Influence Of Supply Pressure Research Articles

Proper orthogonal decomposition analysis of flow characteristics of aerostatic bearings based on Large Eddy Simulation

The driving mechanism of the vibration of aerostatic bearings is still unclear. Although there are several interpretations, none of them is conclusive. The difficulty lies in the complicated information concealed beneath the turbulence flow. To this end, the proper orthogonal decomposition (POD) method was systematically implemented in the aerostatic bearing flow field analysis in the present study, and some new findings have been proposed. First, the accuracy of our large eddy simulation (LES) has been validated through quantitative comparisons with the experimental references in terms of pressure distribution. Then, the mode decomposition has been conducted at a circumferential symmetry plane and bottom surface and the influence of supply pressure has been uncovered. It turns out that the vortices within the recess dominate the flowfield when the supply energy Ps=3atm, which could be recognized as the driving mechanisms of vibrations. The convection and shearing process in the vicinity of the recess inlet becomes intense and corresponding vortices become predominant in the cases of Ps=4atm and 5atm. Eventually, the influences of film thickness have also been discussed when Ps=4atm. Different from the case of h = 10 μm, the low-frequency vortices near the recess outlet could be detected when the film thickness is increased to 20 µm. The control of corresponding flow structures might be helpful for the vibration suppression.

Gripping Device for Textile Materials

Gripping and manipulating non-rigid and porous objects is an important challenge for manufacturing. Now there are many problems in handling textile materials from a stack or oriented in space. Therefore, the paper presents the design of an improved Bernoulli gripping device with an anti-vibration insert. The inventive gripper structure allows gripping and manipulating textile materials and partially eliminates the shortcomings present in the classic design of the gripper. A technique for theoretical modeling of a gripping device for textile materials has been developed. This made it possible to determine the rational parameters of the gripping device in terms of maximum attraction. Experimental study of power characteristics of gripping device for textile materials has been carried out. The choice of the thickness of the anti-vibration insert made by the 3D printing method is justified. The advantages of the design include enabling gripping of textile materials of manipulation at different position, orientation and from a longer distance. Influence of supply pressure on the beginning of object vibration is analyzed. Parameters of anti-vibration insert are defined for the operation of gripper without object vibration. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper was motivated by the problem of gripping and holding textile materials during manufacturing. There are many approaches to gripping a piece of textile material that have high energy consumption or can damage it. This paper proposes the design of the gripper that uses compressed air to lift the textile material at different orientations. Using the proposed theoretical model, one can calculate the lifting force of the gripper at different porosity of the material. Knowing the mass of the material, one can determine which parameters to choose for the gripper based on experimental results. Positive results are highlighted in the capture of porous objects without the loss of force at different orientations. Negative aspects are shown in the formation of vibration of the material when reaching a certain pressure level in the gripper. Future research plans to improve the design of the gripper by modeling the gripper using the finite element method and proposing effective methods of manipulating textile materials.

Structure design and performance analysis of aerostatic thrust bearing with compound restrictors

Aerostatic thrust bearing compensated by multi-orifices and porous material restrictor simultaneously is proposed to improve the static performance of the bearing. Load Carrying Capacity (LCC), stiffness and the flow field characteristics of the bearing are obtained by Computational Fluid Dynamic (CFD) simulation. The influences of supply pressure, orifice number, orifice diameter, orifice distribution, porous material thickness and permeability coefficient on the bearing performance are analysed. It is indicated that LCC and stiffness of the bearing with compound restrictors are much higher than those of the bearing with porous material restrictor or multi-orifice restrictor if gas film thickness is in rational range. The bearing with compound restrictors has better stability than that of the bearing with multi-orifice restrictor. Moreover, the optimum bearing parameters with compound restrictors are given to improving the performance of aerostatic thrust bearing.

Mixing characteristics of a bubble mixing microfluidic chip for genomic DNA extraction based on magnetophoresis: CFD simulation and experiment.

Mixing a small amount of magnetic beads and regents with large volume samples evenly in microcavities of a microfluidic chip is always the key step for the application of microfluidic technology in the field of magnetophoresis analysis. This article proposes a microfluidic chip for DNA extraction by magnetophoresis, which relies on bubble rising to generate turbulence and microvortices of various sizes to mix magnetic beads with samples uniformly. The construction and working principle of the microfluidic chip are introduced. CFD simulations are conducted when magnetic beads and samples are irritated by the generation of gas bubbles with the variation of supply pressures. The whole mixing process in the microfluidic chip is observed through a high-speed camera and a microfluidic system when the gas bubbles are generated continuously. The influence of supply pressure on the mixing characteristics of the microfluidic chip is investigated and discussed with both simulation and experiments. Compared with magnetic mixing, bubble mixing can avoid the magnetic beads gather phenomenon caused by magnetic forces and provide a rapid and high efficient solution to realize mixing small amount of regents in large volume samples in a certain order without complex moving structures and operations in a chip. Two applications of mixing with the proposed microfluidic chip are also carried out and discussed.

