Journal of Natural Gas Science and Engineering

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In fl uence of fl ashboard location on fl ow resistance properties and internal features of gate valve under the variable condition

Zhe Lin

^a^,^b^,^c^,^**

, Guangfei Ma

^a^,^b^,^*

, Baoling Cui

^a^,^b

, Yi Li

^a^,^b

, Zuchao Zhu

^a^,^b

, Nansen Tong

^d

aInstitute of Mechatronic Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China

bThe Zhejiang Provincial Key Laboratory of Fluid Transmission Technology, Hangzhou 310018, China

cZhejiang Institute of Mechanical&Electrical Engineering co., Ltd, Hangzhou 310011, China

dCollege of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou 310053, China

a r t i c l e i n f o

Article history:

Received 26 September 2015 Received in revised form 28 February 2016 Accepted 4 May 2016 Available online 9 May 2016

Keywords:

Gate valve Variable condition CFD

RSM

Flow coefficient Resistance coefficient Pressure coefficient Numerical simulation Experiment

a b s t r a c t

This article is intended to elaborate different inlet velocities that respectively are 13 m/s,15 m/s and 17 m/

s to influenceflow resistance characteristics and the internalflow characteristics of gate valve in the medium-low pressure gas transmission. This paper presents the CFD analysis offlow resistance characteristics and the internalflow characteristics of gate valve in a gate valve with different inlet velocity.

Gate valves under different inlet velocity have eight relative opening degrees that respectively are 1/8, 2/

8, 3/8, 4/8, 5/8, 6/8, 7/8 and 1. For every relative opening degree of gate valve structure, the systematic CFD simulations offlow resistance, pressurefluid, velocityfluid, velocity streamline and pressure coefficient characteristics. The study mainly analyses the pressurefield distribution, velocity distribution, the velocity streamline distribution when the relative opening degree is 1/8, 2/8 and 1. Experimental measurements are also conducted forflow resistance characteristics and then compared with simulated flow resistance results. The CFD simulatedflow resistance results show a good agreement with that of experimentalflow resistance based on the Reynolds Stress Model (RSM) turbulence model provided by fluent software. Through analysis offlow resistance properties and internalflow characteristics, we concluded that it is not stable before the relative opening degree 2/8 that the valveflow resistance characteristics and internalflow characteristics, which need to be optimized; however, the valveflow resistance characteristics andflow characteristics gradually can be gradually stabilized after the relative opening degree 2/8, and does not have the characteristics of regulating valve. In the process of gas transmission, pressure energy loss mainly occurs in the valve core.

1. Introduction

Valve is an important part of the pipeline system. It can control the opening and closing of circulation medium, reversing, ensure the safety of the system, adjust the flow and pressure, etc. Gate valve is a shutter opening and closing pieces. The movement direction of thefluid through gate valve is perpendicular to the gate, which does not alter theflow direction of thefluid. Gate valve fully open when the least of drag coefficient for almost all the valves, and

applicable scope of caliber, pressure and temperature range is very wide. Compared with the same caliber cut-off valve, the installation size of gate valve is small. So it is widely used in the chemical production, gas transmission air inlet and exhaust outlet location.

The gate valve is suitable for the pipe system of conveying air, steam, water, solvents and otherﬂuids, the shutdown does not require high frequent opening and closing of the occasion. How- ever, under different conditions and at different locations, the in- ternalﬂow resistance characteristics and the internal features of gate valve change research remains small.

Researchers commonly use numerical simulation and experimental methods to obtain theﬂow resistance characteristics and internalﬂow characteristics of the valve.Edvardsen et al. (2015) conducted an experimental and numerical analysis of single- phase pressure drops in a down hole shut-in valve. Wu et al.

(2015)elaborate on speciﬁc computational ﬂuid dynamics (CFD)

*Corresponding author. Institute of Mechatronic Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China.

**Corresponding author. Institute of Mechatronic Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China.

E-mail addresses: [email protected] (Z. Lin), [email protected] (G. Ma).

