21 Oct 04 4:23
It seems like there is quite some confusion around these equations. For example, in their book "Chemical Process Safety: Fundamentals with Applications", Daniel A. Crowl and Joseph F. Louvar show the equations as given by 25362 in previous post, and they refer to a lecture by M.G. Zabetakis in 1959. Same is true for Frank P. Lees in his book "Loss prevention in the Process Industries" (equations 16.2.2 and 16.2.3 in 2nd edition of his book).
However, when looking at the curves and equations in the Bureau of Mines Bulletin 627 my conclusion remains that equations as shown in this Bulletin and on site from fkhan are correct, and equations given by 25362, Crowl&Louvar and Lees are not correct.
When we write both possibilities (for LFL) in a similar form, the both look like:
What it all boils down to is whether the term before (T-25) should be (for LFL):
Both Perry's and Lees state that this term has a value of about 0.0008/°C, where Bulletin 627 uses 0.000721.
When we fill in values for methane (from table 2 in Bulletin 627): ?Hc= 191.8 kcal/mole and LFL25=5.0 vol% we get:
0.00391 vs. 0.000782
From this I conclude that the term should be:
this one corresponds to the equation from Bulletin 627 and used on fkhan site.
Note that for UFL the term would be 0.000261 since UFL25 for methane is 15.0 vol%, where Perry, Lees and Bulletin 627 say that term should be about the same as for LFL (so about 0.0008). So my conclusion is that for UFL the equation should actually be: