🚀 go-pugleaf

Hi Nick,


nick@vu-vlsi.ee.vill.edu (Nick Pine) writes:

> 
> george <jeffe@red.seas.upenn.edu> wrote:
> 
> >...the thermal conductivity of soap film isn't in my heat transfer text.
> 
> I wonder what heat transfer text you are using.
> 
> I guess it's like a very thin film of water, or anything else, eg plastic
> film, as far as stopping convection, and good enough to stop some of the
> IR radiation, ie the bubble wall would ideally be thick enough or opaque
> enough slow down IR losses considerably.

I always care about radiation losses last: 
conduction and convection losses come first.

So from my point of view, it could be a problem that the thing is NOT
SOLID: 
The trick in using bubble plastic is, that the walls are too thin for
heatloss via conduction.
And the air in the bubbles is trapped in such small bubbles, that no 
convection can take place in the bubbles.
The only losses left are radiation losses.

With soap bubbles, the water around the bubble can move:

So a water molecule could absorb energy, and while the bubbles are
going up, I'd expect warmer bubbles to go up faster. So on each
sloping or curved construction they tend to reach the outside pretty
soon, losing their heat energy via conduction to the PE film /
outside.

The bubbles would be great if they were stationary. (not moving)
I can't believe they're of great value, when they're moving up,
especially, if the air is exhausted to the outside.

I'd expect it to be equivalent to have a 50 Watt blower blow air
between the two PE sheets which is exhausted through various gaps to
the outside.

Maybe even worse, since the air would absorb some moisture thus also
absorbing heat from the surroundings. (evaporative cooling!!!!)
just imagine the HUGE water surface the bubbles create.

Evaporative cooling would be eliminated, if the PE sheets were leak
free and the water AND air would be cyclead over & over (sucking air
from the top to create the new bubbles).

So what is left is the cycling of the water & air from the inside
sheet to the outside sheet:
There would be a significant amount of water running down the inside
sheet (it's a curved/sloped construction, and gravity does it's job),
absorbing pretty much heat from the inside.
Some of this water is then contacting the outside sheet as it's
re-bubbled, losing its energy to the outside.

What we would need to gain any profit over the blower-alone approach
would be an air-tight construction of the two sheets and a liquid
that'd produce very "sturdy" bubbles, so that the air-movement rate
could be lowered.
As long as we're moving much air, we'll be seeing these
convection/conduction losses. 

just my thoughts....

cheers,
albrecht