Week 9 - Parametric study on Gate valve.

Aim: - To perform a parametric study on the gate valve simulation by setting the opening from 10-80 percent.

Objective: -

1. To obtain mass flow rate at outlet for each opening setting.
2. To calculate the flow coefficient and flow factor for each opening and plot the graph.
3. To compare and discuss the results obtained from simulation.

Theory: -

Gate Valve –

A gate valve is a valve that opens by lifting a barrier (gate) out of the path of the fluid. It requires very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened. It is used to shut off the flow of liquids rather than for flow regulation.

Flow Coefficient (C_V) –

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 C_v (or flow-capacity rating of valve) can be expressed as:

`C_v=Q √((SG)/(∆P))`

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).

It is volume of water (in US gallons) at 60 °F that will flow per minute through a valve with a pressure drop of 1 psi across the valve.

Flow Factor (K_V) –

It is metric equivalent to flow Coefficient, commonly used everywhere else in the world with the exception of the United States. It is calculated using metric units:

`K_v=Q √((SG)/(∆P) )`

where:

Q is the flowrate (expressed in cubic meter per hour)

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

∆P is the differential pressure across the device (expressed in [bar]).

K_V can be calculated from C_V using the equation:

`C_v=0.865*K_v`

Case Setup: -

Geometry –

Gate valve Model

Gate Disc with spindle is used as parameter in providing lift simulating different opening positions

Fluid Volume

Different opening Setting mid-section view

10 % Opened 20 % Opened

30 % Opened 40 % Opened

50 % Opened 60 % Opened

70 % Opened 80 % Opened

Meshing –

Mesh for 10% opening

Mesh size = 6mm, Maximum up to 8mm

No. of nodes = 91460 No. of elements = 460382

Mesh Quality

Number of elements and nodes for ach opening setting

Opening percentage	Nodes	elements
10	91460	460382
20	91054	459007
30	90490	456546
40	89932	454051
50	89595	452123
60	89520	451725
70	89180	449906
80	88955	448678

Fluent setup –

• Pressure based solver and Absolute velocity is used.
• Steady-state Calculation is performed.
• Gravity is enabled in -ve Z axis
• Realizable K-ɛ turbulence model is used with Scalable wall function.
• Material of fluid used is water from fluent database.
• Pressure-inlet type boundary condition is use for inlet with 10 Pa gauge total pressure.
• Standard initialization is done computed from inlet.
• Number of iterations is 250.

Result: -

Residual Plot, Mass flow rate and velocity Contour for each opening setting -

10 % Opened

20 % Opened

30 % Opened

40 % Opened

50 % Opened

60 % Opened

70 % Opened

80 % Opened

Mass Flow Rate -

Flow Coefficient and Flow Factor

Conversion factor: 1 Pa = 1e-5 bar 1 kg/sec = 3.60 m³/hr

Opening percentage	Mass flow rate (m3/hour)	Flow Factor	Flow coefficient
10	0.53813	53.813	62.211
20	0.86249	86.249	99.709
30	1.30597	130.597	150.979
40	1.70395	170.395	196.988
50	2.02644	202.644	234.270
60	2.34684	234.684	271.311
70	2.76160	276.160	319.260
80	2.86603	286.603	331.333

Plot for Flow Coefficient and Flow Factor Vs Opening percentage

Conclusion: -

1. As lift increases Mass flow rate increases.
2. As flow coefficient is volume of water (in US gallons) at 60 °F that will flow per minute through a valve with a pressure drop of 1 psi across the valve, hence it is used in selecting the appropriate gate valve depending upon required pressure head and mass flow rate.
3. As lift increases Flow factor and flow coefficient increases as well.