Flow characteristics and performance evaluation of butterfly valves using numerical analysis

Transcription

1 IOP Conference Series: Earth and Environmental Science Flow characteristics and performance evaluation of butterfly valves using numerical analysis To cite this article: S Y Jeon et al 2010 IOP Conf. Ser.: Earth Environ. Sci View the article online for updates and enhancements. Related content - Experimental study for flow characteristics and performance evaluation of butterfly valves C K Kim, J Y Yoon and M S Shin - Numerical simulation of flow field in waterpump sump and inlet suction pipe A C Bayeul-Lainé, G Bois and A Issa - Impellers of low specific speed centrifugal pump based on the draughting technology C Hongxun, L Weiwei, J Wen et al. This content was downloaded from IP address on 30/04/2018 at 17:15

2 Flow characteristics and performance evaluation of butterfly valves using numerical analysis 1. Introduction S Y Jeon 1, J Y Yoon 2 and M S Shin 1 1 Department of Mechanical Engineering, Hanyang University, 17 Haengdang-dong Seongdong-gu, Seoul, , Republic of Korea 2 Division of Mechanical and Management Engineering, Hanyang University, 1271 Sa-3- dong Sangnok-gu, Ansan, , Republic of Korea lo21c@hanyang.ac.kr Abstract. The industrial butterfly valves have been applied to various fields that transport fluid in volume, especially water supply and drainage pipeline for flow control. The butterfly valves in various shapes are manufactured, but a fitting performance comparison is not made up. For this reason, we carried out numerical analysis of some kind of butterfly valves for water supply and drainage pipeline using commercial CFD code FLUENT, and made a comparative study of these results. Also, the flow coefficient, the loss coefficient, and pressure distribution of valves according to valve opening rate were compared each other and the influence of these design variables on valve performance were checked over. Through flow around the valve disk, such as pressure distribution, flow pattern, velocity vectors, and form of vortex, we grasped flow characteristics. A butterfly valve is a type of flow control device, used to regulate a fluid flowing through a section of pipeline and so on. The butterfly valve is similar in operating way to a ball valve. A disc is positioned in the center of the pipe typically and has a rod through it connected to an actuator on the outside of the valve. The actuator turns the disc either parallel or perpendicular to the flow to control the flow. Regardless of valve position, the disc of a butterfly valve is always positioned within the flow, therefore a pressure drop is always presented in the flow. A butterfly valve is a type of valves called quarter-turn valves. Because fully opening the valve, the disc is rotated a quarter turn so that it allows the fluid to go through in an almost unrestricted passage. There are some kinds of butterfly valves, and each adapted for different pressures and different usage. In case of the high performance butterfly valve, features a slight offset in the disc, which increases the valve's sealing ability and decreases its wearing. For these butterfly valves, the flow coefficient and the loss coefficient are important characteristics to understand overall valve performance, therefore we need to check it over carefully. Some researchers have attempted to numerically predict flow in butterfly valve. Kim and Wu[1] studied the flow pattern, velocity distribution and flow coefficient of butterfly valve through two-dimensional numerical analysis. Huang and Kim[2] studied the velocity field and pressure distribution for three-dimensional incompressible flow in butterfly valve. They also reported about the optimum design of the disk of butterfly valve for stable flow regulation, smooth opening and shutting ability, and decrease of cavitation. The purpose of this work is to investigate flow characteristics for two types of butterfly valve, single disk type butterfly valve and double disk type butterfly valve. In this work, the computational calculation and analysis have made to investigate the flow in single disk type butterfly valve and double disk type butterfly valve for water supply and drainage pipeline by using the CFD code FLUENT. These computational results, the flow coefficient and the loss coefficient for various opening rate of each valve, were compared with experimental results. Flow characteristics around the valve disk, such as pressure distribution, flow pattern, velocity vectors, and form of vortex, were also investigated and discussed. 2. Valve characteristics The valve flow coefficient and the valve loss coefficient to evaluate general performance of a valve calculated through numerical method in this work are defined as follows. These valve characteristics are c 2010 Ltd 1

