Throttling Effect Research Articles

Effect of the convergence flow conditioner on rectifying eccentric jet flow induced by a ball valve

Installing a flow conditioner is an important method for rectifying irregular and unstable flow to stable flow state within a short flow distance in fluid transportation and control industrial applications. However, classical flow conditioners (such as Laws and Zanker flow conditioners in ISO 5167) with parallel pipeline axial orifices ineffectively rectify the distinct eccentric jet flow caused by valve regulation. The convergence flow conditioner with convergent orifices was innovatively designed for rectifying the eccentric jet flow caused by a ball valve in this study. Three convergent orifice angles (8°, 10°, and 12°) defined as angles between orifice and pipeline axes were considered to compare their effect on eccentric jet flow rectification as well as with the classical Laws flow conditioner (characterized by the convergent orifice angle of 0°) under different valve openings with an experimental setup for monitoring downstream pressures that develop along the pipeline and corresponding numerical simulation used. Pressure loss and throttling effect of installing convergence flow conditioners downstream the ball valve was assessed. Analysis of distributions of the pressure, velocity, and streamline for convergent flow conditioners showed that the flow conditioner with a large convergent orifice angle can effectively improve violent eccentric jet flows, especially under a small valve opening. The axial velocity on various downstream cross sections was extracted to evaluate the velocity uniformity. A dimensionless parameter of velocity eccentric ratio was used to quantify the rectification effect of eccentric jet flow evolving in the downstream pipeline. Results showed that a short pipeline length is needed to obtain additional symmetry and uniform flow field downstream of the flow conditioner with a high convergent orifice angle, that is, the convergence flow conditioner with a high convergent orifice angle demonstrated a strong effect of flow rectification on the valve-induced eccentric jet flow. This work can help understand characteristics of flow rectification on valve-induced eccentric jet flow in scientific research, and provide guidance for the flow conditioner design in fluid engineering.

Characterization of Physical Field and Flow Assurance Risk Analysis of Subsea Cage-Sleeve Throttling Valve

The subsea production system is presently widely adopted in deepwater oil and gas development. The throttling valve is the key piece of equipment of the subsea production system, controlling the safety of oil and gas production. There are many valves with serious throttling effect in the subsea X-tree, so the hydrate formation risk is relatively high. In this work, a 3D cage-sleeve throttling valve model was established by the numerical simulation method. The temperature and pressure field of the subsea throttling valve was accurately characterized under different prefilling pressure, throttling valve opening degree, and fluid production. During the well startup period, the temperature of the subsea pipeline is low. If the pressure difference between the two ends of the pipeline is large, the throttling effect is obvious, and low temperature will lead to hydrate formation and affect the choice of throttling valve material. Based on the analysis of simulation results, this study recommends that the prefilling pressure of the subsea pipe is 7–8 MPa, which can effectively reduce the influence of the throttling effect so that the downstream temperature can be kept above 0°C. At the same time, in regular production, a suitable choke size is opened to match the production, preventing the serious throttling effect from a small choke size. According to the API temperature rating table, the negative impact of local low temperature caused by the throttling effect on the temperature resistance of the pipe was considered, and the appropriate subsea X-tree manifold material was selected to ensure production safety. The hydrate phase equilibrium curve is used to estimate the hydrate formation risk under thermodynamic conditions. Hydrate inhibitors are injected to ensure downstream flow safety.

EXPERIMENTAL STUDY ON TILTING STIFFNESS OF OIL HYDROSTATIC SHALLOW RECESS THRUST BEARINGS

Circular shallow recess bearings generate a not rotationally symmetrical pressure profile if they are not aligned parallel. The throttling effect of the shallow recess makes this response possible. Furthermore, the generated pressure profile acts against the tilting. As a result, a shallow recess bearing generates a tilting stiffness. This article outlines an experimental approach to characterize the tilting stiffness of an oil hydrostatic shallow recess thrust bearing with micro step and gap height. For this purpose, we developed a small test bench. The measured tilting stiffnesses are compared with a numerical solution based on the 2D-Reynolds equation.

