Needle Stroke Research Articles

Optimal design of a pelton turbine nozzle via 3D numerical simulation

Currently, untapped water resources in China are mostly located in the southwestern region notable for high ranges of Qingha-Tibet Plateau, Hengduan Mountains and Yunnan-Kweichow Plateau. These water resources have the remarkable property of being high in water head within a short distance. The Pelton turbine counts as the most adequate type of water turbine to harness these water resources. An internal-controlled Pelton nozzle design is elucidated in this paper in line with the formula and an existing model in the case of a1100m water head [1]. The impact exerted by nozzle and spear angle on the nozzle hydraulic efficiency under a set of needle strokes was ascertained from the numerical perspective. Elucidated hydraulic performance of different nozzle design was anatomized. An energy criterion was proposed through acquiring the jet efficiency to select the appropriate hydraulic design of Pelton nozzle [2]. The numerical results were indicative of the design with 100°/70° combination of nozzle and spear angle that was superior in overall hydraulic efficiency. For this reason, this design can be referenced in engineering applications.

Numerical prediction of hydraulic performance in model and homologous prototype Pelton turbine

Pelton turbine is widely used in in utilizing the high water head resource. The multiphase flow in the Pelton turbine is too complex to be analysed detailed as the flow in the reaction turbines. So the hydraulic design of Pelton turbine was mainly based on the know-how. The homologous turbine model was the only way to verify its performance in the past. Although an efficiency scale-up equation for Pelton turbines had established in the IEC 60193 code, researches had shown different internal flow phenomena would influence the efficiency scale effects and lead to different efficiency scale for different turbine design. This paper simulates the internal flow of model and homologous prototype Pelton turbine at three relative needle strokes. Homogenous model and SST k-ω model will be adopted to simulate the unsteady two-phase flow in the rotating buckets. Unsteady simulation results would help to numerical investigate the scale effect of Pelton turbine.

Simulation and Experiment on Droplet Formation and Separation for Needle-Type Micro-Liquid Jetting Dispenser.

The needle-type droplet jetting dispenser has wide applications in the field of microelectronic packaging, and for which the good quality of droplet formation and separation is the key to successful dispensing. This paper simulates the droplet jetting process which has been divided into 5 stages named backflow, growth, droplet extension, breakage, and separation, and analyses the combined effects of system parameters, such as pressure, viscosity, needle stroke, and nozzle diameter, on the changes of morphologies of ejected droplets, which is verified by experiments. The simulation and experiment results show that a higher driving pressure is quite suitable for the high-viscosity liquid to form normal droplets by avoiding adhesion. When increasing the needle stroke, the pressure should also be lowered properly to prevent the flow-stream. Besides, the nozzle with a large diameter is much more likely to cause sputtering or satellite-droplet problems. The results have a great significance for guiding the parameter settings of the needle-type dispensing approach.

Hydro-abrasive erosion in Pelton turbine injectors: A numerical study

Numerical simulations were performed to investigate how the design and the operation conditions of a Pelton turbine injector affect its vulnerability to hydro-abrasive erosion, alongside with its flow control capacity. Use was made of a Volume Of Fluid (VOF) model for simulating the free nozzle jet, a Lagrangian particle tracking model for reproducing the trajectories of the solid particles, and two erosion models for estimating the mass removal. The comparison against earlier studies and the experimental evidence, integrated with a careful sensitivity analysis, gave strength to the reliability of the numerical model. Nozzle seat and needle were the injector components most vulnerable to erosion. As the valve was closing, the erosion of the needle strongly increased, whilst that of the nozzle seat remained broadly constant. The influence of the injector design was also explored, suggesting that a reduction of the needle vertex angle is likely to enhance the risk of erosive wear. Finally, it was found that the possibility to condense the effects of the needle stroke and the needle vertex angle in a single parameter (i.e. the effective opening area) is no more allowed when hydro-abrasive erosion is considered, thereby assessing the need for case-specific wear prediction analyses. • Particle-laden jets generated by Pelton injector nozzles were numerically simulated. • The regulation characteristics of the injectors were estimated. • The injector components most vulnerable to hydro-abrasive erosion were identified. • The extent of erosion was assessed for different operation and design parameters. • A physical interpretation of the obtained results was provided.

