Gate Valve Parametric Study

AIM :- To perform a parametric study on the gate valve model and find out the flow coefficient and flow factor for each design point.

OBJECTIVES :-

For this challenge we have to 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 :-

Gate valve are machine elements which are commonly used to control the flow of volatile, often toxic, liquids and gasses and keep them from being emmited into the atmosphere or spilled into the ground or into the water. This gate valve is widely used in various industies like refineries, petro chemical complexes, fertiliser plants, power generation plants (hydro-electric, thermal and nuclear) steel plant and allied industries etc. for a various processes. This paper gives basic methodology of gate valve body design by using CAD technologies and FEA at maximum operating pressure. The main purpose is structural analysis tobe carried out for determining stresses and strain developed in the valve body.

The first design of a product that has been in the head of the engineers is illustrated in computers and then produced by computer aided machines. The analysis processes of a product of which solid modelling have been accomplished can be carried out by ANSYS and similar analysis programs in digital enviornment, before starting manufacturing. These processes gives the companies flexibility in the development of a new product by providing design capability with minimum cost and minimum waste of time. ANSYS programs, which has been used in this study, can make the analysis of the substances in many subjects including static, dynamic, thermal, harmonic and electromagnetic.

Following are the basic parts of the gate valve parametric study-

1. Gate disc :-

2. Hand wheel :-

3. Spindle :-

4. Bonnet :-

5. Bottom part :-

6. Gate valve assembly :-

This is the assembly of all parts which called parametric gate valve.

QUE.1) Perform a parametric study on the gate valve simulation by setting the opening from 10% to 80%.

ANS.:- I created here total 5 different cases within given range and find out mass flow rate, velocity contours and other different quanities as related. For all cases only meshing at same element size i.e. 10mm but, there have different number of nodes and elements. I describe all the cases are given below-

Here, total diameter = 100mm.

CASE-1 :-

For spindle inside the gate disc = 10mm

Element size = 10mm

Total Number of Elements = 193208

Total number of Nodes = 4032

1. Simple Geometry :-

This is the spaceclaim geometry which get after pulling gate valve. Here,first off all at bottom spindle move 10mm inside the gate valve by using move tool and then select respected part by using prepare -> volume extract and then gate valve pull 800mm outside. and then supress all the part and share the topology into the mesh. Here group 1 (i.e. parameter) are created when gate valve moving.

2. Volume geometry :-

This is the volume geometry \'created after selecting volume, right click on it and click on \'update volume body in context\' we get the respected part as shown above.

3. Section cut geometry :-

This is the section cut geometry after cutting along X-direction. There have not section in gate valve.

4. Mesh :-

This is the meshing at element size = 10mm which is refined mesh we get number of nodes and number of elements as shown in left side at bottom.

5. Cell zone :-

This is the cell zone in set up popup. There manual material select i. e. water liquid after editing material as shown above diagram.

6. Cut plane :-

This is the cut plane where select point and normal method and select default plane as shown above diagram.

7. Mass flow rate plot :-

This is the mass flow rate plot vs each iterations. Here increase the value of mass flow rate with respect to each iterations.

8. Mass flow rate at outlet :-

This is the mass flow rate value at outlet in kg/second.

9. Material selection :-

Here material should be selected from fluent database and copy there for pasting in Fluent fluid materials.

10. Pressure contours :-

This is the pressure contours which is in given range.

11. Pressure at inlet :-

Here inlet pressure must be added i.e. 10 pascals.

12. Solution controls :-

This is the solution controls where shown some basic quantity values.

13. Solution initialization :-

This is the solution initialization where choose standerd initialization methods for getting exact mass flow rate. For calculating Raynold number we get here velocity in Y-directions and compute from inlet.

14. Solution Methods :-

This is the solution methods where selecting coupled scheme and second order upwind momentum.

15. Velocity contours :-

This is the velocity contours within given range where minimum velocity = 0 m/s and maximum velocity = 0.143 m/s.

16. Viscous Model :-

This is the viscous model which is \'k-epsilon\' in which Realizable near Scalable Wall functions.

17. Scaled Residuals Plot :-

This is scaled residuals plot from which we conclude various residuals.

