Week 9 - Parametric study on Gate valve.

 

Theory:  

Introduction:   

Gate valves are designed for fully open or fully closed service. They are installed in pipelines as isolating valves and should not be used as control or regulating valves. Operation of a gate valve is performed doing an either clockwise to close (CTC) or clockwise to open (CTO) rotating motion of the stem. When operating the valve stem, the gate moves up- or downwards on the threaded part of the stem.  

Where are gate valves used?  

Gate valves are often used when minimum pressure loss and a free bore is needed. When fully open, a typical gate valve has no obstruction in the flow path resulting in a very low-pressure loss, and this design makes it possible to use a pipe-cleaning pig. A gate valve is a multiturn valve meaning that the operation of the valve is done by means of a threaded stem. As the valve must turn multiple times to go from open to closed position, the slow operation also prevents water hammer effects.  

A Gate Valve, or Sluice Valve, as it is soey can be parallel. Gate valves are sometimes used for regulating flow, but many are not suited for those pure times known, is a valve that opens by lifting a round or rectangular gate/wedge out of the path of the fluid. The distinct feature of a gate valve is the sealing surfaces between the gate and seats are planar. The gate faces can form a wedge shape, or the pose, having been designed to be fully opened or closed. When fully open, the typical gate valve has no obstruction in the flow path, resulting in very low friction loss and when the gate valve is closed there are many obstructions in the flow path which in turn produces high frictional losses.   To avoid or minimize the frictional losses study of stress distribution in the parts of the gate valve is done before manufacturing of gate valve.  We have selected a 4 1/16” Gate Valve for the analysis of stress distribution. The main reason to choose the gate valve is to carry out the basic analysis process of all the components.  It is tedious and great work for a designer to make the accurate stress distribution of any mechanical component. So, some deficiencies in the design of parts are left. To overcome these deficiencies computer software is used.  Analysis and optimization done by using analysis software give greater accuracy and minimize the time of the designer.   Slab Gate Valve Due to the various environments, system fluids, and system conditions in which flow must be controlled, many valve designs have been developed. A basic understanding of the differences between the various types of valves, and how these differences affect valve function, will help ensure the proper application of each valve type during design and the proper use of each valve type during operation.    

  

PARAMETRIC STUDY  

One of the best ways to get value out of your simulation is to do parametric analysis. With very little marginal work a completed model can be parameterized to simulate scenarios limited only by your computational time and resources.  

As you move forward in your design, you can assess the impact that changing certain parameters can have on the design. The parameters can include dimensional parameters. Parametric studies allow you to nominate parameters for evaluation, define the parameter range, specify the design constraints, and analyze the results of each parameter variation.  

A parametric study requires the following:  

• Design Objective is set to Parametric Dimensions  
• Parameters nominated for use in the simulation  
• parameter ranges identified  
• Design criteria specified  
• Various configurations generated  

When you have the configurations generated you can then evaluate your simulation. You can further refine the parameters or design constraints until satisfied with the results.  

Once you determine that a configuration satisfies your design needs, you can promote that configuration back to the model as a CAD edit. You are prompted to make changes.  

  

Geometry:  

Importing geometry in SpaceClaim The following geometry was imported into SpaceClaim. 

 

 

 It has the following components:  

• The bonnet is placed below the handwheel and prevents the splashing of fluid from the upper region.  
• Handwheel and spindle that can be used to lift or lower the gate disc.  
• 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 an inlet and outlet for the fluid.  

First, we extend the geometry of the inlet and outlet ports by 800 mm each. It will look as shown below.  

  

After extension, create Fluid volume by selecting the inlet, outlet and upper edges of the “Bottom” part. The creation of fluid volume is shown below:  

  

After generating fluid volume, hide all parts and suppress them for physics. Make sure to not hide gate-disc and spindle on behalf of which fluid volume must be created to involve necessary solid boundaries.  

We then lift the gate valve by 10mm by using the move option and click on the icon P alongside the dimension to parameterize the gate valve opening.  

