I’m designing an item that will have cold water running through it and I want to avoid condensation on the outside during humid weather. I could wrap the item in foam insulation, but I would like to optimize whatever insulation properties the infill can provide first. It would be ideal if the infill can provide all the insulation this application requires.
The current design iteration uses walls a minimum of 5MM thick. That design is to provide insulation rather than strength. I’m starting with 25% infill and may play around with that percentage.
The best thermal insulators trap air thereby preventing convection.
Which infill pattern would best prevent air movement inside these 5mm thick walls?
I think the Cubic infill pattern would probably be the most suitable. It is made up of cubes with one corner facing down, so will create lots of small pockets.
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I’d be much more concerned about the 25% plastic, as it conducts heat much better than air.
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Thanks for that solid answer! I’ve made a prototype and I’m testing now. I’ll report the results later. Thanks again!
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Plastic conducts heat much better than trapped air, but not significantly better than free air. Therefore, successful design requires some balance. Low infill density results in larger air pockets, which leads to more convection and less insulation. High infill density results in smaller trapped air pockets, resulting in better insulation, but more thermal conductance directly through the plastic. I guessed that 25% was a good starting point and I’ll test and refine from there.
If would be interesting to learn the composition of fiberglass insulation: What percentage is trapped air and what percentage is fiberglass?
Thanks for the reply!
That also strongly depends on the expected air flow velocity. A 5mm wall with 2 perimeters leaves about 3mm air/infill gap. Even without infill convection velocities would be so low that any infill would transfer heat better than that slow convection. My recommendation is to use as low infill as required for stability.
Try printing test samples, put them on a warm object and check with an IR camera or an IR thermometer.
(Density of glass: ~2500kg/m³, glass wool: ~20-80kg/m³, so around 2% “infill”)
@kmorley just curious what kind of results you ended up with from your testing?
Any updates on your testing? I plan on making a window baffle (anything is better than nothing for my window vent situation), however I am finding interestingly counter intuitive info online where a higher infill density ends up with more thermal resistance. The papers I’ve read seem to have very poor print quality though (i.e. infill collapsing, poor layer adhesion, etc).
I never tested further, because the original design provides sufficient insulation for what I needed. Condensate water in the trap exits the air handler somewhere in the low 40F range. Ambient air temp frequently exceeds 100F, with humidity approaching 100%. With the 5MM infill I left around the water-carrying parts, the trap sweats a small amount on the exterior. But it’s sufficient because it never sweats enough that drips occur. The water tends to evaporate before it drips. Avoiding puddles was my major objective and the existing design accomplishes that goal.
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