Week 9 - Parametric study on Gate valve.

AIM: To perform a parametric study on a gate valve simulation by setting the opening from 10 % to 80%.

OBJECTIVE:

1.To simulate the flow of fluid through a gate valve.

2.To obtain the mass flow rates at the outlet for each design point.

3.To calculate the flow coefficient and flow factor for each opening and plot the graph.

4.Discuss the results of the mass flow rate and flow coefficient.

DESCRIPTION:

A Gate valve also known as 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 restict 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 the pressure on the sealing surface.

Main components of the gate valve are 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 the gate disc via threads.They are considered multi-turn valves as it makes more than one 360 degree turn 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.

PARAMETRIC STUDY:

One of the best ways to get value out of yoour simulation is to do parametric analysis with very little marginal work with a model which can be parameterized to simulate scenarios limited only by computational time and resources. As you move forward in your design you can access the impact that is changing the certain parameters accordingly to the design criteria.The parameters can include dimensional parameters. Parametricc studies sllow you to nominate parameters for evaluation, define the parameter range, specify the design constraints and analyse the results of each parameter variation.

A parametric study requires the following

1.Design objective is set to parametric dimensions.

2.Parameters nominated for use in the simulation

3.Design criteria specified

4.Various configurations generated.

FLOW COEFFICIENT

The flow coefficient of a device is 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 or flow capacity rating Cv can be expressed as

`Cv = Q sqrt((SG)/(DeltaP))`

Where Q is the rate of flow (gallons per minute)

SG is the specific gravity of fluid (for water =1)

`DeltaP` is the pressure drop across the valve expressed in psi.

10 Pa = 0.00145038 psi

The use of 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 modelling the flow of liquids, gases and steam using the discharge coefficient.

FLOW FACTOR:

The metric equivalent factor Kv commonly used in europe and Aisa is calculated using metric units

`Kv = Q sqrt((SG)/(DeltaP)`

Kv can be calculated from Cv using the equation as given below

Kv = 0.865Cv

The Kv factor of the valve indicates, The water flow m3/h at a pressure drop across the valve of 1kgf/cm2 when the valve is completely open.

Opening the space claim and opening the Gate valve model

The model looks as follows

First we will do for the case without parametric study

Now hiding the bottom surface and then gate disc is visible and using move tool with component selection and move the gate disc in upward z direction for 10mm

Now extracting the fluid volume from prepare>volume extract>edges select inlet and outlet and part under bonet

It looks as follows after extraction

Next using the pull tool pulling the inlet by 800mm and for output also 800mm

suppressing for physics and hiding them the solid volumes

Now we are left with only the fluid volume

Now going for meshing

Generating a generaal mesh

Next is naming the parts

Next opening up the Ansys fluent

Using the pressure based steady state with gravity acting in -z direction

For materials using fluent data base water liquid is choosen

Next for cell zone conditions for fluid we change the following to water liquid

For boundary conditions changing the inlet to pressure based and giving as 10Pa

Other boundary conditions are set to as usual, outlet set to pressure based, wall set to wall, and interior volume set to interior

calculating with the velocity as below the Reynolds number we get Re>2000 i.e turbulent flow so we use k-epsilon viscous model

In above image we can see that the velocity at the inlet will be 0.1415488 m/s in Y-direction

So for reynolds number `rho` = 998.2 Kg/m3

V= 0.1415488 m/s

D = 0.1 m

`Re = (rhoVD)/(mu)`

Re = 998.2x0.1415488x0.1/0.001003

Re = 14087.14

Here reynolds number is >2000 so flow is turbulent.

creating the mass flow rate for outlet

creating a plane for viewing the velocity contours

SIMULATION FOR GATE DISC LIFT OF 10MM

Mass Flow Rate [kg/s]

-------------------------------- -------------------

outlet -0.10154317

PROCEDURE FOR PARAMETRIC VIEW

The objective of this parametric study is to study the mass flow rate at the outlet of the gate valve during different levels of the lift of the gate disc.

SO opening up the space claim

By using move tool with component selection moving it by 10mm and creating a parametric view

After updating the volume with context we see the volume is filled

Then pulling both the faces of inlet and outlet for 800mm and then updating the volume with context we see the volume filled up

Next is goimg for meshing

Using the finer mesh of 6mm

Naming the parts

Opening up the fluent with the same setting and setting the parametric settings for mass flow rate at outlet

SIMULATION FOR 20MM LIFT OF GATE DISC

The residuals are

The mass flow rate at inlet is

The mass flow rate at outlet is

The velocity contour is

FOR 30MM LIFT OF GATE DISC SIMULATION

The residuals are

The mass flow rate at inlet is

The mass flow rate at outlet is

The velocity contour is

FOR 40MM LIFT OF GATE DISC SIMULATION

The residuals are

The mass flow rate at inlet is

The mass flow rate at outlet is

The velocity contour are

FOR 50MM LIFT OF GATE DISC SIMULATION

The residuals are

The mass flow rate at outlet is

The velocity contour is

FOR 60MM LIFT OF GATE DISC SIMULATION

The residuals are

The mass flow rate at outlet is

The velocity contour is

FOR 70MM LIFT OF GATE DISC SIMULATION

The residuals are

The mass flow rate at outlet is

The velocity contours are

FOR 80MM LIFT OF GATE DISC SIMULATION

The mass flow rate outlet is

The velocity contour is

The parametric table contents are

We have done simulation for 10mm lift without parametric view and for the next case of 20mm we used the parametric view, so the below table lifts for group1 from DP0 to DP10 is with +10mm in every case so the table contents are starting from 20mm to 90mm lift.

RESULTS

LIFT in mm	FLOW RATE (Q kg/s)	FLOW RATE (Q gpm)	FLOW COEFFICIENT Cv	FLOW FACTOR Kv
10	-0.10155	1.61	42.26	36.55
20	-0.14443	2.29	60.11	51.99
30	-0.22739	3.6	94.5	81.74
40	-0.34314	5.44	142.8	123.52
50	-0.46180	7.32	192.15	166.20
60	-0.56618	8.97	235.46	203.67
70	-0.65501	10.38	272.47	235.68
80	-0.71763	11.37	298.46	258.18

PLOT FOR Cv VS Kv

CONCLUSION:

Mass flow rate gradually increases as the lift of gate disc is increased.

The variation of flow coefficient and flow factor with the opening of the valve is studied by using parametric method.

Parametric study is time reducing option when studying the effects of changes of certain parameters of a system.

Flow coefficient plays an important role in the selection of valve and sizing of a valve, so calculating it is necessary.

Flow coefficient also helps in computing the efficiency of the system and the effectt of pressure on the system.