Backward Leakage Research Articles

Efficiency improvement of Roots vacuum pump working process

SummaryIn this paper influence of rotor profile type of Roots vacuum pumps on backward leakage through channels of rotor mechanism and pumping speed is considered.Elliptical, involute, and circular profiles are widely used. Backward leakage through channels of rotor mechanism with different rotor profiles is determined from conductance which was calculated by angular coefficients method for free molecular flow regime at different rotors rotating angles. It is shown that backward leakage is maximal at rotors rotating angles 25–45° due to maximal inter‐rotor channel opening for gas flow and is minimal at 0°. Elliptical rotor profile provides minimal backward leakage over one revolution.Numerical modeling of Roots pump working process was carried out on the basis of CFD ANSYS‐CFX complex by dynamic meshing method. SST turbulence model was used for calculations. It is confirmed that maximal pumping speed is provided by Roots pump with elliptical rotor profile.

Effectiveness enhancement of non-contact vacuum pumps working process

Three options of rotor profiles of Roots vacuum pump are considered: elliptic, circular, and involute. Rotor profiles are drawn in the same housing and are analyzed from point of view of backward leakage minimization through inter-rotor channel and geometric pumping speed increase. It is shown that coefficient of working volume use is only 3% higher for involute profile. Averaged over one revolution conductance of rotor mechanism channels is minimal for elliptic rotor profile. For inter-rotor channel it is 14% less than for involute profile. The presented approach makes it possible to choose the optimal rotor profile of Roots pump for particular purpose.

Regularity analysis of leakage-field from vertically polarized bounded wave electromagnetic pulse simulator with distributed load

A parallel finite difference time domain (FDTD) method combined with perfectly magnetic conductor (PMC) image method and CST software is firstly presented for computing the leakage field ( including sideward and backward leakage field) from vertically polarized bounded wave electromagnetic pulse (EMP) simulator with distributed load. The results got from simulation agree well with those from experiment. Numerical results show that the leakage field’s peak-value near the ground reaches maximum in the direction of height, but there’s little difference of leakage fields’ peak-values at the testing points under 1.5 m height and far away from the simulator; The peak-values of sideward leakage field from simulator’s transitional section are larger than those from distributed load section, both of them are larger than the backward leakage field from the end of distributed load section, as the testing point is near the simulator, and the backward leakage field may be larger than those sideward leakage fields, as the vertically distance between the testing point and the simulator increases; The regularity conclusion suits for the simulator with different double exponential source. The more excited source component in high frequency domain, the larger backward leakage field in some distance domain. The leakage field from the simulator increases, as ground’s conductivity increases.

Microfluidic Passive Flow Regulatory Device with an Integrated Check Valve for Enhanced Flow Control.

A passive microvalve has appealing advantages in cost-effective and miniaturized microfluidic applications. In this work, we present a passive flow regulatory device for enhanced flow control in a microfluidic environment. The device was integrated with two functional elements, including a flow regulating valve and a flow check valve. Importantly, the flow regulating valve could maintain a stable flow rate over a threshold liquid pressure, and the flow check valve enabled effective liquid on/off control, thus accurate forward flow without any backward leakage was achieved. The flow performance of the flow regulating valve was analyzed through 3D FSI (Fluid-Structure Interaction) simulation, and several key parameters (i.e., fluidic channel height and width, control channel length, and Young’s modulus) were found to influence valve flow rate directly. To examine the flow characteristics of the device, we fabricated a prototype using 3D printing and UV laser cutting technologies, and the flow rates of the prototype under varied test pressures were measured in forward and reverse modes, respectively. Experimental results showed that nearly a constant flow rate of 0.42 ± 0.02 mL s−1 was achieved in the forward mode at an inlet pressure range of 70 kPa to 130 kPa, and liquid flow was totally stopped in the reverse mode at a maximum pressure of 200 kPa. The proposed microfluidic flow regulatory device could be employed for accurate flow control in low-cost and portable Lab-on-a-Chip (LoC) applications.

