Low Pumping Speed Research Articles

Design and investigation of gas cluster ion accelerator

A gas cluster ion accelerator with energies up to 20 keV is described. Parameters of the main components of the equipment were determined. It was demonstrated that a pulse regime of the accelerator can be realized with a relatively low (500 l/sec) pumping speed of the cluster ion source. Conditions for stable cluster beam generation were found. In pulse mode ion clusters appear in the accelerated beam in the first stages of ion beam evolution. A model describing the behavior of the ion beam in the pulse regime is suggested. To analyze the beam mass composition two systems were constructed: a magnetic mass-separation system and a time-of-flight system. Cluster ions Arn+ with number of atoms/charge n ≥ 500 were detected in the beam by using deflection in a homogeneous magnetic field. Clusters up to 3000 atoms/charge were detected by using time-of-flight measurements.

Tadpoles from the Intramolecular Photo-Cross-Linking of Diblock Copolymers

Preparation of tadpoles or globule−coil diblock copolymers from three coil−coil diblock copolymers is reported. The coil−coil copolymers consist of one poly(tert-butyl acrylate)-block-poly(2-cinnamoyloxyethyl methacrylate) or PtBA-b-PCEMA sample and two PtBA-b-P(CEMA-ran-hCEMA) samples. Here P(CEMA-ran-hCEMA) denotes poly[(2-cinnamoyloxyethyl methacrylate)-ran-(2-hydrocinnamoyloxyethyl methacrylate)]. The tadpoles are prepared by photo-cross-linking the PCEMA or P(CEMA-ran-hCEMA) blocks intramolecularly. Intramolecular cross-linking competes with intermolecular cross-linking. The former is encouraged by adding a diblock copolymer solution at a low pumping speed into a solvent under constant UV irradiation and stirring. The irradiation ensures that the newly added copolymer is immediately converted into tadpoles. The slow copolymer addition ensures that the copolymer concentration in the photoreactor remains low throughout the photolysis process. Factors affecting the purity, yield, and compactness of the tadpoles produced are examined.

Target poisoning during reactive magnetron sputtering: Part II: the influence of chemisorption and gettering

As generally accepted gettering of the reactive gas by the sputtered target material plays an important role for most reactive gas/target combinations. The influence of the gettering process and the chemisorption of reactive gas on the target have been modelled by Berg et al. (J. Vac. Sci. Technol. A 5(2) (1987) 202–207). However, in this model the effect of ion implantation was not included. Therefore, a model is proposed which takes ion implantation into account. The model is used to understand the target voltage behaviour during reactive sputtering of aluminium in an argon/oxygen mixture. At high pumping speed or low current, a target voltage increase is noticed before the critical point. This can be attributed to chemisorption of oxygen on the aluminium target. Chemisorption of oxygen reduces the erosion rate of the target, which enhances the poisoning of the aluminium target by reactive ion implantation. At low pumping speed or high current, i.e. when gettering dominates the reactive sputtering process, the effect of chemisorption on the target voltage is less pronounced due to the competition between reactive ion implantation and chemisorption.

Catheter performance.

Venous catheters differ from peripheral arteriovenous (AV) access devices in many important ways. This discussion focuses on their performance as a conduit for blood flow between the patient and the dialyzer and on how catheter function is both limited and enhanced relative to the more common peripheral accesses. Catheter flow is limited by the high resistance inherent in the extended length of venous catheters relative to dialysis needles, but the high rate of flow in central veins also diminishes the opportunity for access recirculation. Cardiopulmonary recirculation is absent in patients with catheter access unless the patient also has a peripheral access. In the latter case, the same detrimental effect on urea clearance is seen regardless of which access device is used. Flow-dependent recirculation through circuits other than the peripheral AV access reduces the efficiency of dialysis (regardless of the type of access, catheter, or peripheral AV device used) across both catheters and peripheral AV devices. The inside diameter of the catheter plays a sensitive role in determining catheter resistance to flow. Slight increases in diameter under the same pressure head are associated with large increases in flow. Negative pressure at the catheter inflow port generated by the blood pump is magnified relative to peripheral devices, predisposing to partial collapse of the pump tubing segment and erroneous blood flow readings by the pump motor speed indicator. Setting a limit on prepump negative pressure can minimize this error. Future applications of dialysis may require lower pump speeds, which would allow more liberal use of catheter access if their potential for infection and clotting can be reduced.

