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-   -   evaporation of water droplet (http://www.cfd-online.com/Forums/fluent/82393-evaporation-water-droplet.html)

padthai November 24, 2010 23:57

evaporation of water droplet
 
Hi all,

I have simulated water injected to the air.I used DPM with species and pressure-swirl atomizer to accelerate water through nozzles.

The inner diameter of nozzle and pressure were 0.16 mm and 6Mpa respectively.The result of this seems to be good.

However, when I increased inner diameter of nozzle to be 16 mm or more than that,droplets can still evaporate as same as 0.16 mm(100% evaporate).I thought this is wrong.According to the theory of evaporation,the large droplet diameter should almost not evaporate.I try to solve this but I can't reach a good result.

Could anyone suggest me how to solve this problem?

Thank

fabriciotb December 29, 2010 07:19

Reply 1
 
Hi,
Your simulations is stead or transient ?

padthai December 29, 2010 23:03

Hi fabriciotb,

I simulated with steady state in both phase.

Thank

goami December 29, 2011 14:42

same problem
 
bro i am working on same kind of problem, the water should come inside the container and it should be heated to about 2000 K and the h2, o2 should be seperated from water vapour.

it seems to be multiphase model usage but i am very much less in knowledge regarding that kind of problem..........does it need any species transport..:confused::confused:

in your case definitely it should be unsteady problem in that thing i am damn sure but i couldn't simulate it i.e. the amount of hydrogen seperated and at what temp. h2,o2 splits from water........

subha_meter May 18, 2012 21:30

Droplet evaporation on solid particles
 
Hi All,

I am trying to simulate droplet evaporation on the free wavy surface of a bubbling fluidized bed. The idea is to investigate vapor concentration profile above the bubbling bed.

I have simulated the bubbling fluidized bed using eulerian model with velocity inlet BC at the bed bottom, Wall BC at both sides up to the solid level,Symmetry BC on the both sides of the top domain above solid bed and Pressure outlet BC at the top.

Now after simulating for enough time (~ 30 sec), I'm introducing an injection of liquid droplet through the pressure outlet boundary on the top of the bed. Evaporation takes place as desired however the droplet injection penetrates through the bed and escapes through the gas inlet boundary at bottom.

The injection needs to stop at the solid free surface and evaporate. I also used a pressure outlet BC at the free solid surface to capture the droplet stream providing a "trap" BC for DPM there however it creates a huge back flow through the boundary and air ingresses in the bed from top instead of going out.

Can anyone suggest how to capture the droplet stream on the solid surface at the bed top?

Any suggestion will be appreciated.

subha_meter July 2, 2012 20:53

Stopping DPM particles on the bubbling bed
 
Fortunately could write a piece of UDF to assign a "no-slip" condition for the droplet particles on bubbling bed surface. It works!

subha_meter July 22, 2012 05:02

Hello Stephen,

Water evaporation at the air/coffee interface Would require use of VOF multiphase model.

Based on the liquid phase temperature, you need to incorporate a negative mass source term to liquid phase and a positive mass source term of equal magnitude to gas phase. This can be computed as

mdot = rv x alpha_l x rho_l x (Tl - Tsat)/Tsat where rv = time relaxation parameter (0 to 1), alpha_l = liquid vol frac, rho_l = liquid density, Tsat = saturation temp, Tl= liquid phase temp.

You can use a species transport equation for water vapor if you are interested to see water vapor conc. around.

An energy source term will also be required which will calculate the energy associated with this mass change during vaporization as E = mdot x lambda (latent heat of vaporization).

There are more evaporation models available and you can customize these source terms accordingly.

Hope it helps.





Quote:

Originally Posted by Stephen Bong (Post 372840)
Dear Subhasish Mitra,

I'm currently confronted with bunch of problems with my current project which is the modelling of evaporation of water in a coffee cup, it's a multiphase flow modelling. What I would like to see is that, the moisture movement of the water, and other parameters. Could you please guide me or mail me your steps and procedures? Since I'm new to Fluent, so there's still a lot of setting which I'm not clear. I'm looking for your favorable reply. And your kind consideration is highly appreciated. Thanks in advanced!


subha_meter July 23, 2012 03:58

@Stephen,

You can contact me at subha_meter@yahoo.com.