Analysis on Leakage Characteristics of Labyrinth Piston Clearance in Reciprocating Labyrinth Compressor

In this paper, the piston clearance leakage model in reciprocating labyrinth compressor is established, and the leakage characteristics of labyrinth piston are analysed. The results show that in the labyrinth entrance section, the gas velocity decreases greatly, and the throttling effect is the most obvious. In the middle section of the labyrinth, the flow velocity descending gradient decreases. In the exit section, the flow rate begins to increase. When the labyrinth clearance is less than or equal to 0.1 mm, the clearance changes has little effect on the leakage. When the clearance is greater than 0.1 mm, the leakage increases rapidly with the clearance increasing. When the piston operates eccentrically, the leakage will increase by 1.5 ∼ 2 times compared with the non-eccentric operation. Therefore, the eccentric operation of the piston should be avoided as much as possible and the clearance should be reduced.

Impact of micro-grooves in scroll wrap tips on the performance of a trans-critical CO2 scroll compressor

Radial leakage was commonly regarded as the primary factor restricting the aero-thermodynamic performance of scroll compressors. In this paper, a passive flow control approach of micro-grooves in scroll wrap tip for the radial leakage in the scroll compressor was proposed, and its flow characteristics were numerically investigated. The impact of micro-grooves geometric parameters, such as groove number, depth, and partitions, on the flow control effect of the radial leakage was discussed, which was obtained by analyzing the evolution of the flow field and its influence on the performance of the scroll compressor. Results showed that the adoption of micro-grooves in scroll wrap tip yielded a significant limitation on the radial leakage, and geometrical parameters of the micro-grooves directly affected the flow control performance. Increasing groove numbers and partitions decreased the radial leakage effectively, while the leakage decreased first and then increased with the increase of the groove depth. The energy dissipation induced by the continuous throttling effect, jet expansion, and vortex in the groove cavity was the main flow control mechanism. The quadruple-grooves with the groove width of 0.5 mm and the groove depth of 100 μm were adopted in this study eventually. The volumetric and isentropic efficiency of the scroll compressor raised up 2.1 and 1.0 percentage point compared to the original case, respectively. Through reasonable working conditions and micro-grooves geometry, the aero-thermodynamic performance of the oil-free scroll compressor could be improved effectively by the scroll wrap tip with micro-grooves.

Effect of metro train on the critical driving force for preventing smoke back‐layering in tunnel fires

SummaryPreventing smoke back‐layering in longitudinal‐ventilated tunnels is an important topic in handling with fires safety issues. Previous studies focused on the critical velocity, while only very few of them paid attention to how to realize this parameter, that is, in a critical state, to overcome the resistance of the tunnel and the fire source to the airflow, the required driving force provided by the ventilation equipment installed in the tunnel. This study addressed this problem in the situation where the coupling effect of blockage and throttling effect was highlighted by conducting theoretical analysis and numerical simulations. The results showed that the presence of metro train blockage reduces the effective cross‐sectional area of the tunnel near the fire source and decreases the critical velocity. On the other hand, the blockage of trains also increases the resistance to the ventilation airflow and exacerbates the throttling effect, leading to the increase of the critical driving force. In such conditions, a stronger driving force to approach the critical velocity was needed. Besides, the length of train blockage was verified to exert limited influence on the value of critical velocity while it significantly affected the critical driving force. Furthermore, the calculated formula for the critical driving force was proposed with the prevention of smoke back‐layering considering the blockage effect to be emphasized.