Cold cathode field emitter array on a quadrupole mass spectrometer: Route to miniaturization

We have improved the quadrupole mass spectrometer by substituting the conventional hot filament electron source by a field emitter array (FEA). Elimination of the hot filament avoids a number of common problems, including thermal cracking of delicate molecules, outgassing of the filament itself and nearby components, high power requirements for the filament, large size, stray light, stray magnetic fields, contamination by thoria and tungsten, and a long warm-up time. The advantages are clearest for portable applications where power requirements dominate. Here, the power savings are not just in eliminating the filament supply, but more important in reducing the largest component of the system, the vacuum pump. This comes about because the filament is the primary gas load and because chemical reactions taking place on it require fast pumping to keep the products from interfering with the spectra. Comparison between hot filament and cold cathode FEA ionization is made using a quadrupole mass spectrometer fitted with both electron sources, independently controlled. The FEA advantage is strongest when the ultrahigh vacuum system is throttled to a low pumping speed, mimicking a portable system with a small pump. FEAs also enable miniaturization and a corresponding decrease in pump size. Moreover, with miniaturization, shorter mean free paths and consequently higher working pressures can be tolerated further decreasing pump requirements.

Effect of pressure-flow relationship of centrifugal pump on in vivo hemodynamics: a consideration for design.

We have been developing centrifugal pumps for an implantable left ventricular assist device. We manufactured 2 prototype centrifugal pumps (PI, PII). These two have similar designs except for the PII having a volute casing and a large output port. To determine the differences in the hydraulic characteristics between the PI and PII, we carried out in vitro and in vivo experiments. In vitro study showed that the PII had a shallower H-Q curve than that of the PI, and the PII required a pump speed faster than the PI for the same flow rate and pressure head. On the other hand, in vivo study showed that the PII demonstrated a flow pulsatility greater than that of the PI at 1,900 rpm and 8 L/min although no significant change was observed at low pump speeds (< or = 1,500 rpm). This greater pulsatility consisted of a large discharge according to the small differential pressure during the systolic phase and a small discharge according to the large differential pressure during the diastolic phase. In contrast, the PI, having the steeper H-Q curve, showed a small discharge in the systolic phase and a large discharge in the diastolic phase. These results showed that pulsatility synchronized with the native heart beating depended on the slope of the H-Q curve. As a result, the slope of the H-Q curve is important to determine the component of pulsatility synchronized with native cardiac output. Regarding the slope of the H-Q curve, a pump having a volute casing and a large outlet port demonstrates a shallow slope in the H-Q curve. In conclusion, we suggest that a centrifugal pump for use in left ventricular aortic bypass should be designed considering the effect on the native heart pulsatility.

Investigation of the effects of pumping speed and Ar/O 2 ratio on the transient time at mode transition in Ti-O 2 reactive sputtering

The effects of the pumping speed and the Ar/O 2 flow rate ratio on the transient time needed to reach a steady-state, after glow discharge ignition in Ti−O 2 reactive sputtering, were investigated. It was shown that the O 2 partial pressure, deposition rate, discharge voltage and the Ti emission intensity change continuously after glow discharge ignition until the process reaches a steady-state. The transient time increases as the pumping speed increases or as the Ar/O 2 ratio increases. The results suggest that a low pumping speed or a low Ar/O 2 ratio shortens the transient time for process operation parameter changes such as a reactive gas flow rate change.

Relationship Between Pump Speed Design and Hemolysis in an Axial Flow Blood Pump.

In an attempt to reduce the hemolysis caused by axial flow blood pumps, we investigated whether the specific speed should be kept within the standard engineering range or whether pump speed should be minimized, thus making the specific speed beyond the standard range. Four pumps with 11.8 mm diameter impellers were designed to accommodate a flow of 5 L/min and a head of 100 mm Hg. The pumps were tested at 4 speeds: A, 14,000; B, 18,000; C, 22,000; and D, 26,000 rpm. Pump performance data were obtained, and the maximum point of total pump efficiency was found for each pump. The maximum efficiencies were A, 50%; B, 58%; C, 52%; and D, 53%. The specific speed of each pump recorded at the maximum efficiency point was calculated as A, 899; B, 954; C, 1,218; and D, 1,951 rpm. Hemolytic tests were performed with fresh goat blood in a closed, mock-loop circuit. Hemolytic indexes were A, 0.036; B, 0.22; C, 0.35; and D, 0.66. We have concluded that decreased hemolysis is correlated with a lower pump speed and that the specific speed for the lowest pump speed is less than the standard range. Having a specific speed outside the standard range was not correlated with reduced total pump efficiency.

The Heart-Hemopump Interaction: A Study of Hemopump Flow as a Function of Cardiac Activity.