Nonlinear Analysis of Stability and Rotational Accuracy of an Unbalanced Rotor Supported by Aerostatic Journal Bearings

This paper presents the nonlinear analysis of stability and dynamic rotational accuracy of an unbalanced rotor supported by aerostatic journal bearings. A finite element method is utilized with the Runge-Kutta fourth order method to solve the transient Reynolds equation and the rotor dynamics equations simultaneously for the dynamic response analysis of the rotor. The dynamic behavior of the rotor center is analyzed under different rotor masses. It is shown that the dynamic responses of the rotor strongly depend on the rotor mass. The periodic, multi-periodic or quasi-periodic motions are observed as the rotor mass changes. Under a given operating speed, the mass at which the resonance occurs is studied and its relationship with the mass of the rotor at the threshold of instability is found for the first time. The influences of supply pressure, bearing clearance, orifice diameter and eccentric distance on the rotational accuracy, the resonance and instability threshold are also investigated. The result of this study can provide guidance for designing aerostatic bearing rotor systems with required running accuracy and stability.

Experimental research on the J-T orifice of a space 4.5 K hybrid J-T cooler

Hybrid J-T cryocooler is commonly employed in space detective missions requiring liquid helium temperature. In fact, nearly all the space applications of mechanical cryocoolers working at 4.5 K, having been launched or under development are hybrid J-T cryocoolers. For instance, mechanical cryocoolers used in Planck, JWST, SMILES, SPICA and so on, are all hybrid J-T cryocoolers. However, there is hardly any research on space 4.5 K hybrid J-T cryocooler in China. Key laboratory of space energy conversion technologies in Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS) has developed a 4.5 K J-T cooler precooled by two-stage pulse tube cryocooler. Base on this cryocooler, the influence of supply pressure and diameter of the J-T orifice on the cooling capacity of the J-T cooler is analyzed and experimentally studied. First of all, the influence of supply pressure and diameter of the J-T orifice is theoretically calculated. Then, experimental research is carried out. For the purpose of shortening experimental time, a two-stage GM cooler instead of pulse tube cooler is used to precool the J-T cycle. Firstly, open loop experiments are conducted because it’s much easier to adjust the supply pressure precisely. The mass flow rate of the J-T cooler rises monotonously as diameter of the J-T orifice decreases. However, the cooling capacity of the J-T cooler goes through an up and down process because the J-T effect turns to be worse when diameter of the J-T orifice increases. That is to say, performance of the J-T cooler turns to be worse when the diameter of the J-T orifice is larger than 34 μm. Based on the research of this paper, 34 μm J-T orifice may be the best choice of the hybrid J-T cooler. Besides, both mass flow rate and cooling power increase as supply pressure increases when supply pressure is below 2.0 MPa. In addition, the no load temperature of the J-T cooler rises with increasing supply pressure which is attributed to the flow resistance of the counter-flow heat exchangers. Secondly, three-stage oil-free linear J-T compressors are used to drive the J-T cooler, and the suction pressure and supply pressure of the three-stage compression system are 0.12 and 2.0 MPa, respectively. Finally, cooling power of 81.5 mW @4.48 K is achieved when the total power consumption of the J-T compressors is 102.7 W. And the temperature fluctuation at the evaporator is lower than ±0.05 K because the cooling capacity of the J-T cooler is provided by the vaporization of liquid helium.

Numerical research of pressure depression in aerostatic thrust bearing with inherent orifice

Abstract The undesirable pressure depression in aerostatic bearing will cause the loss of aerostatic bearing load capacity. Therefore, the method of “separation of variables” (MSV) for solution of laminar boundary-layer equations is utilized to investigate the pressure depression. The influences of supply pressure, orifice diameter, film thickness and pressure ratio on the pressure depression are studied. The results manifest that pressure depression is weakened with decreasing supply pressure and film thickness and increasing orifice diameter. The increase of pressure ratio which is determined by the flow and geometry parameters will weaken the inertial effect and then results in weakening the pressure depression. What's more, when pressure ratio is larger than the critical value 0.9409, the pressure depression will disappear.

