Week 9 - Parametric study on Gate valve.

Aim- To perform a parametric study on a gate valve.

Objective-

• 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.

Explanation-

Gate valves work by inserting a rectangular gate or wedge into the path of a flowing fluid. They are operated by a threaded stem which 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 by lifting and descending the gate. A gate 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 the partially opened valves may experience vibration which may lead to excessive wear. A gate valve's main component is 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.

Geometry-

• Import the gear valve geometry into the space claim.

Hand wheel

Spinlde

Gate disc

Bottom part

Bonnet

• And using the “move” tool move the spindle 10mm up and this will be our baseline simulation constraint at which we enable a parameter so we can perform a parametric on the gear valve.

Section plane

• To set a parameter option, select the spindle on the bottom and enable the parameter by going to groups- set parameter.

• Then perform a “Pull” tool and expand the both sides of the inlet and outlet pipe.

• Perform a volumetric mesh by selecting the edges from where he fluid travels.

• Then supress the remaining geometry using “suppress for physics” option.

Mesh-

• Name the inlet and outlet faces and then perform a mesh with element size 6mm for a refine mesh.

• We gone with 6mm of element size because the elements number satisfy the student license constraints.

Setup-

• For this simulation we go with steady state analysis with pressure based type and velocity formulation as absolute. And we enable a gravity option at z= -9.81m/s and x=0, y=0 because gravity plays role on this simulation.

• We created material by using create material option and selecting “water” as fluid material.
• Then we assign cell zone conditions as water for the volume.
• Then for the boundary conditions-

Inlet- pressure inlet= 10 pascal(gauge pressure)

Outlet- pressure outlet

Wall – walls

• For model we use –

Viscous model – K-epsilon – Realizable – Scalable wall Function

• For this simulation we go with Standard Intialization with 250 interations.
• For plot – Definition - Flux definition - mass flow rate – Outlet

• Create a plane across and for contour definition – velocity contour
• Animate the contour for the animation.

Outcomes-

Mass flow rate

Velocity contour

Paramteric simulation-

A parametric study requires the following:

• The design Objective is set to Parametric Dimensions
• Parameters nominated for use in the simulation
• Parameter ranges identified
• Design criteria specified
• Various configurations generated

• We defined the DP0 and then run the simulation.
• Then we came to the parametric window and defined Dp1- Dp6 by the measurement of 20-70 mm. actually this dimension is for the clearance inside the valve to allow the fluid flow the measurement is of how much the gate disc is held above form the inner bottom surface of the gate valve.

We just have to mention the measurement and the parametric window automatically set up the case and runs the simulation.

Theory-

Flow coefficient(Cv)-The flow coefficient(Cv) 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.

Where,

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).

The metric equivalent flow factor(Kv) is calculated using metric units

Flow Factor(Kv) = 0.865* Cv(Flow coefficient)

Particle Pressure Drop(∆p) = Inlet particle pressure(pascal) – Outlet Particle Pressure(pascal)

S.l no	Lift Height	Mass flow rate outlet(kg/s)	Mass flow rate outlet(m3/hr)	Inlet pressure(Pascal)	outlet pressure(Pascal)	Pressure Drop(∆p)	Flow Factor(Kv)	Flow coefficient(Cv)
1	10	0.14986	0.53733	10	0.18652	9.81252	47.367	57.760
2	20	0.24055	0.86598	10	0.49875	9.50125	78.834	91.143
3	30	0.36038	1.29738	10	1.09581	8.90420	126.034	145.704
4	40	0.47589	1.71320	10	1.84586	8.15423	181.736	210.100
5	50	0.57416	2.06697	10	2.65152	7.34851	243.305	281.277
6	60	0.84683	3.04151	10	3.48541	6.51463	403.846	466.874
7	70	0.85343	3.07232	10	4.24853	5.75152	462.060	534.173

From the above trend plots, we can say that with the increase in the opening of the gate valve the mass flow rate also increases. Along with the mass flow rate, the flow coefficient and flow factor also increase.

In the parametric study of the gate valve, it was found that as the valve stopping is lifted gradually, the mass flow rate of the fluid, and hence the flow factor and flow coefficient increases.

Conclusions-

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. 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 to make changes. Using the parametric study method saves a lot of time in the simulations which require performing the same operations for different settings multiple times.