The ignition characteristics of the pre-chamber turbulent jet ignition of the hydrogen and methane based on different orifices

In this paper, the combustion characteristics of premixed CH4-air and H2-air mixtures with different excess air coefficients ignited by hot jet or jet flame are investigated experimentally in a constant volume combustion chamber (CVCC). The small volume pre-chambers with different orifices (2 or 3 mm in diameter) in the passive or active pre-chamber were selected. Both the high-speed Schlieren and OH∗ chemiluminescence imaging are applied to visualize the turbulent jet ignition (TJI) process in the main chamber. Results show that the variation of orifice has diverse influences on the turbulent jet ignitions of methane and hydrogen. Smaller orifices will reduce the temperature of the jet due to the stronger stretch and throttling effect, including change of lean flammability limit, ignition delay, and re-ignition location. Furthermore, shock waves and pressure oscillations were captured in the experiments with hydrogen jets. The former is related to the jet velocity, while the latter is mainly affected by the mixture thermodynamic states in the main chamber. Furthermore, the re-ignition location is discussed. If the mixture reactivity and the jet energy are sufficiently high, the reaction will be initiated at the tip of the jet in a short time. On the contrary, a relatively long time is required to prepare the mixture during the entrainment when the reactivity is not high enough, and the corresponding re-ignition location will move towards the orifice exit owing to the temperature decline at the tip. Finally, the ignition mode transition of hydrogen jet in lean cases with a 2 mm orifice is explained.

Experimental Investigation of the Characteristics of Supercritical CO2 during the Venting Process

Carbon capture utilization and storage (CCUS) is the technology with the greatest potential to decrease the content of CO2 in the atmosphere, which is the main contributor to global warming and can result in a significant number of environmental problems. The transportation of CO2 is the most important node in the CCUS chain and a pipeline is an economical and efficient means of transportation. In the process of CO2 pipeline building, a certain amount of venting devices should be installed to prevent overpressure of the main pipeline and allow for overhaul of the main pipeline. Hence it is necessary to obtain the characteristics of CO2 inside the venting pipe during the venting process in order to maintain the safety of both the venting pipe and the main pipeline during release. In this study, two 2 m long venting pipes were connected by valves and installed on an industrial-scale pipeline. Two group venting experiments were carried out with two different openings of the valve. Industrial-scale experiment apparatus was used to obtain crucial data and get results closer to an actual industrial setting. During the experiments the evolution of the temperature and the pressure of the CO2 were measured. Based on the pressure and temperature data, the differences of the phase transition of the CO2 in the two experiments were compared. No dry ice was generated inside the pipe during the experiments. A throttling effect was generated in one group experiment but not in the other. In addition, the evolution trend of the Joule–Thomson coefficient was discussed. During the whole venting process, the wall temperature was obtained and the Nusselt number was selected as a parameter to discuss the process of heat transfer between the CO2 and the pipeline wall.

Analysis of the dynamic characteristics of downsized aerostatic thrust bearings with different pressure equalizing grooves at high or ultra-high speed

This study adopts the DMT(dynamic mesh technology) and UDF(user defined functions) co-simulation method to study the dynamic characteristics of aerostatic thrust bearings with equalizing grooves and compare with the bearing without equalizing groove under high speed or ultra high speed for the first time. The effects of air film thicness, supply pressure, rotation speed, perturbation amplitude, perturbation frequency, and cross section of the groove on performance characteristics of aerostatic thrust bearing are thoroughly investigated. The results show that the dynamic stiffiness and damping coefficient of the bearing with triangular or trapezoidal groove have obvious advantages by comparing with that of the bearing without groove or with rectangular groove for the most range of air film thickness, supply pressure, rotation speed, perturbation amplitude, especially in the case of high frequency, which may be due to the superposition of secondary throttling effect and air compressible effect. While the growth range of dynamic stiffness decreases in the case of high or ultra-high rotation speed, which may be because the Bernoulli effect started to appear. The perturbation amplitude only has little influence on the dynamic characteristic when it is small, but with the increase of perturbation amplitude, the influence becomes more obvious and complex, especially for downsized aerostatic bearing.

