Heat exchanger exposed to fire
Heat exchanger exposed to fire
(OP)
Hi,
I'm currently trying to determine the temperature in the metal surface of an insulated heat exchanger when it is exposed to fire. I mean, if there is a fire and the temperature in the surface of the insulation is 1112ºF, what temperature can i expect to have in the metal surface of the heat exchanger if the thermal conductivity of the insulation is 0.62 btu*in/h*ft2*ºF and the insulation thickness is 0.4 in.
If anyone can help me out with this, i would really appreciate it, i can't seem to find the right approach.
Thanks
I'm currently trying to determine the temperature in the metal surface of an insulated heat exchanger when it is exposed to fire. I mean, if there is a fire and the temperature in the surface of the insulation is 1112ºF, what temperature can i expect to have in the metal surface of the heat exchanger if the thermal conductivity of the insulation is 0.62 btu*in/h*ft2*ºF and the insulation thickness is 0.4 in.
If anyone can help me out with this, i would really appreciate it, i can't seem to find the right approach.
Thanks





RE: Heat exchanger exposed to fire
RE: Heat exchanger exposed to fire
Otherwise, it would be a pretty simple radial heat transfer equation with a few layers:
1) Conduction through insulation
2) Conduction through vessel wall
3) Convection from inside surface of vessel wall to... (see initial question).
You could also add a contact resistance between the insulation and the vessel wall if you want to be more precise, but that would lessen any conservatism.
If the inside of the vessel was filled with atmospheric water for example, you'd have a very high convective coefficient on the inside surface of the vessel wall once you hit the boiling case.
If the inside of the vessel is under vacuum, you wouldn't have much of a convective coefficient and the metal temperature would likely rise very high.
A lot more information is required.
RE: Heat exchanger exposed to fire
However, you can calculate the heat transfer rate with insulation, and then back calculate the inside temperature of the insulation and assume that the wall has the same temperate. This will be conservative due to the high conductivity of the metal if the vessel is liquid filled - and worst case if its filled only with a gas.
RE: Heat exchanger exposed to fire
MortenA i was exactly looking at API 521 right before i had this doubt. In API 521 is said that in order to consider insulation in the calculations, the insulation must be fireproof, in this case it isn´t so i'm trying to figure out how much my current insulation works in case of a fire. Any ideas?
RE: Heat exchanger exposed to fire
RE: Heat exchanger exposed to fire
As to the heat input rate used for relief valve sizing for fire cases, see API 520/521- don't make stuff up on your own. There are three values: one assuming adequate drainage and firefighting, and another assuming that plus a fire-durable insulation (i.e. rigid insulation with stainless steel cladding), and I guess a third I've never seen or used for instances where you can't count on adequate firefighting and drainage.
RE: Heat exchanger exposed to fire
RE: Heat exchanger exposed to fire
RE: Heat exchanger exposed to fire