On Sep 15, 2011, at 7:24 PM, Rich Murray wrote:
Horace, thanks for
http://en.wikipedia.org/wiki/Thermal_diffusivity
It's useful to know that water has one of the lowest values -- so if
some of the water flow is stopped in some parts of the Fat Ecat, for
instance by being in some side chamber, bypassed by the main flow,
then it would be slow to come to an equilibrium heat flow, so, for
instance, doubling of the heat input from the electric heater resistor
would send a clear-cut heat pulse slowly across the thickness of the
immobile water,
I don't think this is totally correct. It might apply to a gel, or
ice, but not liquid water. Convection is always present and
significant in effect even at low temperature differentials and
temperatures. Liquid water transfers heat mainly by convection.
Convection is effective even at low temperatures and very low water
velocities. I wrote a post on a related issue, the Mpemba Effect, in
2001:
http://www.mtaonline.net/~hheffner/Mpemba.pdf
OTOH, it also may be of interest that imposing heat pulses into
laminar flows has been used to measure flow velocities at various
cross section points of the flow - and this works largely because the
short induced heat pulse diffuses at a slow rate.
if it doesn't reach boiling temperature, which would
increase turbulent convective heat transfer -- such a heat pulse could
reach the thermister a certain time after the electric power cutoff --
the main point being: we can't assume much about this stunningly
complex system when we have no details about the design or
synchronized measures at many locations at once for hours of stable
operation.
Amen to that.
You present calm, clear, extremely reasonable points to justify
qualified skepticism -- I suspect Jed is likely to agree within a few
days.
within mutual service, Rich
I would not be surprised that most people here, including Jed, feel
there are various points which justify skepticism. The problem seems
to be agreeing on which ones and what a proper course would be. Not
that I expect anyone would take any action based on comments from the
peanut gallery.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
