injection point
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Author(s):  
Daniel Wendler ◽  
Ralph Dux ◽  
Rainer Fischer ◽  
Michael Griener ◽  
Elisabeth Wolfrum ◽  
...  

Abstract The thermal helium beam diagnostic at ASDEX Upgrade is used to infer the electron density ne and temperature Te in the scrape-off layer and the pedestal region from the emission of visible lines of the locally injected helium. The link between ne and Te and the emission is provided by a collisional radiative model, which delivers the evolution of the populations of the relevant excited states as the He atoms travel through the plasma. A computationally efficient method with just three effective states is shown to provide a good approximation of the population dynamics. It removes an artificial rise of Te at the plasma edge when using a simple static model. Furthermore, the re-absorption of the vacuum ultra-violet resonance lines has been introduced as additional excitation mechanism being mainly important in the region close to the injection point. This extra excitation leads to a much better fit of the measured line ratios in this region for larger puff rates.


SPE Journal ◽  
2022 ◽  
pp. 1-12
Author(s):  
Quanshu Zeng ◽  
Zhiming Wang ◽  
Jinchao Wang ◽  
Qiqi Wanyan ◽  
Guosheng Ding ◽  
...  

Summary The leaching of a salt cavern will trigger a series of rock-fluid interactions, including salt rock dissolution, cavity expansion, and brine transport caused by convection, turbulence, and diffusion effects. These interactions have influences on one another. The primary objectives of this study include developing a 3D multiphysical coupled model for horizontal salt cavern leaching and quantifying these interactions. The species transport equation and standard κ-ε equation were combined to describe the brine transport dynamics within the cavity. Based on the velocity and concentration distribution characteristics predicted, the interface movement equation implemented with mesh deformation techniques was applied to describe the cavity expansion. Next, the Volgograd cavern monitored data were collected for model validation. The predicted results are consistent with the field data. The average relative errors are 11.0% for brine displacing concentration and 4.5% for cavity volume. The results suggest that the cavity can be divided into three regions, including the main flow region, circulation region, and reflux region. The results also suggest that the brine concentration distribution is relatively uniform. With the dissolution threshold angle and anisotropic dissolution rates considered, the resultant cavity cross section is crown top and cone bottom. The results also show that the cavity can be divided into dissolution and erosion sections according to its position relative to the injection point.


2022 ◽  
Vol 334 ◽  
pp. 03003
Author(s):  
Marco Cavana ◽  
Enrico Vaccariello ◽  
Pierluigi Leone

The injection of hydrogen into existing gas grids is acknowledged as a promising option for decarbonizing gas systems and enhancing the integration among energy sectors. Nevertheless, it affects the hydraulics and the quality management of networks. When the network is fed by multiple infeed sites and hydrogen is fed from a single injection point, non-homogeneous hydrogen distribution throughout the grid happens to lead to a reduction of the possible amount of hydrogen to be safely injected within the grid. To mitigate these impacts, novel operational schemes should therefore be implemented. In the present work, the modulation of the outlet pressures of gas infeed sites is proposed as an effective strategy to accommodate larger hydrogen volumes into gas grids, extending the area of the network reached by hydrogen while keeping compliance with quality and hydraulic restrictions. A distribution network operated at two cascading pressure tiers interfaced by pressure regulators constitutes the case study, which is simulated by a fluid-dynamic and multi-component model for gas networks. Results suggest that higher shares of hydrogen and other green gases can be introduced into existing distribution systems by implementing novel asset management schemes with negligible impact on grid operations.


Author(s):  
S Sindagi ◽  
R Vijayakumar ◽  
B K Saxena

The reduction of ship’s resistance is one of the most effective way to reduce emissions, operating costs and to improve EEDI. It is reported that, for slow moving vessels, the frictional drag accounts for as much as 80% of the total drag, thus there is a strong demand for the reduction in the frictional drag. The use of air as a lubricant, known as Micro Bubble Drag Reduction, to reduce that frictional drag is an active research topic. The main focus of authors is to present the current scenario of research carried out worldwide along with numerical simulation of air injection in a rectangular channel. Latest developments in this field suggests that, there is a potential reduction of 80% & 30% reduction in frictional drag in case of flat plates and ships respectively. Review suggests that, MBDR depends on Gas or Air Diffusion which depends on, Bubble size distributions and coalescence and surface tension of liquid, which in turn depends on salinity of water, void fraction, location of injection points, depth of water in which bubbles are injected. Authors are of opinion that, Microbubbles affect the performance of Propeller, which in turn decides net savings in power considering power required to inject Microbubbles. Moreover, 3D numerical investigations into frictional drag reduction by microbubbles were carried out in Star CCM+ on a channel for different flow velocities, different void fraction and for different cross sections of flow at the injection point. This study is the first of its kind in which, variation of coefficient of friction both in longitudinal as well as spanwise direction were studied along with actual localised variation of void fraction at these points. From the study, it is concluded that, since it is a channel flow and as the flow is restricted in confined region, effect of air injection is limited to smaller area in spanwise direction as bubbles were not escaping in spanwise direction.