Contents lists available atScienceDirect

j o u r n a l h o me p a g e : w w w . e l s e v i e r . c o m/ l o ca t e / j n g se

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simulation methods forfitting theflow-pressure curve of a pressure control valve.Song et al. (2014)developed a numerical model to investigate the fluid and dynamic characteristics of a direct- operated safety relief valve. Dimitrov, (2013) investigated the flow-pressure coefficient of a pilot-operated pressure relief valve with theoretical analysis and verified the results with experiments.

Valdes et al. (2014)performed and validated a series of CFD simulations of the capitation toflow through a ball check valve. They analyzed the characteristicflow coefficient of the valve and the hydraulic forces on the ball.Aung et al. (2014)analyzedflow forces and energy loss characteristics in aflapperenozzle pilot valve with different null clearance by CFD software. Experimental measurements are also conducted for energy loss characteristics and then compared with simulated results. Chattopadhyay et al. (2012) investigated the flow process inside a pressure regulating valve by using a computationalfluid dynamic approach. The commercial code FLUENT was found to aptly model the complicatedflow pro- cesses inside the domain of interest.Lisowski and Rajda (2013) investigated the reduction of flow resistance in a hydraulic system, which is focused on a spool type directional control valve with pilot operated check valves. The system of designedflow paths is verified by CFD analysis with the use of ANSYS/FLUENT program on a three-dimensional model. Obtained results are compared with the results of the characteristics given in catalogues and coming from experimental research on the prototype. Amirante et al.

(2014) evaluated the effects of cavitation upon the directional valve by means of thorough experimental and numerical in- vestigations.Mougaes and Jagan, (2008)analyzed the ball valve internal three-dimensionalflow field under different opening of the pressure drop and turbulentflow through Commercial software STAReCD. Ye Y et al.Ye et al. (2014)clarify the effects of the groove shape on the flow characteristics of the spool valve through computational fluid dynamics (CFD) and experimental in- vestigations. They simplified the structure of the valve, which was solved by using the RNGkε turbulence model to simulate the pressure distributions of theflowfields inside three notches with their corresponding typical structural grooves. Lisowski et al.

(2014)presented an innovative directional control valve based on the use of logic valves and a methodology followed for the design of

it by using Solid Edge CAD and ANSYS/Fluent CFD software.Posa et al. (2013) carried out an analysis of the discharge coefficient and theflow force of a directional valve utilizing 2D CFD method and, in addition, thefluid-body interaction had been represented by an immersed boundary technique. Although the above studies used numerical simulation or numerical simulation and experimental research method of combining the valve, did not study for flow resistance characteristics and internalflow characteristics of the gate valve at different speeds.

The present study introduces CFD simulation methods to investigateflow resistance characteristics and internalflow characteristics of the gate valve at different speeds. The universal CFD package, Fluent (FLUENT 14.5, 2014), and Gambit grid generator has been applied to perform all the 3D quasi-static numerical compu- tations. It is simplified that theflow channels structure of the gate valve. Flow resistance and the internalflow characteristics of gate valve are simulated by solving the Reynolds Stress Model (RSM) turbulence model at different positions of the gate and under the variable inlet velocity. At the same time, we conducted the flow resistance characteristic experiment of gate valve. The results provide effective guidance for the design of an adjustable gate valve.

2. Physical model and experiment

This article mainly studies for the pipeline structure of the gate valve a rectangular structure. Gate valve working principle is through the stem to drive disc gate valves opening and closing. In order to study theﬂow resistance characteristics of multi conditions and within the rectangular pipe valve ﬂow characteristics.

