flow coefficient for vertical flow in horizontal vents
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Manuel
Jan 31, 2012, 5:37:07 AM1/31/12
to CFAST
Hello All,
for the calculation of smoke vent openings I need to know the flow-
effective cross-section area. So there is a problem in calculations
with CFAST as the flow coefficent isn't a constant value in vertical
vents through horizontal openings.
I want to test if an flow-effective cross-section area, which is given
works within my cases. For CFAST input I have now to calculate a
geometric cross-section area Ageo = Aeff / C. To be on a secure side
in my calculations I want to be sure that the flow coefficient C in
the CFAST-calculation is alltime lower than the estimation I had to
do.
As far as I studied CFAST calculates C=0.68 + 0.17 * eps.
Is it posibile to give a alltime range for eps? Or is there a
possiblity to get an output so that I might recalculate eps by deltaP/
P in CFAST 6.1.1?
for the calculation of smoke vent openings I need to know the flow-
effective cross-section area. So there is a problem in calculations
with CFAST as the flow coefficent isn't a constant value in vertical
vents through horizontal openings.
I want to test if an flow-effective cross-section area, which is given
works within my cases. For CFAST input I have now to calculate a
geometric cross-section area Ageo = Aeff / C. To be on a secure side
in my calculations I want to be sure that the flow coefficient C in
the CFAST-calculation is alltime lower than the estimation I had to
do.
As far as I studied CFAST calculates C=0.68 + 0.17 * eps.
Is it posibile to give a alltime range for eps? Or is there a
possiblity to get an output so that I might recalculate eps by deltaP/
P in CFAST 6.1.1?
CFAST Development
Jan 31, 2012, 9:29:55 AM1/31/12
to CFAST
It's certainly possible, but would require code changes. Luckily, the
calculations are limited to one routine, ventcf in source file flow
vertical.f The source code for cast is available and can be
modified. It would be simple enough to modify the code to put limits
on the calculation (though this code is consistent with the original
algorithm developed by Cooper and based on his experimental work).
Alternatively, you could add printout of the flow coefficient in the
routine rsltflw in the source file output.f (or the equivalent
spreadsheet output in SpreadSheetFLow in the source file output
spreadsheet.f).
calculations are limited to one routine, ventcf in source file flow
vertical.f The source code for cast is available and can be
modified. It would be simple enough to modify the code to put limits
on the calculation (though this code is consistent with the original
algorithm developed by Cooper and based on his experimental work).
Alternatively, you could add printout of the flow coefficient in the
routine rsltflw in the source file output.f (or the equivalent
spreadsheet output in SpreadSheetFLow in the source file output
spreadsheet.f).
Gregor
Feb 1, 2012, 2:29:05 AM2/1/12
to CFAST
On 31 Jan., 11:37, Manuel <bauschinoe...@googlemail.com> wrote:
> As far as I studied CFAST calculates C=0.68 + 0.17 * eps.
Where do you find this formula?
> As far as I studied CFAST calculates C=0.68 + 0.17 * eps.
I find only this description on page 30 in the Technical Reference
Guide:
"The general form for the velocity of the mass flow is given by v = C
* sqrt(delta p / p) where C is the constriction (or flow) coefficient
(0.7), r is the gas density on the source side, and delta p is the
pressure across the interface. (Note: at present we use a constant
value for C for all gas temperatures)."
Gregor
CFAST Development
Feb 1, 2012, 11:32:04 AM2/1/12
to CFAST
This is documented on page 35 of the latest CFAST technical
reference. I comes from two references of the original work by
Cooper:
[42] L. Y. Cooper. Calculation of the Flow Through a Horizontal
Ceiling/Floor Vent. NISTIR
89-4052, National Institute of Standards and Technology, 1989.
[43] L. Y. Cooper. Algorithm and Associated Computer Subroutine for
Calculating Flow
Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment
Fire Model. NISTIR
4402, National Institute of Standards and Technology, 1990.
In the CFAST code (available at http://cfast.googlecode.com), it's in
the routine ventcf in the source file verticalflow.f
reference. I comes from two references of the original work by
Cooper:
[42] L. Y. Cooper. Calculation of the Flow Through a Horizontal
Ceiling/Floor Vent. NISTIR
89-4052, National Institute of Standards and Technology, 1989.
[43] L. Y. Cooper. Algorithm and Associated Computer Subroutine for
Calculating Flow
Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment
Fire Model. NISTIR
4402, National Institute of Standards and Technology, 1990.
In the CFAST code (available at http://cfast.googlecode.com), it's in
the routine ventcf in the source file verticalflow.f
Gregor
Feb 1, 2012, 3:23:09 PM2/1/12
to CFAST
Thanks. Sorry, I found my mistake. I only read the word "vertical
flow" and forgot "horizontal vents".
I'll study the literature.
On 1 Feb., 17:32, CFAST Development <cfast...@gmail.com> wrote:
> This is documented on page 35 of the latest CFAST technical
> reference. I comes from two references of the original work by
> Cooper:
>
> [42] L. Y. Cooper. Calculation of the Flow Through a Horizontal
> Ceiling/Floor Vent. NISTIR
> 89-4052, National Institute of Standards and Technology, 1989.
>
> [43] L. Y. Cooper. Algorithm and Associated Computer Subroutine for
> Calculating Flow
> Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment
> Fire Model. NISTIR
> 4402, National Institute of Standards and Technology, 1990.
>
> In the CFAST code (available athttp://cfast.googlecode.com), it's in
flow" and forgot "horizontal vents".
I'll study the literature.
