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Old   September 6, 2013, 15:01
Default Spray dryer atomization
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Hi, I'm working in drying of tomato juice in my university. There are a tiny equipment in the school which i have to simulate in ANSYS Fluent. I am very new in fluent so I will be so grateful if you could help me. In order to understand fluent i had done some tutorial like "Modeling Evaporating Liquid Spray" and others. However there are a lot of things that i don't know. Firstly, i began making the chamber in SolidWorks. These has one outlet, one velocity inlet for the hot air, and another for the atomizer; this has an outlet of 0.7mm of area. This atomizer is a pressure-nozzle. I did the mesh for Fluent with inflation: program controller and smooth transition through the workbench of ANSYS 14. In fluent, I used the gravity, the energy model, realizable K-e viscous, Species transport for the hot air( O2, H2O, N2) and the discrete phase for the atomizer. However the atomizer is for tomato juice so i have to use a multiphase but i don't know how to do it and if my model is correct. In order to simulate the nozzle I draw a similar air nozzle as the tuto "Modeling Evaporating..." however i don't know if this is necessary or is enough just an injection. If someone can help me. There are some pictures of this work.Thanks.
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Old   September 6, 2013, 15:07
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pictures are not working, can you fix
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Old   September 6, 2013, 15:08
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if you are using DPM, you don't need an inlet for atomizer
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Old   September 6, 2013, 15:18
Default Zones
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Similar to the tuto, i used 3 inlet zones [co-flow-rate-inlet : hot air, central-air: (mass-flow-inlet) for tomato juice, and swirling-air-inlet : pressure air]. And only one pressure-outlet. Could you open the pictures in Drive?
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Old   September 6, 2013, 15:53
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ok start by a very simple case , then make it more complex step by step.
Disable multiphase first, and use steady particle tracking, use 20 iteration per dpm calculation.
have you done that ?
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Old   September 6, 2013, 17:48
Default Simple Case
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Ok First, thanks for your help. I made the first case without a second phase. I put the models that i use and more information in the doc:
Gravity z:9.81
1. Energy Model: ON
2. Viscous: Realizable K-e, Standard Wall Fn
3. Species:
a. Methyl-Alcohol-Air(4 Number of Volumetric Species)
b. Inlet Diffusion
c. Diffusion Energy Source
4. Discrete Phase Model:
a. Interaction with Continuous Phase
b. Number of Continuous Phase Interaction per DPM Interation> 20
c. Steady Particle tracking
d. Any Physical Model

5. Injection-0
a. Type: pressure-swirl-atomizer
b. # of particle streams: 60
c. Particle Type: Droplet
d. Material: Methyl-alcohol-liquid
e. Evaporating Species: Water
f. Position: x=0, y=0, z=0.0015
g. Axis: X=0, Y=0, Z=1
h. Temperature: 25°c,298°K
i. Flow Rate: 8.5e-0.5 Kg/s
j. Injection Inner Diameter(m)=0.00025
k. Spray Half Angle: -45°
l. Upstream Pressure: 1000000Pascal
m. Azimuthal Start Angle:0°
n. Azimuthal Start End:180°
o. Sheet Constant: 12
p. Ligament Constant: 0.5
q. Atomizer Dispersion Angle: 6

6. Boundary Conditions
Central Air Inlet:
Type: Mass-Flow-Rate
Mass-Flow-Rate: 9.167e-05 Kg/s
Direction Vector: (0,0,1)
Turbulence: Intensity and Viscosity Ratio(10%,10%)
Temperature: 298°K
Species: 0.23 n2, 0 o2, 0 h2o

Co-flow-rate-inlet: Hot Air
Type: Velocity Inlet
Temperature 373 °K
Turbulence: Intensity and Viscosity Ratio(5%,5%)

Swirlig-air-inlet: High pressure air
Type: Velocity Inlet
Temperature: 298°K
Velocity: 30 m/s
Cylindrical coordinate System: 0, 0.7071, 0.7071
Turbulence: Intensity and Viscosity Ratio(5%,5%)

Outlet
Type: Pressure-outlet
Temperature: 298°K
Turbulence: Intensity and Viscosity Ratio(5%,5%)

I made 300 iteration to start but it doest converge :S maybe much more
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Old   September 8, 2013, 08:53
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have you first solved the cold flow ? do you have any information about your nozzle like angle and pressure of operation ? Why are you using any physical model for the droplets ?
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Old   September 8, 2013, 15:14
Default Corrections and atomization characteristics
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Thanks you diamondx, you are right. First i have to remove the injection, so, we have three models, energy, viscous and species transport. I do this in order to solve the cold flow? right.

