Relation between HRRPUA and burning rate

[Shashank Tiwari]

I am trying to simulate a simple pool fire of methanol. Whenever I use HRRPUA in the SURF line of methanol pool the values of burning rates obtained in the .csv file are exactly same values for all time intervals though the HRR changes. How is this possible? If I model the fire without mentioning the HRRPUA I get varying burning rates for all time intervals. If the formula followed here is HRR=HeatofComb*AreaofPool*Burningrates and if the HRR output varies with time how can the burning rate remain the same?
Which one is more accurate? should I mention HRRPUA on the surf line or continue without using it. I have calculated the HRRPUA for methanol based on the burning rates given by Babrauskas in the latest version of SFPE handbook which I am using in the simulation (i.e 0.022kg/m2sec for 0.6m<D<3m. so 0.022*20000*1=440kW.)

[Randy McDermott]

"Burning Rate" is a misnomer.  It is the mass loss rate of fuel * heat of combustion * area of the vent.  When you specify HRRPUA, you are specifying a mass flux bc and that gives you a constant burning rate.  The HRR column is the integral of the mean chemical source term times the heat of combustion over the volume.  See 16.10.1 in the user guide.  If there is unburned fuel in the domain, from extinction or under-ventilation, then the burning rate and the HRR column will not match.

On Fri, Feb 13, 2015 at 7:33 AM, Shashank Tiwari <shashank...@gmail.com> wrote:

I am trying to simulate a simple pool fire of methanol. Whenever I use HRRPUA in the SURF line of methanol pool the values of burning rates obtained in the .csv file are exactly same values for all time intervals though the HRR changes. How is this possible? If I model the fire without mentioning the HRRPUA I get varying burning rates for all time intervals. If the formula followed here is HRR=HeatofComb*AreaofPool*Burningrates and if the HRR output varies with time how can the burning rate remain the same?
Which one is more accurate? should I mention HRRPUA on the surf line or continue without using it. I have calculated the HRRPUA for methanol based on the burning rates given by Babrauskas in the latest version of SFPE handbook which I am using in the simulation (i.e 0.022kg/m2sec for 0.6m<D<3m. so 0.022*20000*1=440kW.)

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[Shashank Tiwari]

I got a clearer picture after reading the user guide section on HRR. Thank you.