CFD Analysis and Comparison of Fluid Flow Through A Single Hole And Multi Hole Orifice Plate

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1 CFD Analysis and Comparison of Fluid Flow Through A Single Hole And Multi Hole Orifice Plate Malatesh Barki. 1, Ganesha T. 2, Dr. M. C. Math³ 1, 2, 3, Department of Thermal Power Engineering 1, 2, 3 VTU PG Centre, Mysore/ VTU Belgaum Karnataka India mechmlatesh@gmail.com 1, ganeshtnaik88@gmail.com 2, mcmath1018@yahoo.com 3 Abstract- Flow measurement is one of the most important tasks in many industries. Even today there does not exist a universal flow measuring instrument in many flow applications. The fluid flow through a single hole orifice plate and multi holes orifice plate were analyzed in this paper by using Computational Fluid Dynamics (CFD). For analysis water is used as fluid and is allowed to pass through a pipe across the orifice plate. The geometry of the orifice plate and the pipe section has made using CATIA V5 R20 and the model has meshed using HYPER MESH 11.0, the flow characteristics are studied using ANSYS FLUENT This paper also presents the effect of orifice holes arrangement or distribution in a plate on the performance of flow characteristics such as flow rate, pressure drop, velocity and turbulent intensity. The parameters used for designing the orifice plate are non standard conditions. The analysis is carried out for four diameter ratio (d/d= 0.60, 0.30, 0.20, 0.15 for single hole, four, nine and sixteen holes respectively). The inner diameter of the pipe used is 50 mm and the plate thickness used for analysis is 3 mm for all the plates. The simulation results shows that multi holes orifice plate have better flow characteristics compare to single hole orifice plate for the same area of departure. Index Terms- Orifice plate, diameter ratio, CFD, pressure drop, turbulence intensity, multi hole orifice. 1. INTRODUCTION Orifice meter is device used for the measurement of flow in fluid delivery systems. Orifice plate is an essential part an orifice meter when installing in a pipe system [1]. There are different types of orifice plate exist depending upon applications, they are square edge, quadrant & conic edge, integral, eccentric & segmental orifice plate. The square edge orifice is used widely as restriction for clean liquid, gases, and low velocity steams [2]. The orifice plate is widely used as throttling devices in many industries such as oil wells, power generation units, water treatment and distribution, chemical and petrochemical industries. Orifice meter is widely preferred in many flow applications due to ease in its simplicity, low cost, easy to install or fabricate and easy for maintenance [3]. If the if the t/d ratio is less than 0.5, then it is thin orifice, otherwise it is a thick orifice.[2].in this paper for the analysis the square edge concentric type orifice plate is used. The inner diameter of the pipe used is 50 mm and plate thickness of 3 mm for all orifice plates. (3) It is suitable for liquid, gas and steam flow measurements. [2] 1.2 Draw backs of orifice plate The major draw backs of orifice plates are, (1) Maximum flow rate 4:1 (2) It is affected by upstream swirl. (3) Large head loss. [2] 2. SELECTION OF ORIFICE PLATE The orifice plate is widely used as a restriction in many flow applications. There are different types of orifice plates are there depends on the applications and pipe size. In this paper the analysis is carried out for an inner diameter of 50mm hence the square edge concentric type orifice plate is chosen. Due to ease in easy maintenance and low cost and easy for manufacturing and installation it is selected for analysis [7]. Fig 1 shows a standard concentric type orifice plate. 1.1 Special features of heat orifice plate. The orifice plate has good performances in a certain operating parameter ranges there are, (1) It can be operate up to a temperature of C. (2) It can be operate up to a pressure of 400 bar. 6

2 (b) Four holes orifice plate having β=0.30, D=50 mm, d=15 mm Fig.1. Standard concentric types orifice plate 3. COMPUTATIONAL MODELING AND SIMULATION For the simulations, Computational Fluid Dynamics (CFD) is an effective tool to give an effective results, it includes: Mathematical modeling Solution schemes Solver set up 3.1 Geometry modeling The geometries of the orifice plates are created by using the preprocessor tool as CATIA V5 R20. The data used for creating the geometries are non standard conditions; the diameter ratio is selected between the ranges 0.15 to 0.60 [2]. The inner diameter of the pipe used is 50 mm; the length of the pipe is 4D for both upstream and downstream side and plate thickness of 3 mm for all the orifice plates. Design parameters for orifice along with geometry are shown from figure 2 (a) to (e). The figure 3 shows the assembly of sixteen holes orifice plate in a pipe. (c) Nine holes orifice plate β=0.20, D=50 mm, d=10 mm (d) Sixteen holes orifice plate β=0.15, D=50 mm, d=7.5 mm (e) Nine holes square arrangement β=0.20, D=50 mm, d=10 mm Fig 2 (a) to (e) the geometric models for single and multi hole orifice plates. The arrangement of orifice holes in a orifice plates are as follows: The orifice centre for all the plates are located in concentric. The arrangements of orifice holes are symmetrical as possible. The spacing between the all orifice holes in plate is equal. [4] Fig 3 Sixteen holes orifice assembly. 3.2 Meshing (a) Single hole orifice having β=0.60, D=50 mm, d=30 mm. For the present work meshing is performed by using HYPER MESH Since the geometries are in regular shape, the quadrilateral elements are used for meshing. All the orifice plates surfaces and also surface of the pipe are meshed by using 2D quadrilateral elements. For discretization of all the models 2D quadrilateral elements are used and the 7