Don't hide the bottom, gate disc, and spindle for parametrization, and set the solid part Volume inside the fluid volume to Update concerning context.  

for 0mm

 

to 10mm move

 

Meshing:  

 

Element Size = 8mm    

Named Selections are given as:  inlet and outlet

Setting Up Physics:  

First, the mesh is set up and the solver is defined as below:  

Solver Type: Pressure Based Solver  

Gravity: -9.81 (in negative z-direction)  

Solver: Steady State 

 

Model: k-epsilon model (realizable with scalable wall function)

  

Material: Water  

Cell Zone: Fluid(water)  

Inlet Boundary Condition: Pressure Inlet (20Pa)

  

Outlet Boundary Condition: Pressure Outlet  

The model will be initialized with standard initialization and the data will be computed from the inlet.  

Flux parameter is included for mass flow rate at outlet.  

10mm  

Residuals 

mass flow rate plot

Velocity counter 

 

Pressure counter 

 

Velocity streamline 

 

Velocity Vector flow

 

PARAMETRIC STUDY  

The lift parameter is set, and mass flow rate is included as the output parameter.  

  

 

  

20mm  

Velocity counter 

 

Pressure counter 

 

Velocity streamline  

Velocity Vector flow

  

30mm  

Velocity counter 

 

Velocity streamline 

 

Velocity Vector flow

  

40mm  

Velocity Vector flow

  

50mm  

Velocity Vector flow

  

60mm  

Velocity Vector flow

  

70mm  

Velocity Vector flow

  

80mm  

Velocity Vector flow

CALCULATIONS  

Mass flow rate: - It is defined as the mass of a substance flowing per unit time and it is given by the formula,  

`m = rho * Q` 
 

where m - mass flow rate (kg/s)  

rho - density of the fluid (kg/m^3)  

Q - flow rate (m^3/s)  

FLOW COEFFICIENT AND FLOW FACTOR AT EACH OUTLET: -  

Flow Coefficient: -The Flow Coefficient of a device is a relative measure of its efficiency at allowing fluid flow.  

 `C_v=Q.root(2)(S_g/(DeltaP))` 

Q is Mass flow rate (expressed in US gallons per minute).  

Sg is the specific gravity of water which is 1  

△P is pressure drop (in PSI)  

Flow factor: - The flow factor is the flow coefficient in metric units. It is defined as the flow rate in cubic meters per hour of water at a temperature of 16deg C with a pressure drop of 1 bar. It is given by the formula.  

 `K_v=Q.root(2)(S_g/(DeltaP))` 

Where Kv - flow factor  

Q - volume flow rate (m^3/hr )  

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

ΔP- pressure drop (bar)  

Converting between Flow Coefficient Cv and Flow Factor Kv  

The relationship between Cv and Kv can be expressed as:  

Cv = 1.16 Kv  

Kv = 0.862 Cv  

  

Cases Number	Mass Flow Rate (kg/S)	Mass flow rate (gpm)	Gate Disc lift  (mm)	Flow Coefficient	Flow Factor
1	0.208	3.2968	10	62.519	54.0789
2	0.333	5.2780	20	102.242	88.4393
3	0.501	7.9408	30	159.378	137.862
4	0.707	11.205	40	275.223	238.068
5	0.781	12.378	50	313.996	349.457
6	0.898	14.233	60	369.654	351.258
7	1.03	16.325	70	420.568	376.951
8	1.128	17.878	80	462.546	400.102

 

Conclusion:  

Flow-coefficient and flow-factor increase with increasing opening percentage. 

Differential pressure across the gate valve decreases with increasing opening percentage. This is because there is less blockage to the flow. 

Mass-flow rate and velocity increase with increasing opening percentage. This is because there are more pathways for the water to flow. 

Gate valve should operate in a fully opened or fully closed position. A partially opened valve induces vibration which can damage the gate valve. 

Also the gate valve should be closed gradually rather than suddenly, as it causes a water hammer effect which can again damage the gate valve.