Window Heater

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ucted by convection and the heat transfer by radiation is negligible. For h eat flow horizontal it is some what effective.

I'm not sure what you mean here by 'up' and 'down'--in this context of a refrigerator and a window, the surfaces are both vertical and the heat flow is horizontal, through the insulation.

Vertical surfaces produce convection, but the effects of that are included in my temperature differential measurements across the outboard 'fridge insulation. No attempt was made to block convection.

For the windows I should've noted that I've got either blinds or drapes covering the inside surface to discourage convection, with air gaps between blinds / car shade / window.

= s w (inside) = s w (outside) = s w

blinds: '=' shade: 's' window: 'w'

does not conduct heat well. Argon is similar. So polyurethane foam is a m uch better insulation than polystyrene foam. At least for some years. Eve ntually water vapor gets into the polyurethane foam.

I was surprised to realize / learn that the insulating value of a material is nearly completely inversely dependent on its density--the insulation value comes not from the material, but from the air gaps. The materials' thermal conductivities are nearly always so much higher than their trapped air that the 'insulating' material used almost doesn't matter.

Cheers, James Arthur

He doesn't know. His numbers and arithmetic are inconsistent. You should not be surprised that he does not believe you.

Have you tried putting on a coat?

cloak or superhero cape? :P

You didn't answer my other questions. The 30 watt heater (which is pumping out 40 watts until I can get an adjustable PSU) will cost me about $2.50 to run for a month continuously. Are you saying your electric bill is only around $25 a month? You must live somewhere that doesn't need heating or cooling by electricity.

Ok, ignore my other post then. I'm not sure what relevance this has. I guess just an observation.

What is inconsistent in my numbers or math?

Yes, I do, every time I go out. :)

I had a brainstorm on this: instead of a strip of resistors and a grille, put a strip of resistors in between two metal plates, with a good amount of spacing in between, and with the slot vertical. Put the resistors toward the bottom.

It _should_ create a chimney effect, to get the most air velocity from the power expended by the resistors. Assuming, of course, that's what you actually need.

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nducted by convection and the heat transfer by radiation is negligible. For heat flow horizontal it is some what effective.

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t does not conduct heat well. Argon is similar. So polyurethane foam is a much better insulation than polystyrene foam. At least for some years. E ventually water vapor gets into the polyurethane foam.

Some summer day, I couldn't find my beer cozy (foam cylinder) and so wrapped my can of beer in a piece of aluminized mylar (space/saftey blanket) many layers. Worked great, (it was a bit fussy around the lips.) If you put it in a can and pump vacuum around it. it's called super insulation. (I figure you probably know this) I've always wondered how good it is w/o vacuum, just in air. (guess I'll have to measure some day...)

George H.

On Tuesday, February 14, 2017 at 4:20:49 PM UTC-5, snipped-for-privacy@yahoo.com wro te:

I was commenting on heat flow in general. Not just about the window case. So if you are insulating an attic, in summer the heat flow is down and in t he winter the heat flow is up. So in the summer the foil will help a lot and in the winter foil will have almost no effect.

Dan

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t does not conduct heat well. Argon is similar. So polyurethane foam is a much better insulation than polystyrene foam. At least for some years. E ventually water vapor gets into the polyurethane foam.

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the winter the heat flow is up. So in the summer the foil will help a lo t and in the winter foil will have almost no effect.

OK, I'm not sure in practice, but in theory I don'think it should matter much which side of the foil is hot or cold. It's an IR reflector, pretty much the same from both sides.. (What's the peak wavelength/ frequency at ~300K)

George H.

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It's not which side of the foil is hot or cold. It has to do with the other mechanisms of heat transfer. If the heat is rising, in theory it will contact the foil and convect/conduct the heat to the foil while a cold room won't do that so much. I'm not sure the theory is sound as you get convection regardless of which way the "heat" is moving. Its the same transfer mechanism. But I have seen ratings of foil lined insulation and they do have different ratings for different uses and orientations. The foil will work best if adjacent to a vacuum, but that's not practical other than in a thermos bottle.

The point is the foil prevents radiation emission and/or absorption.

Yes.

My neighbors spend about as much as you.

But instead of heating a whole house to tropical temperature you can dress warmly by day, and only heat the room you're in. Exercise in the morning too--it's good for you, and warms you for hours.

At night several lofty comforters and an electric mattress heater set on 'low' keep things comfy in the coldest of times for perhaps

Oh, and wrap extra insulation around your fridge--it saves electricity. :-)

Cheers, James Arthur

I think the difference is this--if the foam's exposed, IR hits and warms the foam. Then you have warmed foam contacting foil, facing the refrigerator (cold).

OTOH with the foil facing out, the IR is reflected rather than absorbed, and you also get the insulation value of the (cool) foam between the foil and fridge.

Cheers, James Arthur

So you can use two pieces of foiled foam side by side, but facing opposite ways. Then connect the two via a Stirling engine and get free energy!

nter foil will have almost no effect.>

As far as blocking radiation , it does not matter. But as far as blocking heat flow it does.

Say you have a horizontal surface with the air below the surface is hot and the air above the surface cold. The heat from below heats the aluminum foil. THe air immediately above the aluminum foil is warmed and rises. Almost no heat flow effect.

Now with the same surface by cold below and warm above. The air above heats the aluminum foil. The air immediately under the aluminum foil is warmed. But it can not rise because the aluminum foil is above it. It does not radiate down. So little heat flow.

Dan

OK it's complicated. In my simple model the foil is at some intermediate temperature between the cold and hot... (Maybe this is a bad model, 'cause I'm not thinking about other mechanisms effecting the foil temperature.) You get a win because of the low emmisivity of the Al. But it's not something I know a lot about.... Hmm this says that getting rid of the air is important!

George H.

OK, but in either case does it matter if it's foam on top or foil on top?

George H.