The Hemopump is a useful left ventricular assist device. Because it is a rotary blood pump, the pump performance is not constant and is dependent on the cardiac cycle. We measured the static flow delivered by the pump at varying pressure heads (ΔP) in a mock circulation. These data are compared to the pump performance in vivo. On the basis of these results, 5 sheep were instrumented for continuous Hemopump flow measurement as well as left ventricular and aortic pressure measurements. The Hemopump flow was relayed instantaneously to the pressure head. Low filling and ventricular failing (through intravenous administration of a beta-blocker) conditions were applied. The in vivo measured flows also are pressure head dependent, but the flow curve shows hysteresis resulting in a loop during each cardiac cycle. The in vivo peak flows (AP = 0) are similar to the in vitro data. The in vivo means flows (A 50 mm Hg) are similar to the in vitro data for the lower pump speeds but are less than that at the higher pump speeds (3.74 ± 0.55 L/min in vivo at Speed 7 versus 4.6 L/min in vitro). Low filling interrupts the AP-flow loop and reduces flow. In the failing ventricle, AP increases and flow is reduced. The cannula leaks and results in aortic insufficiency (0.36 ± 0.05 L/min) when the pump is turned off. Several conclusions have been drawn from these tests: Cardiac activity is beneficial for the pump performance as well as when the aortic pressure curve is nonpulsatile; the longer the systolic phase, the higher the pump flow; the pump should never be turned off in clinical use; and filling is important for the pump's performance.

Boiler efficiency and gas consumption: Effects of cycling and pump speed

This brief note sets down some results on the effects of decoupling the room thermostat and cylinder thermostat from the pump and boiler in a 'wet' domestic gas-fired central heating system. Decoupling means that the boiler and pump operate continuously, as opposed to coupled control in which the control thermostats switch off the pump and boiler when no heat is required. The results showed that, for decoupled control, the boiler cycling rates were increased by 62%, the mean boiler efficiency was reduced from 68% to 62% and the gas consumption was increased by about 3% across the 1990/91 winter season. In mild weather the deterioration was much worse and it is important that the controls be properly coupled in these conditions. Lower pump speeds also increase boiler cycling and slow down the heating-up rates for space and hot water heating.

Fluorescent Image Tracking Velocimetry of the Nimbus AxiPump

High shear rates and extended residence times causing hemolysis and platelet activation can develop in an assist pump or cannula when inferior flow conditions exist. The high volume output of a miniature axial flow pump presents challenges in avoiding these adverse conditions. To assess the hemodynamics within the continuous flow Nimbus Axi-Pump, vector flow fields inside a translucent inflow cannula and a modified 12 mm AxiPump were mapped. Fluorescent image tracking velocimetry was used to track the motion of neutrally buoyant fluorescent particles (30 microns) using pulsed laser light, high resolution video cameras, and computer image analysis. An acrylic pump housing and cannula were integrated into a mock circulatory loop filled with a Newtonian, optically clear blood analog fluid. The flow parameters were controlled to yield known, physiologic loading conditions, including varying degrees of pulsatility. Cannula flow visualization results exhibited critical recirculation patterns at the bend. These results will be used to further optimize the design of the inflow. Particle impact was seen at the pump inlet in the inducer region of the rotor. Very good attachment of flow from the rotor to stator was observed when the pump operated at normal operating speeds. Intermittent regurgitant flow fields were evident in the presence of increased pulsatility and low pump speed. These results have lead to improvements in impeller design and speed control criteria to avoid potential deleterious flows.

Comparison of Holweck- and Gaede-pumping stages

Wide-range turbomolecular pumps extend the foreline pressure range of conventional turbo pumps from typically 0.1 mbar up to 10 mbar, which allows the use of dry diaphragm pumps with < 10 mbar final pressure and relatively low pumping speed (5–30 l min −1) for backing. This can be attained by different types of molecular pumps, in harness with turbo stage rotors with typical pumping channel sizes and rotor-stator gaps of 1 mm and 0.2–0.4 mm, respectively. The present work compares two types of these molecular pumps with respect to their pumping characteristics and technical risks due to the specific construction parameters. The results of all investigations show significant benefits for the Holweck-pumping stage in all items compared. Even the high compression ratio per axial rotor length of the Gaede stage can be substantially exceeded by interlocked Holweck-stages of different diameters.

The SHOOT orbital operations

The Superfluid Helium On Orbit Transfer (SHOOT) flight demonstration programme will provide the technology necessary to resupply liquid helium in space. If used in a tanker the components in SHOOT will be full scale except for tank size. The SHOOT attached shuttle payload orbital operations are divided roughly into two categories: an experiment and a demonstration. The experiment involves qualitative and quantitative measurements of the behaviour of various liquid management devices such as liquid acquisition devices, phase separators and liquid/vapour discriminators. Total system performance will also be measured in terms of transfer rates, losses, and residual quantities of helium. Parameters such as low level acceleration, temperature and pumping speed will be varied to obtain data needed to verify concepts and theoretical predictions. The demonstration involves combining data from early in the flight with an on board expert system to perform a transfer autonomously from the shuttle, thus simulating an actual superfluid resupply mission. The paper describes the SHOOT on orbit operations, the reasons for the methods used to obtain the experimental data, and the expected results.

