2. Tony Y. Bougebrayel, PE, PhD
Computational Fluid Dynamic (CFD) Analysis of Gas and Liquid Flow Through a Modular Sample System
Tony Y. Bougebrayel, PE, PhD
John J. Wawrowski
Swagelok
Solon, Ohio
IFPAC 2003
Scottsdale, Az
January 21-24, 2003

3. Agenda Objective Cv, K Factor CFD Background
MPC - CFD Model Description, Procedure
Results
Conclusions

4. Objectives
Evaluate the flow capacity (Cv) for a three-position Swagelok MPC substrate flow component
Investigate the effects of using different surface-mount components on the total system Cv
Determine an analytical method for predicting the total system Cv
Investigate the effect of the fluid type on the pressure drop through a substrate flow component
Determine the pressure required to flow a liquid sample through a Swagelok MPC system

5. Cv and K Factors The Cv Approach The K Approach
What causes Cv and K and how are they determined?
How do they relate to the MPC?

6. The Cv Approach Cv: Flow capacity (component) For Newtonian Liquids:
Through control components: q = N1 * Fp * Cv * (Δp / Gf)1/2 (ISA 75.01)
Through straight pipes: Δp = f L  Q2 / d5 (Darcy’s)
For Gases:
Through control components: q = N7 * Fp * Cv * p1 * Y * [x / (Gg T1 Z)]1/ (ISA 75.01)
For Low pressure drop: 1.0 < Y < 2/3, (p1 2p2) and Y = 1 – x / (3Fk xt)
For high pressure flow (choked flow, p1>2p2): Y= 2/3, xt=.5 and q = N7 * Fp * Cv * p1*.471*[1 / T1 Z)]1/2

7. The K Approach K-Factor: Resistance to flow (system)
Head loss through a pipe, valve, or fitting:
hL = K v2 / 2g where: K = f L / D (Darcy’s)
Bernoulli’s equation (mechanical energy):
z p1/1 + v12/2g = z p2/2 + v22/2g + hL
Potential Pressure Kinetic Total Energy Energy Energy Head Loss

8. The Make-up of Cv and K Changes in the flow direction (turns)
Changes in the geometry (expansion, contraction, flow obstacles)
Geometry size
Weight of the fluid (density effects)
Velocity of approach (entry and exit velocity)
Friction between the fluid and solid as well as within the fluid layers (viscosity effects)
Elevation (1psi is about 27.8 inches of water head)

9. The Make-up of Cv and K — Order of Importance
Transition: A sharp 90-degree turn costs the flow more energy (pressure) than the frictional losses or pipe reduction losses (i.e. losses due to a short 90 deg. turn are four times greater than losses due to a half size reduction in the pipe diameter)
Pipe Size: Pipe size reduction has a 5-power effect on the flow where the frictional losses are at 1st order
Friction: The frictional losses are of greater relative importance in smaller components (frictional losses decrease with the increase in flow velocity or pipe diameter)

10. How are Cv and K determined?
Testing (ISA 75.02)
Empirical values (macroscopic approach)
CFD (microscopic approach)

11. Computational Fluid Dynamics —Background
CFD History
How it works
Swagelok’s Effort

12. CFD History Scientific community (space research and power production)
Current Status and Applications
Challenges

13. How Does CFD Work? Geometry Mesh Boundary Conditions Solution Method
Post Processing

14. Geometry

15. Geometry

16. Mesh – External Volume

17. Mesh – Internal Volume

18. Boundary Conditions Mass Flow Rate Pressure Velocity Inlet-Vent
Inlet-fan

19. Solution Method Coupled/Segregated Laminar/Turbulent
K-, RSM, k-, LES,…
Compressible/Incompressible
Steady State/Transient
Set the Boundary Conditions
Initialize the Solution
Solve

20. Post Processing

21. Post Processing

22. Post Processing

23. Swagelok’s Effort Swagelok gained in-house CFD capabilities in 1997
The majority of applications revolve around finding/optimizing Cv and Heat transfer analysis
Swagelok tool box: Fluent®, Floworks®, and Pipeflow®

24. MPC – CFD Model

25. MPC - CFD Model Model: Turbulent, Steady State, Segregated, Implicit
Geometry: 3D with symmetry about the center plane
Viscous Model: Standard k- turbulence model
Medium: Water, Air and some Hydrocarbons
Boundary Conditions:
Inlet: Mass Flow Rate (300 ml/min)
Outlet: Atmospheric pressure
Mesh: Hybrid, 120k order
Convergence Criteria: Conservation of mass, Y+

26. Results
Cv of a three-position system

27. Results
Predicted Cv: 0.040
Tested Cv: 0.045
Flow Direction

28. Results
Cv changes based on surface-mount components

29. Results Total system Cv: 1/Cvtotal 2 = Σ (1/Cvi)2 Cv1 Cv2 Cv3 Cv4 Cv5
Flow Direction

30. Results - Effects of fluid type on required driving pressure
For liquids with similar kinematic viscosities (υ = μ/ρ):
ΔPfluid / ΔPwater = (1/SGfluid) x (mass flow rate of fluid/mass flow rate of water)2
For liquids with different kinematic viscosity (i.e. motor oil):
ΔPfluid / ΔPwater = (υfluid / υwater).5

31. Results – Pressure drop on 3 position assembly
Media
Density
(kg/m3)
Kinematic Viscosity
(m2/s) P
(psi)
Air
1.2
1.5 x 10-5
0.003
Ethyl Alcohol
790
1.5 x 10-6
1.14
Benzene
875
6.7 x 10-7
1.22
Ethylene-Glycol
1,111
1.4 x 10-5
2.74

32. Results

33. Conclusions
A valid model for predicting flow capacity of a Swagelok MPC system
The surface-mount component has the largest effect on total system Cv
Developed a valid equation for predicting pressure to drive liquids
Based on kinematic viscosity
MPC requires minimal driving pressure
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