Heat conduction through Sand or pulverised materials

dwqi0419 · May 17, 2010, 05:28

Hi, everybody

Currently I should simulate the heat conduction through the pulverised materials (like sand) in CFX. I don´t think it´s a good idea to model it as a continous solid because of the gap between the sand grains. So my opinion now is to simulate it as a multiphase flows (model the sand the dispersed solid or transport particle solid and set the air as continous fluid).
Because I am a new user in the CFD area, so I would like to ask, does any of you have any experiences of simulating such problems?

Thanks a lot,
Dawei

ghorrocks · May 17, 2010, 07:45

What are you actually trying to do? There are many different approaches and you have not provided enough information to make an informed decision. Is the sand in air? Or water? Is it moving? What is driving the heat transfer? What is the important outcome of the analysis?

dwqi0419 · May 17, 2010, 09:36

hi, ghorrocks

What I want to do is actually, I set up a stationary container made of steel. There are sand in the container. It is under the atmosphere condition (1 bar, 20 C). And the sand inside can not be modelled just as a continuous solid due to the fact that it is actually millions of small sand grains in the reality, there are gaps between each grain. So we assume it is air, which fills these gaps. As boundary condition I set a heat flow to the outer wall of the container, the sand inside will be heated up. As outputs the temperature profile in the sand should be simulated.
So I´d like to discuss, which possibilities are there in CFX to simulate this. What I have found is model the sand as dispersed solid or particle transport solids, then it will be taken as multiphase flow, which sometimes leads to convergence problems

Thanks!!

ckleanth · May 17, 2010, 11:58

as a first stab at this, multiphase setup and for initial conditions implement a porosity factor based on your sand grain shape ( if assumed spherical particles porosity is somewhere 0.65 )

ghorrocks · May 17, 2010, 19:44

I don't think a multiphase approach to this is wise.

Personally I would either do experiments or look in the literature for thermal conductivity values for sand at the appropriate density and grain size. Then model it as a simple solid using the thermal conductivity and specific heat which represents a sand grain/air pile. This is very easy to do.

ckleanth · May 17, 2010, 21:33

quite true, to be honest I was with the impression that the sand/air was a fluidized bed setup but reading the problem description again I agree with glenn.

dwqi0419 · May 26, 2010, 05:53

Yes, that is actually what I have been doing until now. Now I also think it is not necessary to use multiphase flow to simulate this.
Thanks for the answer, Glenn and George

May 17, 2010, 05:28	Heat conduction through Sand or pulverised materials	#1
dwqi0419 New Member Dawei Join Date: May 2010 Location: Germany Posts: 3 Rep Power: 16	Hi, everybody Currently I should simulate the heat conduction through the pulverised materials (like sand) in CFX. I don´t think it´s a good idea to model it as a continous solid because of the gap between the sand grains. So my opinion now is to simulate it as a multiphase flows (model the sand the dispersed solid or transport particle solid and set the air as continous fluid). Because I am a new user in the CFD area, so I would like to ask, does any of you have any experiences of simulating such problems? Thanks a lot, Dawei

May 17, 2010, 11:58		#4
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	as a first stab at this, multiphase setup and for initial conditions implement a porosity factor based on your sand grain shape ( if assumed spherical particles porosity is somewhere 0.65 ) __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

May 17, 2010, 21:33		#6
ckleanth Senior Member George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18	quite true, to be honest I was with the impression that the sand/air was a fluidized bed setup but reading the problem description again I agree with glenn. __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

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May 17, 2010, 07:45		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	What are you actually trying to do? There are many different approaches and you have not provided enough information to make an informed decision. Is the sand in air? Or water? Is it moving? What is driving the heat transfer? What is the important outcome of the analysis?

May 17, 2010, 09:36		#3
dwqi0419 New Member Dawei Join Date: May 2010 Location: Germany Posts: 3 Rep Power: 16	hi, ghorrocks What I want to do is actually, I set up a stationary container made of steel. There are sand in the container. It is under the atmosphere condition (1 bar, 20 C). And the sand inside can not be modelled just as a continuous solid due to the fact that it is actually millions of small sand grains in the reality, there are gaps between each grain. So we assume it is air, which fills these gaps. As boundary condition I set a heat flow to the outer wall of the container, the sand inside will be heated up. As outputs the temperature profile in the sand should be simulated. So I´d like to discuss, which possibilities are there in CFX to simulate this. What I have found is model the sand as dispersed solid or particle transport solids, then it will be taken as multiphase flow, which sometimes leads to convergence problems Thanks!!

May 17, 2010, 19:44		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	I don't think a multiphase approach to this is wise. Personally I would either do experiments or look in the literature for thermal conductivity values for sand at the appropriate density and grain size. Then model it as a simple solid using the thermal conductivity and specific heat which represents a sand grain/air pile. This is very easy to do.

May 26, 2010, 05:53		#7
dwqi0419 New Member Dawei Join Date: May 2010 Location: Germany Posts: 3 Rep Power: 16	Yes, that is actually what I have been doing until now. Now I also think it is not necessary to use multiphase flow to simulate this. Thanks for the answer, Glenn and George