High-Rate Artificial Lift

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Summary. This paper summarizes the major considerations in the selection, design, installation, or repair of high-rate artificial-lift systems. The majortypes of artificial-lift-sucker-rod pumps, gas-lift systems, electricalsubmersible pumps, hydraulic pumps and jets, and hydraulic turbine-drivenpumps--will be discussed. An extensive bibliography of artificial-lift papersis included. Introduction The need for better design and more efficient operation of high-rateartificial lift continues to be one of the more important artificial-liftproblems. Many of the older fields that are now flowing will require high-rateartificial lift. Also, waterflooding and water injection for pressuremaintenance have increased the need for higher lift rates. Selection Selection of the type of artificial lift is very important. In such aselection, the three major economic factors are income, operating cost, andcapital cost, generally in that order. The type of artificial-lift systemchosen should produce the reserves in a timely fashion with minimum operatingcosts. An efficient system may well be worth some additional capital costs. Making a bad selection will have adverse effects on the net income and mayresult in a change to a different type of artificial lift. One of the initialsteps in any design selection is to set priorities. Such things as location, lift depth, and casing size have a large influence on the type and size ofequipment. Important issues in an offshore field can be significantly differentfrom a dry-land location. The importance of cash flow, total present valueprofit, and reserves must be weighed. High-Rate Rod Pumping Rod pumping is not normally considered to be particularly applicable forhigh-rate artificial-lift systems. However, use of relatively long strokeunits, large plungers, and high pumping speeds should be reviewed if for noother reason than to establish a norm. A good general rule is to install rodpumping if the desired production can be obtained without encountering severeor unusual lift problems. Possibilities range from lifting 4,000 BFPD from1,500 ft [635 m3/d fluid from 460 m] to 1,000 BFPD from 4,000 ft [160 m3/dfluid from 1220 m]. The problems of lifting high rates from shallow wells arequite different from lifting from deep wells. In high-rate, shallow wells, themajor problems are normally rod fall and high peak torques, not rod stress, TheAPI design method (API RP 11L) appears to be inaccurate for design of shallowwells where the conditions of low nondimensional pump speed (N/No) and lownondimensional fluid loads (Fo/Skr) exist. In design of high-rate, shallow rodsystems, we must rely on other design approaches (i.e., use of thewave-equation programs or field experience). In general, for high-rate, shallowlift, relatively large pumps should be installed and the units run as fast asthe rods will fall without excessively overloading the equipment. Larger pumpsizes running at relatively slower speeds are theoretically more efficient thansmaller pumps running at higher speeds. Deep, high-rate rod-pumped wells arelimited primarily by the high rod loads. The API design method usually gives"ballpark" load answers and predicts reasonably well the change in loads fordifferent operating conditions. To deal with high rod loads, the users areforced to go with higher-strength rods, such as the API Type D or specialhigh-strength rods. High cyclic loads and rod abuse will cause repeated rodfailures, which in turn will result in extremely high operating costs andexcessive downtime. Efforts to improve rod life are almost always worthwhile. Good surveillance is essential in rod-pumped fields when lifting high rates. Also, it is very important to provide effective corrosion inhibition as soon aswater becomes the wetting phase. Pumping-unit care and maintenance also deserveto have high priority because the units are the most expensive piece ofequipment in the rod-pumping system. Both the gearbox loads and the structureload must be considered. The API design assumes that the unit is in perfectbalance, which seldom occurs in practice. As water cuts and lift depthsincrease. there is a tendency to overload the gearbox. Loads exceeding thegearbox rating may significantly shorten life. Keeping the structure of theunit from being overloaded is also important. Beam bending or failure of thebase seldom occurs. Occasionally, a base weld may crack but can be easilyrepaired. The primary problem with overloading is bearing failures. JPT P. 277^

The principle of He enrichment in a counterflow leak detector with a turbomolecular pump with two inlets

