velocity in the ceiling jet

[Mardy Owens]

Hi,

I am trying to compare the radial time averaged velocity component in a ceiling jet obtained with FDS, with  the Alpert correlation

Alpert, R.L. Calculation of response time of ceiling-mounted fire detectors. Fire Technol 8, 181–195 (1972). https://doi.org/10.1007/BF02590543

I looked if it was done before in the validation guide, but at pag 144 I found only the comparison with the temperature.

In doing this comparison I found that the values from the alpert law are always higher than mine. So I have a question: 

do you know by chance if Alpert calculate the modulus of the velocity vector instead of the radial component of the velocity? (It is simply called the gas velocity, but in the drawings only radial components are shown)

This would make sense to me, in terms of results.

[fde]

I have no definitive answer but this remark also takes place here:

https://lucris.lub.lu.se/ws/portalfiles/portal/5660006/4246970.pdf


My first approach would be looking at the experimental setup. If bi-directional pressure difference probes were used, maybe this has something to do with measuring angle of the incoming flow towards the probe. It is known that bi-probes are robust devices and can measure flow within ~30 degree with a little error. Maybe radial velocity is not exactly one component but, as you suspected, a modulus of velocity.