R32 and R125 Flmmability limit calculations

[skumar84]

R32 and R125 forms R410A if mixed 50% and 50% by mass. By volume the concentration is around 70% of R32 and 30% of R125.

The resulting mixture 410A is not explosive when R32 and R125 are 50% by mass....What happens when the % of R32 increases from 50% to 70%?

Will the mixture be explosive since R32 is flammable or not since R125 is a fire supressant.

I tried calculating this problem using le chatler principles but could not arrive to a solution since R125 is a fire suppressant and does not have any flammability limits ...

LFL(410A) = 1/((M(R32)/LFL(R32)+M(R125)/(LFL(R125))

M(R32) and M(R125) - Mole fractions of the refrigerants
M(R32) = 0.70. M (R125) = 0.30

LFL(R32) = 14%-32% by volume
LFL (R125) = Not available ...fire suppressant ...

This is what I used...but could not calculate since R125 does not have any limits ...

 

[Flareman]

Skumar84
From the LEL of R32 (14% in air) you know that the amount of diluent which can prevent continued combustion of R32 is in the ratio of 86 : 14 = 6.14 :1 when the diluent is Air.
If you have the relative specific heat of R125 vs that of air you can estimate the amount of R125 needed to prevent combustion by applying the same diluent heat capacity. Remember that this is not a perfect solution but it will point you in the right direction for the LEL. Always use a FOS when doing this home-grown calculation.
That should work for the LEL which is essentially the "too-cold-to-burn" limit, but unfortunately it doesn't necessarily work for the UEL because that is a function of the molecular instability which is temperature related. The ignition energy from the ignition source raises the temperature and destabilizes the molecule. Normally mixtures richer than the UEL can be assumed to not have enough energy release to propagate, but R125 is a molecule which has its own destabilizing characteristics and you may have an energy source which can break down that too if the decomposition temperatures of both components are fairly close together.

I suggest that you speak to someone in the R410A supply business as they may have data which are not available to the rest of us.

David

 

[skumar84]

@ David

Thanks...will try to work on this ...