Evaporation

[Wali Hasan]

Dear FDS User,

I am enclosing FDS and Pyrosim file for your favorable consideration. The objective of my work is to evaporate the water and oil particles and trace the particles of both along with the filtration of grease particulates inside the hood.

Firstly I define the properties of water and oil in liquid as well as gaseous phase via Edit Species option and after that I define it using the particle cloud option. But the issue is that when I visualize the particle file in Smokeview then the particles goes down instead of upward direction. 

Please have a look and guide me that am I going in the right direction or not.

Thanks in advance

 

[dr_jfloyd]

Don't define your own water species. Just use
&SPEC ID='WATER VAPOR'/
and use that species for your water drops.

You have not defined any gas thermophysical properties for your cooking oil. Therefore, FDS will compute these using the MW and the assumption of gamma=1.4 per the discussion in the user's guide. This will result in non-sensical properties as vaporized oil will not have properties that follow gamma=1.4.

What are you expecting to see and what are you seeing? You have defined 500 micron drops of water and oil. The terminal velocity for these is ~ 7 m/s. Unless your upward flow is more than this, the particles will fall.

[Wali Hasan]

Dear jfloyd,

Thanks for your suggestions, I just want to trace the path lines of water vapor and oil particles in the domain using particle cloud. Is it possible without using the tracer because tracer will trace the air flow in the domain but I want to trace the oil.

I  want to share one more point as you have seen the volume of particle cloud region, actually in this I want to put  a water of 5 Kg but when I define the Mass per volume it is approx 2000 kg/m3. when I use this value it shows an error so how I manage this.

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[dr_jfloyd]

Yes you can track droplets with FDS, but you need to have reasonable inputs for them.  The fine fog of water or oil resulting from cooking are very small.  500 microns is a large drop.  The mean diameter of fog is more like 10 microns (but you should research this yoursfelf).

I am not sure I understand what you are trying to do in your second statement.  Water has a density of 1000 kg/m^3 and the oil ~ 900.  A mass per volume of 2000 kg/m^3 is not physically possible.

[Wali Hasan]

Dear,

I am now running my simulation with droplet size of 10 microns but still the water drops goes downward instead of upward direction from particle cloud region. Actually I am not using the tracer option is it possible to visualize the path without using this because the tracer will trace the path of air flow only in the domain which might be different for  oil particle.

Next clarification regarding amount of water, actually I want to vaporize the water of 5 KG what value should I use for mass per volume which is available in particle cloud option.

Thanks for giving your valuable time for my problem. I am waiting your response.

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[dr_jfloyd]

My statement of 10 microns was merely an order of magnitude for comparison with the 500 microns in your input. You need to research this value and detemrine what it needs to be.

Compute the terminal velocity of your droplets, do you have that present as an upward velocity in your calculation where the particles are being injected?  If not, then particles will not rise.

If you are boiling water from a pot, why are you injecting particles as the full water mass at t=0?  This is not how a pot boils.  You are likely only boiling on the order of 1 g/s from the pot (again this is something you need to compute based upon the power of the burner, heat transfer to the pot, heat loss from the pot not going to boiling, etc.).  You should consider injecting the partices with a VENT and SURF rather than INIT.