Gate Valve Parametric Study

Objectives

1. To perform the parametric study on the gate valve by simulating the opening of gate valve ranging from 10mm to 80mm.
2. To obtain the mass flow rate for each design point.
3. Calculate the flow factor and flow coefficient for each design point.

INTRODUCTION:

1. Gate Valve

A gate valve is a valve that opens by lifting barrier or 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.

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 over fluid path, resulting in a very low fluid 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.

2. Parametric Studies

During the design of any component, we can ascertain the impact of changing certain parameters such as dimensional parameters in the design.

Parametric studies allow us 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:

• The design objective is set to Parametric dimensions.
• The parameters are nominated for use in the simulation.
• The parameter ranges are identified.
• The design criteria are specified.
• Various configurations are generated.

After the configuration are successfully generated, we can evaluate the simulation. Further refinement of the parameters or design constraints can be carried out until obtaining desired results.

3. 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 valve) can be expressed as:

In more practical terms, the flow coefficient Cv is the volume (in US gallons) of water at 60F 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 foe specific application that is widely accepted by industry. The general definition of flow coefficient can be excpanded into equations modeling the flow of liquids, gases and steam using the discharge coefficient.

4. Flow Factor:

The metric equivalent flow factor ( commonly used in Europe and Asia) is calculated using metric units:

PROBLEM STATEMENT

1. The fluid flowing through the model is water.

2. The inlet gauge pressure is 10 Pa.

3. Observe the effect of lifting the Gate Disc at different amount of percentage from 10% to 80%.

Simulation Methodology;

Modeling:

Solid Model:

• The mode for the gate valve can be prepared in any CAD software and thus can be imported in Ansys Space Claim.

Initial Lift:

• Hide the "Bottom " Part , so we can clearly see the "Gate Disc".
• Then Select "Gate Disc" component and move it in upward direction by "10 mm" lift.
• To analyze the flow and its effects, we must allow the flow, and for that we have given "10 mm" lift to the "Gate Disc".
• Here we can see the green color arrow in upward direction, which shows the movement of "Gate Disc" in positive Z-Direction.
• Also we can see the symbol of "P".
• This symbol "P" is used to parametrize the lift of the "Gate Disc".
• After selecting the symbol "P", it turns in Grey color, and message shows that a Group has been velated for lift.
• Created group for lift parameter shown in above image.
• On the Left Side, in Tree Structure, if we see the group options, we can see created group and the amount of parameter, which has been set 10 mm lift.
• We can simply change the value of parameters from there directly.

Fluid Volume:

• After lifting the "Gate Disc ", move the both faces at the inlet and outlet of the "Bottom" part by amount of 800 mm just to see the fluid flow and its effects as given below:

Volume Extraction:

• Select Three Region Edge to Extract the volume

Meshing:

Boundary Name Selection:

The boundaries of the geometry are generated using the named selection feature of Ansys-

1. Inlet

2. Outlet

MESH SETTING

1. Element Order: Linear

2. Element Size: 0.005 m

3. Number of Nodes: 119783

4. Number of Elements: 601096

SIMULATION SETUP:

1. Solver: Steady

2. Type: Pressure Based

3. Gravitational Acceleration:

• X: 0 ms2">ms2
• Y: 0 ms2">ms2
• Z: -9.81 ms2">ms2

4. Turbulence Model: Realizable k- epsilon with Standard Wall Function

5.Cell Zone Condition:

• Fluid: Water

6. Material Specifications:

• Material: water-liquid(h2o)
• Chemical Formula: H2o
• Density: 998.2 kgm3
• Viscosity: 0.001003 kgm-s

6. Boundaries:

• Inlet: Pressure = 10 Pa(Gauge Pressure)
• Outlet: Pressure= 0 Pa (Gauge Pressure)

7. Solution Methods: Coupled

8. Initialization:

• Method: Standard Initialization from the Inlet
• Number of Iteration: 250

OUTPUT:

Case 1: Lift = 10 mm:

2) Case 2: Lift = 20 mm:

3) Case 3: Lift = 30 mm:

4) Case 4: Lift = 40 mm:

5) Case 5: Lift = 50 mm:

6) Case 6: Lift = 60 mm:

7) Case 7: Lift = 70 mm:

8) Case 8: Lift = 80 mm:

Calculation:

Flow Factor(Kv):

Flow factor is the flow coefficient in the metric units. It is basically defined as the flow rate in cubic meters per hour for water at the constantr temperature of 16 degree celcius with the pressure drop of 1bar across teh valve.

Flow Coefficient (Cv):

Cv is the flow coefficient in the imperial units. It is basically defined as the flow rate in US Gallons per minute of water at a constant temperature of 60 degree farenheitand a pressure drop of 1 psi across teh vavle. It is used to determine the flow for various conditions and to select the proper valve for the various applications.

The flow coefficient can be defined as :

Compared Result:

S.No	Lift Height	Mass flow rate(outlet)	Pressure Inlet	Pressure outlet	Pressure Drop	Kv	Cv
1	10	0.1502	10	0.1785	8.45	53.51	62.14
2	20	0.315	10	0.4235	8.886	57.24	101.32
3	30	0.3345	10	1.005	8.89	136.45	158.9
4	40	0.4152	10	1.758	8.015	187.65	215.33
5	50	0.5168	10	2.458	7.98	235.4	220.2
6	60	0.6298	10	3.3358	6.12	284.56	328.9
7	70	0.7025	10	4.245	5.23	337.56	380.52
8	80	0.7123	10	5.012	4.58	388.15	452.15

RESULT

1. The negative mass flow rate at the outlet indicates that the fluid is flowing out of the system.

2. The mass flow rate increases with an increase in the lift of the spindle.

3. The flow factor and flow coefficient are proportional to each other.

CONCLUSION

The flow of water through a gate valve at different design points is accurately simulated using a parametric study. The values of the mass flow rate at the outlet are also calculated and analyzed for all the design points.

1. The low lift height refers to the higher pressure drop and thus low flow rate through the valve.
2. The negative mass flow is due to the mass exiting the outlet.
3. With the help of the parameters the solving time and effort can be reduced drastically.
4. Flow factor and coefficient increases as the mass flow rate through the valve increases.