Week 9 - Parametric study on Gate valve.

AIM: TO PERFORM A PARAMETRIC STUDY ON GATE VALVE SIMULATION BY SETTING THE OPENING FROM 10% TO 80%.

OBJECTIVE:

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:

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).

Gate valves are used to shut off the flow of liquids rather than for flow regulation, which is frequently done with a globe valve. 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 mainly 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 force 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.

APPLICATION:

1. Gate valves are used in almost all fluid services such as air, fuel gas, feedwater, steam, lube oil, hydrocarbon, and almost any services.
2. Some special gate valve is used in slurry and powder product also, such as knife gate valve.

ADVANTAGES:

1. Gate valve provides good shutoff
2. Pressure drop during operation is very less
3. Most of the gate valves can be used as bi-directional
4. They are suitable for high-pressure and temperature applications and require less maintenance.

DISADVANTAGES:

1. It cannot be used to control the flow.
2. A gate valve is slow in operation. Opening and closing take time which is good also as it reduces the chance of hammering.
3. When partially open, it creates vibration and noise.
4. Repairs, such as lapping and grinding of seats are more difficult due to limited access.

FLOW COEFFICIENT:

The flow coefficient of a device is a relative measure of its efficiency in allowing fluid flow. It describes the relationship between the pressure drops across an orifice valve or other assembly and the corresponding flow rate. Mathematically the flow coefficient Cv (or flow-capacity rating of the valve) can be expressed as:

where,

Q = rate of flow (expressed in US gallons per minute),

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

ΔP = pressure drop across the valve (expressed in psi).

10pa = 0.00145038psi

In more practical terms, the flow coefficient Cv 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. The use of the flow coefficient offers a standard method of comparing valve capacities and sizing valves for specific applications that are widely accepted by the industry. The general definition of the flow coefficient can be expanded into equations modeling the flow of liquids, gases, and steam using the discharge coefficient.

FLOW FACTOR:

It indicates how much volume of fluid flows through a valve at a given time To calculate the flow rate volume of a liquid, the Kv factor, the density of the medium, and the pressure difference between input pressure and back pressure must be known. The metric equivalent flow factor (Kv; commonly used in Europe and Asia) is calculated using metric units:

Kv can be calculated from Cv using the equation given below:

The Kv factor of a valve indicates "The water flow in m3/h, at a pressure drop across the valve of 1 kg/cm2 when the valve is completely open.

PROCEDURE:

• Import the gate valve file into the space claim and extrude the highlight surface on either side to 500mm to conduct the flow analysis.

• perform volume extraction operation by selecting the fluid interacting surfaces under preparation in SpaceClaim.

• Hide all the components of the gate valve except the gate disc, and spindle, using the move command under design move the gate disc along the z-direction for 10mm so that the flow path is partially open and parameterize this value under groups - create parameter.

• keeping checked-in of the selected components of the gate valve right click on volume - click on update the geometry as per content. Since we are not interested in the analysis of solid geometry, it is suppressed.

MESHING

• Mesh Element Size = Default (63.387mm)
• Nodes = 26904
• Elements = 127828

• cut section view

• naming

SET-UP:

• Solver type = Pressure_Based
• Velocity Formulation = Absolute
• Time = Steady state
• Gravity = at Z direction -9.81 m/s^2

Material Selection

• Material: water-liquid (H₂o)(l)
• Density: 998.2 Kg/m³
• Viscosity: 0.001003 Kg/m-s

Delete air material - Go to cell zone condition - change material name - apply.

Again go to material & now we can delete material (air).

Boundary Condition

At Inlet

At outlet

10 mm lift

• Residual plot

• Mass flow rate

• contour plots

20 mm lift

• Pressure contour

• Velocity contour

30 mm lift

• Pressure contour

• Velocity contour

40 mm lift

• Pressure contour

• Velocity contour

50 mm lift

• Pressure contour

• Velocity contour

60 mm lift

• Pressure contour

• Velocity contour

70 mm lift

• Pressure contour

• Velocity contour

80 mm lift

• Pressure contour

• Velocity contour

Mass flow rate for all cases

Conclusion -

A parametric study is a form of optimization where the user can run a series of analyses to investigate the impact of one or more processing parameters. For each parameter, any number of values can be selected for investigation. Each analysis is one possible combination of the parameter values chosen to be compared.

Here with the parametric study for the gate valve opening and further with this the calculation of the mass flow rate of the particular case is the new learning.

In the fluent for any particular study of any model it is necessary to run the same model under different inlet boundary conditions, doing these changes manually takes a lot of time thus parametric study helps in saving time for such type of study.