How to calculate Mass loss Rate

[Dinesh Myilsamy]

Dear Sir,

I have doubts regarding calculating the Mass loss rate per unit area for the RAMP command.

I have the experimental data of fuel mass with respective to time and the fire area.

I would like to know among these two methods which is the right method to calculate the mass loss  rate.

Method 1: Reference (https://www.youtube.com/watch?v=PyWBZLdQn38)

 

Method 2:

             

Also I would like to know that how to deal when I get negative values of mass loss rate fraction

 

For your more detailed information hereby I have attached an excel sheet.

Please let me know how to calculate mass loss rate.

Best regards,

Dinesh Myilsamy

                     

[dr_jfloyd]

The derivative of y=f(x) is the slope of f(x) at x:

dy/dx = limit as delta x -> 0 of (f(x+delta x)-f(x))/delta x 

In your case y=mass(t) and dy/dx = d mass(t)/dt and the derivative would be

d mass(t)/dt = (mass(t2)-mass(t1))/(t2-t1)

This is your second definition.

Measuring mass loss in fire tests often results in noisy data. Thermal expansion of the scale or items on the scale, boiling of a liquid or settling/collapse of a solid object, air movement, etc. all act to perturb the instantaneous measurement. You should do some form of data smoothing (fitting a monotonically decreasing function, running average, using larger timesteps, etc) when computing your derivative.

[Dinesh Myilsamy]

Dear Mr.Floyd

          Thank you very much for your response!

         For my clear and detailed understanding I kindly request you to provide me an example file for calculating mass loss rate fraction to use in RAMP command.

            Once again thank you very much !!

Best Regards,

Dinesh Myilsamy

        

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[Dinesh Myilsamy]

Dear Mr.Floyd,
    

              I am sorry to bother you,
          

             Can you please give me an example for calculating mass loss rate fraction to use in RAMP command?

            It would be more helpful for the better understanding,

Best Regards,

Dinesh Myilsamy

[dr_jfloyd]

Looking at your data, the scale used a 5 g resolution and it took more than one second for the scale to show a change in mass (i.e. your burning rate is obviously << 5 g/s). You should not be computing dm/dt using 1 s intervals as you have done in the last column. It would make no sense to say that for 5 seconds there was no fire and for 1 second you suddenly burned 5 g. I would recommend you fit a piecewise linear curve to your data. I would also recommend you ignore obvious artifacts in the data (we know that the fuel mass cannot actually increase). For example at 15:03:33 the mass jumps 15 g for a few seconds when the fire is lit. This probably results from the lighter touching the edge of the burner or some other disturbance related to lighting it.It does not mean you briefly saw a mass increase.

[Dinesh Myilsamy]

Thank you very much Mr.Floyd !!!!

Best Regards,

Dinesh Myilsamy

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