Fig. 1shows an Auto CAD generated two dimensional model of the valve used.Fig. 2shows a SolidWorks generated three dimensional flow channel model of the valve used. And according to theflow diagram, we processed the flow channel to conduct the flow resistance characteristics experiment of gate valve. Fig. 3 is the experimentalfield photo and circuit scheme. Pipe structure of gate valve is consisting of the upstreamflow, groove, downstream of three parts.Fig. 4is the two dimensionalflow channel model of the valve.Table 2is the value of pipeline structure. In order to fully develop the turbulentflow, the upstream pipe section of the valve is longer than 5 times of the hydraulic diameter of the pipe, the downstream pipe section of the valve is longer than 10 times the diameter of the pipe (Xue et al., 2009; Chern et al., 2013). In this paper, the hydraulic diameter of the pipeline is 26.7 mm. Therefore, there is 805 mm in length in the upstream before the valve center and 725 mm in length in the downstream after the valve center. The choice of upstream and downstream length is to achieve the fully developed turbulence flow. Opening of the gate valve is fully opened 40 mm. In order to study the variety of the opening of the change, we studiedflow resistance characteristics and the internal flow characteristics of the gate valve that is the relative opening degree of 1/8, 2/8, 3/8, 4/8, 5/8, 6/8, 7/8, 1 under different inlet conditions (during the Table 1). On the basis of obtaining the physical model, the external characteristic experiment of the gate valve is carried out, and theflow coefficient and resistance coefficient are obtained. In order to ensure the repeatability and accuracy of the experiment, each relative opening is carried out 20 experiments, and the data are processed by means of the mean value.

3. Numerical model

In order to study the gate location of gate valveflow resistance properties and the influence of the internal features under the variable condition. CFD simulations using commercial software FLUENT are performed, which can obtain the mass flow rate Nomenclature

Cd flow coefficient of the gate valve x resistance coefficient of the gate valve Cp pressure coefficient of the gate valve r ^thefluid density (kg/m³)

v dynamic viscosity (m²s) RSM Reynolds Stress Model P Centerline pressure (pa) length total length (1530 mm)

height Square tube cross section height (40 mm) Pin inlet static pressure (N/m²)

△P pressure drop between inlet and outlet (bar¼10⁵pa)

Q volumeflow rate (m³/s) Kv flow coefficient of the gate valve U magnitude velocity (m/s) CFD computationalfluid dynamics wb bulk mean velocity of the gas (m/s) width Square tube cross section width (20 mm) 3D Three-dimensional

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through the valve as well as speed streamline, the pressure and velocity contours. The Reynolds Stress Model (RSM) turbulence model is employed to the simulation. The continuity, momentum and turbulence generation and destruction equations are resolved by means of the Finite Volume commercial codefluent. Manyflow domain models with different valve openings would be built in both CFD methods. Given square gate valve structure, a structured grid is generated using the commercial software Gambit. Numerous flow domain models with different valve openings would be built in both CFD methods. Fig. 5shows the 3D images of the flow domain and grid model. The grid model contains 4 million cells, and the grid quality is rigorously checked. The number of grids is already numerous, and the results barely change as the amount increases.Fig. 6shows the coefficient offlow resistance varies with the number of the grid at the gate relative position of the 1 and the inlet velocity of 13 m/s, which indicates the independence of the grid.

3D quasi-static numerical computation is used for the present gate valve study. The inlet and outlet boundary types are deﬁned as velocity inlet and pressure outlet, respectively. The outlet pressure isﬁxed at 0 Pa, and the inlet velocity is varied in the same valve opening simulation cases. The no-slip boundary condition is adopted for all the walls. The well-known SIMPLE strategy is uti- lized to deal with the velocity-pressure coupling. Due to the given gas inlet boundary conditions (inlet velocity is 13 m/s, 15 m/s, 17 m/

s, respectively.) belonging to the low-pressure gas transmission range, the Mach number is less than 0.3, so the media air as incompressible. Theﬂuid density and dynamic viscosity are set to r¼1.225 kg/m³andv¼14.810⁶m²/srespectively.

4. Calculation results and discussion 4.1. Flow resistance properties of gate valve

Flow resistance characteristics (Cui et al., 2015) is the external performance of the valve internalflow and are the main performance parameters of valves, includingflow coefficient and drag coefficient. Flow coefficient is used to measure the valve flow Fig. 1.Two dimensional model of the gate valve.

Fig. 2.Three dimensionalﬂow channel model of the valve.

Fig. 3.(a) Field photo and (b) Circuit scheme.

