MEMORIESOF MY RESEARCHON BOILINGSHIRO NUKIYAMAACCORDINGto the request from the Japan Society of
Mechanical Engineers, I am writing of my experience
under the title “Memories of my research on boiling”
with a slight compunction of self-praise.
When water boils at an atmospheric pressure of 1
atm and a temperature of fOO”C,the heating surface
temperature, t, and the heat rate, Q, show therelationship OACDE, as shown in Fig. 1 which has themaximum C and the minimum D Cl].
Since my college graduation, I have been involved inresearch on boilers for one reason or another. This isprobably because I attended lectures by Prof.
Shigemitsu Niwa and because I happened to startlecturing on boilers as my first job after graduation.
Since1 did not know, however, what specific researchshould be conducted on boilers, I at first, undertook
rather easy measurements of thermal conducti~ty andso on.
Around the end of the Taisho era or the beginning of
the Showa era, there was a Japanese torpedo-destroyer
which was blown ashore and wrecked by a windstorm.
When I asked an officer why the ship did not escape thestorm offshore, I learned that it took 30 min for theboiler to become operative after firing. It usually took
more than 5’ h for a cylindrical boiler. I wanted toshorten this time and my preliminary research led me toa type of boiler known as a flash boiler which had
already gone out of use. If water is sprayed against a redhot iron plate, as is done in this boiler, steam can begenerated instantaneously. But this principle has many
big problems in practical use from scale and water
impurities contributing to low efficiency..
I then decided on the research objectives ofincreasing the ratio of vaporization and decreasing thesize of the boiler. I undertook the above-mentioned
experiment to learn the critical values with such asystem.
Old literature had described the @characteristicup0

to point A in Fig. 1 because it had been assumed thatheat transfer would be through a flat plate or metal
tube. Q increased with t and no way had been found to
supply enough Q to raise t further. I devised a newexperimental method where a metal wire waselectrically heated in the water. The heat transfer
surface area was assumed to be the surface area of themetal wire, and Q and the wire temperature werecalculated from the electric current and resistance,respectively. I am sure that modern research in this fieldstill follows the same or similar methods around theworld. The difference in temperatures between thesurface and the center of the wire is less than 1°C. Whenraising t, it reaches point C. But since the state between
temperatures C and D is unstable, the temperature
passes point C instantaneously to point c’, where thewire becomes red hot and burns out in most cases. The
local temperature of the wire where bubbles areattached, shown in Fig. 2, must be different from thetemperature in other areas. Therefore, there must be acase where the wire burns out at a point on the wire
where the temperature exceeds C even though theaverage temperature of the wire, as calculated from thetotal electric resistance, is still B. I postulated theexistence of point C by observing that the t--Q
characteristic curve bending upwards at low temperatures turned downwards around the burn-out point.
Although it was not so difficult to observe the effect of
the wire diameter, experiments on flat plates were very
hard to perform. Because Q was very large in theseexperiments, I succeeded in the experiments on flat
plates as small as 1 cm2. I do not know of anyone else
who has succeeded in flat plate experiments to observe
point B since my experiments.
In the early stages of my study, I found that thetemperature of a metal wire easily reached as high as
105°C without the water boiling. I was in the skies
because this was contrary, or so I thought, to theinvariable principle that “Water boils at 100°C” (a lone
exception is super-heated water which is not easily
attained). However, when I happened to read an old
textbook, Theory unreal, written by Clerk Maxwell,Lord Rayleigh and others, it was lightly described thatwater boiled when it reached the pertinent boilingfFIG. 1.

FIG. 2.

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SHIRO

temperature for a certain pressure plus the temperature
at which the cohesion of the water and its contact
surface was overcome, and I realized they had alreadyknown the phenomenon.
Since then, I have never written carelessly in theintroductionof any paper that such and such has notbeen known and therefore I have done research on it.
I also tried to experimentally observe the region CDin Fig. 1. When the temperature of the heating surface
exceeds point C, the amount of heat generated is greaterthan the amount of heat transferred to the water, andthe temperature of the wire rises rapidly. I wanted toobserve this phenomenon,and so purchased
anoscilloscope to observe the changes in the current andvoltage between the ends of the wire, and to calculate
the curve of region CD from them. But this apparatus
turned out not to have sufficient accuracy and theexperiment was not successful. Thereafter my research
assistant Mr Kurose fell ill. Then World War II brokeout and I was too busy with one thing or another tocontinue this research.
After the war two incidents relating to this research ofmine took place.
One day I got a phone call from the head office of myuniversity informing me that there had been a phone
call from the Ministry of Education to the university
with a message from the departmentof chemistry atG.H.Q. that they had something to ask Dr Nukiyama, aone time professor at the University of Tohoku. They
expected me to go to Tokyo. Though it was funny thatthey called me a former professor, they were wondering
how they should reply.
Since the department of chemistry had something totell me, I went to Tokyo and visited G.H.Q. in front ofthe Imperial Palace. Several Americans came out to seeme, shook hands with me, thanked me for coming, hadme sit in a chair and showed me the following letter
which had come from California or somewhere. “I amworking for such and such university and the research
paper by Dr Nukiyama in Japan [with the title of myown paper] had been the most helpful in my research. I
have surveyed his papers after that and he seems to havechangedhis area of research.
Considering
theimportanceof his research, however, I am sure thatsomeone else must have continued the research in hisplace. I hope that you can contact Dr Nukiyama andask him about the current status of the research in thatarea in Japan. Furthermore, I want his paper translated
into English as I do not understandJapanese. All Iknow about Dr Nukiyama is that he was a professor at
the University of Tohoku before the War.”I replied that I had heard of the research continued inthe U.S.A. but I did not think it was currently being
done in Japan. I think this reply of mine was almostcorrect.
At that time, America had absolute power, and I had
a slight antipathy toward Americans. When I asked
that my travel expenses between Tokyo and Sendai bereimbursed when I left, because I came to Tokyo for thesake of the U.S.A., they agreed it was reasonable andNUKIYAMA

