Week 9 - Parametric study on Gate valve.
Aim:-
To perform a parametric study on the gate valve simulation by setting the opening from 10% to 80%
Objective:-
- To obtain the mass flow rate at the outlet for each design point .
- To calculate the flow coefficient and flow factor for each opening and plot the graph.
- Discuss the result of the mass flow rate and flow coefficient.
Theory:-
What is gate valve and where it is used?
- 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, 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 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.
Photo of a gate valve
Related terms
Flow Coefficient:
The flow coefficient of a device is a relative measure of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop 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:
Q is the rate of flow (expressed in US gallons per minute)
SG is the specific gravity of the fluid (SG for water= 1)
ΔP is the pressure drop across the valve (expressed in psi)
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:
The metric equivalent flow factor (Kv; commonly used in Europe and Asia) is calculated using metric units:
Q is the rate of flow (expressed in m^3/h)
SG is the specific gravity of the fluid (SG for water= 1)
∆P is the pressure drop across the valve (expressed in bar).
The Kv factor of a valve indicates "The water flow in m3/h, at a pressure drop across the valve of 1 kgf /cm2 when the valve is completely open.
Procedure
- Open space claim and import the valve model.
- Extract the volume out of solid body
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Extend the inlet and outlet end of the valve to see the proper flow of the fluid.
- Move the gate disc upside to open the gate by 10 mm.
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- Go to the group option and create parameter.
- Close the space claim and go to meshing for the nest procedure.
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Setup
Solver- pressure based
Time -study
Turn on gravity
- Add material-water
- Boundary condition
- Inlet condition
- Outlet condition
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Cases:
- Case 1 = gate lift 10 mm
- Case 2 = gate lift 20 mm
- Case 3 = gate lift 30 mm
- Case 4 = gate lift 40 mm
- Case 5 = gate lift 50 mm
- Case 6 = gate lift 60 mm
- Case 7 = gate lift 70 mm
- Case 8 = gate lift 80 mm
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Case 1 = gate lift 10 mm
Mass flow rate
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Velocity contour
Streamline
Vector
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Pressure
Case 2 = gate lift 20 mm
Mass flow rate
Velocity
Vector
Streamline
Pressure
Case 4 = gate lift 40 mm
Mass flow Rate
Velocity Contour
Vector
Streamline
Pressure
Case 5 = gate lift 50 mm
Velocity Contour
Streamline
Vector
Pressure
Case 6 = gate lift 60 mm
Mass flow rate
Velocity Contour
Vector
Streamline
Pressure
Case 7 = gate lift 70 mm
Mass flow rate
Velocity
Vector
Streamline
Pressure
Case 8 = gate lift 80 mm
Mass flow rate
Velocity
Streamline
Vector
Pressure
Conclusions:
- The low lift height refers to the higher pressure drop and thus low flow rate through the valve.
- The negative mass flow is due to the mass exiting the outlet.
- With the help of the parameters the solving time and effort can be reduced drastically.