OT Insulation, aluminized mylar vs foam

perhaps you're going to see some shrinkage of the inner layers, like a balloon in LN2, how much depends what gas is filling the foam/bubbles.

--
umop apisdn

dogs,

too

e air gap stops convection pretty much as effectively. The literature on do uble glazing says a wider gap isn't as effective for thermal insulation, th ough it is more effective for acoustic insulation.

le-wrap type bubbles should work as spacing. Check that the material doesn' t get brittle at liquid nitrogen temperatures - I've never run into that as a problem, but my imagination suggests that one might.

e rather large bubbles, hence are nowhere near as effective as polystyrene or PIR foams.

Larger bubbles are better than smaller bubbles, up to somewhere around the

6mm wall-to-wall spacing, not that it makes a lot of difference. All solids conduct heat about a thousand times more effectively than any static atmos pheric pressure gas, so smaller bubbles just have more conducting wall to b y-pass the gas.

You seem to think otherwise.Why? Where's your data?

--
Bill Sloman, Sydney

he dogs,

de

m.

t too

ide air gap stops convection pretty much as effectively. The literature on double glazing says a wider gap isn't as effective for thermal insulation, though it is more effective for acoustic insulation.

bble-wrap type bubbles should work as spacing. Check that the material does n't get brittle at liquid nitrogen temperatures - I've never run into that as a problem, but my imagination suggests that one might.

ave rather large bubbles, hence are nowhere near as effective as polystyren e or PIR foams.

e 6mm wall-to-wall spacing, not that it makes a lot of difference. All soli ds conduct heat about a thousand times more effectively than any static atm ospheric pressure gas, so smaller bubbles just have more conducting wall to by-pass the gas.

Maybe you're right. I'm not sure its that simple though, smaller bubbles do also mean thinner walls. PIR foam has smaller bubbles and is higher densit y, yet is higher insulation than EPS.

NT

: :

the dogs,

side

oam.

not too

wide air gap stops convection pretty much as effectively. The literature o n double glazing says a wider gap isn't as effective for thermal insulation , though it is more effective for acoustic insulation.

bubble-wrap type bubbles should work as spacing. Check that the material do esn't get brittle at liquid nitrogen temperatures - I've never run into tha t as a problem, but my imagination suggests that one might.

have rather large bubbles, hence are nowhere near as effective as polystyr ene or PIR foams.

the 6mm wall-to-wall spacing, not that it makes a lot of difference. All so lids conduct heat about a thousand times more effectively than any static a tmospheric pressure gas, so smaller bubbles just have more conducting wall to by-pass the gas.

do also mean thinner walls. PIR foam has smaller bubbles and is higher dens ity, yet is higher insulation than EPS.

Polyisocyanurate is a stiffer plastic than polystyrene, so you end up with less wall and more gas. You need to spell out what you mean by density - yo u may be confusing it with stiffness.

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Bill Sloman, Sydney

Aerogel would be a good choice for this. It is an incredibly good insulator and is non-flammable.

John

Solids range from diamond and copper, up above 400 W/m/K, down to common plastics at around 0.1. Room temperature air is about 0.025, about a quarter that of ordinary plastic.

So the plastic has more effect on the heat capacity than on the average conductivity.

Cheers

Phil Hobbs

he dogs,

de

m.

t too

ide air gap stops convection pretty much as effectively. The literature on double glazing says a wider gap isn't as effective for thermal insulation, though it is more effective for acoustic insulation.

bble-wrap type bubbles should work as spacing. Check that the material does n't get brittle at liquid nitrogen temperatures - I've never run into that as a problem, but my imagination suggests that one might.

ave rather large bubbles, hence are nowhere near as effective as polystyren e or PIR foams.

e 6mm wall-to-wall spacing, not that it makes a lot of difference. All soli ds conduct heat about a thousand times more effectively than any static atm ospheric pressure gas, so smaller bubbles just have more conducting wall to by-pass the gas.

No data at the moment. I will look at the holding time of a ss tube, closed at one end, filled to some level with ln2. I first thought of foam. I'll try that first. My new thought is multi layers of AM. It seems to me, though I could certainly be wrong, that the more surface layers the heat has to transfer through, the higher the resistance. AM also "does" the radiation part of heat transfer to a Tee.

