Nukiyama in Microscale at Higher Pressures

Nukiyama in Microscale; High Pressure:
Subcritical, Transcritical, Supercritical

This entry will take several days as slides are uploaded and paragraphs are written.   Indeed, this is Nukiyama in microscale.  Nukiyama made his discoveries via experiments.  About twenty years later, the mathematicians got in the game and since then the gang of "experts" insists that nothing is discovered in the absence of deep analysis.

Nevertheless, Leyse has produced and reported a set of transformative discoveries in the field of microscale heat transfer to subcooled water over a pressure range of 200 to 6000 PSIA.  These transformative discoveries are listed at the end of this collection of slides.

Nukiyama was the first to use a platinum
wire simultaneousllyas a heat transfer 
element and a resistance thermometer. 

Leyse thus pioneered application of the  
Nukiyama procedure in microscale.

The Nukiyama element is mounted 

within a pressure tube.  The quartz

tube is replaced with a stainless steel

tube for higher pressure runs.

 The assembly of the apparatus has
the pressure tube, the pneumatic
pressurizing pump, programmed power 
supply, PC with Microsoft EXCEL for
data logging and analysis, and a 
Rosemount pressure transducer.

Data is collected every 0.1 seconds.  
Heat flux is smoothly ramped up to
4100 W/cm2 in 5.5 seconds and then
ramped back down in 5.5 seconds.

 Above is the Nukiyama plot.

Here are several runs: three subcritical 
at 200, 1000 and 2500 PSIA, one 
transcritical at 3000 PSIA, and four 
supercritical at 3600 to 6000 PSIA.    

                                  

Here are the plots of the several runs
with the data points at increasing power.
Below are separate plots with details.

Here are two of the four supercritical runs,
3600 and 6000 PSIA.

This has the transcritical runs at 3000 PSIA 
along with the two supercritial runs.Note the 
onset of nucleate boiling very close to the 
critical temperature and the jump of about
480 Centigrade in 0.1 seconds across the
supercrtical region. In contrast, the return to
natural circulation takes one second.

These are the four supercritical runs and the 
transcritical run in decreasing power. It
will be revealing to conduct these runs at 
much faster recording rates; perhaps
every 0.001 seconds rather than 0.1 seconds.

At 3000 PSIA the saturation temperature is 
very nearly the critical temperature which 
likely accounts for the transformative 
characteristic. It is proposed to determine 
the pressure at which the transformative 
characteristic is initiated.  There are several
factors.  I prefer operating with cold water.
More later on this.

This has only the increasing power data for the
three subcritical runs at 200, 1000, and 2500 PSIA 
and the initial aspects of the transcritical runs at
3000 PSIA.  Nore that the onset of phase change 
is only a few degrees Centigrade above the 
saturation temperature at 2500 and 3000 PSIA, 
however, it is grossly above the saturation 
temperature at 200 and 1000 PSIA.

Professor Victor V. Yagov reviewed this work
and produced the above table of his analysis.
At 200 PSIA he reports substantial temperature
difference between the onset of phase change
and the saturation temperature.  At 3000 PSIA
that difference is very little.

With a 12.5 micron element, limited runs show
that performance is substantially the same as 
for 7.5 microns, although at lower heat fluxes.
At 1000 PSIA the onset of phase change is at
the same temperature in each case.  Likewise, 
the 2900 PSIA data at 12.5 microns mimics the
3000 PSIA data in all aspects, the onset of 
nucleate boiling, the jump across the supercritical
region, and the return to natural circulation. (Note 
that the saturation temperature at 2900 PSIA is
very close to that at 3000 PSIA; 366.1 and 368.9.)

This nested set of runs is fantastic, and it has
been in the public arena for over 15 years.  Again,
this is 7.5 micron data, and the runs were 
completed as an afterthought, a worthwhile 
afterthought.  The procedure is original and
straightforward.  The assembly is pressurized to
about 6000 PSIA,  full power is applied and 
substantially constant heat flux is maintained as
the pressure is smoothly reduced over a period 
of about twenty seconds.  Power is turned off at
about 200 PSIA.
Again, the discoveries are fantastic.  For run 
2630 W/cm², the lowest heat flux, the plot is
smooth over the entire span.  It starts at 348  ^oC,
increases gradually until it crosses the critical 
pressure at 358   ^oC (about 16  ^oC less than the 
critical temperature), then increases very slightly 
to 360^oC at 2700 PSIA where it is equal to the
saturation temperature.  At this point the heat 
transfer mechanism changes to nucleate boiling
and the temperature decreases significantly to
about 200 ^oC when the run ends at 250 PSIA.
During this nucleate boiling regime the difference 
between the temperature of  the 7.5 micron 
element and the saturation temperature increases
substantially as the pressure decreases from 
2700 to 250 PSIA.  This is consistent with the 
onset of phase change, slide 22, and the Yakov
analyses, slide 23.
Next, run 2930, an increase in heat flux of only
300 W/cm² yields a remarkably change perfprmance
increasing temperatures,  240, 307 and 349 ^oC