Effect of a casing fence on the tip-leakage flow of an axial flow fan

The effect of a casing fence on the tip-leakage flow of an axial flow fan is investigated using large eddy simulation. A fence is attached on the shroud near the trailing edge of an axial flow fan used in an outdoor unit of air conditioner. The Reynolds number is 547,000 based on the blade tip radius and tip velocity. At the design condition, the fan efficiency is increased by the casing fence. The roles of the fence are to block backward leakage flows near the shroud and to weaken the movement of the tip-leakage vortex (TLV) in the azimuthal direction. Also, the fence reduces the double-leakage tip-clearance flow generated at the aft part of the blade tip due to the TLV-blade interaction, reducing the strength of the tip-separation vortex. Consequently, the tip leakage and total pressure losses are reduced, and the efficiency is increased. The pressure fluctuations on the aft part of the blade tip of the pressure surface caused by the TLV-blade interaction are also significantly reduced by the fence, indicating reduction of the noise source. According to the interaction between the fence and backward leakage flow induced by the TLV, the fence significantly and slightly increases the aerodynamic performances at the design and peak efficiency conditions, respectively, but reduces them at an overflow condition.

A microfluidic circulatory system integrated with capillary-assisted pressure sensors.

The human circulatory system comprises a complex network of blood vessels interconnecting biologically relevant organs and a heart driving blood recirculation throughout this system. Recreating this system in vitro would act as a bridge between organ-on-a-chip and "body-on-a-chip" and advance the development of in vitro models. Here, we present a microfluidic circulatory system integrated with an on-chip pressure sensor to closely mimic human systemic circulation in vitro. A cardiac-like on-chip pumping system is incorporated in the device. It consists of four pumping units and passive check valves, which mimic the four heart chambers and heart valves, respectively. Each pumping unit is independently controlled with adjustable pressure and pump rate, enabling users to control the mimicked blood pressure and heartbeat rate within the device. A check valve is located downstream of each pumping unit to prevent backward leakage. Pulsatile and unidirectional flow can be generated to recirculate within the device by programming the four pumping units. We also report an on-chip capillary-assisted pressure sensor to monitor the pressure inside the device. One end of the capillary was placed in the measurement region, while the other end was sealed. Time-dependent pressure changes were measured by recording the movement of the liquid-gas interface in the capillary and calculating the pressure using the ideal gas law. The sensor covered the physiologically relevant blood pressure range found in humans (0-142.5 mmHg) and could respond to 0.2 s actuation time. With the aid of the sensor, the pressure inside the device could be adjusted to the desired range. As a proof of concept, human normal left ventricular and arterial pressure profiles were mimicked inside this device. Human umbilical vein endothelial cells (HUVECs) were cultured on chip and cells can respond to mechanical forces generated by arterial-like flow patterns.

A virtual sizing tool for mitral valve annuloplasty.

Functional mitral regurgitation, a backward leakage of the mitral valve, is a result of left ventricular growth and mitral annular dilatation. Its gold standard treatment is mitral annuloplasty, the surgical reduction in mitral annular area through the implantation of annuloplasty rings. Recurrent regurgitation rates may, however, be as high as 30% and more. While the degree of annular downsizing has been linked to improved long-term outcomes, too aggressive downsizing increases the risk of ring dehiscences and significantly impairs repair durability. Here, we prototype a virtual sizing tool to quantify changes in annular dimensions, surgically induced tissue strains, mitral annular stretches, and suture forces in response to mitral annuloplasty. We create a computational model of dilated cardiomyopathy onto which we virtually implant annuloplasty rings of different sizes. Our simulations confirm the common intuition that smaller rings are more invasive to the surrounding tissue, induce higher strains, and require larger suture forces than larger rings: The total suture force was 2.2N for a 24-mm ring, 1.9N for a 28-mm ring, and 0.8N for a 32-mm ring. Our model predicts the highest risk of dehiscence in the septal and postero-lateral annulus where suture forces are maximal. These regions co-localize with regional peaks in myocardial strain and annular stretch. Our study illustrates the potential of realistic predictive simulations in cardiac surgery to identify areas at risk for dehiscence, guide the selection of ring size and shape, rationalize the design of smart annuloplasty rings and, ultimately, improve long-term outcomes after surgical mitral annuloplasty. Copyright © 2016 John Wiley & Sons, Ltd.

Near-Complete Radiation of Plasmonic Mode From Nano-Slit to Free Space

We propose here an optical antenna structure that can efficiently out-couple metal-insulator-metal plasmonic mode to free space. For high emission efficiency, we focus on suppressing backward reflection and leakage to nonradiating surface mode. To block nonradiating surface mode, we design a trench structure at the exit plane of the nanoslit. By properly balancing the reflectance at the nanoslit exit and additional reflectance due to the returning surface mode, near-zero reflection characteristics are obtained by destructive interference. The design rules for parameter optimization are derived by using the scattering coefficients of the nanoslit and the trench. The proposed scheme can be used to determine the conditions for near-complete transmission through subwavelength slits.

