I had a brief conversation at ICCF-15 with Takahashi about mixing in
the Kitamura experiment. I got the impression that they use some sort
of mechanical mixing, but that is incorrect. He sent me an e-mail
that clarifies the situation:
We do not need stirrer (magnetic or else), as our spiral Cu coolant
tube wound on to the reactor cell is long enough and with small diameter.
Actually, his paper says this. I should have paid closer attention:
"A sheath heater and a cooling water pipe made of copper are wound on
the outer surface of the reaction chamber . . ." Kitamura, A., et
al., Anomalous effects in charging of Pd powders with high density
hydrogen isotopes. Phys. Lett. A, 2009. 273(35): p. 3109-3112.
A copper tube explains a lot. Let me explain the source of confusion
on my part. The calorimeters I am familiar with use something like a
plastic tube with a fairly large inner diameter, say ~5 mm. The
temperature probe is inserted into the tube via a screw-in hatch
(which often leaks). The tube has to be large enough to fit the
probe, which sits in the flow of water. With a flow rate as low as 6
ml/min, I would expect streamlines and thermal gradients making the
measurement inaccurate. That is what I learned working with a variety
of calorimeters.
A copper tube is quite different. From the schematic, it looks like
the thermocouple is placed on the outside of the tube tube. The heat
from the water conducts evenly throughout the copper and the
temperature sensor measures the average temperature of the water.
This is similar some of the calorimeters made by Miles, where he
wrapped the cell in a copper sleeve and then measured the temperature
outside the cell wall.
Also, since there is no temperature probe in the tube, it can have a
small diameter, so the water will move fairly quickly without streamlines.
If the copper tube were exposed to the air this would not work, but
you can see from the figure that it is wrapped around the cell which
is inside another cell, so this is not an issue. The Miles
calorimeter is also a cell inside a larger cell.
I have been fretting about this low flow rate for a long time,
because I have never heard of a flow calorimeter that works at less
than ~30 ml/min. A copper pipe with this arrangement is a different
animal. Preconceived ideas about small details often lead to
incorrect conclusions.
- Jed
- [Vo]:More from Takashashi about mixing Jed Rothwell
-
