Gate Valve - Parametric Study

Aim: To perform a parametric study on the gate valve simulationby setting the opening from 10% to 80%.

Objective:

• To obtain the mass flow rates at the outlet for each design point.
• To calculate the flow coefficient and flow factor for each opening.

Description:

A gate valve is a valve with a sliding plate that controls the flow of a fluid in a pipe or a channel.Gate valves consists of Gate Disc,Bonnet, Spindle, Hand wheel and body(casing). Gate valves are usually operated using handwheel which turns a screw to lift or lower the gate. Gate valves contain a sliding disk that moves vertically, perpendicular to the path of the fluid flow. The diskof the gate valve is completely removed when the valve is fully open i.e. the disk is fully lifted into the valve bonnet.Hence an opening for the flow through the valve at same inside diameter as the pipe system in which the valve is installed. It can be used for a wide range of liquids and provides a tight seal when closed. Selecting a gate valve,the material used to construct the valve is an important decission to prevent premature value failure. In order to select the proper valve material there are several important things to consider i.e. service temperatures, operating pressures, effectiveness of coating on materials, material availibility and its cost and compatibility of materials with the injecting fuel/liquid.

Advantages of Gate valves:

• Gate valves are multydirectional and hence can be used in both directions.
• The pressure loss through the valve is minimal, as the flow region of the valve exactly matches the diameter of the pipe.
• It also has a good leakproof feature.

Disadvantages of Gate valves:

• Opening and closing of valve cannot be done quickly as it is mechanically operated.
• Gate valves are not suitable to regulate the flow or throttle flow.
• They undergo heavy vibration when the flow passes through them due to heavy pressures.
• Repair or machining of valve seats in place is very difficult.

Applications of Gate Valve:

• Gate valves are generally used in air, fuel gas, feedwater, lube oil and other systems.

Procedure:

• To begin the simulation process open the Workbench > select Fluent Module.
• Click on Geeometry to open spaceClaim. In spaceClaim > Import Geometry.
• Initially perform the analysis without the parametric study as a reference simulation.
• For this, we give a rise of 10mm for the Gate disc.
• To visualize clear visualisation of Gate disk > unselect the Bottom casing.
• Now, in Edit > select the Move option > click on Select Component (to select entire Gate disk component) > by clicking Move the gate disk and enter the lift value as 10mm. To paramatrise select 'P'.
• To extract the Fluid volume go to Prepare > select Volume Extract > and use Select Edges > now select Inlet , Outlet and other Edge of fluid volue is below the Bonnet i.e. untick the Bonnet to visualise the edge and select the third Edge > click Ok.
• After this we need to extend the fluid flow regions i.e. select Pull tool > select the surface of inlet and pull it out and enter the value as 800mm > similarly on the outlet side also.
• Now Uncheck and Supress all the solid geometries one by one. See that only Fluid Volume exists. Close spaceClaim.
• Opne the Meshing Module > check if the Fluid volume is loaded sucessfully.
• Generate a baseline mesh for the imported geometry.
• Assign the Named Sellection i.e Inlet and Outlet. Then close the Meshing module and Update the Mesh.
• Further to proceed with the simulation > open Fluent(Setup). Here use Douple Precission with four processors for fast calculations.
• To set up the case, unable Gravity. In this casde z-direction is pointing upwards. Hence z=-9.81. For this case consider Solver > Time = steady state, Type = Pressure Based and Velocity Formulation = Absolute.
• Go to Physics > select Viscous Model= k-epsilion model, Realizable, Scable Wall Functions > click Ok.
• To define the Material go to Setting Up Physics > Materials > go to Fluent Database > select Water-Liquid > click on Copy > Close.
• Now we should define the fluid that is existing inside the Fluid Volume. For this go to Zones > Cell Zones > select Volume > edit Material Name = Water-Liquid > click Ok.
• To protect the mixing of fluids, go to Materials > go to Fluent-Fluid Materials > delete Air > click Close.
• Now go to Boundary Conditions > select Inlet > Type=pressure-inlet > select Guage Toatal Pressure=10 pascal > click Ok.
• Before Initialization, go to Initiallization > select Method=Standard > then go to Options > Solution Initialization page opens > here select compute from= Inlet > now Initialize(t=0).
• After this, go to Postprocessing > create a plane > inorder to view the velocity magnitude- create a contour > click OK.

