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From: tron@fluke.UUCP (Peter Barbee)
Newsgroups: net.cooks,net.flame
Subject: Re: Truth in Advertising?
Message-ID: <803@vax1.fluke.UUCP>
Date: Fri, 16-Nov-84 10:55:50 EST
Article-I.D.: vax1.803
Posted: Fri Nov 16 10:55:50 1984
Date-Received: Wed, 28-Nov-84 03:31:37 EST
References: <2559@dartvax.UUCP> <642@watdcsu.UUCP> <> <2409@cornell.UUCP>
Organization: John Fluke Mfg. Co., Everett, WA
Lines: 51

Peter Fenyes states: I believe at stovetop temperatures radiation is 
insignificant.

Without doing the calculations I tend to agree, although convection is
not the driving factor in how "good" a pot is either.  The purpose of a 
pot is to conduct the heat from the source (the burner) to the food.
Conduction depends on the thermal conductivity of the pot (a material
property) and on the thickness.  It can easily be modeled like electrical
resistance:

		R(conduction) =  L / kA

	where R is the thermal resistance
	      L is the distance the heat must be transferred
	      k is thermal conductivity (expressed as watts/(meters*degrees))
	      A is area (normal to the heat path)

Actually radiation and convection can be similarly modeled.

The problem on the stovetop is to distribute the heat from the burner to
all parts of the pot.  Often the pot is larger than the burner and so the
heat must be conducted out to the edges.  Thus the thickness becomes the
area in the above equation.  Values for k for typical pot materials;

	stainless steel -  14.4
	aluminum 	-  164 (if pure - 236)
	cast iron	-  52
	pure copper	-  399

These values were taken out of "Basic Heat Transfer" by Frabk Kreith & William
Black and are only approximate for actual pot materials.

It is easily seen that stainless steel must be many times thicker than aluminum
to conduct as much heat (read "distribute it as evenly").

Many people care about how long the pot takes to heat up also, mass is now the
driving force so thickness becomes a liability.  (Simplified argument)

Many people also want the pot to store heat, suffice it to say this is an 
inverse function to that os heating up, although radiation is now more of
a factor.

I'll quit now before I bore too many of you,

Peter Barbee

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