Re: [Phys-L] stovetop physics

[John Denker <jsd@av8n.com>]

On 10/14/2012 08:16 AM, Jeff Bigler wrote:

> 1) Glass doesn't conduct heat. 

The thermal conductivity of glass is definitely nonzero ... 
it's just small compared to metal.

Note that CorningWare and Corelle are essentially glass.
They're opaque, but they're still glass.

>  Why would anyone want to use it on a stovetop? 

Because the objective is not simply maximum heating.
You also want /even/ heating.

I'm not an expert, but AFAICT ideally you want 
 a) enormous lateral conductivity (to promote evenness) 
 b) enough conductivity in the other direction to transport 
  energy into the food ... but not so much as to short out 
  the aforementioned lateral conductivity
 c) enough heat capacity to smooth out short-term changes in
  heat input and changes in load, making the temperature-changes
  more compatible with human reaction time ... but not so much
  as to waste heat or cause undue delay.

As a means to that end, I've always thought a layered structure
would make sense: thin layers of high/low\high/low\high thermal 
conductivity or something like that.  Specifically, thin layers of 
steel/glass\copper/glass\steel or steel/glass\aluminum/glass\steel

If you are willing to spend $200 for a skillet, you can get a 
five-layer structure, e.g.
  http://www.cutleryandmore.com/coppercore.htm
However, the details don't make much sense, because all three inner
layers (Al-Cu-Al) have good conductivity AFAICT.  Maybe they
have found some strange alloy they call "aluminum" that has a
lowish thermal conductivity, but I doubt it.  At room temperature,
it's hard to find an "aluminum" alloy with conductivity much less
than 75% compared to pure aluminum.
  http://www.kayelaby.npl.co.uk/general_physics/2_3/2_3_7.html
In contrast, you can get steel alloys with conductivity less 
than 10% compared to pure aluminum.

If you want to get serious about this:  I can imagine a two-
dimensional heat-pipe, e.g. steel/heat-pipe\steel.  It might
be a major R&D effort to make this work, but the performance
would be awesome.

=================

Again, I am not an expert, but it seems to me that a lot of
what goes on in an ordinary domestic kitchen is pretty dubious
from the efficiency point of view ... and from the safety
point of view.

When you consider the hundreds of billions of hours people spend
cooking each year, you would think that even small improvements
in efficiency and safety would be well worthwhile.  Sometimes it
seems like half each bookstore and half of the TV shows are
devoted to cooking, but mostly it's about fiddling with the
ingredients, rather than worrying about safety and efficiency
of the implements and procedures.

As you might imagine, OSHA regulates safety in industrial kitchens
in the US.  Domestic kitchens are unregulated and are very very 
much less safe.