Study on the eccentric jet-flow characteristics induced by the opening regulation with a gate valve

Valve-induced flow characteristics were often concerned in many fluid transportation and control industries. In this paper, the eccentric jet-flow characteristics induced by a gate valve have been studied by considering the influence of valve opening regulation. The experimental setup of monitoring the downstream pressures along the pipeline was developed, and corresponding numerical simulation was employed. The downstream-monitoring pressure distribution caused by valve opening regulation was investigated to verify the flow simulation. The generation mechanism of eccentric jet-flow was revealed as a strong pressure gradient caused by the throttling effect at the valve throat. It was found that the eccentric jet-flow evolved in the pipeline was accompanied by shearing vortices, extremely under a small valve opening. The pressure and axial velocity distributions at various downstream cross-sections of the eccentric jet-flow evolving in the pipeline were analyzed. The axial velocities on four monitoring lines in downstream cross-sections were extracted, and the radial location of the maximum axial velocity was derived to assess the eccentric characteristics of jet-flow. A dimensionless parameter of velocity eccentric ratio was introduced to quantify the eccentric intensity of the evolving jet-flow in the downstream pipeline, and its correlation with the pipeline length could be adequately expressed by a natural decreasing exponential curve via fitting analysis. By virtue of that correlation, the critical pipeline length was proposed that can be used as the judgment to the terminal of the eccentric jet-flow evolving in the downstream pipeline. This study was helpful to characterize the valve-induced flow characteristics in scientific research and provide useful insight into fluid and mechanical engineering.

Numerical simulation of the effect of chimney configuration on the performance of a solar chimney power plant

Previous studies have shown that the crosswind reduces the output power of a SCPP (solar chimney power plant) with the deflection of the plume at the exit and separation of wind flow there at the downstream. The present numerical investigation was focused on the effect of the stack configuration on the performance of a SCPP. In this paper, the SCPP of the prototype in Manzanares was simulated, where the Boussinesq approximation was used for solving the continuity, Navier–Stokes and energy equations by the standard k-epsilon turbulence model in finite volume method. Governing parameters are taken as oblique angles from 27° to 45° and wind velocity from 0 to 10 m s−1. Investigation revealed that by changing the stack configuration, the performance of the SCPP could be improved. Numerical simulation of the conventional chimney was compared with the simulation data of the proposed altered chimney geometry (outlet bevel cutting) and observed that the throttling effect on the outlet of the chimney could be reduced. It was noticed that by changing the chimney oblique angle from 27° to 45°, the efficiency of the power plant was dropped. Further, the results illustrated that the oblique angle relies on the wind velocity and it needs to increase with the increase in the wind velocity to obtain a reasonable change in power output. The present investigation was further enhanced to incorporate a comparison of solar chimney power output in two cities (Kuala Lumpur and Kerman) for a better understanding of the effect of environment on constructing the solar tower power plant. The result shows that Kuala Lumpur is appropriated for the installation of SCPP although, the Kerman is suitable too, but the wind velocity in that city is higher than that in Kuala Lumpur.

Hydrate predictions on the China-Russia eastern gas pipeline during the pipeline goes into production

The China-Russia eastern gas pipeline has the characteristics of large pipe diameter and high pressure. During the pipeline goes into production, the temperature along the pipeline was low, and the conditions of low temperature and high pressure brought the risk of hydrate formation. Based on the multiphase flow theory and the CSMHyK hydrate growth kinetic model, this paper studied the hydrate formation region, the amount of hydrate formed and the influence of hydrate formation on the temperature drop and pressure drop of the China-Russia eastern gas pipeline in the first winter the pipeline goes into production. The results show that in the first winter the pipeline goes into production when the water content is more than 150 mg/kg the hydrate formation risk exists in the pipeline. Hydrate accumulates mainly in the ascending part of the low-lying pipe section, and the greater the height difference of the pipe section, the more hydrate accumulation. In the stage of mass hydrate formation, the temperature in the pipeline will rise due to hydrate formation, but when hydrate growth reaches equilibrium, the temperature in the pipeline is mainly controlled by the external soil temperature. In addition, a large amount of hydrate accumulation will generate a throttling effect, which will lead to increased temperature drop and pressure drop of the pipeline. When the water content is 350 mg/kg, the maximum additional pressure drop generated by hydrate aggregation is 2.27MPa.

