Parametric study on Gate valve.

 

                                                            PARAMETRIC STUDY ON THE GATE VALVE SIMULATION USING ANSYS FLUENT

                                                                                                        

1. AIM

Our aim is to perform parametric study on the gate valve simulation to calculate the mass flow rate by varying the opening of gate disc from 10 to 80 percent using ANSYS FLUENT.

2. THEORY/EQUATIONS/FORMULAE USED

ANSYS FLUENT academic version CFD package is used to carry out the simulation. It is a user friendly interface which provides high productivity and easy-to-use workflows. Workbench contains all workflow needed for solving a problem such as pre-processing, solving and post-processing.

Parametric Study

It’s a study of how geometric or physical parameters or both influence the solution of the problem. This type of analysis is also known as a sensitivity analysis. Parametric analysis is an important tool for design exploration, for example is our problem, to examine the influence of the gate disc lift on the mass flow rate of a Gate Valve.

It is based on user-defined solving scenarios, producing “unrefined” solutions. These results need to be post-processed in order to find the optimal solution or trade-off for an overall better design. 

Gate Valve

It’s a valve that allows the flow to happen by lifting a barrier called gate disc. It is also known as sluice valve. Gate Valve consists of the following parts such as hand wheel, spindle, bonnet, gate disc, etc as shown in the below figure.

Working - The valve in closed position completely restricts the flow as the gate disc has no lift to pressurize the seal which makes sure zero flow rates. Then with the lift in gate disc the valve opens and allows the flow to happen and corresponding flow rate is achieved. In fully opened condition there is hardly any restriction and maximum flow rate can be achieved.

                                                                               

The lift and the control of control disc are done by the spindle and hand wheel. Gate Valves are used to shut on and off the flow of fluid in the hydraulic systems.

Gate valves are typically constructed from cast iron, cast carbon steel, ductile iron, gunmetal, stainless steel, alloy steels, and forged steels.

All-metal gate valves are used in ultra-high vacuum chambers to isolate regions of the chamber

Flow Coefficient

The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an orifice valve or other assembly and the corresponding flow rate.

                                                                                                   

                                                                       where Q = rate of flow (US Gallons per minute)

                                                                                 SG = Specific Gravity of the fluid (Water = 1)

                                                                                 ΔP = pressure drop across the valve (psi)

In more practical terms, the flow coefficient C_ν is the volume (in US gallons) of water at 60 °F (16 °C) that will flow per minute through a valve with a pressure drop of 1 psi (6.9 kPa) across the valve.

Flow coefficient value can be used as a standard method of comparing valve capacities and sizing valves for specific applications that is widely accepted by industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases and steam using the discharge coefficient.

Flow Factor  

It’s a metric equivalent flow factor (K_ν; commonly used everywhere else in the world with the exception of the United States) is calculated using metric units 

                                                                                                   

                                                                         where K_ν = flow factor (m³/hr)

                                                                                   Q = rate of flow (m³/hr)

                                                                                   SG = Specific Gravity of the fluid (Water = 1)

                                                                                   ΔP = pressure drop across the valve (bar)

Relation between C_ν and K_ν

Flow factor can also be calculated from the below relation,

                                                                                        K_ν = 0.865 * C_ν

Problem – Parametric Study on a Gate Valve Simulation

Parametric study on the gate valve simulation by varying the opening of gate disc from 10 to 80 percent to calculate the mass flow rate, flow coefficient, flow factor and discuss the results.

Calculation - Steady State Simulation

Fluid chosen for the problem – Water Liquid

Density = 998.2 kg/m3, Viscosity = 0.001003 kg/m-s

Pressure Drop

Pressure drop (ΔP) is defined as the difference in the total pressure between the inlet and outlet of across any flow system.

Pressure drop (ΔP) = Total Pressure at the inlet - Total Pressure at the Outlet

Pressure drop is inevitable in any system as there will be losses for sure. The losses are such as frictional losses, kinetic energy losses, etc. In order to calculate the flow coefficient and flow factor the pressure drop across the gate valve is important factor. So its monitoring is very important in order to minimize it and improve the performance.    

