# Jet Fire Calculations

1. Dec 31, 2008

### neorich

I am trying to calculate the effects of a Jet fire from a pipe rupture where the pipe contains flammable gas. I have come across a model by D.A. Carter which predicts the heat flux at a distance x from the fire. The problem that I have is that I want to also calculate the length of the flame and the angle of tilt of the flame due to any wind.

I have found some references to calculate flame length but they give different answers and some are only valid for vertical releases with no wind.

I see refeences to the API 521 standards and a calculation involving:

Length=0.00604*Q^0.4776 (taken from ChE forums website)......(1)
(Assuming Q in BTU/hr and Length in feet)
and another one given as:

Height = 0.0042*Q^0.478 again from ChE forums although credited to Milten R. Beychok in "Fundamentals of Stack Gas Dispersion." .......(2)
Note here Q is in BTU/hr and Height is in feet.

Another one was found again linked to API 521 as:

Length=0.00326*(Q)^0.478 .......(3)
(Vertical release with no wind)
Q is the mass flow rate * heat of combustion. The numbers I am working with are 43.7kg/s flow rate and 47710000J/kg.

Results:
Equation1 - 93m
Equation2 - 65m
Equation3 - 93m

It would seem 1 & 3 are simply for different unit systems.

The problem I have is that neither of these match the value given by Carter of 39m for flame length.

Can anyone please explain why this discrepancy exists (2.3x) and help me to rectify it? Also How can the tilt angle be calculated? If the above methods are the appropriate onesI should be using, how do I take account of the wind's effect on flame length? I have found the resources for this problem to be very sparse when related to jet fires. Help would be much appreciated.

Kind Regards

neorich