Research on the Influence of Throttle Valve Cage Sleeve Structure on Throttling Effect

Throttle valve is the key equipment of ultra-high pressure natural gas well, and the research on the structure and performance of the throttle valve is particularly important. Among them, the cage-type throttle valve has been studied more and more in recent years because of its many advantages. This article mainly studies the cage of the cage type throttle valve, and makes an in-depth analysis of its structure on the basis of theoretical calculations. Corresponding models are established through the wired element analysis software, and the opening positions of the valve core cage, the opening degree of the cage and the flow area change rule, the number of cage holes and the diameter of the cage are discussed. Studies have shown that when the number of small holes in the valve core cage is fixed, the flow area of the cage increases, the flow velocity in the small holes increases, and the static pressure decreases; when the flow area of the cage is fixed, the number and diameter of the throttle holes are changed, The flow rate of the flow valve is basically unchanged. It is recommended to change the diameter of the small hole and the flow area under the condition that the structure of the valve core cage is determined, and the throttling effect will be more significant.

CONTROL OF THE SUPERSONIC FLOW STRUCTURE DURING ETHYLENE COMBUSTION WITH THE USE OF GAS-DYNAMIC PULSES

A supersonic flow in a channel with a variable cross section is numerically simulated in the case of ethylene injection along the channel under the action of a jet generating a throttling effect. The averaged Navier–Stokes equations closed by the $$k$$ – $$\varepsilon$$ turbulence model are solved. Ethylene combustion is modeled with the use of one reaction. The results are compared with experimental data on the pressure distribution over the channel wall. It is found that gas-dynamic pulses produce an irreversible effect on the flow structure. The formation of a transonic flow region and its structure are described.

Improvements on performance and emissions of a heavy duty diesel engine by throttling degree optimization: A steady-state and transient experimental study

Heavy duty diesel engines emit over half of mobile source NOx, so SCR is used to reduce NOx. But in applications, SCR is hard to work in desired temperature range. In this work, we try to improve exhaust thermal management and finally reduce NOx through intake throttling effect. Firstly a throttle was designed and its response characteristics were widely explored through steady-state experiment. Results showed that exhaust temperature can be raised largely through intake throttling degree (TD) control, it has obvious effect only after 60 % TD. At 1100 r/min and 65 % TD, exhaust temperature rises by 123.3 °C, 74.2 °C, 49.7 °C and 33.5 °C for 600 N·m, 400 N·m, 200 N·m, and 50 N·m loads, respectively. TD demand for rising transition point becomes larger as engine load decreases, at 600 N·m transition point occurs at 61 % TD, but it increases to 68 % TD at 50 N·m. Finally the intake flow rate was optimized continuously with whole cycle level consideration in transient operation. NOx decreased by 43 % with fuel consumption and HC keeping unchanged, while CO increased by 24.6 %. We hope to provide a good example for diesel engine performance improvement from optimization of existing technologies without too much cost.

Dynamics of the in sac cavitating flow for diesel spray with split injection strategy

IC engines consume a large amount of fuel and produce plenty of emissions, thus reducing fuel consumption, and emissions are important. Nozzle internal flow which dominates spray breakup is the key to improve spray atomization and reduce fuel consumption. In this study, microscopic imaging technique was employed to investigate the effects of needle oscillation and injection strategy on the nozzle internal flow under cold (20°C) and hot (140°C) conditions. Needle oscillation was found to affect spray morphology, leading to obvious spray asymmetry under both cold and hot conditions with stronger spray radial propagation under hot condition. Cavitation in the sac appeared when needle oscillated due to enhanced turbulence. Besides, cavitation in the sac was introduced when the needle was insufficiently open due to throttling, especially under hot condition because of reduced viscosity. By contrast, when the split-injection strategy was employed, cavitation was considerably boosted because of the consistent flow transition and the resultant throttling effect. Effective injection duration of the first injection governed the corresponding peak relative cavitation area. The appearance of cavitation was delayed during the initial stage for each split injection after the fuel flows out due to laminar flow regime.

