Parametric study on Gate valve using ANSYS Fluent

Week9 Report:

• 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%.

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

• Introduction: Gate Valve - A gate valve, also known as a sluice valve, is a valve that opens by lifting a barrier (gate) out of the path of the fluid. Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened. The gate faces can be parallel but are most commonly wedge-shaped (in order to be able to apply pressure on the sealing surface).
  
  Applications of Gate Valve - Gate valves are used to shut off the flow of liquids rather than for flow regulation. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low flow resistance. The size of the open flow path generally varies in a nonlinear manner as the gate is moved. This means that the flow rate does not change evenly with stem travel. Depending on the construction, a partially open gate can vibrate from the fluid flow.

  Gate valves are mostly used with larger pipe diameters (from 2" to the largest pipelines) since they are less complex to construct than other types of valves in large sizes.

  At high pressures, friction can become a problem. As the gate is pushed against its guiding rail by the pressure of the medium, it becomes harder to operate the valve. Large gate valves are sometimes fitted with a bypass controlled by a smaller valve to be able to reduce the pressure before operating the gate valve itself.

  Gate valves without an extra sealing ring on the gate or the seat are used in applications where minor leaking of the valve is not an issue, such as heating circuits or sewer pipes.

  Parametric Study - A parametric study is a study that influences design variables in the product design model to explore design alternatives that can effectively support product concept designs. A parametric study is simple and easy to perform as long as the mapping between CAD and simulation models has been established. The mapping supports fast simulation model generation for performance analysis.
  
  
  

• Procedure:

This is a classic model of a Gate Valve. The dimensions may vary according to application and needs.

The image below is a complete assembly of different components.

Below we can see a hand wheel and spindle that can be used to lift or lower the gate disc.

The bonet is placed below the handwheel and prevents the splashing of fluid from the upper region.

The gate disc is attached to the spindle at the bottom.

The bottom is a casing that covers the gate disc and the water flows through it. Two ports serve as inlet and outlets for the fluid.

• Geometry Preparation -

For this case, we calculate the velocity of fluid across the length of the pipe and the geometry of the bottom. First, we extend the geometry of inlet and outlet ports by 800 mm each. It will look as shown below.

To calculate the velocity of fluid inside the geometry, we need to extract the fluid volume. In prepare option of the space claim modeler, we select volume extract. And select edges that are needed for extraction. It will look like this :

The extracted fluid will look as shown below.

In this case, we are verifying the effects of lifting the gate valve of fluid velocity. So we suppress all geometry parts except fluid volume for physics.

• Meshing :

Element Size = 5.5 mm

Number of Nodes = 99905

Number of Elements = 497225.

• Set-up:

Geometry - Pressure based steady solver

Model - K-Epsilon Realizible with scalable wall functions enabled.

Materials - Fluid : Water(liquid)

Boundary Conditions - Inlet : Pressure Inlet = 10 pa.

Initialization - Standard initialization.

Report Definitions - Mass Flow rate.

Computing From - Inlet.

Number of Iterations - 250.

• Case I : Lift = 10 mm.

• Case II : Lift = 20 mm.

• Case III : Lift = 30 mm.

• Case IV : Lift = 40 mm.

• Case V : Lift = 50 mm.

• Case VI : Lift = 65 mm.

• Case VII : Lift = 80 mm.

• Results:

• 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 pressuredrop across an orifice valve or other assembly and the corresponding flow rate.

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

where:

Q is the rate of flow ,

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

ΔP is the pressure drop across the valve .

In more practical terms, the flow coefficient C_v is the volume of water at 60 °F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

• Flow Factor :

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 ).

Q is the flowrate (expressed in cubic metres 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 :

• Calculations -

In this case

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

ΔP">ΔPΔP= 10-0 = 10 Pa = 10*10^-5 bar = 10^-4

Calculating Kv">KvKvfor each case

1. Kv">KvKv= 3.6⋅0.1941⋅110-4">3.6⋅0.1941⋅√110−43.6⋅0.1941⋅110-4= 53.676 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5
2. Kv">KvKv= 3.6⋅0.24032⋅110-4">3.6⋅0.24032⋅√110−43.6⋅0.24032⋅110-4= 86.5152 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5
3. Kv">KvKv = 130.54 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5
4. Kv">KvKv = 170.53 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5
5. Kv">KvKv = 204.40 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5
6. Kv">KvKv = 244.52 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5
7. Kv">KvKv = 281.48 m3hr.Bar0.5">m3hr.Bar0.5m3hr.Bar0.5

Similarly Cv">CvCv for each case

Cv=Kv0.865">Cv=Kv0.865Cv=Kv0.865

1. Cv">CvCv = 62.04
2. Cv">CvCv = 100.01
3. Cv">CvCv = 150.91
4. Cv">CvCv = 197.14
5. Cv">CvCv = 236.30
6. Cv">CvCv = 282.68
7. Cv">CvCv = 325.41

• Plots -

MATLAB code for plots

l = [10,20,30,40,50,65,80];
Cv = [62.04,100.01,150.91,197.14,236.30,282.68,325.41];
Kv = [53.67,86.51,130.54,170.53,204.40,244.52,281.48];

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');

Lift	Cv	Kv
10	62.04	53.67
20	100.01	86.51
30	150.91	130.54
40	197.14	170.53
50	236.3	204.4
65	282.68	244.52
80	325.41	281.48