paid for it instantly. 1 think today that it was rathermean, but it was a demonstrationof my resistance.
About that time, an American chemist, Mr Fox andseveral membersof his staff came to Sendai toinvestigate the research done at our university. He
inquired about my research in detail including that
described above. He was one of the few persons who
understoodcorrectly
the difficulties which I had
experienced in my research, and asked some searchingquestions. Finally he asked, “In which area is the resultof your research applied to practical use?” “Japaneseindustries are conservative in the application of new
research results.” “How come?” “One reason might bethat many applications
end in failure because theresearch itself is incomplete
for direct application.
Another might be that they do not want any wastefulfailure.” “But graduates rely on the work of theirteachers and want to apply it, don’t they?” “When theapplication did not turn out to be successful at once,
they would not be free from interference from others. Ido not want my graduates to assume such a burden.” “Iam sorry to hear that. Why don’t you come to the U.S.A.
to carry on your research?”
I could not answer easily because I understood thatwhat the American said was exactly what he thought.
After a while, “Nowadays it’s hard for a Japanese to getbread. I have led my long life for the sake of Japan. I can
not take it into my head to work comfortably in theU.S.A. I would like to contribute to the development ofJapanese industries and then think about it when theJapanese have achieved a more comfortable life.““Thatidea is very good.”
Since about that time, I have extended my researcharea to include heat management in plants, tests andevaluations of boilers and so on to contribute to fuelsavings. I am afraid, however, that this is far from theresearch intended by the title of this essay.
Immediately after the termination of the war, I did
not have funds for research but I wanted to continue theresearch describedabove. Therefore,I undertook
experiments, where red-hot iron was put into water ofconstant temperature. The change in the temperature
at the center of the sample was measured and changes intemperatures over time at the surface of and at various
points in the sample were calculated from it. The
amount of heat transfer was also calculated from thetemperature
gradient to trace the DCBA line frompoint D in Fig. 1. In this case, however, it was not mymajor purpose to obtain the exact DCBA line but tomeasure the height of point B for use in research on
quenchingliquids. Since I assumed that the line
downwards curved around point B because the amountof vapor with poor heat conductivity
increased andcovered
the heating
surface, I used a sodium
bicarbonate
aqueoussolution.
Contrary
to myexpectations point B got higher. I then assumed thatsalt or muddy water would have the effect of lowering
point B because a solid would be left on the surface after
evaporation, but the result was that point B rose higher.
This is probably because the intense boiling prevents

951

Memories of my research on boiling
salt or mud from forming a membrane on the heating
surface.
When I happened to have some sulfite pulp liquor on
hand, and diluted it with water, point B lowered withthe concentrationof the liquor. I interpret this as theresult of an organic compound like this being charred
onto the metal surface, which impairs the contact of thewater with the metal surface, lowering point B. This
must be the reason why oil quenching makes for milder
quenching than water.
This means that a substance like sulfite pulp liquor,
which can be diluted with water and is likely to becharred makes it possible to get a point B of any height.
In other words, this makes quenching controllable toany degree desired. In this sense, this type of liquid issuperior to oil. However, oil quenchinggives thequenched material an almost constant hardness since
point B is hardly affected by the oil temperature, and oil
prevents rust from forming if the materials are left asthey are after quenching. This is why oil quenching
cannot be abandoned.
In Showa 22 (1947), Dr Tanazawa
and his coworkers published an article asserting the existence ofthe maximum of cooling, like point B, through theirexperimental research, where iron plate was quenchedby spraying water on it [Z].
In March 1947, at the Tokai regional meeting of thissociety, Dr Takeyama
presented the results of hisresearch where he obtained theline in Fig. 1 through theexperiments with a metal wire and a water spray, thewater-air ratio was varied and the line lay in between
the solid line for water and the broken line FG for air inFig. 1. On the other hand, Dr Yamagata and Dr
Nishikawa are studying boiling form, that is to say theshape of bubble, and are conducting other analyses ofheat transfer.
In Showa
34 (1959), Dr Tanazawa
made apresentation in London showing that in his research on
IC engines he found that the relationship between thevaporization rate and the wall temperature when an oil
drop hits against a hot wall was the same as shown inFig. 1 [3]. I was deeply moved when I listened to therecording of his speech and the audience applauded
when he said, “If you would agree, I would like to namepoint B the Nukiyama point.” which corresponds
topoint D, called the Leidenfrost point.
When I happened to undertake the experimental
research on boilers, it was ahead of that in Europe andthe U.S.A. Recently this research is attracting attention
because the vaporization ratio in the boilers for nuclear
energy is very high. Also, research has become more
active in Europe and the U.S.A. than in Japan.
However, nowadays, much good research is being
done in Japan. I am very happy to see my researchfading as a result of recent excellent work.
REFERENCES

S. Nukiyama, The maximum

and minimum values of theheat Q transmitted
from metal to boiling water underatmosphericpressure, J. Japan Sot. Mech Engrs 37(207),367 (1934).
Tanazawa et al., J. Me&. Engng 50(342), 9 (1947).
Z. Tamura and Y. Tanazawa, 7th Symp. on Combustion,
p. 502 (1959).