Week 9 - Parametric study on Gate valve.

AIM:

    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.

INTRODUCTION

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 (to be able to apply pressure on the sealing surface).

Use

• 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.
• 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.
• Generally in pipelines with high pressure, the gate valve opening can be quite difficult due to the high force exerted on the gate. So they are generally connected with a smaller bypass valve to release the pressure and then they are operated.

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.

Geometry:

Geometry which was provided has been increased in length by value of 800 mm on both face so that fluid volume and fluid flow analysis can be carry out.

                               BOTTOM                                                                                 TOP ASSEMBLY

using the move tool in design and then move the z axis pull up and then set it as 10mm 

Now we can extract the volume using volume extract in prepare

MESHING PART

SETUP PART

Model setup:

• Solver type: Pressure based
• Time steady : Steady
• Enable gravity with - 9.81 m/s2 on required axis
• Turbulence model: K epsillon > Realizable > Scaled wall function
• Fluid material: Water
• Cell zone : volume-volume > fluid > water

Boundary conditions:

• Inlet> pressure inlet = Gauge total pressure 10 Pascal
• Outlet>pressure outlet = Gauge total pressure 0 Pascal

Initialization : Hybrid

Run iterations = 250

CASE 1: LIFT 10mm

CASE 1: LIFT 20mm

CASE 1: LIFT 30mm

CASE 1: LIFT 40mm

CASE 1: LIFT 50mm

CASE 1: LIFT 60mm

CASE 1: LIFT 70mm

CASE 1: LIFT 80mm

CALCULATION PART 

Flow-Factor(kv):

Kv is the flow coefficient in metric units. It is defined as the flow rate in cubic meters per hour [m3/h] of water at a temperature of 16º celsius with a pressure drop across the valve of 1 bar. Cv is the flow coefficient in imperial units.

Flow-coefficient(Cv):

The coefficient of flow (Cv) is a formula which is used to determine a valve's flows under various conditions and to select the correct valve for a flow application. The Cv was designed for use with liquid flows, it expresses the flow in gallons per minute of 60º F water with a pressure drop across the valve of 1 psi.

      K=Q.√Sg/ΔP

K = Cv , when k is referenced in [gpm] [psi] unit

K = Kv , when k is referenced in [m3/hr] [bar] unit

where Q = mass flow rate

          Sg = Specific gravity of water which is equal to 1 

          DeltaP = Change in pressure or pressure drop across valve

Q obtained is in kg/s so we have to convert it into m3/hr

Q m3/hr = 3.6 * Q kg/s

To convert the pacsal to bar divide the pressure value by 100000

COMPARING THE RESULTS WITH GRAPHS

Conclusion:

• The negative sign in the mass flow rate term comes due to mass leaving at the outlet.
• Parametric study helps a lot to reduce the solving time in studying the effect of change of parameters on the system.
• From Graphical analysis we can say that, As lift of the gate valve is increased, increase in mass flow rate of fluid is observed and decrease in the level of pressure drop.
• As flow rate is increased, flow factor (Kv) increases as a result of which flow co-efficient (Cv) also increased
• 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.