2021 ◽  
Author(s):  
Andrew Fyfe ◽  
David Nichols ◽  
Myles Jordan

Abstract Sulphate scale can be predicted from thermodynamic models and over recent years better kinetics data has improved the prediction for field conditions. However, these models have not been able to predict the observed deposits where flow disruptions occur such as chokes, gas lift and safety valves. In recent years it has been recognised that the turbulence found at these locations increases the likelihood of scale formation and experiments have been able to demonstrate that with increased turbulence there is an increase in the mass of scale observed and an increased concentration of scale inhibitor is required to prevent its formation. In this paper a field case is investigated where strontium sulphate was observed in a location downstream of a gas lift valve. Laboratory tests were conducted to confirm whether the expected scaling was observed in a low shear flow loop and also to investigate whether the location of the scale changed when additional turbulence (gas injection) was introduced to the system. The flowrate was chosen so that the shear stress generated on the test piece was approximately 1-2 Pa, similar to the value expected in typical field pipe flow. At the end of the test, the scale adhered to each of the five sections of the test piece pipe work was analysed separately to give data on both the mass and location of scale. A second test was also carried out to investigate the effect shear and turbulence induced by gas lift had on scale formation by modifying the test piece to introduce a flow of gas into the system. The test method was then used to evaluate a scale inhibitor and assess whether its performance was affected by the different flow regimes. The introduction of the ‘gas lift’ had a significant effect on the location of scale. Instead of being spread evenly throughout the test piece, the majority of the scale deposited upstream of the gas injection point. This is likely due to the induced turbulence and expansion in the tubing diameter at the T-piece increasing the residence time and thereby enhancing scale growth. A significant difference in scale location was also observed when the inhibitor dose was too low to prevent deposition and a higher dose was required to achieve complete inhibition in the ‘gas lift’ system. The findings from this study have significant impact on the design of test methods of evaluating scale risk in low saturation ratio brines and the screening methods for scale inhibitor for field application that should be utilised to develop suitable chemicals that perform better under higher shear conditions.


Author(s):  
Jie Tang ◽  
Fei Liu ◽  
Chong Zhang ◽  
Qiang Xue

Abstract In comparison of modified nanoscale zero-valent iron (NZVI), bare NZVI used to remediate deep contaminated groundwater source areas has more advantages. However, the influences of injected bare NZVI deposition on the permeability of aquifer remain unclear, which are still the key factors of engineering cost and contamination removal. Hence, this study sought to assess method of measuring hydraulic conductivity with constant head device and examine the permeability loss mechanism of NZVI injected into different saturated porous media, using column tests. The results showed that it was feasible to determine hydraulic conductivity by the constant head device. The permeability loss caused by NZVI injection increased with a decrease in grain size of porous media, and was determined by the amount and distribution of NZVI deposition. NZVI distribution area had a good linear correlation with dispersivity of the porous media. Additionally, although surface clogging occurred in all porous media, the amount of NZVI deposition at the injection point in fine sand was largest, so that its permeability loss was the most, which was more likely to cause hydraulic fracturing and then expand the area of contaminant source zone. These results have implications for NZVI field injection to successful groundwater remediation.


Diagnostics ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2010
Author(s):  
Milos Kasparek ◽  
Ludmila Novakova ◽  
Jan Malik

