Week 9 - Parametric study on Gate valve.

Parametric study on Gate valve

Aim:

To perform a parametric study on the Gate valve.

Objective:

1. Simulate the flow of fluid through a gate valve.

2. Perform the parametric study on the gate valve by setting design points corresponding to the positions of the lift of the spindle.

3. Calculate the mass flow rate corresponding to all the design points

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).

Theory:

Gate valves work by inserting a rectangular gate or wedge into the path of a flowing fluid. They are operated by a threaded stem that connects the actuator (generally a hand wheel or motor) to the stem of the gate. If the valve has a rising stem its position can be seen just by looking at the position of the stem. A gate valve is used to control the fluid flow through lifting and descending the gate. A gate's distinct feature is to provide an unobstructed passageway, which includes minimal pressure loss over the valve.

When the gate is fully opened there is no restriction to the flow hence the pressure drop is low comparatively. Generally, the gate valve are fully closed or fully open as a partially opened valves may experience vibration which may lead to excessive wear. A gate valve's main component is the body, seat, gate, stem, bonnet, and actuator. the primary mechanism is straight forward where the handwheel is rotated to move the gate up and down via threads. they require more than a 360-degree turn to fully open the valve.

Gate valves tend to be slightly cheaper than ball valves of the same size and quality. They are slower in actuation than quarter-turn valves and are for applications where valve operation is infrequent, such as isolating valves. Gate valves should be used either fully open or fully closed, not to regulate flow. Automated gate valves exist with either an electric or pneumatic actuator, but a manual gate valve is cost-effective since they have infrequent usage. Gate valves are widely used for all types of applications and are suitable for both above-ground and underground installation. They are suitable for most fluids including steam, water, oil, and gas, etc.

Functioning Principle:

The main Components of a Gate Valve are the body, seat, stem, bonnet, and actuator. The main operation mechanism is very simple. When the hand wheel is turned, it rotates the fluid, which is translated into the vertical movement of a Gate Disc via threads. They are considered multi-turn valves as it makes more than one 360⁰ turns to fully open/close the valve. When the Gate is lifted from the path of the flow, the valve opens and when it returns to its closed position, it seals the bore resulting in a full closure of the valve.

Applications of Gate Valve:

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.

Parametric Study:

One of the best ways to get value out of your simulation is to do a parametric analysis. With very little marginal work a completed model can be parameterized to simulate scenarios limited only by your computational time and resources. As you move forward in your design, you can assess the impact that changing certain parameters can have on the design. The parameters can include dimensional parameters. 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

When you have the configurations generated you can then evaluate your simulation. You can further refine the parameters or design constraints until satisfied with the results.Once you determine that a configuration satisfies your design needs, you are able to promote that configuration back to the model as a CAD edit. You are prompted whether to make changes.

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:

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).

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:

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 kgf /cm2 when the valve is completely open.

SIMULATION PROCEDURE:

GEOMETRY:

• The geometry is imported into SpaceClaim.

• Then the gate disc component is selected and given a lift of 10mm by using the move tool available in the Ansys SpaceClaim and the lift is parameterized.

• Then the inlet and outlet faces are pulled up to a distance of 800mm.

• Then the fluid volume is extracted from the model by using the volume extraction tool available in Ansys Spaceclaim.

• Then the solid components are suppressed for physics.
• The final geometry obtained will look like the image shown below

MESHING:

• The inlet and outlet named selection are created for the left and right faces of the model as shown below.

• The mesh size of 10mm is applied to the model.

• The final meshed model will look like the image shown below.

SETUP:

GENERAL:

• Analysis type – steady state
• Solver – pressure based
• Gravity – 9.81m/s2 in z-direction

MODEL:

• Viscous – realizable k-epsilon with scalable wall function

MATERIAL:

• Fluid – water liquid

CELL ZONE:

• Fluid - water-liquid

BOUNDARY CONDITION:

INLET:

• Pressure inlet – gauge total pressure: 10 pa

OUTLET:

• Pressure outlet – gauge total pressure : 0 pa

WALL:

• Wall – no slip stationary wall.

INTERIOR:

• Interior

INITIALIZATION:

Standard initialization.

The simulation is run for 600 iterations.

RESULTS:

CASE 1 – LIFT = 10MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

PRESSURE CONTOUR:

MASS FLOW RATE:

VELOCITY VECTOR:

VELOCITY STREAMLINE:

CASE 2 – LIFT = 20MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

MASS FLOW RATE:

CASE 3 – LIFT = 30MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

PRESSURE CONTOUR:

MASS FLOW RATE:

CASE 4 – LIFT = 40MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

MASS FLOW RATE:

CASE 5 – LIFT = 50MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

MASS FLOW RATE:

CASE 6 – LIFT = 60MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

MASS FLOW RATE:

CASE 7 – LIFT = 70MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

MASS FLOW RATE:

CASE 8 – LIFT = 80MM:

SECTIONAL VIEW:

RESIDUAL:

VELOCITY CONTOUR:

MASS FLOW RATE:

MASS FLOW RATE PARAMETRIC RESULTS:

Flow coefficient:

Pressure Drop = Total pressure at the inlet - Total pressure at the outlet.

Therefore, = 10 - 0 = 10 Pa

`C_v = Q⋅sqrt (S G)/( Δ P)`

Conclusion:

Disc Lift	Mass Flow Rate	Flow Coefficient	Flow Factor
10 mm	0.14976	84.2987	72.9183
20 mm	0.23915	134.7027	116.5178
30 mm	0.36216	203.7608	176.253
40 mm	0.47264	266.0268	230.1131
50 mm	0.56986	320.8708	277.5532
60 mm	0.65795	367.8724	315.6146
70 mm	0.69473	390.9793	338.197
80 mm	0.78115	439.81	380.43

• As the disc lift height increases, the value of the flow coefficient and flow factor increases.
• The value of pressure below the discs decreases as the resistance to flow decreases.
• A higher value of the Flow coefficient indicates lower resistance to the flow and a lower Flow coefficient indicates higher resistance to flow.
• Flow coefficient and pressure drop are essential parameters for designing the valve and could be a great justification for the material selection of the valve.
• The mass flow rate of water increases with an increase in disc lift height, as more water can flow through the gap and there is less resistance.