Computational fluid dynamics approach and its application in food processing

BYLavanya M NPh.D. (FPE)

• CFD is a simulation tool, which uses a power computer

and applied mathematics to model fluid flow situations.

• In 1928, the application of CFD started in fluid flow

• Daimler Chrysler was the first company to use CFD in

Automotive sector.

• Speedo was the first swimwear company to use CFD

• The adoption of CFD technology by food engineers

began in the 1990s.

Computational fluid dynamics approach

It provides qualitative and sometimes quantitative prediction

of fluid flow by

• Mathematical modelling (partial differential equations),

• Numerical methods (discretization and solution techniques),

• Software tools (solvers, pre- and post-processing utilities).

Computational fluid dynamics approach

FundamentalsThe fundamental basis of almost all CFD problems uses the set of

Navier–Stokes equations

• Governing the equation: conservation equations (Conservation of

mass, conservation of momentum and conservation of energy)

• Numerical analysis: The most important techniques are finite

difference, finite elements and finite volumes.

• Solving the flow problems

• Interpreting the solutions

Fundamentals of CFD

The analyst should have a knowledge to state

the problem and to use scientific knowledge to

express it mathematically

Stages in CFD

Pre-processing Processing Post-

processing

Problem thinking,

meshing and generation

of a computational

model.

Solving equations

Evaluation

The simulation and analysis within a CFD Stages

Pre-processing: meshing

Create shape of the problem domain

CAD/CAE integration

Engineering drawings

Coordinates include Cartesian

system (x,y,z), cylindrical system (r,

θ, z), and spherical system(r, θ, Φ)

Stages in CFD

Initial condition involves knowing the state of

pressure (p) and initial velocity (u) at all points

in the flow.

Boundary conditions such as walls, inlets and

outlets largely specify what the solution will be.

Geometry of problem is defined .

Volume occupied by fluid is divided into discrete

cells.

Stages in CFD

Pre-processing: Initial boundary conditions

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Problem domain: Example

• It involves computer to solve the

mathematical equations of fluid

flow

• Solves thousands of equations

• Equation discretization

Sample grid established by Gambit of FLUENT

Processing

• Calculation of derived variables

• Calculation of integral parameters: forces,

moments

• Visualization (usually with commercial

software)

• Simple X-Y plots

• Simple 2D contours

• 3D contour carpet plots

• Animations (dozens of sample pictures in

a series of time were shown

continuously)

Post-Processing: Evaluation of generated data

• Gives much better and deeper understanding of what is happening in a particular process or system.

• Less time and cost than would be involved in laboratory testing.

• It can answer many ‘what if’ questions in a short time.

• Reduce scale-up problems

• It is particularly useful in simulating conditions where it is not possible to take detailed measurements such as high temperature or dangerous environment in an oven.

• Since it is a pro-active analysis and design tool, it can highlight the root cause not just the effect when evaluating plant problems.

Advantages of CFD

Commercial codes for CFD

1. CFX

2. FLUENT

3. PHOENICS

4. STAR-CD

5. FLOW3D

6. CFD-ACE

7. ICM CFD

8. AMI-VSAERO

9. STORESIM/TETMESH

10. IGGTM

11. TECPLOT

12. PAM-FLOW

13. FLOVENT

14. AVS/EXPRESS

15. FLO++

16. CFD++

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Where is CFD used? (Aerospace)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

F18 Store Separation

Wing-Body Interaction Hypersonic Launch Vehicle

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Where is CFD used? (Appliances)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Surface-heat-flux plots of the No-Frost refrigerator and freezer compartments helped BOSCH-SIEMENS engineers to optimize the location of air inlets.

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Where is CFD used? (Automotive)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

External Aerodynamics Undercarriage Aerodynamics

Interior Ventilation Engine Cooling

Where is CFD used? (Biomedical)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Temperature and natural convection currents in the eye following laser heating.

Spinal Catheter

Medtronic Blood Pump

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Where is CFD used? (Chemical Processing)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Polymerization reactor vessel - prediction of flow separation and residence time effects.

Shear rate distribution in twin-screw extruder simulation

Twin-screw extruder modeling

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Where is CFD used? (HVAC&R)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Particle traces of copier VOC emissions colored by concentration level fall behind the copier and then circulate through the room before exiting the exhaust.

Mean age of air contours indicate location of fresh supply air

Streamlines for workstation ventilation

Flow pathlines colored by pressure quantify head loss in ductwork

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Where is CFD used? (Hydraulics)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

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Where is CFD used? (Marine)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

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Where is CFD used? (Oil & Gas)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Flow vectors and pressure distribution on an offshore oil rig

Flow of lubricating mud over drill bit

Volume fraction of water

Volume fraction of oil

Volume fraction of gas

Analysis of multiphase separator

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Where is CFD used? (Power Generation)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Flow pattern through a water turbine.

Flow in a burner

Flow around cooling towers

Pathlines from the inlet colored by temperature during standard operating conditions

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Where is CFD used? (Sports)

• Where is CFD used?– Aerospace– Appliances– Automotive– Biomedical– Chemical Processing– HVAC&R– Hydraulics– Marine– Oil & Gas– Power Generation– Sports

Application of CFD in food industry: Drying

CFD to analyse the flow and performance of process equipment, such as• Baking ovens• Refrigerated display cabinets • Stirred tanks • spray dryers • Heat exchangers• some other equipment. In design and development,

CFD programs predict • Fluid flow behaviour, • Transfer of heat, mass (such as in perspiration or dissolution), • Phase change (such as in freezing, melting or boiling), • Chemical reaction (such as combustion or rusting), • Mechanical movement (such as an impeller turning, pistons, fans or

rudders)• Stress or deformation of related solid structures (such as a mast

bending in the wind).

Application of CFD in food industry

Application of CFD in food industry: DryingProblemDescriptions

Model geometry Software Findings Author

Evaluation of dropletdrying models ina spray dryer fittedwith rotary atomizerusing CFDsimulation

3D Fluent The concept ofparticle rigidityprediction in a CFDsimulation wasexplored and theeffect of initial feedmoisture content onthe drying modelswas also studied.

Woo et al. (2008a)

Simulation ofindustrial scale spraydryer attached witha Fluidized bed,using ReactionEngineeringApproach (REA).

2D Fluent Smaller spray coneangle facilitates easymovement of particles to the fluidized bed. The accuracy of REAmodel in predictingthe single dropletdrying kinetics wasalso explained.

Jin and Chen (2009)

Application of CFD in food industry: Cold storage.

Contours of iso-temperatures in the most sensitive plane of a refrigerated truck (a)

without air ducts (b) with air ducts

Application of CFD in food industry: Pasteurization

a)

Temperature (C) profiles of pasteurisation (85C) process of milk in stationary position of can at (a) 60 s (b) 120 s (c) 240 s and (d) 360 s.

b)

c) d)

Thank you