For the parametric study,

• As we selected Parametric while entering the lift, just below the Results we can find Parameter set is created.
• Click Parameters to open > we can see the Table of Design Points > we have 3 coloumns i.e. Name, GROUP-1(p1) and mass flow rate-report (p2).
• Enter the value of lift required in coloumn-Group1 in coloumn sequence i.e 10% - 80%.
• In order to calculate all the cases > click on Update All Design Points. Once the calculation starts the values of mass flow rate are displayed in report (p2).
• If we get any wrong value in mass flow rate, then check the generated residuals and reduce the momentum value and run the calculation only for that particular case. Here to open the particular case, juct right click on the case > click Set as Current. Then we can access that particular cases.

Finally residuals, report for mass flow rate is generated and velocity magnitude is visualised. On generating the data plots are plotted as required.

Geometry:

Gate Valve:

Gate Disc with Wheel:

Fluid Volume Extraction:

Meshing:

Named selection:

Observations :

Case-1 Lift=10mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-2 Lift=20mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-3 Lift=30mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-4 Lift=40mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-5 Lift=50mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-6 Lift=60mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-7 Lift=70mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

Case-8 Lift=80mm

Valve Opening:

Residuals:

Mass Flow Rate plot :

Velocity Magnitude:

Velocity Contour:

# Obtaining the mass flow rates at the outlet with 10%-80% lift:

Parametric table for Mass-Flow rate:

# Calculating the flow coefficient and flow factor for each opening:

Flow Coefficient: The flow coefficient describes the relationship between the pressure drop across the pipe and the corresponding flow rate.

The flow coefficient is defined as the volume of the fluid that will flow per minute across a pipe with the pressure difference of 1psi. Helps to calculate the efficiency of flow across the pipes.

Flow coefficient(C_v) is given by the following equation;

Where Q - rate of flow.

SG - specific gravity of fluid (water=1).

ΔP - pressure drop across the valve.

Flow Factor: The metric equivalent flow factor (K_v)

Where K_v - flow factor. (m^3.h^-1.bar^-0.5)

Q - flow rate. (m^3/h)

SG - specific gravity of fluid (water=1).

ΔP - pressure drop across the valve. (bar)

Also, flow factor can be calculated using the flow coefficient.

K_v =0.865(C_v)

Calculating the flow factor and flow coefficient:

Here, Q=1kg/s i.e. Q=3.6 m^3/hr

ΔP= 10pascal

= 10 * 10^-5 bar (pascal to bar conversion= 1*10^-5 bar)

ΔP= 10^-4 bar.

Also, 1 ÷ √(10^-4) = 100

>> K_v = Q * (( Mass flow rate value in each case) * 1 /√(10^-4)).

Lift or Valve Opening(%)	Mass Flow Rate (kg s^-1)	Flow factor - Kv	Flow coefficient - Cv
10	0.13488	48.56	56.14
20	0.24032	86.52	100
30	0.36238	130.47	150.81
40	0.47128	169.66	196.14
50	0.56493	203.37	235.12
60	0.63856	229.88	265.76
70	0.7142	257.11	297.24
80	0.78031	280.91	324.75

Plots showing flow coefficient and flow factor for each opening of valve:

From the figure, it is observed that with the increase in valve opening, the mass flow rate also increases. Which concludes that the volume of the fluid flow increases gradually by increasing the lift of the valve.

The above plot i.e the flow coefficient and the flow factor against various valve openings clearly shows that there is increase with the flow with opening of the valve. At higher lifts the output pressure increases gradually.

Results:

• From the above contours, as the opening of the gate disc increases-the mass flow rate of fluid also increases.
• It is observed that, the maximum lift of the gate disk helps the fluid flow freely without any disturbance or restriction in the flow.
• Similarly, from the generated data it is noted that for different valve openings there is rise in the flow coefficient.
• Hence, all the parameters studied above are directly praportional i.e. as lift increases the flow factor and the flow coefficient raises.
• The calculated flow coefficient is useful to find the overall efficiency of the gate valve.
• The velocity contour shows how the fluid flow behave on opening the gate valve and also indicates the maximum velocity throught the flow.

Conclusion:

The parametric study on the gate valve is performed by varying the lift from 10% to 80%. During the parametric study several parameters and its effects are plotted for representation. Its clear that the fluid flow rate gradually increases with the increase in the lift of the gate disc. Also the flow coefficient and the flow factors are plotted in order to observe the effect during the simulation. Hence in this study the effect of opening the gate valve on the fluid characteristics are established.