18. Converged solution :-

This is the converged solution at which solution must be converged and stop at specific point.

19. Pressure at wall contours :-

This is the pressure contours on wall in results in the range of -4.702 to 9.99 Pascals.

20. Velocity at wall contours :-

This is the velocity contours at wall within the range of 0 to 0.1146 m/s.

21. Eddy viscosity at wall contours :-

This is the Eddy viscosity contours at wall within the given range from 1.975e-4 to 2.931e-2.

22. Report :-

This is the report file in which given domain, boundaries, number of nodes and elements...etc.

23. Animation File :-

This is the animation file for the given solutions.

Same as above case I calculated some other casaes which are describe through plots and figures as shown below-

CASE-2 :-

For spindle inside the gate disc = 20mm

Element size = 10mm

Total Number of elements = 196365

Total Number of Nodes = 40551

1. Section Cut Geometry :-

2. Mesh :-

3. Mass flow rate at outlet :-

4. Converged solution :-

5. Velocity contours :-

6. Scaled residuals :-

7. Report :-

CASE-3 :-

For spinle inside the gate disc = 40mm

Element size = 10mm

Total number of elements = 203421

Total Number of Nodes = 42233

1. Section cut geometry :-

2. Space claim geometry :-

3. Mesh :-

4. Converged solution :-

5. Mass flow rate plot :-

6. Scaled residuals :-

7. Report :-

CASE-4 :-

For spindle inside the gate disc = 60mm

Element size = 60mm

Total number of elements = 215195

Total number of Nodes = 43158

1. Section cut geometry :-

2. Mesh :-

3. Converged solution :-

4. Mass flow rate plot :-

5. Scaled residuals :-

6. Pressure at wall contours :-

7. velocity at wall contours :-

8. Eddy viscosity at wall contours :-

9. Report :-

CASE-5 :-

For spindle inside the gate disc = 80mm

Element size = 10mm

Total Number of elements = 219885

Total number of nodes = 44558

1. Section cut geometry :-

2. Mesh :-

3. Converged solution :-

4. Mass flow rate plot :-

5. Scaled residuals plot :-

6. Pressure at wall contours :-

7. Velocity at wall contours :-

8. Eddy viscosity at wall :-

9. Report :-

QUE.2) Calculate the flow coefficient and flow factor for each opening and plot the graph .

ANS.:- 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.

Mathmatically, the flow coefficient Cv (or flow capacity rating of valve) can be expressed as-

Cv = rate of flow*sqrt(specific gravity/pressure drop)

In more practical terms, the flow coefficient Cv is the volume of water at 60F that will flow per minute through a valve with a pressure drop of 1psi across the valve.

The use of the flow coefficient offers a standerd method of comparing valve capacities and sizing valves for specific applications that is widely accepted by industry. The general definitions of the flow coefficient can be expanded into equations modelling the flow of liquids, gasses and stream using the discharge coefficient.

For gas flow in a pneumatic system the Cv for the same assembly can be used with a more complex equations. Absolute pressures must be used for a gas rather than simply differential pressure.

For air flow at room temperature, when the outlet pressure is less than 1/2 the absolute inlet pressure, the flow becomes quite simple with Cv =1 and 200 psi at inlet pressure the flow is 100 standerd cubic feet per minute (scfm). The flow is proportional to the absolute inlet pressure, so the flow in scfm would equal the Cv flow coefficient if the inlet pressure were reduced to 2 psi and the outlet were connected to a vaccum with less than 1 psi absolute pressure.

Flow Factor :- The metric equivalent flow factor (Kv; commenly used in Europe and Asia) is calculated using metric units -

Kv = flow rate*sqrt(specific gravity/pressure drop)

Kv can be calculated from Cv using the equations-

Kv = 0.865*Cv

The Kv factor or value as it is also called is defined in VDI/VDE Richtlinien No. 2173. A simplified version of the definition is: the Kv factor of a valve indicates \' The water flow in m^3/h \', at a pressure drop across the valve of 1 kg/cm^2 when the valve is completely open. The complete definition also says that the flow medium must have a specific gravity of 1000 kg/m^3 and a kinematic viscosity of 10^-6 m^2/s. e.g. water.

