Gate Valve Parametric Study

A gate valve is a valve that opens by lifting a barrier out of the path of the fluid. The gate valve operates when the disc inside the valve is lifted from the patch of flow and obstructs the flow of fluid when the disc returnsto its position. Gate valves are available in many options including various sizes, materials, temperature and pressure ratings, and gate and bonnet designs. They are generally used for fully open or fully closed service and not used for regulating flow. Here we are conducting a simulation on the gate valve by varying the degree to which the gate valve is opened.

Objective:

• To conduct a parametric study on a gate valve simulation.
• To obtain mass flow rates by changing the degree of opening of the gate valve.
• To calculate the flow coefficient/flow factor for the different degrees of opening and discussing the results.

The simulation was to be carried out from 10% to 80% gate valve opening.

Flow co-efficient (`C_v`): It describes the relationship between flow rate and pressure drop across a valve. It measures the efficiency of a device at allowing fluid to flow.

Flow coefficient is given by;

`C_v= Qsqrt((SG)/(DeltaP))`

Where, Q= volumetric flow rate(US gallons per minute)

SG= Specific gravity( water = 1)

`DeltaP`= Pressure drop acrossthe valve(psi)

Flow factor (`K_v`) : Fow factor is equivalent to flow co-efficient but in metric units.

Flow factor can be found from flow co-efficient from the equation;

`K_v = 0.865*C_v`

Geometry:

The gate valve geometry shown below has the following components;

1. Pipe section
2. bonnet
3. Spindle
4. Hand wheel
5. Gate disc

Pipe inner diameter = 100 mm

A closer look at the gate disc is shown below;

The gate disc was moved upwards by 10mm using move tool to simulate opening of the valve and it was set as a parameter. A group was created by this for controlling the gate disc lift.

The fluid volume was extracted from the geometry and suppressed all the solid parts for the simulation.

Meshing:

Meshing was done on the geometry with max element size set as 5.5mm and total cell count being 456403

Mesh element metrics:

SETUP:

Absolute pressure based steady state solver was used and gravity was enabled as well. K-epsilon realizable viscous model with scalabe wall functions were chosen for the simulation to capture the fluid properties at the gate disc region clearly. The fluid chosen for flow the simulation was water.

Boundary conditions:

1. Inlet- Pressure inlet- 1psi
2. outlet- pressure outlet- 0 psi

Solution:

The solution was standard inizialized from inlet. Reports for mass flow rates were created and output parameter for the same was set active. Later,ran the simulation for 700 iterations.After running simulation for first design point(10% opening of gate valve), the simulation for other design points( till 80% gate valve opening) was carried out by updating for the design points from the parameters section.

• Solution at 10% opening of valve:

Residuals:

Velocity contour:

• Solution at 80% opening of valve:

Residuals:

Velocity contour:

The table below shows the output obtained by parametric study of gate valve. The gate disc was lifted from 10% to 80%( 10 mm to 80 mm).

Observations:

Design point	Gate valve opening(%)	Mass Flow Rate(kg/s)	Volumetric flow rate(Gallons/min)	Flow Co-efficient	Flow factor
1	10	-4.1029766	65.15068123	65.15068123	56.35533926
2	20	-6.6606913	105.7643311	105.7643311	91.48614641
3	30	-10.033902	159.3271457	159.3271457	137.8179811
4	40	-13.019062	206.7281491	206.7281491	178.819849
5	50	-15.520556	246.4490771	246.4490771	213.1784517
6	60	-17.792402	282.5234516	282.5234516	244.3827857
7	70	-19.179455	304.5483025	304.5483025	263.4342817
8	80	-21.079949	334.7260225	334.7260225	289.5380094

• Mass flow rate was shown as negative because, mass/ fluid was exiting the body.
• Volumetric flow rate was found by dividing mass flow rate by density and converting to gallons per minute.
• Flow co-efficient was equal to volumetirc flow rate as;

Pressure drop = 1 psi

Specific gravity of water = 1

Hence, `C_v = Q` which is volumetric flow rate in gallons per minute.

• Flow factor was found by multiplying flow co-efficient by 0.865

• Gate valve opening ve mass flow rate:

• Gate valve opening vs Flow co-efficient / Flow factor:

Inferences:

• As expected, mass flow rate of fluid through valve keeps increasing while opening the valve.
• The flow coefficient and flow factor are proportional to mass flow rate due to the fact that they measure the efficiency of a valve at allowing a fluid to flow.
• Hence, a higher flow co-efficient or flow rate for a device implies the fluid mass flow rate will be higher for the said device.