MODELING OF KEROSENE COMBUSTION IN A SUPERSONIC FLOW UNDER THE ACTION OF A THROTTLING JET

Structural changes in a supersonic flow in a variable-section channels with axial injection of kerosene induced by the action of a jet generating a throttling effect are numerically simulated. Reynolds-averaged Navier–Stokes equations closed by the $$k$$ – $$\varepsilon$$ turbulence model are solved. Kerosene combustion is modeled by equations of simplified chemical kinetics. The evolution of the processes in the channel is analyzed numerically and analytically for different types of the fuel (hydrogen, ethylene, and kerosene), and comparisons with experimental data are performed. It is found that high-intensity gas-dynamic pulses have to be used to form a transonic region in the case where kerosene is used as a fuel.

Formation of a transonic region in a variable-section channel for different stagnation temperatures of the flow

Initiation of operation of a ramjet engine with distributed fuel injection along the combustion chamber is studied numerically. A principally important issue is the presence of a compressed air jet producing a throttling effect and preliminary deceleration of the flow to transonic velocities. The Reynolds-averaged Navier-Stokes equations closed by the SST k-ω turbulence model are solved. Hydrogen is used as a gaseous fuel. Transverse injection of the fuel is considered. A pulsed transonic flow regime is obtained. It is demonstrated that the characteristic scale of vortex regions increases with an increase in the stagnation temperature approximately to 1700 K; consequently, the degree of air-hydrogen mixing is significantly enhanced.

Experimental investigation of an Organic Rankine Cycle Tesla turbine working with R1233zd(E)

The increasing interest in micro power generation is pushing the research world to find new solutions for increasing the efficiency of micro Organic Rankine Cycles. One of their main issues is the efficiency and the reliability of the expander. The Tesla turbine is an old/new expander, which has found a renewed interest in the last years because of the increasing appeal towards distributed micro generation, where this expander becomes competitive.This peculiar technology seems adapted to micro generation in Organic Rankine Cycle thanks to its main characteristic, which is its simple structure that allows for high reliability and cheapness. In recent years, this expander has been analytically and numerically assessed when working with organic fluids. In this study, the experimental investigation of a Tesla turbine working with R1233zd(E) is presented. One of the main achievements was the assessment of the blockage effect of disks edges when the pressure drop through the machine is relevant as in case of Organic Rankine Cycles (e.g. higher than 3–4 bars), resulting into a relatively large amount of flow deviation through the clearances between the rotor disks package and the case, which implies a throttling effect thus resulting into a relevant performance loss. This effect was accounted by a model that well fitted the experimental data.The achieved results confirmed the validity and the large applications potential of this emerging technology, especially in the fields of micro power generation, low inlet temperature and low expansion ratios. A maximum net power output of 371 W was obtained, proving the feasibility of utilizing Tesla turbines in Organic Rankine Cycle applications. A maximum shaft efficiency of 9.62% and a maximum adiabatic efficiency of 30% were achieved. The results and the developed model of disks edge losses effects represent an important step ahead, in physical depiction of the phenomenology, over the currently available literature, fundamental for the improvement of the design procedure of Tesla turbines for Organic Rankine Cycles.

Supply system of cryo-compressed hydrogen for fuel cell stacks on heavy duty trucks

The work presents the design and analysis of a novel cryo-compressed hydrogen (CCH2) supply system. It aims to storage CCH2 (around 20 MPa and 20 K), but supply hydrogen under suitable conditions (0.16 MPa and 338 K) for fuel cell stacks. Generally, thermal waste of fuel cell occupies nearly half of the entire outcome and cannot be applied for truck driving. But in this system, original wasted energy can be reused to heat cool hydrogen, which relieves the heat burden of cooling device. This process is carefully designed and demonstrated for a 25-ton heavy duty truck. Mass flow rate in the specified CCH2 system is verified by theoretical calculating. Also, negative throttling effect of hydrogen is carefully considered for comprehensive utilization. At last, different efficiency of cryogenic heat exchangers are compared to explore the characteristics of energy consumption.