Basic thermal energy transfer physics: Insulation value in open airways vs sealed airways

[dacad]

TL;DR

Wanting to determine the change in insulation value in open airways vs sealed airways

Been around 40 years since I took basic physics in college and while I remember doing some examples of insulation values / energy conduction, I doubt I could to the math now even if I could find the formulas.

I have some some corrugated plastic sheet (think of the plastic signs you see on the side of the road) that is used in bee hives. Also have some used in a green house though a bit different in dimensions than this example but the general approach should still apply.

Typically, both ends of the corrugated sheet are open to atmosphere. This allows air flow and I do remember that moving air is far less insulating than static or contained air. So my question is, by how much for this particular example. Attached pdf file has approximate dimensions of a typical corrugated plastic board. Figure polyethylene or similar plastic for the board itself for any values needed for that material but again, just looking for the delta between free flowing air versus contained air. The exact geometry may be a bit different but I'm strictly trying to determine a delta value for the insulation properties.

Not even sure what units the result should be in but if I can get something, I can probably research enough to translate into units that I can compare with other solid materials in the bee hive.

Pretty basic stuff I'm sure but again, it's been 40 some years and energy transfer is outside of my field.

Thanks !!!!

 

[jrmichler]

TL;DR Summary: Wanting to determine the change in insulation value in open airways vs sealed airways

Been around 40 years since I took basic physics in college and while I remember doing some examples of insulation values / energy conduction

I'm strictly trying to determine a delta value for the insulation properties.

Been almost 50 years since I took basic heat transfer in college, so I had to do some homework in order to do heat transfer film coefficient calculations last week. Some general rules of thumb for corrugated plastic signboard:

Channels vertical, open ends = maximum heat transfer (worst insulation)
Channels horizontal, closed ends = minimum heat transfer (best insulation)

I have never seen thermal conductivity numbers for corrugated plastic. If I needed a working number for a proof of concept calculation for the case of horizontal channels and closed ends, I would use the value for a double pane glass window without any coatings and without gas fill. For the case of vertical channels and open ends, I would expect the thermal conductivity to slightly better than a single pane glass window without any coatings.

A well known trade name is Coroplast. The manufacturer with that trade name has a web site: https://www.coroplast.com/. I did not see any thermal conductivity information on their site, but admit that I did not look very hard. You could contact them and ask. I do not know of any way to calculate heat transfer any better than the glass comparisons mentioned above.

Pretty basic stuff I'm sure

We both wish. Not for this product.

 

[Chestermiller]

I assume that the heat flow is in the vertical direction and the bottom is hotter than the top, so we do not need to include natural convection. Is this correct?

 

[256bits]

We both wish. Not for this product.

One can approach this from an insulation aspect to hinder heat flow from one area to the next, or from a heat transfer aspect removing heat from a hot area to a colder area. Modeling would be complex as one would have to determine fin boundary conditions, convective heat transfer coefficient(s), temperatures, mass flow for the heat exchanger model or the insulator model.

Your approach should simplify those complex calculations that start from scratch.

 

[Lnewqban]

Welcome @dacad

Please, see:
https://www.engineeringtoolbox.com/convective-heat-transfer-d_430.html