Week 9 - Parametric study on Gate valve.

Objectives of the Parametric study on gate valve: 

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. 

Theory: Gate valves work by inserting a rectangular gate into the path of flowing fluid .They are operated bya threaded stem which connects the actuator (hand wheel or rotor) to the stem of the gate. If the valve has a rising stem its position can be seen just by looking at the position of the stem. 

When it is fully open, gate valve has no any restrictions in the path of fluid flow and has very low pressure drop. If the fluid is more viscous, special type of gate valve known as knife gate valve is used. 

But, normally gate valves are not used very much beacuse flow rate of fluid is not proportional to the amount that the valve is open. Partially open gate valve may suffer from vibration in which the valve may move from its assigned position. Also the gate and seat may be subject to excessive wear if valve is partially open. 

Some of the important terms: 

Flow coefficient, Cv

The flow coefficint of the device is a relative measure of its efficiency at allowing fluid  flow. It describes the relationship between the pressure drop across the orifice valve or other assembly and the corrosponding flow rate. 

Mathematically , flow coefficint of flow capacity rating of valve can be expressed as below, 

where Q is rate fo flow, US gallons/minute

SG is specific gravity of fluid, 1 for water

delta P is pressure drop across valve , psi

Flow factor, Kv

Kv is flow factor, in m3/hr 

Q is flow rate ,m3/hr 

SG is specific gravity of fluid, 1 for water 

delta P is pressure drop across valve , bars

Simulation steps 

step 1: Geometry loading 

Let us import geometry step file into spaceClaim. 

1. First we have to input an initial lift of 10mm (10% of the lift) , for that Move option in y-direction is selected and 10 mm is given. 

Then it is parameterised by pressing P button next to input given for the lift or it can also be created in the groups tab.

2. Then the fluid volume is extracted using edge selection, left and right side part is elongated upto 800mm on outlet and inlet to increase teh fluid volume hence flow can be seen in detail. 

3.  All solid parts are suppressed for physics. 

step 2: Meshing 

Mesh size: 8 mm by adding sizing and globally 20mm 

Mesh Quality: 

1. Element quality

2. Skewness

3. Orthogonal quality

step 3: Set up

a) Gravity is enabled in z direction as -9.81 m/s2.

b) Steady state analysis is chosen. 

c) Material as water is added and air is deleted. 

d) Inlet boundary condition is changed from velocity inlet to pressure inlet and value of 10Pa is given which is acceptable value for pipe flow. 

e) Viscous model k-Epsilon is slecetd with Realizable and scalable wall funcitons as the flow is turbulent. 

f) For report definitions , mass flow rate at outlet is monitored. 

g) Plane is created to create velocity and pressure contours. 

 Case 1) Lift height = 10% (10 mm) 

case 2) Lift height 20% (20 mm)

case 3) Lift height =30% (30 mm)

case 4) Lift height 40 % (40 mm) 

case 5) Lift height 50% (50 mm) 

case 6) Lift height 60 % (60 mm) 

case 7_) Lift height 70 % (70 mm) 

case 8) Lift height 80% (80 mm) 

For flow factor calculation, the pressure is converted into Pascals from Bar. 

10Pa = 0.0001 bar 

as CG os water is 1, 

Conclusion: 

a) We found the mass flow rates at different levels of lift height. (10 to 80%)

b) Found flow factor and flow coefficient for all cases. 

c) Contours showing pressure and velocity variataion are plotred.