Sheldon wrote:
> Edwin Pawlowski wrote:
> > "Bob (this one)" <"Bob > wrote in message
> > >
> > > The bottom-heating process won't get the stone above oven setting because
> > > it's relying on the air temp to do the heating.
> > >
> > > Pastorio
> >
> > Not rue. There will also be infrared heating from electric elements ora
> > broiler element.
> >
> > Three ways to heat. Conduction, convection, radiation.
>
> Precisely. But with radiation heat transfer proximity is of primary
> importance, typical home ovens are not constructed to take advantage of
> radiation heat transfer.
That's really not so true. The bit about proximity being of primary
importance in radiative heat transfer that is. What matters is the
energy that is incident on the stone. Now, admittedly the further the
stone is from the source, the more of the energy from the source that
will be incident on the walls of the oven rather than the stone. But
there's still quite a large portion of that energy that falls onto the
stone, and that won't be effected by distance (well, ok, ignoring the
air effects, but those'll be quite trivial.) Plus, the oven as a whole
is a pretty fair approximation of a blackbody, so most of the energy
that hits the walls will be reemitted too and eventually hit the stone.
Really, proximity is a very minor matter in this case. I recommend
looking up the Stefan-Boltzmann law and reading up on how radiative
heat transfer actually works.
>With commercial baking ovens the heating
> elements are typically situated intimately proximate to the oven's
> brickwork, often set within slots or even through holes in the brick,
> whereas it is via radiation that the bricks actually become signicantly
> hotter than the oven chamber because then the oven chamber is heated
> via conduction directly from the bricks rather than directly from the
> elements. With a commecial oven the bricks are actually part and
> parcel of the heating elements, essentially the bricks *are* the
> heating elements. However, pizza stones added to a residential oven
> cannot be situated so they can take advange of radiation heat transfer
> to any meaningful degree, and in fact they tend to hinder the oven's
> normal convection, even with forced convection ovens. And of course
> residential elements are not nearly powerful enough, or configured
> properly, to transfer meaningful thermal energy to slabs of stone. And
> the fact that they take so long to heat (stone is a very good good
> insulator precisely because it's a very poor conductor) is significant
> in that once cooled they do not recover well, especially via
> conduction. And stone can in fact be cooled remarkably rapidly.
This is also really terribly true. In fact, it's pretty much the
opposite of true and one of the main advantages of a stone. You're
right, it is a poor conductor, but that helps explain why it's slow to
cool down.
> In
> fact a slab of stone can be lava flow hot on one side and
> simultaniously be stone cold on the other (again, stone is a lousy
> conductor), which is why NASA uses ceramic tiles for space ship reentry
Comparing pizza stones to HRSI tiles is such an apples to oranges
comparison that I'm a bit amazed that anyone would make it. HRSI is
made from low-density silicon fibers, pizza stones are made from ...
rock. HRSI has many properties which are benificial to the extreme
environments involved in reentry. Pizza stones ... do not.
> and which is *precisely* why pizza stones are essentially worthless.
> Imagine, idiots are paying $30 for 40¢ worth of fire brick, just to
> convince only themselves that they know about baking. And then the
> imbecilic cooking supply ads (written probably by moronic restaurant
> critic types who never actually cooked anytrhing) claim "porous" and
> "dense"... which is it, can't be both. The very same idiot restaurant
> critics who write prattle like the perfectly rare steak arrived at the
> table steaming hot. duh
>
> http://www.efunda.com/formulae/heat_...e/overview.cfm
That site doesn't do one darned thing to support your case.
--
Ernest