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%.

Objectives:

• 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:

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).

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.

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.

Gate valves are typically constructed from cast iron, cast carbon steel, ductile iron, gun metal, stainless steel, alloy steels, and forged steels.

The flow coefficient - C_v - or the flow factor - K_v - are commonly used to specify capacities of control valves.

Application of gate valve:

A typical gate valve application includes

• Cooling water systems.
• Fuel oil systems.
• Feedwater or chemical feed system.
• Boiler and main steam vents and drains.
• Turbine lube oil system.

Flow Co-efficient:

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).

In more practical terms, the flow coefficient C_v is the volume (in US gallons) 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 everywhere else in the world with the exception of the United States) is calculated using metric units .

where

K_v is the flow factor expressed in m^3.h^-1

Q is the flowrate (expressed in cubic metres 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_v can be calculated from C_v using the equation:

Steps Followed:

a) Geometry preperation

b) Meshing

c) Setup

d) Results

Geometry preperation:

Given 3D model:

3D model inlet & exhaust has been extended to accommodate fluid volume necessary to simulate gate valve.

The valve has been opened 10mm to calculate mass flow rate of water.

The fluid volume extracted using Volume extract option by selecting boundaries to make it closed volume.

Final fluid volume

Suppress all the solid volumes.

The simulation has been carried out number of valve opening from 10mm to 90mm. The dimension of valve opening has been parameterize to simplify simulation process of similar type with different valve opening. The parameter has been created for valve opening by creating group shown in the below image.

Meshing:

Create Named Selections

Mesh:

Setup:

Following options are selected.

Materials:

Cell zones:

Boundaries:

• Create a mass flow rate report :

• Create a pressure at inlet report :

• Create a pressure at outlet report :

Initialization:

The standard method is selected and the initialization is done by selecting it from the inlet of the pipe.

Results:

The following results were obtained with 10mm open.

Geometry:

Mesh:

Pressure Contour:

Velocity Contour:

The following results were obtained with 30mm open.

Geometry:

Mesh:

Pressure Contour:

Velocity Contour:

The following results were obtained with 50mm open.

Geometry:

Mesh:

Pressure Contour:

Velocity Contour:

The following results were obtained with 70mm open.

Geometry:

Mesh:

Pressure Contour:

Velocity Contour:

The following results were obtained with 90mm open.

Geometry:

Mesh:

Pressure Contour:

Velocity Contour:

Conclusion:

The following table was obtained from the parametric study.

The mass flow rate at each opening of the valve are available in the parametric study table.

Graph between opening of the valve in mm and flow co-efficient.

Smaller the valve opening, more the pressure loss and lesser the flow rate. We need to design the valve such that it has large value of the Flow co-efficient at operating conditions.