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capacity of the indicators. The greater the flow coefficient, the greater theflow capacity of the valve,fluidflow through the valve the pressure loss is smaller. Resistance coefficient is also a measure of the valveflow capacity of the indicators, the greater the resistance coefficient, the smaller theflow capacity of the valve, the greater the pressure loss offluid flow through the valve (Raisee et al., 2006a).

The most convenient method of relatingflow rates to pressure drop through valves isflow resistance coefficient of the valve. It is purely empirical and varies according to the type, size and opening of the valve. It will also depend on detail design and construction (Alimonti, 2014).

According to the previous definition,flow resistance of the valve coefficient is calculated from the relation below.

Flow coefﬁcient:

K_V ¼Q ffiffiffiffiffiffiffi

D r

^P r

(1) whereQis the totalflow rate across the valve (l/min),r^{is the}fluid density (kg/m³), andD^pis the measured pressure drop (bar). Valve flow coefficient is normally given for 100% opening.

Resistance coefﬁcient:

Fig. 4.Two dimensionalﬂow channel model of the valve.

Table 1

Different inlet conditions.

Inlet velocity Value(m/s)

1 13

2 15

3 17

Table 2

The value of pipeline structure.

Flow channel Value(mm)

Upstream (length) 785

Downstream (length) 705

Pipe groove (height) 20

Pipe groove (length) 40

Fig. 5.The 3D images of theﬂow domain and grid model.

Fig. 6.Independence of the grid veriﬁcation.

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x

¼2

D

^p

r

^U² ⁽²⁾

whereD^pis the measured pressure drop (bar),r^{is the}ﬂuid density (kg/m³), andUis the speed of medium in the pipeline (m/s). Valve resistance coefﬁcient is normally given for 100% opening.

4.1.1. Flow coefﬁcient of gate valve

Flow coefficient is a dimensionless quantity; it reflects theflow capacity of the valve. In order to study under the variable condition, the size of theflow coefficient of different gate location value.Fig. 7 shows under three different inlet velocities, different gate location gate valveflow coefficient of the simulation value and experiment value. Can be seen from Fig. 7, the gate valve flow coefficient increased with the increase of relative opening degree increase;

Under different inlet velocity, the gate valveflow coefficient values under the same relative opening degree is basically the same, its range is very small. When the relative degree of opening of 2/8, gate valve flow coefficient changes slightly obvious, but in a relative degree of opening between 2/8 and 5/8, in close agreement again;

The relative degree of opening between 5/8 and 7/8, gate valveflow coefficient significantly increase acceleration and deceleration increase. When after the relative opening degree of 7/8, the relative opening degree of gate valve is close to the fully opened; valveflow coefficient exhibits a linear increase. This shows that, in the gate valve opening and closing of the entire process, the gate valveflow coefficient increases as a whole, increasing way valveflow coefficient is not the same, which increases when approaching the fully open manner to achieve a stable increase linearly, different inlet velocity changes between micro flow coefficient is significantly reflected. These results are a direct reflection that gate valve is not suitable forflow regulation valve.

4.1.2. Resistance coefﬁcient of gate valve

Resistance coefficient is a dimensionless quantity; it reflects the fluid through the valve resistance. Fig. 8 shows under three different inlet velocities, different gate location gate valve resistance coefficient of the simulation value and experimental value. As it can be observed in theFig. 8, both the experimental value and the simulation value, when the valve relative opening degree is 2/8, the resistance coefficient of thefluid appears demarcation point. Before relative opening degree of 2/8, namely, the opening of the valve relative is very small, fluid resistance coefficient sharply is increased; indicating that the valve is coming off closing will be

greatly impacted. After relative opening degree of 2/8, the resistance coefficient decreases rapidly; There is a clear micro change between the relative opening degree of 2/8 and relative opening degree of 3/8. However, 3/8 after opening degree relative such micro change is almost zero. This shows that, at different inlet velocity, when thefluid is through the gate valve, resistance coefficient and its maximum has a most dramatic change before the relative opening of 2/8. This very small impact on the opening of the gate valve is very serious. These results suggest that if you like to take in a small valve opening, it is necessary to have a powerful compression and wear resistance, the material selection is very strict.