Flow driven by a stamped metal cooling fan – Numerical model and validation

This paper presents a numerical fluid flow model for the stamped metal cooling fans popularly employed in electric motors. An experimental system is constructed to measure the performance of the cooling fan. The agreements between model prediction and experimental data are reasonably good. Parametric studies with the numerical model indicate that the viscous heating in the fluid and the variation of the air density have negligible effects on the fan performance. The blade edge thickness affects the flow driving capability of the fan. With various pressure differentials, three flow regimes are recognized. The first is the axial component dominated flow. In the second regime, the flow has a forward axial flow and a backward leakage flow. The third one is the leakage flow dominated regime, when the pressure differential across the fan is large.

Electrical Properties of Beta-Irondisilicide/Germanium Heterojunctions

AbstractThe electrical properties of heterojunctions composed of polycrystalline films of beta-irondisilicide and n-type germanium substrate are investigated. The heterojunctions have been prepared by co-sputtering of iron and silicon on germanium substrate followed by thermal annealing. The samples were prepared over various annealing temperature and chemical compositions. Most of the samples showed rectifying characteristics in current-voltage characteristics measurement. However, large backward leakage current was observed. The result is consistent with that in the case of beta-irondisilicide/silicon heterojunctions. In addition, the leak current showed significant dependence on annealing condition and chemical composition. It was suggested that the high density of trap levels existing at the interface caused by diffusion of Fe into substrate induce the inadequate electrical properties of the samples.

Responsive biomimetic hydrogel valve for microfluidics

A biomimetic hydrogel valve capable of directional flow control in response to the local fluid environment in microfluidic channels is described. The valve consists of a pair of photopolymerized hydrogel bistrips with different pH sensitivities, and becomes activated or deactivated reversibly based on local pH as a result of volume and shape changes. When activated at pH 8, the valve mimics anatomic venous valves both functionally and structurally, allowing fluid flow in one direction under forward pressure while restricting flow in the opposite direction. At an applied pressure of 0.71 psi, the forward flow rate was 140 μL/min, compared to a backward leakage rate of 2.3 μL/min.

Schottky Barrier Heights of Cr Contacts on n- and p-Type 6H-SiC

The Schottky contact characteristics of Cr on n- and p-type 6H-SiC have been investigated by using I-V and C-V methods, and the barrier heights and ideality factors have been measured. Results obtained show that Cr is also an appropriate metal to form Schottky junction on n type 6H-SiC, as the barrier height of ∼ 1 eV is moderate for both low forward turn on voltage and low backward leakage current in device applications. However, the interfacial properties of Cr to p type 6H-SiC results in nonideal Schottky junctions.

An Improved Flow Simulation Model for a Tangential Counter-Rotating Twin Screw Extruder

Abstract In this paper we simulate the flow of a Newtonian fluid in a tangential counter-rotating twin screw extruder using a cylindrical coordinate lubrication theory model. Special attention is given to the material flows leading to mixing specially to inter-screw and backward leakage between the screws, and how they vary with process conditions.

Study on the Resin Behavior in Intermeshing Twin Screw Extruder

This study was conducted both experimentally and theoretically in order to elucidate the behavior of particulate resin such as PVC compound in the compacting and plasticizing step in an intermeshing counter-rotating twin screw extruder. Firstly, the compaction and friction characteristics of PVC compound were measured, since they play an important role in the plastication of solid polymer. Then by using a counter-rotating twin screw extruder of 91.2mm diameter, measurements of bulk density distribution, pressure and temperature rise in the plasticizing step were undertaken under various processing conditions in order to clarify the compacting and conveying behavior and to theoretically formulate the solids conveying efficiency and in-channel pressure rise.It was found that the bulk density distribution is formed along the C-shaped chamber while exponential pressure rise is generated. The particulate solids conveying characteristic is determined by the amount of backward leakage flow through the intermeshing region and formulated as a conveying efficiency depending upon the screw shape and bulk density distribution due to the frictional forces on the plug state resin in the C-shaped chamber. Also, it has been clarified that over 80% of the plug temperature rise in the compacting and plasticizing step is due to frictional and viscous heat generation during passage through the intermeshing region. Observations of in-channel resin sampled after the barrel was pulled out, confirmed that material through the intermeshing region leaks backwards with a thin folded pattern being developed.

