Limitations regarding large compartment

[andreas...@gmail.com]

Hi, 

 

I'm a new user of CFAST and I use it to test different ventilation conditions. After using the program for a few days, some questions have appeared:

 

1) What's the limitations regarding large compartments and HRR in version 7. Are those the same as presented in Table 3.2 in Technical Reference Guide version 6? I have read the same chapter in version 7 but it does'nt mention anything about it. 

 

2) When simulating a large compartment (150x30x5) and comparing different size of natural ventilation using the same fire, there is approx. no difference in HRR and temperature. Shouldn’t the oxygen level control the HRR and the temperature be higher with larger openings?

 

Thanks,

Andreas

[Richard Peacock]

1) We did remove the discussion of compartment size limitation in the version 7 Technical Reference Guide as it was just causing confusion.  CFAST has been validated over a wide range of compartment sizes up to more than 100 000 m^3 in size.

2) The HRR is just a user input so it would not get larger with changing ventilation.  If there is not sufficient oxygen in the compartment and the vent size is small enough that sufficient oxygen cannot flow into the compartment, the fire size can be reduced to that which will burn with available oxygen. With such a large compartment as your example, it would take quite a large fire to reach that point.

[GCR_VE]

Sorry Andrea I ask Richard a question instead of answering you.

CFAST vers. 7 - Vol. 3 (Verification and Validation Guide)  give in Tab. 4.1 limits for application field: W/H > 4.9 and L/H < 7.1 and 150/5 = 30, perhaps plume is out of application field ?

I always apply all conditions of Tab. 4.1, p. 35.

I'm doing it wrong ? 

Thank you and to Richard.

Giancarlo

[GCR_VE]

I correct my previous message.

W/H < 4.9, L/H < 7.1 and in Anreas test we have L/H = 150/5 = 30.

Giancarlo 

[andyta...@yahoo.com]

Dear Giancarlo,

I think that the Table of the summary of important experimental parameters as shown in the V&V guides provides details of the ranges of parameters being covered by the experiments. This information indicates that CFAST (the models being used to describe different heat transfer and/or phenomena) is being validated with experiments in these conditions.

When CFAST is being used outside of the conditions listed in the table, it doesn't mean that results generated by CFAST are wrong. However, I think that users will just have to be mindful and check if the results make sense.

Thanks,

Andy

[gcr039 - gmail]

Ok, I agree.

In not a binary result but to prove that results have sense you need a parametric analisys.

Thank you.

Giancarlo

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Saluti Giancarlo Rossi

[gcr039 - gmail]

Ok, I agree.

In not a binary result but to prove that results have sense you need a parametric analysis.

Thank you.

Giancarlo

Il 01/10/2018 16.44, andytamhk168 via CFAST ha scritto:

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Saluti Giancarlo Rossi