Parametric Study of a Gate Valve using Ansys Fluent

OBJECTIVE

The aim of the project is to perform a parametric study on the gate value by varying the opening from 10% to 90%.

TASK

• 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.

Gate Valve

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 components of a gate valve are body, seat, gate, stem, hand wheel, bonnet and actuator. The main operation mechanism is very simple. When the handwheel is turned, it rotates the stem, which is translated into the vertical movement of a gate via threads.

PROCEDURE

• The Gate valve file is imported into the Space claim & --> move to move the gate disc by 10 mm & click on P icon to create it as a parameter.
• Design --> pull & choose the outer edges & provide the value as 800.
• Prepare --> volume extract select 3 edges to create a fluid volume.
• Volume --> volume --> update volume body in context so the changes in the gate valve reflect on the volume extract.
• Open mesh create two named selection i) Inlet ii) Outlet & create a baseline mesh for the file.

• Open fluent i) Solver - Pressure based type & steady-state. ii) Gravity = -9.81m/s^2 @ z. iii) Viscous model - k-epsilon - The turbulent model is chosen since the Reynolds number at inlet flow greater than 2000. iv) Add water material for fluid flow & change the material in cell zones & delete the air material. v) Boundary conditions at the inlet are set to pressure & gauge value was set to 10 Pa. vi) Standard solver --> options --> compute from --> Inlet & intialise the solver. vii) Definition --> mass flow rate --> outlet --> report file & plot & choose create output parameter. viii) Create a plane by providing the coordinates (0,-0.9185,-0.2172793), (0,-0.9185,0.02), (0,0.9185,0.02) ix) Create velocity contour on the plane & also animation files for the contour & run the simulation for 250 iterations.

Scale Residuals Plot

Mass flow rate

RESULTS

Case 1 - Lift -10mm.

Velocity contour

Mass flow rate

Case 2 - Lift -15mm.

Velocity contour

Mass flow rate

Case 3 - Lift -20mm.

Velocity contour

Mass flow rate

Case 4 - Lift -25mm.

Velocity contour

Mass flow rate

Case 5 - Lift -30mm.

Velocity contour

Mass flow rate

Case 6 - Lift -35mm.

Velocity contour

Mass flow rate

Parametric Study Results

Mass Flow rate @ Outlet

Case 2 alone failed the volume flow rate is calculated from the mass flow rate divided by density.

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 C_v can be expressed as :

where:

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

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

ΔP is the pressure drop across the valve (psi)

i) Cv = 2.3547240059 * (1/0.00145038)^0.5

= 61.89.

	Flow coefficient Cv
Lift value(mm)	Pressure drop (psi)	Vol flow rate (gal/min)	Flow Coefficient
10	0.00145038	2.354724	61.82998043
15	0.00145038	2.986028	78.40666372
20	0.00145038	3.784582	99.37497176
25	0.00145038	4.7167392	123.8514121
30	0.00145038	5.7709442	151.5325647
35	0.00145038	6.7775982	177.9651306

Chart

Flow factor

The flow factor is calculated using metric units & It describes the relationship between the pressure drop across an orifice valve

where

K_v is the flow factor

Q is the flow rate ( ).

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

∆P is the differential pressure across the device [bar].

i) Kv = 0.533844 * (1/ 10-4)^0.5

= 53.3844.

	Flow factor Kv
Lift value(mm)	Pressure drop (bar)	Vol flow rate (m3/hr)	Flow Coefficient
10	1.00E-04	0.533844	53.3844
15	1.00E-04	0.678201	67.8201
20	1.00E-04	0.859572	85.9572
25	1.00E-04	1.071288	107.1288
30	1.00E-04	1.310724	131.0724
35	1.00E-04	1.53936	153.936

Chart

K_v can be calculated from C_v using the equation:

INFERENCE

The value lift is set as a parameter & the study is done by varying the lift value by 5mm. The negative sign is due to the flow of the fluid out of the gate valve & the mass flow rate increases with the increase in the valve opening which is basic physics. The mass flow rate doesn\'t increase by any factor it mainly depends on the geometry of the gate valve.