Analysis of dynamic characteristics and stability prediction of gas bearings

PurposeThe prediction model to estimate the stability of a rotor-bearing system is established, which can predict the stability of gas bearings by applying Routh–Hurwitz stability criterion. This paper aims to provide the theoretical foundation for controlling actively the bearing running stiffness and damping and stemming the instability of a gas film.Design/methodology/approachThe nonlinear dynamic lubrication analysis mathematical model of spherical hybrid gas bearings is established. Perturbation control equation is derived by the partial derivative method. The finite difference method is used to discrete the perturbation control equation in generalized coordinate system, and the difference expression of perturbation pressure is derived. The relational expression which involves the relationship between the dynamic characteristic coefficients of HSGHGB systems and perturbation pressure is deduced. So, the transient perturbation pressure distribution of a three-dimensional micro gas film, nonlinear gas film force, dynamic stiffness and dynamic damping coefficients of bearings are numerically computed using VC++6.0 programs.FindingsThe results show that the influence of supply pressure, speed and eccentricity on the dynamic characteristics of bearings is significant.Originality/valueThe influence law of supply pressure, speed and eccentricity ratio on the dynamic stiffness and damping coefficients of HSGHGB systems is researched. The prediction model to estimate the stability of rotor-bearing system is established, which can predict the stability of gas bearings by applying the Routh–Hurwitz stability criterion.

Dynamic Coefficients Identification of Water-Lubricated Hybrid Bearings Used in High-Speed Spindles with Different Excitation Methods

Rotor stability and rotation accuracy, which are highly dependent on the dynamic coefficients of supporting hybrid bearings, are two important issues of high-speed water-lubricated spindles. To improve the spindles’ performance, the dynamic coefficients of high-speed water-lubricated hybrid bearings were experimentally identified by the noncontact harmonic excitation method and the additional unbalance excitation method, respectively. Comparisons between experimental results and theoretical predictions were made. The experimental technique and the identification model were validated to be effective. Besides, the influence of supply pressure and rotating speed on dynamic coefficients was also presented. As for different operating conditions, valuable guides were provided to investigate the dynamic performance of high-speed and ultra-high-speed spindles.

Application Research for Performance of Refrigeration Units with Flash Tank Economizer

This paper studies the influence of flash economic system on performance of refrigeration unit using Refrigerant R290. Theoretical analyses of refrigeration system with flash type economizer are carried out firstly, which provide theoretical basis for working parameters. Under different evaporation temperature, influences of supply pressure on the refrigerating capacity and COP are studied and verified through experimental. Experimental results show that, using the economizer can effectively improve the cooling capacity and COP, and achieve the effect of saving energy. With the increase of supply pressure, refrigeration capacity of refrigerating unit and shaft power decreases gradually and the refrigeration coefficient rise first and then drop, to determine the best economic position.

A Study on Influence of System Parameters on Servo Pneumatic System and Multi-Response Optimization Using Taguchi – Grey Methodology

Servo pneumatics is a mechatronic approach that enables accurate position control of pneumatic drives with high speed. Simulation model of the servo pneumatic system with fuzzy PD controller has been created in Matlab-Simulink software using nonlinear mathematical model of the system. The influence of supply pressure and size of the cylinder on the positioning accuracy and speed has been studied. It is observed that the supply pressure is the most influencing factor in positioning accuracy and speed compared to the size parameters of the cylinders. Further a multi-response optimization of the system parameters minimize settling time, overshoot and ITAE (Integral of time-weighed absolute error) values has been carried out using Taguchi based Grey relational analysis methodology. The optimal system characteristics have been observed when supply pressure is 0.2 MPa, diameter of the cylinder is 0.05 m and length of the cylinder is 0.15 m.

Experimental Investigation of the Performance of a Hermetic Screw-Expander Organic Rankine Cycle

In this study, the authors experimentally investigate the performance of the organic Rankine cycle (ORC) and screw expander under the influence of supply pressure and pressure ratio over the expander. Three tests were performed with expander pressure ratios of 2.4–3.5, 3.0–4.6, and 3.3–6.1, which cover the over-expansion and under-expansion operating modes. The test results show a maximum expander isentropic efficiency of 72.4% and a relative cycle efficiency of 10.5% at an evaporation temperature of 101 °C and condensation temperature of 45 °C. At a given pressure ratio over the expander, a higher supply pressure to the expander causes a higher expander isentropic efficiency and higher cycle efficiency in the over-expansion mode. However, in the under-expansion mode, the higher supply pressure results in a lower expander isentropic efficiency and adversely affects the cycle efficiency. The results also show that under the condition of operation at a given pressure ratio, a higher supply pressure yields a larger power output owing to the increased mass flow rate at the higher supply pressure. The study results demonstrate that a screw-expander ORC can be operated with a wide range of heat sources and heat sinks with satisfactory cycle efficiency.