4.2. Flowﬁeld analysis

Numerical simulation and experimental study of the flow resistance characteristics of multi-valve conditions were, just got a change in its external characteristics, changes in its internalflow field and cannot get a straight pipe of understanding. At 2/8 relative degree of opening, theflow resistance of gate valve is beginning a significant change, we focus on the relative degree of opening of 1/

8, 2/8 opening degree relative, the relative degree of opening 1 gate valve internalflow pressurefield distribution, velocityfield distribution and velocity streamline distribution.

4.2.1. Pressureﬁeld distribution

Fig. 9shows under three different inlet velocities, gate valve internalflow pressurefield contour distribution that is simulated by thefluent software on the relative degree of opening of 1/8. The pressure drop through the gate valve is concentrated on the downstream of the rectangular pipe and the pipe groove within the entire range of the XOY section. In other words, the throttling effect of the spheroid-shape groove is provided by theflashboard. How- ever, under different inlet velocity, pressurefield distribution inside the gate valve is not the same. Greater speed generated greater negative pressure area range. This shows that when the in the1/8 relative opening, the smaller the gate valve inlet velocity through the spool, the resistance coefficient of the gate valve is greater.

Fig. 10shows under three different inlet velocities, gate valve internalflow pressurefield contour distribution that is simulated by thefluent software on the relative degree of opening of 2/8. The pressure drop through the gate valve is almost same in inlet velocity 13 m/s and 15 m/s. Compared to the inlet velocity of 13 m/s and 15 m/s, when the inlet velocity is 17 m/s, pressure field Fig. 7.Flow coefficient of gate valve.

Fig. 8.Resistance coefﬁcient of gate valve.

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distribution of the gate valve in the XOY section has obvious dif- ferences. However, the pressure distribution is exactly uniform in the import and export, so here is basically the same outer characteristic.

Fig. 11shows under three different inlet velocities, gate valve internalflow pressurefield contour distribution that is simulated by thefluent software on the relative degree of opening of 1. The pressure drop through the gate valve is almost same distribution tendency in inlet velocity 13 m/s, 15 m/s and 17 m/s. However, when the inlet velocity is 17 m/s, the scope of high pressure is obviously more than 13 m/s and 15 m/s. This shows that in the low- pressure gas transmission, the transmission speed is greater; the high pressure range is greater inside the pipe. Then, there is a greater pressure on the pipeline and the gas compressibility increases, which have higher requirements for piping material.

4.2.2. Velocityﬁeld distribution

Fig. 12shows under three different inlet velocities, gate valve internalflow velocityfield contour distribution that is simulated by thefluent software on the relative degree of opening of 1/8. When the relative opening degree of 1/8, thefluid through the gate valve has an obviously different velocity distribution in inlet velocity 13 m/s, 15 m/s and 17 m/s. As thefluid is through the valve core, 17 m/s high speed jet is significantly higher than the 13 m/s and 15 m/s. This is because the inlet velocity is large, the inletflow is big, in theflow cross section of high speed to increase.

Fig. 13shows under three different inlet velocities, gate valve internalflow velocityfield contour distribution that is simulated by thefluent software on the relative degree of opening of 2/8. As can be seen from thefigure, the higher the inlet velocity speed, the higher high-speed regional distribution. While in the front portion of the spool speed distribution is completely atypical, the distribution trend of speedflowfield is of similar hierarchical structure in the back of the valve core speed. Soflow resistance characteristics come out the cut-off point at the relative opening degree of 2/

8.

Fig. 14shows under three different inlet velocities, gate valve internalflow velocityfield contour distribution that is simulated by thefluent software on the relative degree of opening of 1. When Fig. 9.Pressure distribution of gate valve XOY section on the relative degree of

opening of 1/8.

Fig. 10.Pressure distribution of gate valve XOY section on the relative degree of opening of 2/8.

Fig. 11.Pressure distribution of gate valve XOY section on the relative degree of opening of 1.

