Sprinkler capped simulation

[SaiSantosh1824]

Hi,
I would like to clarify a few items regarding modelling a sprinkler capped fire.

The most common method is to have a fixed area for the fire, define a ramp-up as a multiplying factor to the HRRPUA based on a suitable growth rate and use the FREEZE TIME function to cap the fire size based on sprinkler activation. In this method, the area remains the same but the HRRPUA is varied.

Is there a similar method but to have the HRRPUA constant and cap the area of the fire which has a defined spread rate based on a suitable growth rate? Is it possible to have this done automatically in a single simulation as opposed to two separate sims with the pilot sim to compute the time of activation of the sprinkler.

Finally, if we assume a fixed location of the sprinkler, which of the two methods will result in a larger fire (theoretically). My understanding is both have the same HRR relation with time (first method being continuous function and the second method being similar to a step function, https://firedynamics.github.io/LectureFireSimulation/_images/pool_fire_10mw_sealed_hrr_spread.svg) and therefore should cap the fire size almost at the same time. Please correct me if I am wrong.

Thank you

[drjfloyd]

With spread rate, the fire starts with just one grid cell burning and the area grows over time with the burning rate constant over the area burning. Without spread rate and varying HRRPUA with a RAMP the area is constant and the burning rate varies over time. While you have the same heat release rate, the fire diameter is not the same. The same fire with different diameters will see some differences in the plume temperature as a function of height and the plume temperature at the ceiling becomes the source for the ceiling jet temperature. You could take Heskestad's plume correlation and see what fire size is needed for the constant HRRPUA vs constant area approach to see your sprinkler activation temperature at the ceiling. Then use the growth rate to get a time. That would give you an estimate of how much difference there might be.

There isn't a way currently in the code to turn off spread rate. You could script the spread rate and then use the freeze method. That is define your burner as concentric rings of squares where the innermost square starts following the HRR curve until you reach the desired peak HRRPUA, then the next ring starts growing from zero until the peak HRRPUA, etc (a SURF and RAMP_Q for each ring). Then all the RAMP_Q can be set to use the same time frozen DEVC for TIME.

[SaiSantosh1824]

Thank you for your guidance!

I will look into this further and update!

[mpachera]

Hi, I made a script that keeps the HRRPUA constant and increases the area including the effect of sprinklers suppression, you can find it here: https://fireworkbench.com/firespread