Re: Flat conductors (was I need help).

[Bernard Cleyet <anngeorg@PACBELL.NET>]

Initially I thought: 100 milli-W / cm^2,  what discomfort!, but then I plugged
in 1.5 kW / m^2  (radiates from both sides) and got 130 deg. C!!!

At that temp., convection will cool at ~ half k W / m^2  so maybe 100
deg. C.  where's the error?   BTW  for a 1 % change in current, I
calculate ~ 10 C deg change is
necessary.  (T. coefficient ~ -1 E-3)

The Pasco paper is ~ 23 X 30.5 cm  so only 43 W /m^2

Using my 10 X 10 cm square (one pair opposite edges Ag'd) 140 V ~ 21 ma
(2.8 W)   stabilized at ~ 23 mA (five min.)  so 10% change   thermal
coefficient not as claimed by Harnwell as only slightly warm i.e. ~ 38
deg. C. (PTC spot surface thermometer)

bc


Brian Whatcott wrote:

> I'll take a shot at responding - interspersing my
> responses with your text.
>
> At 04:39 PM 2/26/02, you wrote:
> > 1) Correction: the current at 300 volts was 11 mA, not 5.5 mA,
> > as posted about two hours ago. This is probably irrelevant, as
> > far our problem is concerned. But it shows that the new sheet
> > has exactly the same R as the one I used before. The sheet is
> > very linear (in terms of the mA versus volts) up to at least
> > 300 V.
>
> I am uncomfortable at dissipating 3 watts over 30 cm2 or so.

cut