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-   -   discrete model problem (water droplet evaporation) (http://www.cfd-online.com/Forums/fluent/38073-discrete-model-problem-water-droplet-evaporation.html)

rabaeto1984 October 1, 2005 12:27

discrete model problem (water droplet evaporation)
 
Could anybody help me regarding the following problem?

I am simulating water droplet evaporation in a horizontal air pipe flow. Without droplet injections, the flow has a uniform 2 m/s velocity parallel to the axial direction of the pipe. The case is inviscid. When I model particle evaporation, I use coupled implicit steady solver, flow solution per DPM iteration is set to 1, underrelax for DPM sources is 0.01. I set appropriate particle diameter and mass flow for injection. The problem is that if I set the diameter above a certain value (10e-6), particles burst through the whole pipe without any sign of heat or mass exchange with the bulk phase (air). However, if I set the diameter lower than 10e-7, the particles evaporate right at the inlet. So my question is whether the method I use is right to track evaporation of particles or not. It seems strange to me that a 10e-6 particle does not have heat and mass transfer at all.

Thanks for all responses in advance.

RoM October 2, 2005 05:45

Re: discrete model problem (water droplet evaporat
 
Quote fom fluents defect data base:

"One of our customers is doing DPM simulation with rather small solid particles (d<100 nm). He found that in Fluent6.1 all the particles smaller than 100 nm just evaporated within the first cell. However, in Fluent6.0,the particles just travel through the domain fine. They are all solid inert particles. They shouldn't be evaporated. I have prepared a simple test case. I will put them in the usual bug area. Please try it on Fluent6.0 and 6.1. You will see completely different results. Cheers Jin"

Although this bug was fixed in 6.1.23 it may be only fixed for the intert particles. Maybe it still occurs for droplets. Lots of maybes here...

Have you calculated the saturation pressure for your domain? If you mixture is saturated there will be no evaporation. And 0.01 underrelax is verly low. It may take a while to see any effects.

RoM

rabaeto1984 October 2, 2005 08:10

Re: discrete model problem (water droplet evaporat
 
Thanks a lot for you kind answer!!!!!!!! You helped me a lot.

apo February 3, 2015 07:00

hello to everyone,
I' modeling a solid coal combustion and i use species transport model and injection from surface. Also, i use dpm model. At injections, in particle type i have combustion. When i run the solution, at DPM iteration, it shows me "number tacked=3000, escaped=3000, evaporated=0". Is it right? Once i have combustion, i shouldn't have evaporated particles?
Thank you


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