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Re: Supercard
Henry wrote:
I just can't see how 5v will keep your cup warm though? Traces on the
Motherboard of the system are probably a little warm too.
Yeah, interesting. They all claim to maintain a cup of coffee at 40-50
degrees Celcius, but I can't get my 'paper napkin' calcs to work...
Given that USB is limited to 500mA @5V = 2.5W.
I based it on a 420ml coffee cup (already) at 40 deg C, and an ambient
temperature of 20 deg C, assuming such a cup would take 30 mins to cool
to ambient temperature. I also assumed a linear temperature gradient
over the 30 mins (I believe the temperature gradient would actually
*decrease* as it cooled).
By my calcs, it would require 19J to be transferred to the liquid every
second... (19W)... to *keep* it at 40 degs..
... out by a factor of 10!
--
Mark McDougall, Engineer
Virtual Logic Pty Ltd, <http://www.vl.com.au>
21-25 King St, Rockdale, 2216
Ph: +612-9599-3255 Fax: +612-9599-3266