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gate valve fully open, it is consistent that the velocity ﬂow ﬁeld distribution trend under the three kinds of working conditions.

Pipe groove is the low speed distribution. High speed region is almost full of the whole running piping. So when in full resistance coefficient is almost zero, theflow coefficient is very close.

4.2.3. Speed streamlines distribution

Fig. 15shows under three different inlet speeds, gate valve internal ﬂow velocity streamlines distribution that is simulated by theﬂuent software on the relative degree of opening of 1/8. When the relative opening degree of 1/8, three kinds of inlet velocity, the velocity distribution is very cluttered and streamline distribution inside the gate valve completely different; Entrance velocity 13 m/s and 15 m/s the number of the vortex is more than 17 m/s speed

obviously; At the inlet velocity of 15 m/s, downstream pipeline valve appears wake vortex, which is the biggest reason forﬂow resistance characteristics of numerical simulation value and experiment value micro change.

Fig. 16shows under three different inlet speeds, gate valve internalflow velocity streamlines distribution that is simulated by thefluent software on the relative degree of opening of 2/8. 2/8 relative degree of opening, gate speed streamline internal distribution began to become more consistent, the number is also consistent vortex region; At the inlet velocity of 15 m/s, trailing vortex disappear; These results demonstrate the reason that the relative opening degree in 2/8, the gate valve flow resistance characteristics appear the demarcation point.

Fig. 17shows under three different inlet speeds, gate valve in- ternalﬂow velocity streamlines distribution that is simulated by Fig. 12.Velocityﬁeld distribution of gate valve XOY section on the relative degree of

opening of 1/8.

Fig. 13.Velocityﬁeld distribution of gate valve XOY section on the relative degree of opening of 2/8.

Fig. 14.Velocityﬁeld distribution of gate valve XOY section on the relative degree of opening of 1.

Fig. 15.Streamline distribution of gate valve XOY section on the relative degree of opening of 1/8.

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thefluent software on the relative degree of opening of 1. When relative opening degree is 1, internal speed streamline distribution of gate valve is identical at three inlet velocities. Only in the pres- ence of pipe groove channel eddy current, eddy current is not occurring throughout the running pipeline. These results explain gate valve fully open when maximumflow coefficient, resistance coefficient smallest reason.

4.3. Pressure coefﬁcient analysis

Pressure coefﬁcient (Raisee et al., 2006b; Tsai and Sheu, 2007) is used to measure, the pressure loss of size in the gas transmission.

Fig. 18shows the stream wise distribution of the pressure coefﬁ- cient across the center line direction of gate valve upstream pipe, pipe groove and downstream pipe for the entire three-dimensional model.

Fig. 16.Streamline distribution of gate valve XOY section on the relative degree of opening of 2/8.

Fig. 17.Streamline distribution of gate valve XOY section on the relative degree of opening of 1.

Fig. 18.The pressure coefficient of the centerline of the gate valveflowfield distribution is simulated by thefluent software in the inlet velocity 13 m/s, 15 m/s and 17 m/

s.

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Cp¼ pp_in

0:5

r

^w²_b ⁽³⁾

whereP_inis the gas pressure at the inlet (Pa) andw_bis the bulk mean velocity of the gas (m/s).

Fig. 18is respectively in the inlet velocity 13 m/s, 15 m/s and 17 m/s, the pressure coefficient of the centerline of the gate valve flowfield distribution that is simulated by thefluent software. As can be seen from theFigs. 13e15under different gate valve relative opening degree, when the relative opening degree of 1/8, there is the negative absolute maximum in the gate valve’s upstream and downstream pipeline pressure coefficient; When the relative opening degree of 2/8, negative absolute value significantly decreased; In the relative opening degree after 2/8, pressure coefficient has a basically the same negative absolute value. However, in pipe groove parts of the gate valve and different relative opening degree, the pressure coefficient variation range is quite obvious, especially when the relative opening degree of 1/8, negative absolute value is quite large. With the increase of relative opening degree, negative pressure coefficient absolute value began to decrease. These results indicate that the gate valve when the relative opening degree of 1/8, pressure loss is most serious in the valve core.