Influence of Bi-piezoelectric micro-valve’s parameters on jet performance

Piezoelectric Micro-valve is significant device in semiconductor packaging, surface mount and LED packaging field. The jetting dispensing process related needle high-speed acceleration movement and mechanism of droplets generation in complex coupling environment is the theoretical basis of the jet dispenser design. In this paper, a two-dimensional axisymmetric model based on Volume of fluid (VOF) method is built by computational fluid dynamics(CFD) software. Fluent dynamic grid technique is introduced in numerical simulation to analyzed the fluid-solid coupling process. The mechanism of on-demand dispensing is analyzed by simulation. Then the jetting dispensing platform is built. The results show that the volume of droplet will increase with the increase of the needle stroke and the filing pressure linearly, and the needle stroke is the main factor. It will provide theoretical basis for improving consistency of mechanical collision based jet dispenser.

Numerical Analysis of Pelton Nozzle Jet Flow Behavior Considering Elbow Pipe

In Pelton turbine, the dispersion of cylindrical jet have a great influence on the energy interaction of jet and buckets. This paper simulated the internal flow of nozzle and the downstream free jet flow at 3 different needle strokes. The nozzle model consists of the elbow pipe and the needle rod which supported by 4 ribs. Homogenous model and SST k-ω model were adopted to simulate the unsteady two-phase jet flow. The development of free flow, including a contraction process followed by an expansion process, was analysed detailed as well as the influence of the nozzle geometry on the jet flow pattern. The increase of nozzle opening results in a more dispersion jet, which means a higher hydraulic loss. Upstream bend and ribs induce the secondary flow in the jet and decrease the jet concentration.

Non-contact measurements of water jet spreading width with a laser instrument

Jet spreading width is one of the important characteristics of water jets discharging into the air. Many researchers have dealt with measuring this width, and contact measuring methods on the water jet surface were employed in a lot of the cases. In order to avoid undesirable effects caused by the contact on the jet surface, we introduce non-contact measuring methods with a laser instrument to the measurements of jet spreading width. In measurements, a transmitter emits sheet-like laser beam to a receiver. The water jet between the transmitter and the receiver interrupts the laser beam and makes a shadow. The minimum and maximum values of the shadow width are measured. In addition, pictures of the water jet are taken with a scale, and the shadow width is measured from the pictures. The experiments on various needle strokes were performed. Three kinds of width consistent with the jet structure were obtained. In the results, it can be concluded that our non-contact measuring methods are feasible. The data of jet spreading widths and jet taper were obtained and are useful for future applications.

Control and Jetting Characteristics of an Innovative Jet Valve With Zoom Mechanism and Opening Electromagnetic Drive

In order to develop jetting technology in LED and microelectronics packaging, an innovative electromagnetic jet valve with zoom mechanism and opening electromagnetic coil is suggested, and an improved method of double voltage drive is applied in the electromagnetic control. It is found that the needle stroke of the new jet valve is increased to 1.3 times, and the needle velocity is raised to 1.8 times, and the temperature of opening electromagnetic coil is lowered to 6.7 °C. The jet valve can successfully jet 4 Pa·s high-viscosity adhesives at room temperature due to the improvement of dynamic characteristics. It will provide a new method for jetting high-viscosity adhesives.

MODELING AND STUDY OF HYDROELECTRIC GENERATING SETS OF SMALL HYDRO POWER PLANTS WITH FREQUENCY-CONTROLLED PERMANENT MAGNET SYNCHRONOUS GENERATORS

Currently, the hydroelectric generating sets of small HPPs with Pelton turbines employ as their generating units conventional synchronous generators with electromagnetic excitation. To deal with the torque pulsatile behaviour, they generally install a supplementary flywheel on the system shaft that levels the pulsations. The Pelton turbine power output is adjusted by the needle changing water flow in the nozzle, whose advancement modifies the nozzle area and eventually – the flow. They limit the needle full stroke time to 20–40 sec. since quick shutting the nozzle for swift water flow reduction may result in pressure surges. For quick power adjustment so-called deflectors are employed, whose task is retraction of water jets from the Pelton turbine buckets. Thus, the mechanical method of power output regulation requires agreement between the needle stroke inside the turbine nozzles and the deflector. The paper offers employing frequency-controlled synchronous machines with permanent magnets qua generating units for the hydroelectric generating sets of small HPPs with Pelton turbines. The developed computer model reveals that this provides a higher level of adjustability towards rapid-changing loads in the grid. Furthermore, this will replace the power output mechanical control involving the valuable deflector drive and the turbine nozzle needles with electrical revolution rate and power output regulation by a frequency converter located in the generator stator circuit. Via frequency start, the controllable synchronous machine ensures stable operation of the hydroelectric generating set with negligibly small amount of water (energy carrier). Finally, in complete absence of water, the frequency-relay start facilitates shifting the generator operation to the synchronous capacitor mode, which the system operating parameter fluctograms obtained through computer modeling prove.