By using the above formulae I calculated the flow coefficient and flow factor as given below-

Given quantities are-

Specific gravity of water =1

Pressure drop = 10 pascal

Velocity = 0.1415488 m/s

For case-1,

Inlet diameter = (100 - 10) = 90mm = 0.09m

Area = pi*radius^2 = 3.14*0.045*0.045 = 0.0063585 m^2.

Flow rate = Q = Area*velocity = 0.0063585*0.1415488 = 0.0009 m^3/sec

Flow Coefficient = Cv = 0.0009 * sqrt(1/10) = 0.0002846.

Flow factor = Kv = 0.865 * 0.0002846 = 0.000246 m^3/(hr*bar^0.5).

For case-2,

Inlet diameter = (100-20) 80mm = 0.08m

Area = pi * radius^2 = 3.14*0.04*0.04 = 0.005 m^2.

Flow rate = Q = Area*velocity = 0.005*0.1415488 = 0.00071 m^3/sec

Flow coefficient = Cv = 0.00071*sqrt(1/10) = 0.0002247

Flow factor = Kv = 0.865*Cv = 0.0002 m^3/(hr*bar^0.5).

For case-3,

Inlet diameter = (100-40) = 60mm = 0.06m

Area = pi*radius^2 = 3.14*0.03*0.03 = 0.002826 m^2

Flow rate = Q = Area*velocity = 0.002826*0.1415488 = 0.0004 m^3/sec

Flow coefficient = Cv = 0.0004*sqrt(1/10) = 0.0001264

Flow factor = Kv = 0.865*Cv = 0.000109 m^3/(hr*bar^0.5).

For case-4,

Inlet diameter = (100-60) = 40mm = 0.04m

Area = pi*radius^2 = 3.14*0.02*0.02 = 0.001256 m^2

Flow rate =Q = Area*velocity = 0.001256*0.1415488 = 0.000178 m^3/sec

Flow coefficient = Cv = 0.000178*sqrt(1/10) = 0.000056

Flow factor =Kv = 0.865*Cv = 0.0000486 m^3/(hr*bar^0.5)

For case-5,

Inlet diameter = (100-80) = 20mm = 0.02m

Area = pi*radius^2 = 3.14*0.01*0.01 = 0.000314 m^2

Flow rate = Q = Area*velocity = 0.000314*0.1415488 = 0.0000444 m^3/sec

Flow coefficient = Cv = 0.0000444*sqrt(1/10) = 0.000014

Flow factor = Kv = 0865*Cv = 0.000012 m^3/(hr*bar^0.5).

RESULTS :-

QUE.3) Discuss the results for mass flow rate and flow coefficient.

ANS.:-

Mass Flow rate :- The mass flow rate is the mass of a liquid substance passing per unit time. In other words, Mass flow rate is defined as the rate of movement of liquid mass through a unit area. The mass flow is directly depended on the density, velocity of the liquid and area of cross section. It is the movement of mass per unit time. The mass flow is denoted by \'m\' and the unit in kg/sec.

The mass flow rate is given by-

m = rho * V * A.

rho -> density of fluid

V -> velocity of the liquid and

A -> Area of cross section

I calculated here both mass flow rate and flow coefficient for each case are-

Here I calculated mass flow rate at each case of outlet, when opening is minimum then mass flow rate is more and when opening is maximum then mass flow rate is minimum ( here, opening means spindle contact with the gate valve). Beacause mass flow rate is depends on the area of opening i.e. cross section. So, all quantities are same only diameter is decreases and thats why mass flow rate decreases.

In other words, as opening decreases flow coefficient also decreases because, it also depends on the cross sectional area of gate valve.

CONCLUSIONS :-

In this way I calculated Mass flow rate, flow coefficient and flow factor in the given range from 10% to 80%, and I concluded that as the opening range increases we get less mass flow rate because velocity from inlet to outlet decreases. Parametric gate valve is most important and useful device in the Industrial area.

Meshing refining also plays an important role in parametric study, because as mesh refining increases we get converged solution at faster rate and the other results also very schematic. Also attached animation file which shows the velocity contours.

So, in this way I calculated every respected and relative quantities which describes the exact and detailed overview of parametric study of gate valve.