Week 9 - Parametric study on Gate valve.

Aim:

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

Objective:

• 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 a gate valve provides a positive sealing a high pressure of liquids & gases.

Flow coefficients 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.
Mathematically the flow coefficient C (or flow-capacity rating of the valve)

`Cv=Q*root*((SG)/(deltaP))`

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 metric equivalent flow factor (Kv; commonly used everywhere else in the world except for the United States)calculated using metric units :

`kv=Q*root*((SG)/(deltaP))`

where
K is the flow factor.

Q is the flow rate (expressed in cubic meters per hour `m^3/h`)

SG is the specific gravity of the fluid (for water = 1),
∆P is the differential pressure across the device (expressed in [bar]).
K can be calculated from C using the equation:

Kv=0.865*Cv

SimulationSteps in simulation: Open Ansys workbench, drag & drop fluid flow (Fluent) onto project schematic. below are steps we need to follow to solve a particular engineering system from a CFD standpoint.
1. Geometry: Spaceclaim is used to import geometry & other CAD-related functions like geometry clean-up, etc.
2. Mesh: used to generate mesh & other mesh control options there, also assign name which helps during BCs setup.
3. Setup: used to define physics of the problem, like BCs, material & type of solving method, iterations, etc.
4. Solution: where runtime results visualization done.
5. Results: CFD-Post, where post-processing of results will be done.

CAD

setup import gate valve geometry into Spaceclaim.

As the imported model is solid, so we need to carry out an analysis of the fluid volume, hence extract the fluid volume.
Prepare->select volume extract->select edges.
Select front & back edges of the circles (for inlet & outlet).
suppress the geometry except for fluid volume.
Parametrize the lift by clicking on the P symbol.

Mesh Generation-

Name selection: an inlet for one end & outlet for another end.
Mesh element size is 8 mm.

Fluent set physics setup selects k-epsilon, realizable with scalable wall functions.
Pressure-based solver.
Steady state solver & enable gravity in z-axis -9.81 m/s^2.
Material Selection:
For liquid- water
density= 998.2 kg/m^3
viscosity= 0.001003 kg/m-s
Boundary conditions:
Inlet type- pressure type
assign gauge pressure 10 Pa, for pipe flow 10 Pa inlet pressure is acceptable.
Create a velocity contour.
Assign mass flow rate output parameter for the parametric study.

Name selection:

Setup name selection for Gate valve

Inlet-

Outlet-

simulation for lift 10mm results.

Setting up the parametric for gate valve simulation by setting the opening from 10 % to 80%.

parametric table.

The calculation is done for the above formulas Cv and Kv :

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

ΔP

= 10-0 = 10 Pa = 10*10^-5 bar = 10^-4

lift in mm	Cv	Kv
10	86.04	74.42
20	130.41	112.80
30	170.60	147.56
40	204.26	176.68
50	232.64	201.23
60	262.30	226.89
70	283.10	244.88
80	304.50	263.37

Plots -

Matlab code:

l = [10,20,30,40,50,60,70,80];
Cv = [86.04,130.41,170.60,204.26,232.64,262.30,283.10,304.50];
Kv = [74.42,112.80,147.56,176.68,201.23,226.89,244.88,263.37];
figure(1)
plot(l,Cv,'color','r','Marker','*');
hold on
plot(l,Kv,'color','b','Marker','*');
xlabel('Lift Position (mm)');
ylabel('Cv and Kv');
title('Lift vs Cv and Kv');
legend('Cv','Kv');

plotted graph for lift, Cv and Kv

Conclusion:

Mass flow rate gradually increases as the lift of the gate disc is increased.

A parametric study is a time-reducing option when studying the effects of changes of certain parameters on a system.

Flow coefficient plays important role in the selection of valve and sizing of a valve, so calculating it is necessary.

Flow coefficient also helps in the computing efficiency of the system and the effect of pressure on the system.