Simulation of the Gate Valve with a Parametric Study using Ansys Fluent

GATE VALVE SIMULATION:

Aim: To perform a Parametric Study on Gate valve.

Objectives: For this challenge, you will have to perform a parametric study on the gate valve simulation by setting the opening from 10 % to 80%.

• Obtain the mass flow rates at the outlet for each design point.
• Calculate the flow coefficient and flow factor for each opening and plot the graph.
• Discuss the results of the mass flow rate and flow coefficient.

Theory:

Gate valves are machine elements that are commonly used to control the flow of fluids as the gate valve provides a positive sealing at high pressure of liquids and gases. Gate valves are used when a straight-line flow of fluid and minimum restriction is desired. Gate valves are so named because the part that either stops or allows the flow of fluid through the valve acts somewhat like the opening or closing of a gate and is called, appropriately, the gate.

Flow Coefficient(Cv):

Flow coefficient is a device’s capacity for a liquid or gas flow through it. The larger the opening of the valve the larger the Cv.

Mathematically the flow coefficient C_v (or flow-capacity rating of the valve) can be expressed as :

where:

Q is the rate of flow (expressed in US gallons per minute),

SG is the specific gravity of the fluid (for water = 1),

ΔP is the pressure drop across the valve (expressed in psi).

Flow Factor(Kv)

The metric equivalent flow factor (K_v; commonly used in Europe and Asia) is calculated using metric units :

where

K_v is the flow factor (expressed in m^(3)*h^(-1)*bar^(-0.5)).

Q is the flow rate (expressed in cubic meters per hour)

SG is the specific gravity of the fluid (for water = 1),

∆P is the differential pressure across the device (expressed in [bar]).

K_v can be calculated from C_v using the equation

Kv=0.865*Cv

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SIMULATION:

Steps in Simulation:

Open Ansys Workbench. Drag and drop Fluid Flow (Fluent) onto Project Schematic.

Here, we will see Steps we need to follow to solve a particular engineering system from a CFD standpoint.

1. Geometry: Spaceclaim, where we import the geometry.
2. Mesh: Ansys Mesh, where Boundary naming, element sizing and mesh generation with required grid size will be done.
3. Setup: Ansys Fluent, where the actual case setup will be done.
4. Solution: Ansys Fluent, where runtime results visualization done.
5. Results: CFD-Post, where Post Processing of Results will be done.

CAD Cleanup:

Import Graphics card geometry into Spaceclaim, Spaceclaim is CAD cleanup software that can be used to prepare CAD models for simulation setup. It could be for CFD or FEA.

In below sectional view the fluid volume has adopted the lift of the valve

In below sectional view the fluid volume has not adopted the lift of the valve

As we can see above figure is the Solid model. We need to carry out an analysis of the fluid volume, so extract the fluid volume. Select Prepare, select volume extract, select edges. Select front and back edges of both the circles(for inlet and outlet).

Suppress the Geometry except for Fluid volume.

Parametrize the lift by clicking on P symbol.

Mesh Generation

Name Selection: Inlet for one end and Outlet for the other end.

Mesh element size 8mm.

Generate and update the Mesh.

Fluent Setup:

Setting up physics: Select k-epsilon, Realizable (to provide superior performance for flows involving rotation, boundary layers under strong adverse pressure gradients, separation, and recirculation.) with scalable wall functions.

Solver: Pressure-based as Mach number is less than 3.

Assign Time as Steady-state Solver. Enable gravity in y-axis -9.81 m/s^2

Material Selection:

For liquid- water

Properties of Material:

For Air: Density = 997 kg/m^3

Viscosity = 0.00089 Pa

Boundary Conditions:

Inlet type-Pressure type (Fluid flow can be changed by adjusting the inlet pressure)

Assign Gauge pressure 10 Pa (For pipe flow 10 Pa pressure inlet is acceptable)

Create a velocity contour.

Assign the Mass flow rate output parameter for the parametric study.

Calculate.

Case 1: Without Parametric Study for lift = 10mm

Plots and Results:

Cad setup:

Residuals:

Velocity Contour:

Case 2: With Parametric Study

In the above figure, the parametric study is applied to the Valve lift for 20,30,40,50,60,70 and 80mm. (As the earlier lift of without parametric study is 10mm, hence this earlier lift is already added to the above valve lift)

Plots and Results for Valve Lift = 20,30,40,50,70, and 80mm respectively:

Cad setup:

Residuals:

Velocity Contour:

Calculation the flow coefficient and flow factor for each opening

Flow Coefficient(Cv):

Q = 1kg/s = 3.6 m^3/hr

P = 10-0 = 10 Pa = 10*10^(-5) bar = 10^(-4) bar

For 10,20,30,40,50,60,70, and 80mm valve lift:

`Cv = 3.6*0.1477*sqrt (1/10^(-4))` = 53.172

Cv = 85.68

Cv = 121.68

Cv = 169.56

Cv = 201.6

Cv = 227.88

Cv = 1771.2

Cv = 1845.36

Flow Factor(Kv):

Kv = 0.865*Cv

For 10,20,30,40,50,60,70,& 80mm valve lift:

Kv = 0.865*53.172 = 45.99 m^(3)*h^(-1)*bar^(-0.5)

Kv = 85.68 m^(3)*h^(-1)*bar^(-0.5)

Kv= 105.25 m^(3)*h^(-1)*bar^(-0.5)

Kv = 146.669 m^(3)*h^(-1)*bar^(-0.5)

Kv = 174.384 m^(3)*h^(-1)*bar^(-0.5)

Kv = 197.1162 m^(3)*h^(-1)*bar^(-0.5)

Kv = 1532.088 m^(3)*h^(-1)*bar^(-0.5)

Kv = 1596.23 m^(3)*h^(-1)*bar^(-0.5)

Effect of Valve lift on Mass flow rate, Flow Coefficient(Cv), and Flow factor(Kv):

Valve Lift (in mm)	10	20	30	40	50	60	70	80
Mass flow rate (kg/s)	-0.1477	-0.238	-0.338	-0.471	-0.5607	-0.633	-4.92	-5.12
Flow Coefficient(Cv)	53.172	88.68	121.68	169.56	201.6	227.88	1771.2	1845.36
Flow factor (Kv)	45.99	85.68	105.25	146.669	174.384	197.116	1532.088	1596.23

Conclusion:

• As the Valve lift increases, Mass flow rate and Flow Coefficient and Flow factor also increased.

• The negative value of the Mass flow rate indicates the mass is flowing out of the valve.

• The use of the flow coefficient offers a standard method of comparing valve capacities, to determine the inlet pressure and sizing valves for specific applications.
• Simulation time can be reduced to a great extent by performing a Parametric study.