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-   -   Wood combustion initialization--help needed (http://www.cfd-online.com/Forums/fluent/118474-wood-combustion-initialization-help-needed.html)

roderick.blevins May 28, 2013 10:13

Wood combustion initialization--help needed
 
I am almost completely new to Fluent, but my Master's thesis is centered around constructing a CFD model for biomass (wood) combustion in a small cookstove. I am attempting to model said combustion using Species Transport while injecting "Combusting" Discrete Phase wood particles. However, I cannot seem to figure out how to achieve ignition without creating unrealistic boundary conditions for the application. Once combustion is begun I believe that my model can sustain it to steady-state; however, without setting a very high thermal wall boundary condition (which I would rather not do, as wall temperature is an output of interest) or constructing some high-temperature or heat-generating smaller volume (which I would rather not do, as it affects the outlet pollutant mass fractions and the feed rate of the fuel), I cannot seem to achieve combustion. Is there a way to initialize combustion in Fluent when attempting a steady-state simulation of this sort?

A relatively comprehensive bulleted list of my set-up:
  • Wood particles injected at ambient temperature through one inlet with a very low accompanying fluid flow velocity with a very small mass fraction of wood volatiles
  • A separate air inlet, also arriving at ambient temperature (300 K), with no mass fraction of volatiles
  • A "Mixed" thermal boundary condition incorporating external radiation and free convection on the exterior surface (or at least that's what I hope the convection is referring to) with a specified wall thickness
  • A pressure outlet boundary condition at the top of the geometry with a relatively high (1000 K plus) backwash temperature
  • Intuitively-set DPM boundary conditions for each (i.e. escape for all inlets/exits, reflect for wall--although if someone could explain the reflect settings I would appreciate it)

I believe that's it...I would sincerely appreciate any guidance or assistance that anyone could offer. As I'm said, I'm a complete rookie at Fluent and CFD in general, so I'm aware of my glaring inexperience. Thanks in advance.

mercy.gh July 25, 2013 09:07

Sorry, I don't have the answer to your question, I have a question of your kind almost;I am simulating a soaking pit furnace, used for reheating slabs in steel production route. I am not sure if I can use this "mixed thermal boundary condition" while working with furnaces, loaded with ingots (B.C of ingots' surface)... may I ask if you are using 'mixed' thermal boundary condition for the exterior walls, from inside? like you are considering it as the effect of heat transfer of combustion on the surface of walls? how sure you are of picking such a BC? I've been told that I can not use it since its inside the domain,..

bahramnourani October 28, 2013 17:14

Hi Roderik
 
I think that u can use patch option after your initializing.I think that patch option let u to increase your temp for a moment.


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