Quote:

Originally Posted by subha_meter (Post 372849)
Hello Stephen,

Water evaporation at the air/coffee interface Would require use of VOF multiphase model.

Based on the liquid phase temperature, you need to incorporate a negative mass source term to liquid phase and a positive mass source term of equal magnitude to gas phase. This can be computed as

mdot = rv x alpha_l x rho_l x (Tl - Tsat)/Tsat where rv = time relaxation parameter (0 to 1), alpha_l = liquid vol frac, rho_l = liquid density, Tsat = saturation temp, Tl= liquid phase temp.

You can use a species transport equation for water vapor if you are interested to see water vapor conc. around.

An energy source term will also be required which will calculate the energy associated with this mass change during vaporization as E = mdot x lambda (latent heat of vaporization).

There are more evaporation models available and you can customize these source terms accordingly.

Hope it helps.


Stephen Bong August 29, 2012 05:54

Thanks for reply, but now the situation is boiling. Help Needed!
 
Dear Subhasish Mitra,

I'm currently confronted with bunch of problems with my current project which is the modelling of boiling of water. What I would like to see is that, the moisture movement of the water, and other parameters. Could you please guide me or mail me your steps and procedures? Since I'm new to Fluent, so there's still a lot of setting which I'm not clear. I'm looking for your favorable reply. And your kind consideration is highly appreciated. Thanks in advanced!

mali28 August 29, 2012 07:56

Quote:

Originally Posted by Stephen Bong (Post 379264)
Dear Subhasish Mitra,

I'm currently confronted with bunch of problems with my current project which is the modelling of boiling of water. What I would like to see is that, the moisture movement of the water, and other parameters. Could you please guide me or mail me your steps and procedures? Since I'm new to Fluent, so there's still a lot of setting which I'm not clear. I'm looking for your favorable reply. And your kind consideration is highly appreciated. Thanks in advanced!

Modelling boiling of water is quite different from evaporation of moisture from droplet.

Stephen Bong August 29, 2012 21:28

Help Needed!
 
Quote:

Originally Posted by mali28 (Post 379290)
Modelling boiling of water is quite different from evaporation of moisture from droplet.

Dear Mali28,

Yea, I know about it. Since it's very hard for me now to simulate a multiphase flow, so our group have change our directions to simulate boiling of water, which is a single phase flow and heat transfer. Due to we're new to FLUENT, do you have any suggestions or steps which we need to do in order to run the simulations. Example like the settings, and so on. Hope to hear from you soon. Your kind considerations will be highly appreciated, and million thanks to you.

Regards.

subha_meter August 30, 2012 20:10

Hi Stephen,


Are you trying to model boiling of water in a closed container? If it is, use a 2D domain with wall at the bottom, side and pressure outlet at the top.
Apply temperature BC on the bottom wall, and zero flux on the side walls.

Use VOF model.
Enable energy model.

Take air, water(liq),water (vap) as the materials.

Enable species transport with water vapor and air as the components.
Enable mass transfer and surface tension in phase panel.
Set mass transfer from water to air with water vapor as the migrating species and select "evaporation/condensation as the mass transfer mechanism".
Set boiling frequency = 1.0 and condensation frequency as default.

Fill the domain by patching water volume fraction = 1.0.
With a low time step (1e-05/06), start the simulation.


Hope it helps,


Quote:

Originally Posted by Stephen Bong (Post 379264)
Dear Subhasish Mitra,

I'm currently confronted with bunch of problems with my current project which is the modelling of boiling of water. What I would like to see is that, the moisture movement of the water, and other parameters. Could you please guide me or mail me your steps and procedures? Since I'm new to Fluent, so there's still a lot of setting which I'm not clear. I'm looking for your favorable reply. And your kind consideration is highly appreciated. Thanks in advanced!



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