Not enough layers in thick bubble wrap.

George H.

Near room temperature the volumectric heat capacity of everything is about the same... which is kinda depressing. Heat wise there are no magic materials. (well diamond and other hard ceramics)

George H.

I presume you jest

NT

Solid polyethylene sits at 0.5, about twenty times more conductive than of air. Which "ordinary" plastic did you have in mind?

Not entirely true - to the point of being downright misleading.

--
Bill Sloman, Sydney

HDPE is a bit better, true.

Polystyrene, of course, is the one most relevant to foams--it comes in at about 0.15 W/m/K. Polyimide is around 0.12. Nylon, LDPE, and PTFE are around 0.25. Within a factor of 5x or 10x of air.

A pretty far cry from "All solids conduct heat a thousand times more effectively than any static atmospheric gas".

How so? The volumetric heat capacity difference between air and plastic is pretty startling--much much bigger than 10x.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

True - I was remembering stuff from the 1960s.

But who was interested in the heat capacity? This thread is all about insulation, not heating and cooling rates.

You are starting to sound like James Arthur, who always tries to move away from what's actually being discussed to some area where he can sound good.

--
Bill Sloman, Sydney

Hi Bill, I think I mumbled something about heat capacity in this thread. At some point (thermally) you always care about heat capacity. I could get the same insulation value with six feet of dirt or something, but it would take months to get to temperature... whether that is a good or bad thing depends on the application.

For a variable temperature dewar, I think I want it as snappy as possible. Though there are lots of other constraints... compromises. (in this case heat capacity is not of primary importance... insulation, cost, repair/reliability... )

George H.

Of course, nobody had ever made a parenthetical comment on SED previously, so I understand Bill's consternation. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

n E

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insulation, not heating and cooling rates.

away from what's actually being discussed to some area where he can sound g ood.

.

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d

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It may have been a parenthetical comment - but we are used to them here. Wh at got up my nose was Phil Hobbs taking the chance to exhibit his broad-spe ctrum expertise where it wasn't actually serving any useful purpose (except in image building, an activity which Phil does seem to enjoy).

And consternation is a rather different state of mind from being irritated, which I clearly was - and remain, even if Phil's major point - that my tho usandfold difference in thermal conductivity was something of an exaggerati on - is perfectly valid, if essentially irrelevant.

--
Bill Sloman, Sydney

And sometimes you *want* a material with high volumetric heat capacity. This goes up dramatically when a phase shift is involved. I recently was looking for high heat capacity material at room temperature and found a number of papers on using paraffin as a heat moderator in homes by making walls containing it. I'm not sure how they might mitigate the fire hazard aspects.

They use a purified paraffin with just one compound rather than a mixture. However, I couldn't find a source for a pure hydrocarbon that seemed a reasonable price. That put me on the trail of a commonly available material that will do the same thing by changing to a liquid at room temperature. What I found was coconut oil which changes phase

--

Rick

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t insulation, not heating and cooling rates.

e away from what's actually being discussed to some area where he can sound good.

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What got up my nose was Phil Hobbs taking the chance to exhibit his broad-s pectrum expertise where it wasn't actually serving any useful purpose (exce pt in image building, an activity which Phil does seem to enjoy).

Wow OK, look we hang out here for different reasons. If Phil H. wants to share some of his wisdom, about a problem I'm thinking about, then I'm all ears.. It's my choice to take his advice or not. (most of the time he's right on.. (I'm not sure about where to put the temp sensor in a control loop... I still want to stick it as close to the thing I want to control as possible.))

d, which I clearly was - and remain, even if Phil's major point - that my t housandfold difference in thermal conductivity was something of an exaggera tion - is perfectly valid, if essentially irrelevant.

n E

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insulation, not heating and cooling rates.

away from what's actually being discussed to some area where he can sound g ood.

.

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Oh phase changes are a whole different beast. The heat of fusion for water is huge. (I just peaked at wiki.. 79 cal/ gram... and the specific heat of water is 1 cal/gram)

George H.

Yep, that is why they could cut ice from a lake or river in the winter, pack it in saw dust in a large warehouse and have ice all year long.

--

Rick