in many aspects such as discretization of Reynolds equation, building clearance function, determinating boundary conditions, constructing continuity equation, deducing the models of oil inlet flow, solving the carrying capacity were conducted. The computational results show that the bearings with capillary or orifice restrictor have lower carrying capacity and oil film rigidity than those with sliding valve feedback or film feedback restrictors.

Combined Influence of Wear and Misalignment of Journal on the Performance Analysis of Three-Lobe Three-Pocket Hybrid Journal Bearing Compensated With Capillary Restrictor

The multirecess noncircular hybrid journal bearings have been receiving wide importance in order to overcome the adverse effects on performance characteristics of multirecess circular journal bearings. During the lifetime of a machine, bearings are quite often required to be operated over a number of years and are subjected to several start and stop operations. As a consequence of this, the bush becomes progressively worn out and thereby changing the clearance space between journal and bearing. The present paper presents an analytical study investigating the effect of wear along with both aligned and misaligned conditions of journal on the performance of a capillary compensated three-lobe three-pocket hybrid journal bearing system for the various offset factors δ = 0.8,1.0, and 1.2. The wear caused on the bearing surface due to the transient (start/stop) operations has been modeled using Dufrane’s wear model. The modified Reynolds equation governing the flow of lubricant in the clearance space of a three-lobe multirecess worn hybrid journal bearing system along with both aligned and misaligned conditions of journal has been solved using an iterative scheme based on FEM. The influence of offset factor (δ), the wear depth parameter (δ¯w), and journal misalignment factors (σ¯,δ¯) on the performance of the three-lobe three-pocket hybrid journal bearing and three-pocket circular hybrid journal bearing system have been investigated. The results have been presented for the capillary compensated three-lobe three-pocket hybrid journal bearing system. The simulated results suggest that a bearing with a higher value of offset factor (δ>1) provides better static and dynamic performance characteristics as compared with a three-pocket circular journal bearing but the bearing with offset factor (δ < 1) is predominantly affected by the wear defect and misalignment of journal. The numerically simulated results suggest that the wear defect and offset factors significantly affect the bearing performance. Therefore, it becomes imperative to account for the influence of wear and offset factors during the design process so as to generate accurate data of bearing performance. The numerically simulated results have been presented in terms of maximum fluid-film pressure, minimum fluid-film thickness, lubricant flow rate, direct fluid-film stiffness, damping coefficients, and stability threshold speed margin. The present study demonstrates that the performance of bearing is significantly affected by wear along with both aligned and misaligned conditions of journal and the loss is partially compensated by keeping the offset factor δ>1.

612 毛細管絞り下流の流れ特性に関する実験(GS 流体工学1)

612 毛細管絞り下流の流れ特性に関する実験(GS 流体工学1)

Numerical Investigation of Static and Dynamic Characteristics of Water Hydrostatic Porous Thrust Bearings

A moving table supported by aerostatic bearings can achieve excellent accuracy of motion because of its noncontact support and, hence, it is used in various precision machine tools and measuring equipment. However, because of low viscosity of air, the damping coefficient of aerostatic bearings is not very high, causing vibration with nanometer-order amplitudes. The accuracy of machine tools and measuring equipment could deteriorate because of this vibration. It is expected that water hydrostatic bearings would have a higher damping coefficient than aerostatic bearings due to the higher viscosity of water. In addition, water, like air, does not pollute the environment. In this paper, the static and dynamic characteristics of water hydrostatic thrust bearings using porous material were numerically investigated and comparedwith conventional pocket hydrostatic bearings with a capillary restrictor. Hydrostatic porous bearings can be easily constructed because the porous material becomes a viscous restrictor itself. It was consequently found that water hydrostatic porous thrust bearings have higher maximum load capacity and slightly lower stiffness than water bearings with a capillary restrictor.

Analysis of capillary compensated hydrostatic journal bearing operating with micropolar lubricant

PurposeThe paper seeks to study, theoretically, the performance characteristics of capillary compensated multi‐recessed hydrostatic journal bearings operating with micropolar lubricant. The finite element method is used to solve the modified Reynolds' equation governing the micropolar lubricant flow in the clearance space of a hydrostatic journal bearing. The performance characteristics of bearing operating with micropolar lubricant are presented and compared with that of Newtonian lubricant, for a wide range of non‐dimensional load, capillary restrictor design parameter and micropolar parameters.Design/methodology/approachThe modified Reynolds' equation governing the flow of the micropolar lubricant is solved along with restrictor flow equation by finite element method so as to obtain fluid‐film pressures. The iterative procedure is repeated until the converged solution for the fluid‐film pressure field is obtained.FindingsA study of four‐pocket hydrostatic journal bearing system capillary compensated and operating with micropolar lubricant is presented. The following conclusions are made from the results presented in this study: at a constant load, pocket pressures and minimum film thickness, stiffness coefficients and, the damping coefficients increase with increase in micropolar effect of lubricant as compared to the Newtonian lubricant; the influence of the micropolar parameters of lubricant is more significant upon the minimum fluid‐film thickness at higher values of load and lower values of restrictor design parameter; the non‐dimensional flow decreases with increase in the micropolar effect of the lubricant a given values of restrictor design parameter and load; and the stiffness coefficient in the direction of load is found to be influenced by the micropolar parameters and more significantly at lower values of restrictor design parameter and load.Originality/valueStudies of capillary compensated multi‐recess hydrostatic journal bearing operating with micropolar fluid/lubricant are not available in the existing literature to the best of authors' knowledge. Although, such bearing has been studied with Newtonian lubricant and available in open literature. Therefore, this paper is an original piece of work in the area of micropolar lubrication and compensated hydrostatic bearings.