Parameter identification for single‐action membrane‐type restrictors of hydrostatic bearings

PurposeThe purpose of this paper is to present the identification method of restriction parameter and deformation parameter for membrane‐type restrictors.Design/methodology/approachA worktable mounting on the open‐type hydrostatic bearing is utilized to calibrate recess pressures for regulating outlet pressures of restrictors by changing the load and then both restrictor parameters can be identified from the measurements of the inlet pressure, the outlet pressure, and the flow rate of a restrictor by minimizing the difference between measured and identified flow rates. Furthermore, the influences of supply pressure and restrictor designs on both parameters are also studied.FindingsAn identification method for single‐action membrane‐type (SAM) restrictors is obtained directly from experimental results. The measurements of inlet pressure, outlet pressure, and flow rate of the restrictor are substituted into the combined equations for minimization of error between measured and identified flow rates to be solved for restriction and deformation parameters. The identified results show that both parameters can be described by polynomial functions of supply pressure. Both polynomials are regressed by curve fitting from identified results.Originality/valueThe paper shows how to calibrate inlet and outlet pressures of restrictors for designing a hydrostatic bearing system by changing supply pressure and load applied on worktable for the measurements of both pressure and the flow rate of restrictor.

305 斜板式ピストンモータのスリッパ挙動計測(OS3-(3)オーガナイズドセッション《熱・流体・エネルギー変換工学の進展》)

The slippers behavior in swashplatetype axial pist on motors was measured by the test rig. The operating conditions were supply pressure of up to 35 MPa and rotational speeds of 0-26.7 s −1 . A petroleumtype hydraulic oil with a viscosity grade of 46 was used as the test fluid, and the temperature was maintained at value between 30 and 60 oC. The experiment examined the influences of supply pressure, rotational speed and oil temperature. The displacement between a slipper and a rotational disk, tilt angle, azimuth angle of a slipper and frictional torque are reported. As the supply pressure increased, the clearance between the slipper and the disk, the slipper tilt angle and the slipper azimuth angle decreased, and the frictional torque increased. As the rotational speed increased, the displacement and the slipper tilt angle increased. As the oil temperature increased, the displacement decreased and the slipper tilt angle increased.

Research on Impact Mechanism of Hydraulic Rock Drill

This paper introduces the working principle of the impact mechanism which is belonging to the double-chamber scavenge oil hydraulic rock drill. On the basis of some fundamental hypothesis, a mathematical model of hydraulic impact mechanism is established, then carrying out a dynamic simulation. Focusing on the influence of supply pressure, supply flow and precharge pressure on the working performance of impact mechanism, some research is implemented, and some regularity conclusions are obtained.

Experiments on a metal hydride based hydrogen compressor

A metal hydride based hydrogen compressor is studied experimentally by varying the operating parameters such as supply pressure and heat source temperature using MmNi 4.6 Al 0.4 alloy. The compressor performance is found to improve at higher heat source temperatures. For a given hot fluid temperature, the influence of supply pressure on system performance is prominent up to about 10 bar. Maximum efficiency of 7.3% is obtained at a pressure ratio of 8.8 at 95 ∘ C heat source temperature. Results obtained by a simulation compared well with the experimental data.

The Influence of Oil Supply Pressure on the Behavior of a Rigid Symmetrical Balanced Rotor in Journal Bearings With Circumferential Feeding

A theoretical-experimental investigation was carried out on the behavior of a rigid symmetrical balanced rotor in short, cylindrical, circumferentially fed journal bearings under low load conditions. The influence of supply pressure on bearing static characteristics and oil film instability threshold was evaluated for the above system. The experimental results are shown along with the theoretical predictions of the static characteristics and limit stability curves for different values of the ratio between supply pressure and specific load.

Aspects of the performance of externally pressurized journal bearings

Abstract The performance of externally pressurized journal bearings with four and six pockets was investigated experimentally. The influences of supply pressure, rotation and restrictor characteristics on the behaviour of the bearings operating under static loading are examined in the light of available theoretical and design information. Load capacities were found to be generally higher with the greater number of pockets but for both bearings the loads supported at given eccentricities are strongly influenced, in some ways unexpectedly, by restrictor non-linearity and the effects of rotation. At low supply pressures the loads are enhanced by increased rotational speeds whereas at high supply pressures the opposite occurs.