Vascular access is a lifeline for hemodialysis patients. Its lifetime is affected by many hemodynamic factors such as pressure, flow regime and wall shear stress. During hemodialysis, changes in hemodynamic parameters occur due to the flow from needles inserted into the vascular system. Primarily, there is a change in shear stress that affects the vascular wall. Pathological effects of high or low WSS are known. The effect of jet from a venous needle on hemodynamics parameters was studied, but the influence of the arterial needle on hemodynamics parameters is not sufficiently studied. To understand its possible effects, we performed in vivo and in vitro studies. Methods. In vivo experiment: The existence of flow reversal around the suction needle was visualized in a group of 12 randomly selected patients using ultrasound velocity profiling (Doppler ultrasonography) during hemodialysis. In vitro experiment: The flow field was measured using the stereo particle image velocimetry method (stereo PIV). Two regimes were studied. In the first regime, the fluid in the extracorporeal circuit was pumped by a peristaltic pump. In the second regime, the continuous pump was used in the extracorporeal circuit. The conditions were set to resemble those in vascular access during a hemodialysis session. Flow volume was set to 600 mL/min for vascular access and 200 mL/min for the extracorporeal circuit. Results. The main finding of this study was that the wall in the region of the arterial needle was stressed by backflow through the arterial needle. Since this was a variable, low-shear stress loading, it was one of the risk factors for the development of stenosis. Cyclic flow reversal was apparent in all of the included hemodialysis patients. The stereo PIV in vitro experiment revealed the oscillating character of wall shear stress (WSS) inside the model. High shear stress was documented upstream of the injection point of the arterial needle. An area of very low WSS was detected right behind the injection point during a pulse of the peristaltic pump. The minimal and maximal values of the WSS during a pulse of the peristaltic pump in the observed area were −0.7 Pa and 6 Pa, respectively. The distribution of wall shear stress with the continual pump used in the extracorporeal circuit was similar to the distribution during a pulse of the peristaltic one. However, the WSS values were continual; the WSS did not oscillate. WSS ranged between 4.8 Pa and 1.0 Pa.


2021 ◽  
Vol 58 (3) ◽  
pp. 121-128
Author(s):  
Leslie Sanchez-Castillo ◽  
Dorian Nedelcu ◽  
Misaela Francisco-Marquez

This study presents a Solidworks� Plastics application in a company in the Automotive Industry for the aftermarket of auto parts manufactured by the injection molding process, the focus is on the redesign of an injection vein plate for achieve uniform filling of a 16 cavity mold with a geometry made up of a mixture of natural rubber and two metal components. This work proves that the use of symmetrical commands is not always the best option. The distances between runners were not taken into account as a source of the future wears problems in the mold. A layout is created with a combination of 2D and 3D sketches by turning the injection chanels 180� in the problem cavities to increase the distances between runners and the filling of the 16 cavities is verified by simulation. It is also demonstrated by simulation that increasing the injection point size is not necessarily always the best option for cavity filling.


2021 ◽  
Vol 5 (1) ◽  
pp. 64-69
Author(s):  
Tetiana Psiarnetska ◽  
Maksym Tsysar ◽  
Oleksandr Lyeshchuk

The concept of form stability is considered. A semifinished product in the form of a ring from a thermoplastic mass based on SiC powder has been made on the installation for injection molding developed at the Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine  in accordance with the established technological parameters optimized by the results of computer modeling. Schemes of loading and dividing the ring into samples in the form of prismatic segments are presented. A technique for the preparation of experimental samples is proposed. The study of the compressive strength of the samples from the injected semi-finished product has been carried out on the FP-5 mechanical test machine and a corresponding здще of its change has been constructed. The formation of a barrel shape during compression tests of samples, both along the radial and tangential directions, has been established. The values of the minimum and maximum loads at which the samples are destroyed have been determined. An increase in the compaction of the thermoplastic mass around the injection point has been experimentally proved. The scheme and the actual image of crack distribution as a result of destruction of samples have been presented. It is shown that the failure occurs in the area of the presence of the calculated parting lines, which have become stress concentrators.


2021 ◽  
Author(s):  
Abdallah Ghazal ◽  
Ida Karimfazli

Abstract Oil wells are often abandoned when they become uneconomic. Normally, several cement plugs should be placed along cased wells to seal the producing formations. Proper placement protocols, especially for off-bottom plugs, are therefore required to prevent the seepage of oil. Often, heavy cement slurry is injected into wells filled with lighter wellbore fluids, through a centralised tube. To form the cement plug successfully, the injected cement slurry should accumulate at the target zone, over wellbore fluids that typically have a lower density. Therefore, the current practices involve a major hydrodynamic challenge that can result in failing plugs. In a previous work, we had shown that injecting cement slurry in wellbore fluids can result in developing a cement finger that advects downstream the well. The finger then breaks and aids the formation of a mixed layer below the injection point. Consequently, the injected cement slurry starts accumulating to form the plug. These flow events were observed in a symmetrical flow domain. In this study, we consider different configurations of the injection process to investigate how the previously observed dynamics change. To that end, we consider different sizes and positions of the injector inside the well. We conduct numerical simulations based on representative hydrodynamic models using OpenFOAM, an open source CFD software. The preliminary results reveal broadly similar dynamics for symmetrical flow domains of different injector sizes. However, marked differences are observed when the injector is not centralized in the well. The injected fluid diverts directly into the gap between the injector and casing walls, with preference to flow through the wider gap side.


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