ASTM - Intensive Quenching Systems - Engineering and Design 2010 - N I Kobasko, M A Aronov, J A Powell, G E Totten

CHAPTER 2 n TRANSIENT NUCLEATE BOILING AND SELF-REGULATED THERMAL PROCESSES 43
d o bubble departure diameter
f bubble release frequency (Hz)
g gravitational acceleration (m/s 2 )
q
K ¼
r 0000 r Tolubinsky number (dimensionless)
W 00
K Kondratjev form factor (m 2 )
Kn Kondratjev number (dimensionless)
n s nucleation sites density (m 2 )
p pressure (Pa)
q heat flux density (W/m 2 )
r coordinates (m)
r * latent heat of evaporation (J/kg)
R cr critical radius of a bubble (m)
S surface area (m 2 )
T temperature (K or °C)
T S saturation temperature (K or °C)
T c core temperature (K or °C)
T m medium (bulk) temperature (K or °C)
V volume (m 3 )
W 00 vapor bubble growth rate (m/s or mm/s), ¼ d o f
x coordinates (m)
a heat transfer coefficient (W/m 2 K)
b parameter depending on properties of liquid and vapor
b 0 volumetric expansion (1/K)
# I wall superheat at the beginning of self-regulated thermal
process
# II wall superheat at the end of self-regulated thermal
process
# c T c – T S
k thermal conductivity (W/mK)
l dynamic viscosity (kg/mÆs)
m kinematic viscosity (m 2 /s)
r liquid density (kg/m 3 )
r 00 vapor density (kg/m 3 )
r surface tension (N/m)
s time (s)
2.9 SUMMARY
1. The generalized equation for the determination of the
duration of transient nucleate boiling has been
obtained, which includes the self-regulated thermal process.
This equation is a basis for development of intensive
steel quenching methods.
2. The generalized equation is verified by experiments and
is widely used for the development of quenching recipes
when designing the above-mentioned technologies.
3. Wall overheat during the self-regulated thermal process
changes very slowly and can be derived from the equation:
a nb ¼ bq m , where b ¼ 7.36 and m ¼ 10/3.
4. Equations of Labuntsov and other authors, which were
established on the basis of heating thin wire immersed
into boiling liquid, can be used only qualitatively, not
quantitatively, for designing of quenching processes.
5. During the self-regulated thermal process, one can consider
surface temperature as a constant value, that is,
T sf ¼ T S þ # I þ # II
, and use this approach for simplified
2
temperature field calculations with an accuracy of ±3 %.
6. During quenching of steel parts in cold water salt solutions
of optimal concentration, film boiling is absent.
The initial stage of quenching includes shock boiling,
which is not widely and deeply investigated yet.
7. During quenching of real machine components, including
massive rollers and rotors, heat flux density after
establishing the self-regulated thermal process is less than
q ¼ 0.1q cr1 , and therefore partial boiling is observed and
Tolubinsky investigations are very useful here.
8. Taking into account characteristics of the self-regulated
thermal process, it is possible using plain water instead
of oils when quenching alloy and high-alloy steels, which
improves environment conditions significantly.
9. The self-regulated thermal process extends the possibility
of high-temperature and low-temperature thermomechanical
heat treatments to the manufacture of very
high-strength materials using plain carbon steels.
10. Further special investigations are needed here, which
can be successfully done by an international team [52].
11. There is a need to develop standards for intensive quenching
technologies and to publish books for heat treaters and
engineers to explain the new discovered processes.
References
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Kyiv, 1980.
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Profiles in Overheated Boundary Layer over Horizontal
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[20] Kobasko, N. I., Thermal Processes in Quenching of Steel, Metal
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