3 generally obtained by experimental method because of pressure drop between upstream and downstream of valve. 2.1 Valve Flow Coefficient The valve flow coefficient have respect to valve type, diameter of valve, opening rate of valve and operating fluids. This valve flow coefficient is an important characteristic to investigate a valve performance and determined by differential pressure between upstream and downstream. In case of the specified differential pressure ( P = 1 psi) with temperature 5 ~ 40 of water, the valve flow coefficient is defined as Equation (1)[9,10] G C v = Q (1) ΔP 2.2 Valve Loss Coefficient The fluid in a piping system passes through various valves, bends, elbows, inlets, exits, enlargements, and contractions in addition to the pipes. These components interrupt the flow of the fluid and cause additional losses because of the flow separation and mixing. A partially closed valve may cause the largest head loss in the system by the drop in the flow rate. Flow through valves is very complex, and a theoretical analysis is generally not plausible. Therefore these losses, called the valve loss coefficient is determined experimentally and expressed as another representation of relation between pressure difference, fluid density and fluid average velocity following Equations (2)[9,10]. 2 u Δ H = K [SI and British unit] 2g (2) 2 γu Δ P = K [SI unit] 2g 3. Experimental method The experimental apparatus to measure flow rate was constituted by IEC (1997)[2], which used a reservoir for recirculating water, throttling valves on upstream and downstream, thermometer, electromagnetic flow meter, 400mm diameter pipes for test section including test valves(single disk type or double disk type butterfly valve) and the pressure taps were located in 2D and 6D from each test valve as computational domain for numerical study in Fig. 1. And then the flow rate was measured experimentally at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% rated opening of butterfly valves for single disk type and double disk type under fixed differential pressure( Δ P = 1 psi) between upstream and downstream and these experimental data were compared to the numerical results for validation. 4. Numerical method The computational calculation and analysis using numerical method have made to investigate the flow in butterfly valve used in water supply and drainage pipeline. For single disk type and double disk type butterfly valves, the body of valve and the disk were modeled in three-dimensional. The computational domain was made up according to IEC as Fig. 1. The three-dimensional models of the butterfly valves were comprised of valve disk part and valve body part using pre-processor, GAMBIT of the commercial CFD code FLUENT. To improve the computational efficiency, the nodes of the grid were clustered in valve disk compare to inlet and outlet relatively. For each calculation cases, the unstructured grids were generated about 500,000 shown in Fig. 2 and adjusted in ±5,000. 2

4 Fig. 1 Computational domain 4.1 Scheme and algorithm The numerical analysis has been carried out on the assumption that the flow in the butterfly valve was steady state incompressible flow and the operating fluid was water in standard atmospheric pressure and temperature. The second-order upwind scheme was used for descretization of governing equations and applied SIMPLEC algorithm for revision of the velocity and pressure, the standard κ-ε model for turbulent flow. These scheme and algorithm in this work have generally been applied to numerical study. 4.2 Initial condition and boundary condition No slip boundary condition to consider fluid viscosity and generalized log wall function to define turbulence intensity around wall were applied as solid boundary conditions. Inlet and outlet conditions were set as differential pressure between upstream and downstream. Using the flow rate from experimental results and conditions above, the valve flow coefficient and the valve loss coefficient were calculated numerically at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% rated opening of butterfly valve for single disk type and double disk type butterfly valves. Fig. 2 Schematics of the computational grid system 3

5 5. Results and discussion The results of numerical and experimental study are shown in Fig Figure 3 shows the valve flow coefficient and Fig. 4 shows the valve loss coefficient according to each opening rate of valve. 5.1 Comparison of valve flow coefficient The experimental results of the butterfly valve were used for the validation of numerical results, valve flow coefficient. Fig. 3 represents the valve flow coefficient relative to the maximum valve flow coefficient at each opening rare of butterfly valve( Cv(%) = Cv / C ) and the comparison between the numerical and experimental v max results for two types of butterfly valve: single disk type and double disk type butterfly valve. As shown in Fig.3, the difference between the numerical and experimental values is less than 6% in whole range of valve opening rate, this results represent that the numerical analysis predict actual flow in butterfly valve properly. Fig. 3 Valve flow coefficient, C v 5.2 Comparison of valve loss coefficient The valve loss coefficients in log scale value of two types of butterfly valve are presented in the vertical axis, and compared with experimental results in Fig. 4. For double disk type butterfly valve in Fig. 4(b), the difference between the computational and experimental values is less than for Single disk type butterfly valve slightly. It considered that this result was associated with the better water sealing ability of double disk type butterfly valve. Fig. 4 Valve loss coefficient, K 4