From theFig. 18, you can also see that different inlet velocity on the conduit gate valves upstream and downstream pipeline pressure loss affects basically consistent. But in the valve core, the inlet velocity is smaller, the smaller the absolute value of negative pressure coefﬁcient, the less pressure loss. At the inlet speed of 15 m/s, when the relative opening degree of 1/8, the pressure loss has the biggest losses, in turn when the relative opening degree over the 2/8, overall pressure losses are reduced, the result shows that with the increase of gate entrance velocity, in the gate when the relative opening degree is more than 2/8, the whole pressure loss in decline, but the relative opening degree is uncertain before 2/8.

5. Conclusions

This paper introduces a CFD method the Reynolds Stress Model (RSM) turbulence model to study the influence of flashboard location on flow resistance properties and internal features of rectangle-shaped gate valve under the variable inlet velocity condition. At the same time, the article has carried on the gate valve flow resistance characteristics experiment. The observed phe- nomena in different inlet velocity are qualitatively and quantita- tively compared and also verified with CFD simulated results and experimental results. We are able to draw the following conclusions.

(1) Under the different inlet velocity, when the valve opening degree relative 1/8, valveflow coefficient is very small, the resistance coefficient is large; In the valve opening degree relative 2/8, gate valveflow coefficient and resistance coefficient inflection point; After the opening of the 2/8, there is a rapid reduction in resistance coefficient of gate valve, with the opening of more and more, resistance coefficient is close to zero; Between the relative opening degree of 2/8 and 5/8, flow coefficient increase accelerated; Between 5/8 and 7/8 of the opening of the relative, flow coefficient reduction increased; After the relative opening degree of 7/8, stable parallelflow coefficient increased. These results suggest that in the opening process of the gate valve flow coefficient change does not have the characteristics of the stability of the regulator.

(2) Based on different inlet velocity of analysis of gate valve internal flowfield, we can conclude that when the relative opening degree of 1/8, gate valve pressurefield, velocityfield distribution and speed streamline distribution obviously is different; When the relative opening degree of 2/8, gate valves of theflowfield distribution began to close to agreement; In the relative opening degree 1, gate valve pressure field, velocityfield distribution and speed streamline distribution is exactly uniform; In the relative degree of opening 1/

8, valveflowfield distribution is very messy, speed streamline distribution of eddy current number is different, there is no certain regularity. These results suggest that the relative degree of opening of the valve in 2/8 before, miscellaneous internalflow characteristics of no rules, appear high-speed jet, uneven distribution of pressure on the valve seal impact seriously affected.

(3) At different inlet velocity, upstream and downstream pipe pressure coefﬁcients of the gate valve are basically the same.

However, in the valve channel (i.e. spool lower), at relatively the opening of 1/8, inlet velocity 15 m/s comes out the maximum absolute value of the negative pressure coefficient, but the overall absolute value of the negative pressure coefficient decreases; 2/8 after the relative degree of opening, under three inlet velocity, pressure coefficient absolute value of the negative trends are basically the same, and with other relative opening degree of the pressure coefficient began to converge. These results suggest that in the low pressure gas transmission, the conduit gate valves upstream and downstream pipeline pressure loss is very small; In the gate valve core, the pressure loss is very serious, mainly concentrated in the relative opening degree before 2/8, and before the relative opening degree, gate valve pressure loss with no clear rules.

These results show that the square gate valve in use does notfit in before the opening of the relatively long-term open 2/8; after the relative degree of 2/8, square gate valve is unfit forflow control valve inadequacy.

Acknowledgements

This research was supported by the National Natural Science Foundation of China (Grant No. 51406184), the Zhejiang Provincial Natural Science Foundation of China (Grant No. LZ15E090002) and the Open Fund of the State Key Laboratory of Fluid Power and Mechatronic Systems (Grant No. GZKF-201415).

Appendix A. Supplementary data

Supplementary data related to this article can be found athttp://

dx.doi.org/10.1016/j.jngse.2016.05.025.

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