3. PROCEDURE

• In the process, firstly the geometry is imported in SpaceClaim and suitable clean up procedures are followed.
• Suitable geometry clean-up for Gate Valve model are done such as pulling up the bottom part to visualize the fluid flow, volume extract to create the fluid domain and then lifting the gate disc to add it to the input parameters group.
• Baseline meshing is done to understand the problem and then to know how much and where the refinement is required in order to study the flow and all the boundaries are named respectively. Also checked the mesh quality is good enough to carry out the simulation.
• Solver type, the initial and boundary condition, gravity, suitable turbulence model are defined as per the problem.
• In the current problem 5 cases are defined with changes in gate disc lift from 10 to 80 % with inlet pressure of 10 Pascal.
• In this case k-epsilon turbulence along with realizable model and scalable wall function as near wall treatment is used as the flow is turbulent.
• The report definition for the total pressure of inlet and outlet, input parameter is created for mass flow rate at the outlet and contours of velocity and pressure both stream-wise and span-wise is initiated in order to visualize and validate the essential features.

4. NUMERICAL ANALYSIS (Software used – ANSYS 2018 R1)
   • Geometric Model

The 3D geometry of Gate Valve is imported in SpaceClaim and the cleanup is done as per the figure given below.

3D Geometry – Gate Valve

                                                                               

                                                                                                               Fig: Geometry

Modified Geometry and Extracted Volume – Gate Valve

                                             

                                                                                                   Fig: Modified Geometry

                                               

                                                                                                             Fig: Extracted Volume

Mesh

                                                        

                                                                        Fig: Mesh                                                                          Fig: Close-up view                  

• Boundaries

                                                          

                                                                                     Fig: Boundaries for the complete domain

• Solver Set-up

1. The mesh file is imported into the FLUENT software for the analysis of the modeled surface.
2. Once the mesh file is loaded and displayed, it is checked for the units, scale, and mesh.
3. There are two types of numerical solver methods pressure–based and density-based solver. The pressure based solver was used rather than the density based solver as the simulation is for lower Mach number. Absolute velocity formulation, steady state was used for the analysis. Gravity on z-axis is also initiated.

                                                                                      

    4. k-epsilon turbulence with realizable model along with scalable wall function for near wall treatment is used for the analysis as the flow is turbulent.

                                                                                      

    5. The fluid material chosen is water liquid.

                                                                  

   6. Cell zone of the domain is defined as water-liquid.

                                                                        

    7. Convergence and monitor are checked for absolute criteria of 0.00001 for all the residuals.

                                                                        

    8. Solution methods – COUPLED Scheme used for Pressure-Velocity coupling and the methods for Spatial Discretization are as per the below image.

                                                                                  

    9. Standard initialization is done and computing starts from inlet. Numbers of iterations are set for running the steady simulation.

                                                              

                                                                                

     10. Surface report for Total Pressure is set at inlet and outlet to monitor the variation during run time.

             

     11. Flux report for Mass flow rate at outlet is set to monitor the variation during run time and the output parameter is checked.

                                                                   

12. Parameter Study is set by adding design points with different input parameter (Gate disc Lift) and the output parameter (Mass flow rate) is calculated automatically by clicking update all the design points without changing the geometry, meshing, setup manually and individually.

                                                                                                                                                                     

13. Solution animation is created to see the velocity field across the gate valve in .mp4 format.

                                                                                     

Initial Setup and Boundary Condition

Zone	Type	Boundary Condition	Additional conditions (if any)
Inlet	Pressure - Inlet	10 Pa	Steady State, Pressure Based, Absolute   Switched OFF Energy equation   Turbulence Model – k-epsilon Realizable
Outlet	Pressure - Outlet	0 Pa
Interior-Volume	Interior	Interior
Wall	Wall	Stationary wall without slip

                                                                

                                         Fig. Cell Zone Conditions & Boundaries                                      Fig. Inlet Boundary – Pressure Inlet

      5. RESULTS

• Case – 1 - 10%         

                                                              

                                        Fig: Cut Section of Gate Disc - 10% Lift              Fig: Convergence Criteria – Residual

 

                                   

                                                                                                   Fig: Inlet Pressure Plot

                                         

                                                                                                  Fig: Outlet Pressure Plot

                                                   

                                                                                                     Fig: Mass Flow Rate

                                                                

                                                  Fig: Pressure Contour - Stream wise                                    Fig: Pressure Contour - Span wise

                                                                   

                                                Fig: Velocity Contour - Stream wise                                       Fig: Velocity Contour - Span wise

• Case 2 – 20%

                                                                        

                                              Fig: Cut Section of Gate Disc - 20% Lift                              Fig: Convergence Criteria – Residual

     

                                                 

                                                                                                Fig: Inlet Pressure Plot   

                                                    

                                                                                                 Fig: Outlet Pressure Plot

                                                            

                                                                                                      Fig: Mass Flow Rate

                                                                           

