How can I calculate view factor using MCNP for radiation heat transfer?

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Discussion Overview

The discussion revolves around calculating the view factor for radiation heat transfer using the MCNP (Monte Carlo N-Particle Transport Code). Participants seek advice on using surface sources and interpreting tally results from output files, focusing on the challenges of obtaining accurate measurements for radiation transfer.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about using MCNP to calculate view factors and expresses confusion regarding the number of particles emitted from a surface source and the interpretation of F4 tally results.
  • Another participant suggests that tally results are normalized to a single source particle, which may clarify the small values observed in the output.
  • A participant expresses concern that the F4 tally may not be suitable for their needs, as they expect the sum of values to equal one, but their results exceed this expectation.
  • It is proposed that F2 tallies, which measure surface flux, may be more appropriate than F4 tallies, which measure cell flux.
  • A participant mentions the need to segment surfaces to obtain individual flux measurements and seeks advice on calculating these values simultaneously.
  • Another participant acknowledges limited experience with MCNP and suggests consulting the manual for guidance on surface segmentation.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of using F4 versus F2 tallies, indicating a lack of consensus on the best approach for measuring surface flux in this context. The discussion remains unresolved regarding the optimal method for calculating view factors.

Contextual Notes

Participants note potential limitations in their understanding of the MCNP output and the implications of scattering, as well as the need for further exploration of surface segmentation techniques.

seedsluis
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hello, everybody, I try to use mcnp to calculate view factor of radiation heat
transfer, could somebody give me some advice? I want to use surface
source, but I do not know how to get the number of the particles
emitted from the source from the output file? and I use F4 tally, I do
not know how to use the values of the tally from the output file, the
values seem to be very small?
Thanks a lot. The attachment is the output file, Hope you can help me .
 

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It has been a while since I've used MCNP, but since no one else has responded I'll give it a shot answering your question.

I believe the tally results are normalized to a single source particle. That actually explains both your questions in one. You don't need to know the number of source particles because the answer is PER source particle. It also explains why your answer is so small.
 
Thanks so much for your respond. I know I should not care the magnitude about the value. I think F4 tally is not so good in my case, 'cause usually the sum of all value should be 1, but in my case it is far more than one, there should be some where I should modify in my input, F4 gives flux inside the cell, but what I really need is # of particles passing through the surface, even through I made everything is void, maybe scattering will influence the process, I tried to use boundary condition to solve the problem, but I still did not find the correct way to do so.
 
Since you only care about the surfaces I believe you should be using the F2 tallies which are surface flux instead of F4 tallies which are cell (volume) flux. Give that a try and see if you get better results. Also, if all your materials are void than scattering in MCNP should not be an issue.
 
OK, since scattering will not be an issue. Now I'm using F2 tally, since I should divide the whole surface into many segments, and I need the flux through individual segment, I try to use FSn to get it, I still try to find an way to calculate it in one time, since now I only can get one flux for one time, do you have some advice?
 
My MCNP experience is pretty limited so I don't remember how segmenting surfaces work. I believe the segmentation let's you divide a surface (from the surface card) into smaller sections for the tally. You'll have to read the manual and play around. Maybe someone else here with more experience can help you.
 
Sure, Thanks for your help. I am using the most time-assuming way to do so, I think. Maybe later I will find a better method, *.*
 

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