6 5.3 Pathline A pathline is defined as the actual path traveled by an individual fluid parcel over some time period and it is Lagrangian concept which express the path of an individual fluid particle as it move around in the flow field. Therefore pathlines are the useful way to understand the flow patterns. Fig. 5 shows the pathline around valve disk on valve opening rate 50% for each type of valve. As shown in Fig. 5, the developed flow at the rear of valve disk reattaches to the valve disk, and form some recirculating eddies. The pattern of recirculating eddies for double disk type butterfly valve is more complex than single disk type butterfly valve. It is supposed valve that this difference have resulted from the divided flow channel of the double disk type butterfly. Fig. 6 shows the pathline around valve disk on valve opening rate 100% for each type of valve and displays a smoother pathline for the double disk type butterfly valve than the single disk type butterfly valve slightly. This can be explained that the cross section of the double disk type butterfly valve, which stacks up the fluid particles, is smaller than the single disk type butterfly valve. Fig. 5 Pathline in butterfly valve (valve opening rate: 50%) 6. Conclusion Fig. 6 Pathline in butterfly valve (valve opening rate: 100%) A side of view of the valve performance, the valve flow coefficient and the valve loss coefficient according to the valve opening rate were calculated numerically and flow pattern around the disk of butterfly valve were presented. The experimental results were used to validate the numerical results and we concluded that there was not much in the valve performance between the single disk type butterfly valve and the double disk type butterfly valve. However, the double disk type butterfly valve showed more complex flow pattern, recirculating eddies, at the rear of valve disk compared with the single disk type butterfly valve. Through these comparisons, we obtained that grid type, analytical models, initial and boundary conditions applied to numerical analysis have made a description of the flow in butterfly valves to the purpose. 5

7 Acknowledgments This work was supported by Korea Water Resources Corporation and the second stage of the Brain Korea 21 Project. Nomenclature C v G K Δ H Δ P The valve flow coefficient Specific Gravity of Water Valve head loss [m] The valve loss coefficient Differential pressure[n/m 2 ] Q u g γ Volumetric flow rate[m 3 /hr] Mean velocity in pipe [m/s] Gravity acceleration[m/s 2 ] Specific weight[n/m 3 ] References [1] Kim R H and Wu N Y 1992 Numerical Simulation Butterfly Valve Fluid Flow Proc. of the FLUENT User s Group Meeting (Burlington, Vermont, 5-7 October 1993) pp [2] Huang C and Kim R H 1996 Three Dimensional Analysis of Partially Open Butterfly Valve Flows ASME J. of Fluids Eng [3] Skousen P L 2004 Valve Handbook (New York: McGraw-Hill, Inc.) [4] Eom K 1988 Performance of Butterfly Valves as Flow Controller ASME J. of Fluid Eng [5] Kimura T, Tanaka T, Fujimoto K and Ogawa K 1995 Hydrodynamic Characteristics of a Butterfly - Prediction of Pressure Loss Characteristics ISA Transactions vol 34 pp [6] Kang S K, Yoon J Y and Lee B H 2006 Numerical and Experimental Investigation on Backward Fitting Effect on Valve Flow Coefficient (Proc. IMech) Part E: J. of Process Mechanical Eng [7] Yi S I, Shin M K, Shin M S, Yoon J Y and Park G J 2008 Optimizing of the eccentric check butterfly valve considering the flow characteristics and structural safety (Proc. IMech) Part E: J. of Process Mechanical Eng [8] James A D and Mike S 2002 Predicting Globe Control Valve Performance Part I: CFD Modeling (ASME) J. of Fluid Eng [9] Guillermo P-S, Pablo G-A and Jaime A-V 2008 Three-dimensional modeling and Geometrical influence on the hydraulic performance of a control valve (ASME) J. of Fluid Eng. Vol. 130 Issue [10] IEC Industrial-process control valves: flow capacity - sizing equations for fluid flow installed conditions International Electrotechnical Commission (Geneva, Switzerland) [11] ANSI/ISA Flow Equations for Sizing Control Valves ISA-The Instrumentation, Systems, and Automation Society (North Carolina, USA) [12] IEC Industrial-process control valves: flow capacity - testing procedures Int.Electrotechnical Commission (Geneva, Switzerland) 6