On 1 Feb., 17:32, CFAST Development <cfast...@gmail.com> wrote:
> This is documented on page 35 of the latest CFAST technical
> reference. I comes from two references of the original work by
> Cooper:
>
> [42] L. Y. Cooper. Calculation of the Flow Through a Horizontal
> Ceiling/Floor Vent. NISTIR
> 89-4052, National Institute of Standards and Technology, 1989.
>
> [43] L. Y. Cooper. Algorithm and Associated Computer Subroutine for
> Calculating Flow
> Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment
> Fire Model. NISTIR
> 4402, National Institute of Standards and Technology, 1990.
>
Manuel
Feb 2, 2012, 2:42:14 AM2/2/12
to CFAST, oe...@gmx.de
This is a good information for further literature studies, which I
found in the Technical Reference Guide, too.
But as the model CFAST has limitations in usage there must be a range
for eps and then also for C within that CFAST calculations (as long as
they are within model limitations). If 0 < eps < 1 then 0.68 < C <
0.89. But that seems to be a too wide range. Perhaps -0.1 < eps <
0.1 ?
Further I won't change CFAST code. But I want to use existing outputs.
And there's no problem for me to calculate some values by hand. There
is a pressure output for compartments in the .out-File. But this
pressure value is not absolute. There is a ambient pressure for the
Outside. It is absolute.
How do I have to calculate eps for a flow out of Compartment 1 to
outside. If I use the pressure value from the out-file as deltaP it
might be correct but then P = 0? Or do I have to use P as absolute
value ( ambient exterior pressure )?
Thanks a lot Manuel
>
> - Zitierten Text anzeigen -
found in the Technical Reference Guide, too.
But as the model CFAST has limitations in usage there must be a range
for eps and then also for C within that CFAST calculations (as long as
they are within model limitations). If 0 < eps < 1 then 0.68 < C <
0.89. But that seems to be a too wide range. Perhaps -0.1 < eps <
0.1 ?
Further I won't change CFAST code. But I want to use existing outputs.
And there's no problem for me to calculate some values by hand. There
is a pressure output for compartments in the .out-File. But this
pressure value is not absolute. There is a ambient pressure for the
Outside. It is absolute.
How do I have to calculate eps for a flow out of Compartment 1 to
outside. If I use the pressure value from the out-file as deltaP it
might be correct but then P = 0? Or do I have to use P as absolute
value ( ambient exterior pressure )?
Thanks a lot Manuel
> This is documented on page 35 of the latest CFAST technical
> reference. I comes from two references of the original work by
> Cooper:
>
> [42] L. Y. Cooper. Calculation of the Flow Through a Horizontal
> Ceiling/Floor Vent. NISTIR
> 89-4052, National Institute of Standards and Technology, 1989.
>
> [43] L. Y. Cooper. Algorithm and Associated Computer Subroutine for
> Calculating Flow
> Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment
> Fire Model. NISTIR
> 4402, National Institute of Standards and Technology, 1990.
>
> In the CFAST code (available athttp://cfast.googlecode.com), it's in
> reference. I comes from two references of the original work by
> Cooper:
>
> [42] L. Y. Cooper. Calculation of the Flow Through a Horizontal
> Ceiling/Floor Vent. NISTIR
> 89-4052, National Institute of Standards and Technology, 1989.
>
> [43] L. Y. Cooper. Algorithm and Associated Computer Subroutine for
> Calculating Flow
> Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment
> Fire Model. NISTIR
> 4402, National Institute of Standards and Technology, 1990.
>
> the routine ventcf in the source file verticalflow.f
>
> On Feb 1, 2:29 am, Gregor <gregor.jae...@googlemail.com> wrote:
>
>
>
> > On 31 Jan., 11:37, Manuel <bauschinoe...@googlemail.com> wrote:
>
> > > As far as I studied CFAST calculates C=0.68 + 0.17 * eps.
>
> > Where do you find this formula?
>
> > I find only this description on page 30 in the Technical Reference
> > Guide:
> > "The general form for the velocity of the mass flow is given by v = C
> > * sqrt(delta p / p) where C is the constriction (or flow) coefficient
> > (0.7), r is the gas density on the source side, and delta p is the
> > pressure across the interface. (Note: at present we use a constant
> > value for C for all gas temperatures)."
>
> > Gregor- Zitierten Text ausblenden -
>
> On Feb 1, 2:29 am, Gregor <gregor.jae...@googlemail.com> wrote:
>
>
>
> > On 31 Jan., 11:37, Manuel <bauschinoe...@googlemail.com> wrote:
>
> > > As far as I studied CFAST calculates C=0.68 + 0.17 * eps.
>
> > Where do you find this formula?
>
> > I find only this description on page 30 in the Technical Reference
> > Guide:
> > "The general form for the velocity of the mass flow is given by v = C
> > * sqrt(delta p / p) where C is the constriction (or flow) coefficient
> > (0.7), r is the gas density on the source side, and delta p is the
> > pressure across the interface. (Note: at present we use a constant
> > value for C for all gas temperatures)."
>
>
> - Zitierten Text anzeigen -
fde
Jan 18, 2019, 7:46:06 AM1/18/19
to CFAST
I have a question related to the thread.
Technical guide 4.2 Horizontally-Oriented Vents (Ceiling Vents)
Equations do not have Cd discharge rate coefficient. I looked up to the referenced paper (L. Y. Cooper. Calculation of the Flow Through a Horizontal Ceiling/Floor Vent. NISTIR) but also did not understand if it is taken into account.
Could you please clarify this issue?
Simply said, do we write free area or Cd applied area to the input of CFAST?
Thank you.
Richard Peacock
Jan 22, 2019, 2:33:08 PM1/22/19
to CFAST
the vertical flow algorithm uses the typical flow coefficient of 0.68 so you should input the actual vent area
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