Process Parameters Optimization of Needle-punched Nonwovens for Sound Absorption Application

This paper reports a study on the optimization of process parameters of needle-punched nonwoven fabrics for achieving maximum sound absorption by employing a Box-Behnken factorial design. The influence of fiber type, depth of needle penetration, and stroke frequency on sound absorption properties were studied. These parameters were varied at three levels during experimental trials. From multiple regression analysis, it was observed that the depth of needle penetration alone was the most dominant factor among the selected parameters, which was followed by the interaction between depth of needle penetration and stroke frequency. Fiber type was the least dominant parameter affecting sound absorption. A maximum sound absorption coefficient of 0.47 was obtained from the selected parameters. The results showed that for a process such as needle-punching, which is influenced by multiple variables, it is worthwhile to study the interactive effects of process parameters for achieving optimum sound absorption.

Design and performance evaluation of a new jetting dispenser system using two piezostack actuators

This paper presents a new jetting dispenser system which is adaptable to various packaging processes such as light emitting diode packaging and flip chip packaging. The proposed dispenser system is driven by piezostack actuators and a lever-hinge mechanism. In order to improve jetting performances such as accurate dispensed amount and adaptability to high viscosity fluid, two piezostack actuators are used. By activating the two actuators dually, the angular displacement of the lever can be controlled to produce a required motion of the needle. Firstly, the configuration and working principles of the proposed jetting system are explained, the design of the dispenser is then conducted and significant geometric dimensions of the dispenser are presented. In the design process, several operational requirements such as the maximum needle stroke, operational frequency, and amplification ratio of the lever-hinge are considered. The principal design parameters of the jetting dispenser system are determined from static and modal analysis using the finite element analysis. After obtaining the dimensional characteristics, the control logic for the dispensing operation is explained using a feed-forward controller. The piezostack-driven jetting dispenser system and control devices are then fabricated to evaluate the dispenser performance. It is shown experimentally that by changing the input voltage conditions, the amount of fluid dispensed by the proposed jetting system can be effectively controlled to achieve the desired jetting performance.

Qualitative Estimation Criterion of Direct Injection Diesel Engines Performance Prediction for Stationary and Industrial Applications

Our approach is to define as accurately as possible, the opportunities of forecasting the environmental and energetically qualities of direct injection Diesel engines for stationary and industrial applications. This research requires the validation of new energy solutions or injection process. Knowing that test bench research of internal combustion engines is a task that requires highly qualified personnel and very expensive equipment for investigate the combustion process, a research program to define the best technical solution involves significant costs. The energetically solution of an internal combustion engine, similar to those examined in this paper, is defined by the following guidelines and parameters: - Control of mixture formation; - Compression ratio; - Average swirl intake number channel; - Geometry of the intake and exhaust cams; - Diagram of distribution; - Drive cam type injection pump; - Geometry of the combustion chamber; - Type and nozzle geometry (sack configuration and l / d ratio ); - Needle stroke; - The diameter and length of the injection pipe; - Amount of injector opening pressure (for hydraulic injectors); - Type of delivery valve; - Time of injection. Based on experience gained during the test at the test bed, we proposed a criterion for assessing qualitative performance of Diesel class discussed above. This criterion refers to environmental and energetically performance, as a prediction of performance at nominal regime, after shorten tests with cold engine.

Numerical prediction of Pelton turbine efficiency

This paper presents a numerical analysis of flow in a 2 jet Pelton turbine with horizontal axis. The analysis was done for the model at several operating points in different operating regimes. The results were compared to the results of a test of the model. Analysis was performed using ANSYS CFX-12.1 computer code. A k-ω SST turbulent model was used. Free surface flow was modelled by two-phase homogeneous model. At first, a steady state analysis of flow in the distributor with two injectors was performed for several needle strokes. This provided us with data on flow energy losses in the distributor and the shape and velocity of jets. The second step was an unsteady analysis of the runner with jets. Torque on the shaft was then calculated from pressure distribution data. Averaged torque values are smaller than measured ones. Consequently, calculated turbine efficiency is also smaller than the measured values, the difference is about 4 %. The shape of the efficiency diagram conforms well to the measurements.

