Tank Insulation

mostly the extinguisher is designed in such a way that the end user does not have to take any measures of protecting it.

But anyways here is what you should do.

first select the material which you will use as the insulator.

Determine the values of "h" and "k" for that material.

"h" is the coefficient of convective heat transfer

"k" is the coefficient of conductive heat transfer.

then find out critical radius by the formula Rc = h/k.

this is your insulation thickness.

note that for circular members the more you increase the insulation thickness the more the heat transfer takes place.

you can get the values of h and k using data book.

first of all thanks for your reply.

It's not an extinguisher, it's a polyethylene tank used to store the foam concentrate used in the firefighting system. Usually we don't insulate these tanks because the chance of the foam reaching those temperatures is slim, but the client company requested it.

Anyway, so lets say I'm going to use "mineral wool" insulation. I can easily find it's conductive heat transfer coefficient "k" but nothing for the "h". any suggestions.

And is this the method used to determine the insulation thickness for any application or is there other methods?

I am afraid that what you are considering may not be feasible. No insulation has infinity resistance. If your tank is immersed in an atmosphere whose ambient is 60 Celsius, the contents will reach that temperature sooner or later. The 'h' referred to is the overall heat transfer coefficient which is the characteristic of the films involved rather than the materials. In your case the lfoam film inside and the air film outside. Usually the value for h will be 10 kCal/(sq.mtr.hr.degC)at near ambient temperatures. Better circulate water at 30 degC or so in a jacket around the tank.