3 hexahedral mesh elements are used for 3D fluid elements. Mesh size selected are coarse mesh for all the orifice plates. For the all models the geometry is divided in to 5 components. The meshed model for one case that is for four holes orifice plate model in 2D and 3D discretization is shown in figure 4 and 5 respectively. The details of the discretization for single and multi holes orifice models are shown in table 1. Table 1 Discretization details for different orifice models. Sl. No Orifice model nodes Cells Faces 1 Single hole Four holes Nine holes Sixteen holes Nine holes (square arrangement) The 2D and 3D Discretized meshed model for four holes orifice are show in figure 4 and 5 respectively. 4. SOLVER SET UP The solver set up is very important in any of the fluid flow problem; the solver setting indicates the method and also a procedure for solving (analysis) the problem. The flow analysis has studied using ANSYS FLUENT (6.3.26) [8] 4.1 Turbulence Modeling The turbulence model used for this work is standard k-epsilon (2 eqn.) The 3D space pressure based solver is used and implicit formulation is used for solution scheme. Solution controls uses flow and turbulence equations. The simple algorithm is used for pressure velocity coupling and for discretization second order scheme is used [9]. The convergence criteria for all case studies are taken as Governing Equations The governing equations of the flow are modified according to the conditions of the simulated case. Since the problem is assumed to be steady, time dependent parameters are dropped from the equations. The resulting equations are: [5] Conservation of mass :.( ρvr) =0. (1) Momentum equations X-momentum:.(ρuVr)=-( p/ x)+( τxx/ x) +( τyx/ y) + ( zx/ z) (2) Y-momentum:.(ρvVr)=-( p/ y)+( τxy/ x) +( zy/ y) + ( zx/ z) +ρ g (3) Z-momentum:.(ρwVr)=-( p/ z)+( τxz/ x) + ( yz/ y) + ( zz/ z) +ρ g (4) Fig.4. Discretized domain for four holes orifice model with 2D quadrilateral elements 5. BOUNDARY CONDITIONS The boundary conditions are the important values for the mathematical model. The boundary condition is applied to different zones. There are different kinds of boundary conditions for the fluid flow to enter and exit the domain. The boundary condition is depending on type of fluid use for the analysis. The fluid used for this analysis is incompressible hence velocity inlet condition applies. Inlet velocity profile was assumed, slip condition assigned to all surfaces [6]. The boundary conditions used for the analysis are listed in table 2. Table 2 Boundary conditions used in CFD analysis Sl.No. Quantities Condition/value Fig.5. Discretized fluid domain for four orifice holes model with 3D hexahedral mesh 1 Working fluid Water 2 Gauge pressure Zero Pascal 3 Inlet velocity profile 1 m/sec 4 Slip No slip 8

4 6. RESULTS AND DISCUSSION The fig. 6 to 9 shows the pressure contours and Fig. 11 to 15 shows the velocity contours obtained for different orifice holes. 6.1 Pressure Contours. Fig. 6 to 9 shows the cross section of pressure contour plots for all orifice holes along the length.. Fig.6. pressure distribution for single hole orifice plate. Fig.7. pressure distribution for four holes orificd plates. Fig.8.pressure distribution for nine holes orifice in circular arrangement. 9

5 Fig.9. Pressure contour for nine holes orifice in square arrangement. 6.2 Velocity contours The figures 11 to 15 shows the cross section of velocity contour for different orifice geometries. Fig 10 pressure distribution for 16 holes orifice plate. Fig.11. velocity contour for single hole orifice plate. 10

6 Fig.12. velocity contour for four holes orifice plate. Fig.13. velocity contours for nine holes orifice in circular arrangement. Fig.14. velocity contour for nine holes orifice in square arrangement. Fig.15. velocity contour for sixteen holes orifice plate 11

7 6.3 Turbulence Intensity The turbulence intensity contours for single and multi holes orifice geometries are shown from fig 16 to 20 Fig.16. turbulence intensity for single hole orifice plate. Fig.17. turbulence intensity for four holes orifice plate Fig.18. turbulence intensity for nine holes orifice in circular arrangement. 12

8 Fig.19. turbulence intensity for sixteen holes orifice plate. No. of Orifice holes Fig.20. turbulence intensity for nine holes orifice in square arrangement Table 3 Summary of the results obtained for single hole and multi holes orifice Holes Arrangement Volumetric flow rate (m 3 /s) Pressure drop (Pa) Magnitude of velocity (m/s) Turbulence intensity (%) 1 circular circular circular circular square Table 3 shows the values of different characteristics of fluid such as pressure drop, velocity magnitude, volumetric flow rate, and turbulence intensity for single and multi holes orifice for the same area of departure are obtained from computational analysis. By using the values from the table 3 the different graphs are plotted. Thus the different characteristics of fluid for the same area of departure can be discussed. 6.4 volumetric flow rate The volumetric flow rate for single and multi holes orifice are shown in fig 21.The volumetric flow rate is plotted against the number of holes. It can be observed from the fig.21 the volumetric flow rate is maximum for single hole 13