Effect of dynamic loading on pore size of needlepunched nonwoven geotextiles

Nonwoven geotextiles are widely employed in civil engineering applications for the functions of separation, filtration, drainage and protection. These functions are highly dependent upon pore size as it is one of their major requirements and it becomes more critical when geotextile is subjected to a compressional load. In this study, the effect of loading cycles on the compressional characteristics has been investigated by two parameters, i.e. compressional (α) and recovery (β) (Kothari and Das, 1992, 1994). The effect of process parameters, i.e. feed rate, depth of needle penetration and stroke frequency on the pore size has also been reported. Furthermore, the relationship between fabric area density and pore size has been discussed.

3D ultrasound in core breast biopsy

To evaluate the potential of three-dimensional ultrasound (3D US) in core biopsy of suspicious breast lesions. 3D US controlled core biopsy was performed in 107 breast masses in 100 women by using an automated biopsy system (11G coaxial needle, 12 G biopsy needle). Mean diameter of the lesions was 1.55 cm (0.5 - 3.5 cm). A linear 3D US volume scanner was used for the procedure. Localization of the lesion and placement of the needle were initially done under 2D US guidance. After core needle stroke a 3D US volume acquisition was performed to correlate lesion and needle position. In the case of eccentric needle position the needle was repositioned under 3D control. 5 specimens were taken from each lesion. The histological results from the specimens were correlated with the results from surgery or clinical follow-up (> 2.5 years). Biopsy was taken from 59 probably benign (BI-RADS 3 - 4) and 48 malignant (BI-RADS 5) lesions. 3D US revealed 61 central, 44 eccentric and 2 marginal needle positions after the initial 2D guidance. Central repositioning of the needle was achievable under 3D guidance in all patients. Histological examination of the specimens revealed 41 invasive carcinomas and one in-situ carcinoma (DCIS). In one lesion, the carcinoma was missed in the core biopsy, despite central hits of the biopsy needle. This led to a sensitivity of 98 %, specificity of 100 %, PPV of 100 %, NPV of 98.5 % and accuracy of 99 % for the diagnosis of a malignant lesion. 3D US improves needle positioning as well as the depiction of correct needle placement in freehand core biopsy.

Prevention and Management of Complications Resulting from Common Spinal Injections

When spinal injections are performed, a needle is placed in or around the spine making the risk of complications unavoidable. Spinal structures or adjacent organs are at risk for direct needle trauma, infection, hematoma, hemorrhage, nerve damage, stroke, allergic reaction, or spinal anesthesia with cardiorespiratory arrest. As a result, physician knowledge and patient preparation and monitoring are critical in maximizing patient safety during the procedure being performed. This review describes complications that may result from commonly performed spinal injections and their treatment.

A New Method for Investigating the Sampling Technique of Fine Needle Aspiration Biopsy

An automatic sampler of fine needle aspiration biopsy for cytology (FNAC) is presented in order to study the technical performance of FNAC in vitro. The effects of the following sampling technique variables on specimen size and quality can be independently and quantitatively studied: suction force, duration and rate of increase of suction; count, frequency, amplitude and angle between the needle strokes; length, diameter, content and tip configuration of the needle; and target tissue. The efficacy of the sampler was compared with a manual method. It was demonstrated that the poor reproducibility of manual FNAC, combined with inaccuracy in following instructions regarding changes in sampling technique, render the manual system unsuitable for quantitative studies. The clumsiness of the manual system may be responsible for contradictory recommendations on how FNAC should be carried out. With the new in vitro sampler FNAC sampling can be studied under fully controlled conditions.

Peripheral neural correlates of cutaneous anaesthesia induced by skin cooling in man

The effect of local skin cooling on the behavior of low- and high-threshold mechanoreceptive afferents innervating glabrous and non-glabrous skin was studied in microneurographic recordings on awake human subjects. Cooling with ice or ethyl chloride to a skin surface temperature below 10 degrees C caused a reduction of receptor sensitivity in 49 out of 52 studied low-threshold afferents. This effect was reversible upon warning but some reduction often persisted for a few minutes after normal skin temperature had been reached. The subjects' sensations of application and removal of von Frey hair stimuli were more resistant than had reappeared before the sensation of sustained pressure. This could be explained by shorter recovery times for fast than for slowly adapting units and by a relative preservation of the dynamic responses of the slowly adapting units. During the recovery phase some low-threshold mechanoreceptive afferents exhibited a transient 'spontaneous' discharge in the absence of external mechanical stimulation. The suppression of afferent C-fibre responses to needle strokes was more pronounced and long-lasting than the effect on A-fibre responses and largely paralleled the recovery of sensation of pain. It is concluded that the local anaesthetic effect of skin cooling is to a large extent explicable in terms of receptor desensitization although other mechanisms may contribute.