The information that i have about the nozzle is that it is a pneumatic double flow atomizer from Buchi, which is working at 250 KPa (2.5 bar), air flow rate is 7.6 Kg/h and 0.09 Kg/h of tomato juice, droplet size is 1-25um(dp=5um), nozzle diameter is 0.7mm(7e-4m) and 0° angle.
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Old   September 8, 2013, 16:29
Default I used this models...
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1. Modelo de Energía: ON
2. Viscocidad: Realizable K-e, Standard Wall Fn
3. Species:
a. Methyl-Alcohol-Air(3 Number of Volumetric Species)
b. Inlet Diffusion
c. Diffusion Energy Source
4. Condiciones de Frontera (Boundary Conditions)
Central Air Inlet: Jugo de tomate
Type: Mass-Flow-Rate
Mass-Flow-Rate: 9.167e-05 Kg/s
Direction Vector: (0,0,1)
Turbulence: Intensity and Viscosity Ratio(10%,10%)
Temperature: 273+25°K=293°K
*(Species: 0 ch3oh, 0.21 o2, 0 h2o, 0 air) i don’t know
Co-flow-rate-inlet: Aire Caliente
Type: Pressure inlet
Pressure: 100 000 Pascal
Temperature 408 °K (135°C)
Turbulence: Intensity and Viscosity Ratio(5%,5%)
Gauge total pressure=100 000 P
Turbulence: Intensity and Viscosity Ratio(5%,5%)
(Species: 0 ch3oh, 0 o2, 0 h2o, 1 air)

Swirlig-air-inlet: Aire a presión
Type: Pressure Inlet
Temperature: 298°K (25°C
Pressure: 250 000 Pascal
Turbulence: Intensity and Viscosity Ratio(5%,5%)
(Species: 0 ch3oh, 0 o2, 0 h2o, 1 air)

Outlet
Type: Pressure-outlet
Temperature: 358°K (85°C)
Turbulence: Intensity and Viscosity Ratio(5%,5%)
(Species: 0 ch3oh, 0 o2, 0 h2o, 0 air)

it is converged at 345 iterations, now ill put the injection... case and data of this : https://docs.google.com/file/d/0Bz3M...it?usp=sharing
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Old   September 8, 2013, 17:18
Default Discrete phase model and Injection
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Now I try to simulate the injection with this parameters:
5. Discrete Phase Model:
a. Interaction with Continuous Phase
b. Number of Continuous Phase Interaction per DPM Interation> 20
c. Unsteady Particle tracking
i. Particle time step size: 1e-03
ii. Number of time steps: 1000
(is this for in 1 second, one particle every 0.001 s?)
d. Physical Models:
i. Breakup
I just can use this because DEM Collision is not enable with breakup model, What more I need?
e. Drag parameters
Should I use dynamic-drag or spherical?, I used dynamic-drag
Injection-0
a. Type: pressure-swirl-atomizer
b. # of particle streams: 2
c. Particle Type: Droplet
d. Material: Methyl-alcohol-liquid
e. Evaporating Species: Water
f. Position: x=0, y=0, z= 0.0050
g. Axis: X=0, Y=0, Z=1
h. Temperature: 25°c,298°K
i. Flow Rate: 0.000025 Kg/s (0.09 Kg/h) -> 0.045 Kg/h because I just simulate a half
j. Start time: 0s, stop time: 60 s
j. Injection Inner Diameter(m)=0.000025
k. Spray Half Angle: 0°
l. Upstream Pressure: 250000Pascal
m. Azimuthal Start Angle:0°
n. Azimuthal Start End:30°
o. Sheet Constant: 12
p. Ligament Constant: 0.5
q. Atomizer Dispersion Angle: 6
Turbulent dispersion
- Discrete random walk model
- Random eddy lifetime
Materials
Material Type: droplet particle
Density: 1019 Kg/m^3
Cp: 4077 J/Kg°C
Viscosity: 103 .55 din*s/cm^-2 (10.355 Pa*s)
Droplet surface : 0.0222

However I am not sure about many things :S
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Old   September 9, 2013, 08:29
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make the number of time step 5000.
Your evaporating species is water ? how come ? it should be the liquid that you are injecting !
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Old   September 9, 2013, 17:34
Default Injection
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Quote:
Originally Posted by diamondx View Post
make the number of time step 5000.
Your evaporating species is water ? how come ? it should be the liquid that you are injecting !
I used water as evaporating species because the liquid injection is tomato juice, moisture is 95.2% with a concentration of 22 of solids. How can i simulate this mixture?. Other thing, there is some picture where i can see all the parts of an injection. Because in the theory guide don't have a good information of this. I am not sure about some characteristics.
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Old   September 10, 2013, 14:07
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you need to refine the mesh ! see what it does. in the evaporating species , the material has to be the same as the one used it the mixture... any progress ?
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Old   September 18, 2013, 13:49
Default Refine mesh
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Quote:
Originally Posted by diamondx View Post
you need to refine the mesh ! see what it does. in the evaporating species , the material has to be the same as the one used it the mixture... any progress ?
https://docs.google.com/file/d/0Bz3M...it?usp=sharing

I refined the mesh however now it doesn't converge... some idea? what am i doing wrong? Or its ok?

Last edited by luisUTM; September 18, 2013 at 18:46.
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