http://www.jsme.or.jp/ted/NewsLetter42/Auracher_J.pdf
http://www.jsme.or.jp/ted/NewsLetter42/Auracher_J.pdf
Some Remarks on the Nukiyama Curve
Hein Auracher
Professor, Dr.−Ing.
Institut für Energietechnik
Techniche Universität Berlin
auracher@iet.tu-berlin.de
It was about 70 years ago when Shiro Nukiyama published his pioneering paper on “Maximum and Minimum Values of Heat Q Transmitted from Metal to Boiling Water under Atmospheric Pressure” [1]. A milestone at the beginning of a long way towards the “truth” in boiling heat transfer. Numerous researchers
discovered a lot on this way but the more we find out the more difficult it becomes to really understand this extremely complex process.
Basically Nukiyama’s boiling curve has never been disputed. Only specific aspects were and are subject of studies or disagreements. The shape of the boiling curve, for instance, is still a subject of discussions in terms of its behavior in the transition region, its change in a transient situation with respect to the steady-state case, its dependence on contaminations on the heating surface etc.
The shape of the boiling curve and its change under
different system conditions is, of course, a result of different boiling mechanisms and their change. Since pure empirism can never solve such problems, several physical models for the different boiling modes have been developed. We should trust these models only after experimental verification. Moreover, due to the improvement of our experimental techniques and also of the mathematical tools in recent years, older and relative simple models can now be improved and new ones can be developed.
The present report makes some remarks on the aspects mentioned above. Of course not comprehensive and – subject of excuse – focused mainly on our own work. It is just meant as a small tribute to Nukiyama’s pioneering work. Those who need a sort of survey on new developments may look into the “Proceedings of the 5th Int. Boiling Heat Transfer Conf. in Jamaica, May 2003”. A selection of the papers presented there will soon be published in the “International Journal of Heat and Fluid Flow”.
HYSTERESES ALONG THE NUKIYAMA CURVE
No contradiction exists about a hysteresis in the region of nucleation incipience (see Fig. 1). In contrast, in transition boiling and for steady-state conditions a hysteresis was postulated [2] consisting of a transitional nucleate boiling–and a film boiling–branch, both overlapping with respect to the heat flux. However, if a precise temperature control system [3] is available and with a clean heating surface, boiling curves even for liquids with large contact angles (water) show no hysteresis regardless in which direction they are measured: stepwise from
film to nucleate boiling or vice versa. In contrast, if surface contamination is involved, boiling curves are not reproducible. Each test run, even under carefully established steady- state conditions, results in a shift of the curve already at a minimal change of the deposit [3,4].
log
CHF
MHF
surface
evaporation
nucleate
boiling
transition
boiling
film
boiling
incipience of
nucleation
∆T = TW - Tsat
q
heat
flux
wall superheat
B
A
A
B
Fig. 1: The Nukiyama curve.
The boiling curve behavior log
changes under transient conditions,
even on clean surfaces. Recently it
was argued that “how the unsteady
process influences the hysteresis is not
cleared, yet” [5]. Objection! It is, as
shown by systematic experiments in
[6]. There, measurements with
controlled heating and cooling rates
were carried out, of course, by taking
into account the “coupling problem
[5]” between heater and fluid which
requires the solution of an inverse heat
conduction problem. One typical
result is shown in Fig. 2: The
steady-state curve was measured with
JSME TED Newsletter, No.41, 2003
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