Heat loss through a hole in insulation 1

[Andy.C]

hi,i am needing to record the heat transfer through a penetration hole in an insulation panel. Hot side will be around 350°C / cold side ambient around 30°C. Hole diameters between 5-30mm, some penetrations will have structures through them.
what would be the best way to mease the heat flux? as the sensors i currently use need to have a solid contact with a surface, and i can not just suspend these over the hole.
is it possible to use thermocouples and calculate somehow? or are there any better methods?

 

[MintJulep]

The "best" way would be to make representative samples of each construction, with and without hole.

Test them in something similar to an ASTM C1363 "Hot box" or C177 Guarded Hot-Plate as appropriate for your boundary conditions.

The difference between the with hole sample and the without hole sample will be the hole.

 

[racookpe1978]

What "fills" the "hole" in the overall insulation blanket will control how much is lost from the combined "system" of each hole. Your problem is NOT just 2d either: The heat loss differences between a simple 200 mm x 200 mm insulated flat plate, and a 200 x 200 flat plate with a 25 mm hole in the insulation and a thermowell, a pipe, a support piece of metal, a access port, a view port, etc are extreme.

As above, you can calculate the nominal 200 x 200 flat insulated plate, then build it and measure. Built models of the 4 most common penetrations, use those results to calibrate the equations for different sized hole and different types of gear filling the holes.

 

[georgeverghese]

You wouldnt get much by way of natural convection for heat loss through a plain cylindrical perforation in the insulation. Most of the heat loss would be in radiant mode, I would guess.