© Swagelok Company, 2002 Computational Fluid Dynamic (CFD) Analysis of Gas and Liquid Flow Through...

© Swagelok Company, 2002

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


Agenda

Objective

Cv, K Factor

CFD Background

MPC - CFD Model Description, Procedure

Results

Conclusions


Objectives

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


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?


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 = .000216 f L Q2 / d5 (Darcy’s)

For Gases:Through control components:

q = N7 * Fp * Cv * p1 * Y * [x / (Gg T1 Z)]1/2 (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


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):

z1 + 144 p1/1 + v12/2g = z2 + 144 p2/2 + v2

2/2g + hL

Potential Pressure Kinetic Total

Energy Energy Energy Head Loss


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)


The Make-up of Cv and K — Order of Importance

1. 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)

2. Pipe Size: Pipe size reduction has a 5-power effect on the flow where the frictional losses are at 1st order

3. Friction: The frictional losses are of greater relative importance in smaller components (frictional losses decrease with the increase in flow velocity or pipe diameter)


How are Cv and K determined?

Testing (ISA 75.02)

Empirical values (macroscopic approach)

CFD (microscopic approach)


Computational Fluid Dynamics —Background

CFD History

How it works

Swagelok’s Effort


CFD History

Scientific community (space research and power production)

Current Status and Applications

Challenges


How Does CFD Work?

Geometry

Mesh

Boundary Conditions

Solution Method

Post Processing


Geometry


Mesh – External Volume


Mesh – Internal Volume


Boundary Conditions

Mass Flow Rate

Pressure

Velocity

Inlet-Vent

Inlet-fan


Solution Method

Coupled/Segregated

Laminar/Turbulent

K-, RSM, k-, LES,…

Compressible/Incompressible

Steady State/Transient

Set the Boundary Conditions

Initialize the Solution

Solve


Post Processing


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®


MPC – CFD Model


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+


ResultsCv of a three-position system


Results

Predicted Cv: 0.040 Tested Cv: 0.045

Flow DirectionFlow Direction


ResultsCv changes based on surface-mount components


Results

Total system Cv: 1/Cvtotal 2 = Σ (1/Cvi)

2

Cv7Cv7Cv6Cv6Cv5Cv5Cv4Cv4Cv3Cv3Cv2Cv2Cv1Cv1

Flow DirectionFlow Direction


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

Viscosity vs. Pressure Drop Correlation

Water

Ethylene-Glycol (C2H6O2)

Ethyl Alcohol (C2H5OH)

Ethylene-Glycol (C2H6O2)

Water

Benzene

Ethyl Alcohol (C2H5OH)

Benzene

Delta P total

KinematicViscosity


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


ResultsPressure Required to drive 300 ml/min through

Swagelok's MPC (3-position assembly)

0

5

10

15

20

25

30

Benzene Water Ethylene-Glycol(C2H6O2)

Ethyl Alcohol(C2H5OH)

Air

To

tal P

res

ss

ure

Re

qu

ire

d, p

sig


Conclusions

A valid model for predicting flow capacity of a Swagelok MPC systemThe surface-mount component has the largest effect on total system CvDeveloped a valid equation for predicting pressure to drive liquids

Based on kinematic viscosityMPC requires minimal driving pressure

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© Swagelok Company, 2002 Computational Fluid Dynamic (CFD) Analysis of Gas and Liquid Flow Through...

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