On Oct 12, 2009, at 9:07 AM, Jed Rothwell wrote:
Horace Heffner wrote:
In earlier reports I expressed concern about the calorimetry
employed by Kitamura et al. The flow rate of the cooling fluid is 6
ml per minute.
I wonder if there is a typo, i.e. it should be 6 ml/s.
Nope. Definitely 6 ml/min. 360 ml/min would be far too much.
It is notable that such a slow a flow rate of 6 cm^3/min or 0.1 g/s
would limit the calorimeter to a maximum of (4.186 joule/gram °C)*
(0.1 g/s)*(70 °C) = 29 W total, assuming an input temperature of
30 ° C, and that would be pushing the calorimeter fluid to
boiling, which
can cause errors.
It is nowhere near that limit. I think the maximum output has
lately been around ~2 W, I think. It was more like 0.2 W before.
The heat added to the water by the stirrer is apparently too small
to measure. I do not know what kind of stirrer it is.
- Jed
OK, well then 6 ml/min is not a problem then because a faster rate
would significantly reduce the precision. Measuring temperature to
0.1 C absolute is a typical for NIS calibrated instruments, and 2 W
would only produce a 4.8 °C difference, and 0.2 W would only produce
only a 0.48 °C difference, much less than the wattage of a typical
lab stirrer. If the flow rate were run up to 60 ml/min the results
would be useless.
Best regards,
Horace Heffner
http://www.mtaonline.net/~hheffner/
