Gate Valve Parametric Study
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 (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. 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.
Flow factor
The floe factor 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 factor `k_v`(or flow-capacity rating of valve) can be expressed as :
`k_v=Q((SG)/(DeltaP))^0.5`
where:
- Q is the rate of flow (expressed in `m^3/h`),
- SG is the specific gravity of the fluid (for water = 1),
- ΔP is the pressure drop across the valve (expressed in bar).
Flow coefficient(`C_v`)
`c_v=1.1560*k_v`
Geometry
Import the given geometry in Ansys fluent
Extract the fluid volume of given gate valve using volume extract
The gate valve is lifted by 10mm using the move options and parameter is created for the lift value.
Meshing
Setup
Pressure based solver is used, gravity is enabled in the -ve z direction. K-epsilon model ,relizable,scalable wall functions is used for the analysis. Water enter from the inlet at a gauge pressure of 10 pa . Mass flow rate at the outlet is calculated at different design point.
Base line simulation
Position of the gate valve at 0 mm lift
Mass flow rate at outlet
Average mass flow rate=-0.1014 kg/s
Average velocity at outlet= 0.01300 m/s
Parametric study
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
By changing the position of the valve at different desing point and update the value of each design point for mass flow rate, pressure and velocity at outlet.
Cross- sectional view at 80 mm design point
Result
Parameter table gives the value of different parameter at each design point.
| DP | Mass flow rate (kg/s) | Pressure at outlet(pa) | Avg velocity at outlet(m/s) | Volume flow rate (m^3/h) | Flow factor(`m^3h^-1 b a r^0.5`) | Flow coefficient(m^3h^-1 b a r^0.5) |
| 10 mm | -0.14974 | 0.18442 | 0.01915 | -0.53906 | 54.41 | 62.89 |
| 20 mm | -0.23985 | 0.48204 | 0.03098 | -0.86346 | 88.50 | 102.30 |
| 30 mm | -0.36123 | 1.07839 | 0.04645 | -1.30042 | 137.67 | 159.14 |
| 40 mm | -0.39753 | 1.88231 | 0.06140 | -1.43110 | 158.83 | 183.60 |
| 50 mm | -0.56520 | 2.65825 | 0.07249 | -2.03472 | 237.46 | 274.50 |
| 60 mm | -0.67242 | 3.7875 | 0.08652 | -2.31271 | 293.41 | 339.18 |
| 70 mm | -0.71929 | 4.52185 | 0.09431 | -2.58944 | 349.855 | 404.42 |
| 80 mm | -0.78701 | 5.18906 | 0.10157 | -2.83323 | 408.47 | 472.19 |
-ve sign denote the mass flow rate and volume flow rate goes out side the system.
It can be observed from the above table when lift increases mass flow rate , pressure and velocity increases.
Conclusion
The variation of flow coefficient and flow factor with the opening of the valve is studies by using parametric.