                                                         Fig: Pressure Contour - Stream wise                             Fig: Pressure Contour - Span wise

                                                                               

                                                        Fig: Velocity Contour - Stream wise                                Fig: Velocity Contour - Span wise

• Case 3 - 40%

                                                                                                   

                                               Fig: Cut Section of Gate Disc - 40% Lift                               Fig: Convergence Criteria – Residual

                                                                         

                                                                                                            Fig: Inlet Pressure Plot

                                                                        

                                                                                                              Fig: Outlet Pressure Plot

                                                                               

                                                                                                                    Fig: Mass Flow Rate

                                                                                        

                                                                   Fig: Pressure Contour - Stream wise                           Fig: Pressure Contour - Span wise

                                                                                      

                                                                      Fig: Velocity Contour - Stream wise                          Fig: Velocity Contour - Span wise

• Case 4 - 60%

                                                                                                        

                                                              Fig: Cut Section of Gate Disc - 60% Lift                   Fig: Convergence Criteria – Residual

                                                                            

                                                                                                               Fig: Inlet Pressure Plot  

                                                                 

                                                                                                              Fig: Outlet Pressure Plot

                                                                    

                                                                                                                Fig: Mass Flow Rate

                                                                       

                                                   Fig: Pressure Contour - Stream wise                           Fig: Pressure Contour - Span wise

                                                                       

                                                  Fig: Velocity Contour - Stream wise                               Fig: Velocity Contour - Span wise

• Case 5 – 80%

                                                                                  

                                      Fig: Cut Section of Gate Disc - 80% Lift                              Fig: Convergence Criteria – Residual

                                                                

                                                                                               Fig: Inlet Pressure Plot

                                                                   

                                                                                               Fig: Outlet Pressure Plot

                                                                      

                                                                                             Fig: Mass Flow Rate

                                                               

                                                    Fig: Pressure Contour - Stream wise                           Fig: Pressure Contour - Span wise

                                                            

                                                  Fig: Velocity Contour - Stream wise                               Fig: Velocity Contour - Span wise

Parametric Study Results – Gate Valve Simulation

                                 

         Graphs

                                    

 

                                    

      6. CONCLUSION

1. Convergence plot shows that for the first 3 cases the residual gets converged around 200 iteration and for case 4 and 5 the residuals fluctuates as the gate disc lift is higher but the fluctuations are constant, hence can be considered as converged solution in all cases.
2. Inlet pressure will remain constant at 10 Pascal’s as it’s a user-defined parameter. Outlet pressure varies with respect to the opening of gate valve. Simulation shows that the outlet pressure increases with increase in gate disc lift which means that the pressure drop reduces.
3. Parametric Study shows that the mass flow rate increases with increase in gate disc lift with decreasing pressure loss.
4. Mass flow rate and Pressure drop is converted from kg/s into units such as US Gallons/min, m3/hr and Pa into units such as psi and bar in order to calculate the flow coefficient and flow factor.
5. Parametric Study shows that both flow coefficient and flow factor increases with increase in gate disc lift among the simulated cases i.e, the higher the opening higher the mass flow rate, efficiency of fluid flow and lower the pressure loss.
6. Hence the results are in good agreement and the underlying physics is visible clearly.

      7. REFERENCES

1. https://en.wikipedia.org/wiki/Pressure_drop
2. https://en.wikipedia.org/wiki/Flow_coefficient
3. https://en.wikipedia.org/wiki/Gate_valve#:~:text=A%20gate%20valve%2C%20also%20known,the%20gate%20is%20fully%20opened.
4. https://www.google.co.in/imgres?imgurl=https%3A%2F%2F5.imimg.com%2Fdata5%2FGP%2FZZ%2FBH%2FSELLER23368291%2Fgatevalve500x500.png&imgrefurl=https%3A%2F%2Fwww.indiamart.com%2Fproddetail%2Fgatevalve22307124333.html&tbnid=xitLXRQHxXldCM&vet=12ahUKEwj48sm_urn2AhXO0qACHVMUBJEQMygAegUIARDWAQ..i&docid=9AwXnshV1Re5M&w=500&h=243&q=gate%20valve&ved=2ahUKEwj48sm_urn2AhXO0qACHVMUBJEQMygAegUIARDWAQ
5. https://www.altair.com/newsroom/articles/parametricanalysisvsoptimization2/#:~:text=A%20parametric%20analysis%2C%20also%20known,the%20solution%20of%20the%20problem.
6. https://www.traditionaloven.com/tutorials/flow-rate/convert-kg-1-second-water-mass-to-gal-usperminute.html