背面漏れ状態で使用される船尾管オイルシール

Conventional sealing system using the lip type oil seal is based on the concept that the forward pressure is always kept higher than the backward pressure. However, the new type of sealing system “AIRGUARD 3AS” is applied the idea that the air or lub oil always flows from the backward side to the forward side through the lip part of seal ring.We have carried out various investigation by use of test stands with #155 and #600 seal rings which is used under the backward leakage condition.As a result, the cracking pressure of seal ring and oil flow ratio of forward side to backward side are always constant in all cases. Furthermore, the lift of the lip part of seal ring on sleeve liner increases almost exponentially to the air or oil flow rate.

A non-Newtonian model of flow in forward and backward pumping screw regions of a modular tangential counter-rotating twin-screw extruder

The flow of a non-Newtonian fluid in forward and backward pumping elements of a tangential counter-rotating twin-screw extruder has been modeled. A simulation has been carried out for a power law fluid model using hydrodynamic lubrication theory and a modified flow analysis network procedure. The model predicts pressure fields from which mean flux fields and screw characteristic curves may be computed. Large backward leakages between the screws are predicted for the forward pumping elements. This leakage induces distributive mixing. The backward flow is much greater for staggered as opposed to matched screw flights. The pumping characteristics are much less than for two equivalent single-screw extruders. The non-Newtonian behavior reduces the relative amount of backward leakage between the screws but, as in a single-screw extruder, non-Newtonian viscosity behavior reduces pumping ability. For backward pumping screws, there is a forward surging flow between the screws. The screw characteristic curves indicate negative pressure gradients for positive fluxes. These screw characteristic curves are much less non-linear.

Light dependence of the decay of the proton gradient in broken chloroplasts

The initial rates and steady-state values of proton uptake by broken chloroplasts have been measured as functions of light intensity at various concentrations of chlorophyll, pyocyanine, supporting electrolyte, buffer, as well as pH and temperature. Kinetic analysis of the data shows that the rate of decay of proton gradient due to backward leakage depends on light intensity. Under steady illumination, the decay constant k L is equal to k D + mR 0, where R 0 is the initial rate of proton uptake which is a function of light intensity, k D is the decay constant in the dark and m is a parameter which is independent of light intensity. Treatment of chloroplasts with lysolecithin, neutral detergent, 2,4-dinitrophenol, or valinomycin in the presence of K + increases k D without affecting m. Treatment with N, N′-dicyclohexylcarbodiimide or adenylyl imidodiphosphate under appropriate conditions decreases m without affecting k D. Treatment with glutaraldehyde makes k L independent of light intensity and hence m = 0. These results suggest that the light-dependent part (mR 0) of k L is due to leakage of protons through the coupling factor (CF 1-CF 0) complex which can open or close depending on light intensity and that the light-independent part ( k D) of the decay constant k L is due to proton leakage elsewhere.

Sialography: a simplified technique.

A simplified method of sialography is described. A wedged catheter tip positioned in the duct prevents backward leakage of contrast material into the oral cavity.

Use of Alluvial Faults in the storage and Retention of Ground Watera

AbstractAlluvial faults are generally treated as impermeable boundaries. Recent investigations of the faults in Califoria's Owens Valley, however, reveal that they are semi‐pervious, or leaky in nature. The rate of ground‐water movement through a semi‐pervious alluvial fault is dependent upon the hydraulic conductivity of the fault gouge, the thickness of this zone, and the water‐level differential across the fault. Optimization of the ground‐water resources in the Owens Valley is currently being practiced using these faults in a controlled RECHARGE‐EXTRACTION‐SALVAGE System. In a system of this type, artificial recharge is induced into the Valley's aquifers upgradient from alluvial fault zones by impounding and diverting the creek flow tributary to the area. Extraction of ground water is effected by means of large‐diameter supply wells located near the faults on the upstream side. Salvage of ground water is accomplished by lowering the water table in the vicinity of these faults, thereby causing phreatic growth to die out. When predicting water levels in the vicinity of semi‐pervious faults, a solution is obtained for the induced water‐level decline caused by backward leakage through the faults.

Active circulators—The realization of circulators using transistors

An approach in realizing circulators using three transistors is described. The authors propose two circuit configurations. In the one configuration, the transmission efficiency has some relations to the impedance level and the efficiency is theoretically less than unity under the matched termination condition, but the backward leakage can be null in the frequency range limited by the frequency characteristics of the transistors. Experimentally, the efficiency η v =0.71, the forward/backward transmission ratio is 53 dB, and the frequency range extends from 100c/s to 3Mc/s with the input resistance of 200Ω (40 dB at the limit frequencies). In the other configuration, the efficiency is essentially unity independent of the impedance level. A circulator with η v =1.0 and the maximum transmission ratio of 70 dB with 40 dB at 300 kc/s is obtained in experiment.