9 orifice have a value of m 3 /s. compare to multi holes orifice plate. Comparing the holes arrangement for 9 holes orifice plates, it is observed that 9 holes in circular arrangement shows more volumetric rate compare to square arrangement. have a minimum pressure drop compare to square arrangement. 6.6 Magnitude of Velocity The velocity magnitude for single and multi holes orifice plate are shown in fig.23. Fig.21. Volumetric flow rate for different orifice holes 6.5 Pressure Drop The pressure drop for single and multi holes orifice plates are show in fig.22. Fig.23. velocity magnitude for single and multi holes orifice plate From the figure.23 it is observed that the magnitude of velocity is maximum for single hole plate compare to multi hole. For single hole orifice the maximum velocity achieved, have a value 3.84 m/s, when the number of holes increases the velocity magnitude decreases. For single hole orifice the flow concentrated at the center, for multi holes the flow distributed over the all orifice holes hence velocity decreases for multi holes orifice plate. Comparing the holes arrangement for 9 holes orifice plate, it can be observed that 9 holes in circular arrangements show the more velocity have a value of 3.49 m/s compare to square arrangement. 6.7 Turbulence intensity Fig 22. Pressure drop for single and multi holes orifice plate. It can be observed from fig 22 the net pressure drop for single hole orifice is Pa, gradually decreases from four holes to sixteen holes, it can be observed that the net pressure drop is minimum at nine holes orifice in circular arrangement it has value of Pa. Further the pressure drop is increases for sixteen holes orifice plate, because the diameter ratio used is 0.15 for sixteen holes orifice plate, further decrease in diameter ratio the pressure drop increases. But comparing with single hole orifice plate the net pressure drop is decreases multi holes orifice for the same area of departure. The effect of orifice hole arrangement shows that the 9 holes orifice in circular arrangement Fig 24. Turbulence intensity for single and multi holes orifice plate. From the fig.24 it is observed that the turbulence intensity increases for multi hole orifice compare to single hole orifice. The turbulence intensity is more for the nine holes orifice plate have a value of 94%. Then it is decreased for sixteen holes. By comparing the holes arrangement, the maximum 14

10 intensity is achieved for 9 holes orifice plate with circular arrangement compare to square arrangement. 7. CONCLUSION Analysis is conducted on single hole orifice plate and multihole orifice plate for single stage by considering the same area of departure. Based on the analyzed results, the conclusion can be summarized as follows: For the same area of departure the single hole orifice plate have more volumetric flow rate compare to multi holes orifice, because the velocity is more for single hole orifice plate. The pressure drop is minimum for multi holes orifice plate compare to single hole. The minimum pressure drop achieved for nine holes circular arrangement orifice for the same area of departure. The pressure recovery for a single hole orifice plates needs much longer straight pipe it can be seen from fig.6. Whereas multi holes orifice needs shorter pipe for pressure recovery it can be observed from fig.7 to 9. Multi holes orifice plate gives better performance for short straight pipe applications, hence effective savings in pipe material costs. The fluid flow distribution is more steady and uniform for multi holes orifice plates compare to single hole orifice, it can be observed from fig.16 to 20. The effect of holes arrangement on the fluid flow characteristics for nine holes orifice plate, it can be shows that the nine holes in circular arrangement has better performance compare with square arrangement. assemblies under non-standard conditions Indian Journal of Engineering & Material Science. Vol.17.December 2010, pp [7] R W Miller, Flow measurement engineering handbook, 3 rd Ed (McGraw-Hill, New York), [8] Fluent I, Fluent 6.3. User Guide. (ANSYS, Inc., Lebanon) REFERENCES [1] Smith Eiamsa-ard, Ariti Ridluan, et al. Numerical Investigation of turbulent flow through a circular orifice KMTIL Sci.J.Vol.8 No.1 January-June, 2008 [2] D.Chisholm, Two-phase flow in pipelines and heat Exchangers, London: Longman Group Ed., [3] Manmatha k.roul, Sukanta k.dash Numerical Modeling of pressure drop due to single phase flow of water and two phase flow of air-water mixtures through thick orifices. International Journal of Engineering Trends and Technology Volume 3 Issue ISSN: [4] Tianyi Zhao, Jili Zhang and Liangdong Ma. A general structural design methodology for multi holes orifice and its experimental application. Journal of Mechanical Science and Technology 25(9) (2011) [5] Patankar.S.V, Numerical Heat Transfer and fluid flow, McGraw-Hill, Hemisphere. Washington DC USA, [6] R K Singh, S N Singh and V Seshadri Performance evaluation of orifice plate 15