The pumping time required to render helium leak detectors operational can be greatly reduced by increasing the He concentration in the gas flow entering the detector. Since this gas flow is composed chiefly of water vapor, a cold trap with liquid nitrogen is a very effective method for concentration. Because the procurement and handling of liquid nitrogen can be difficult, the counterflow principle was proposed and introduced as an alternative many years ago. The tester takes advantage of the fact that the compression ratio of diffusion pumps and turbomolecular pumps for heavy gases is far greater than for light gases. Hence by allowing gas to enter on the forevacuum side it is possible to greatly concentrate light gases such as helium on the high-vacuum side. The sensitivity is then no longer based on the pumping speed of the high-vacuum pump (as with customary leak detectors) but instead on the product obtained by multiplying the compression ratio for He by the pumping speed of the backing pump. As far back as 1967, Becker suggested placing a second high-vacuum pump in the inlet to avoid the relatively long response time arising due to the low pumping speed of the backing pump. Because of the expense entailed, this improvement has not yet been implemented. The problem can be solved at little cost by employing a turbomolecular pump featuring two opposing rotors on a single axle. In this manner one obtains high sensitivity with high pumping speed and no hydrocarbons at the inlet.

Comparison of the synchrotron radiation induced gas desorption in aluminum vacuum chambers after chemical and argon glow discharge cleaning

In a dedicated synchrotron radiation beam line at the DCI storage ring at Orsay, France a series of measurements were made to evaluate the effect of argon glow discharge cleaning either as a pretreatment in the laboratory, or in situ, following the installation and pumpdown of the vacuum system in the LEP (Large Electron Positron storage ring) machine. On exposure to synchrotron radiation the gases desorbed were H2, CH4, CO, and CO2 with Ar in the glow discharge cleaned chambers. With continued exposure the gas desorption decreased with time except that the Ar showed a definite reluctance to clean up. When applied to LEP conditions, chemical cleaning only gave the required beam-gas lifetime after the shortest exposure. The worst overall situation results from the in situ Ar discharge cleaning due to the low pumping speed for Ar in the LEP machine.

A double differentially pumped supersonic secondary beam

The authors have investigated a double differentially pumped supersonic secondary beam, primarily designed for helium and neon. The performance for helium, neon, argon, and krypton can be described in terms of the virtual source distribution and the attenuation by collisions with residual gas atoms in the differential stage and in the expansion chamber. Both theoretical insight and experimental result show that with differential pumping it is possible to produce a compact secondary beam with very low pumping speed at both the expansion chamber ( approximately 1000 l/s) and the differential stage ( approximately 10 l/s). The collimator in the differential stage has mainly a (positive) geometrical effect, resulting in narrow beam profiles at the scattering centre without far wings. The virtual source distribution and the center line intensity are only slightly affected by the collimator. The model can be used in the design phase of a secondary beam to predict the performance of the resulting supersonic beam.

A Rod Pumping System To Reduce Lifting Costs

Rising costs of artificial lift operations are a continuing concern to oil producers in maintaining efficient and profitable performance. A new long-stroke sucker rod pumping system has been developed to minimize the impact of these rising costs. This new system results from a broad development project based on system design considerations having major influence on overall cost effectiveness of the system. The basis of these evaluations is discussed, resulting equipment design is described, and field operating results are presented. Performance results to date confirm achievement of reduced overall operating costs as a result of the performance characteristics of this system.

Characteristics of Fluidborne Noise Generated by Fluid Power Pump : 3rd Report, Discharge Pressure Pulsation of External Gear Pump

This paper presents characteristics of discharge pulsating pressure generated by an external gear pump. Based on the theoretical and experimental examinations, it is pointed out first that the former mathematical model for flow ripple is insufficient in the case of high working pressure or low pump speed. It is found experimentally that a large amount of leakage through relief grooves takes place intermittently in the vicinity of the central position of trapping. This leakage affects dominantly the fluctuation of a discharge flow (flow ripple), especially its higher harmonic components. The calculated values of discharge pressure pulsations based on the presentmathematical model for flow ripple taking the leakage mentioned above into consideration agree well up to about tenth harmonic with the experimental values.

Ultimate pressure of mechanical pumps and the effectiveness of foreline traps

The ultimate pressure attainable with two‐stage, rotary vane‐type mechanical pumps is often obscured by the presence of the lubricating oil. Its reported value depends on the method of measurement. Experimental results are presented with trapped and untrapped pumps using McLeod, ionization and diaphragm gauges (capacitance manometers). Partial pressure measurements performed with both zeolite and liquid nitrogen trapped pumps continuously monitored over a two month period indicate the possibility of maintaining ultimate pressure near 1×10−3 Pa for a few months. This depends on the frequency of atmospheric exposure and the duration of operation at higher pressures. However, the usefulness of mechanical pumps at such reduced pressure is limited by the relatively low pumping speed for a given size and cost. The primary benefit is in reducing the condensable vapors by approximately one hundred times.