machine design, Vol.3(2011) No.4, ISSN 1821-1259
pp. 247-250
Preliminary note
EXPLORATION OF THE EFFECT OF MATERIAL PROBE ON THE PARAMETERS OF
COOLING PROCESS BY THE WOLFSON´S TEST INTO OIL ISOMAX 166
1,2,3
Štefan HAJDU1, * - Ján ŠPANIELKA2 - Bohumil TARABA3
Slovak University of Technology in Bratislava, Faculty of Materials Science and Technology, Institute of Production Systems
and Applied Mechanics, Department of Applied Mechanics, Trnava, Slovak Republic
Received (27.03.2011); Revised (08.06.2011); Accepted (12.12.2011)
Abstract: Aim of this article was to assess the material impact of Wolfson´s probe test conditions for heat transfer from
the probe surface to the cooling oil. Combining the experimental temperature measurements and computer modeling
were quantified thermal boundary conditions, which were active during the process of cooling the heat transfer surface
area probe. The main of the article was to consider the influence of probe material by Wolfson´s test for the conditions
of heat transfer from probe body into cooling oil. Using the connection experiment temperature measurement and
computer modeling the thermal boundary conditions which affected the heat transfer probe surface during cooling
process were predicted. Materials of probe were stainless steel STN 41 7255 and copper 99.9%-purity STN 42 3001.
The cooling medium was quenching oil Isomax 166 kept on steady-state temperature 60 °C. From obtained results was
concluded that the heat transfer under Wolfson´s test conditions is able to saturate cooling possibility of tested cooling
oil. The numerical simulations have been processed using the program ANSYS.
Key words: ANSYS, heat transfer, cooling simulation
1. INTRODUCTION
The one from the international tests, which is used for
obtaining experimental cooling curve, is known as the
Wolfson´s test, ISO 9950 [1]. Material of the Probe is
Inconel 600 alloy, which has value of the mean
coefficient of thermal conductivity of 21.5 W.m−1.K−1 for
the temperature interval from 0 to 900 °C. Since most
heat-processed components are made from steel, which
has a coefficient of thermal conductivity [2] greater than
the material of the probe. The question arises whether
heat flux from the probe surface sets on the side to the
probe or on the side of the cooling oil.
The answer to that question is possible to get by changing
the material of the probe with the high value of the heat
conductivity coefficient (copper STN 42 3001) and
subsequently to evaluate the modified Wolfson´s test
together with the determination of combined heat transfer
coefficient according to [3].
2. THEORETICAL BACKGROUNG
The theoretical background of the task is the law of
conservation of energy in the form of the first law of
thermodynamics for the closed system. Energy in form of
heat spontaneously passes from the probe body into the
cooling oil. It is expected that there are no dissipative
effects and the energy of the rising elastic and plastic
deformation is neglected. The qualitative aspect of this
process is described in the literature [4]. If reconsidering
the cooling effect as the combination of radiation, boiling
and free convection the law of conservation of energy can
be formulated by Fourier´s boundary condition of the 3rd.
type for the immediate state on the probe radius R and
in time ti [4]
−λ ( T )
dT
dr
R,t i
= hcomb (Ts ) ⎡⎣Ts ( ti ) − Tr ⎤⎦ , ⎡⎣ W.m −2 ⎤⎦
(1)
where λ(Τ) is the coefficient of heat conductivity of probe
material [W.m−1.K−1], hcomb(Ts) is the combined heat
transfer coefficient [W.m−2.K−1], Ts(ti) is temperature of
probe surface [°C], Tr is the unagitated oil temperature
[°C] and R is the probe radius [m]. [1, 2]
The left side of equation (1) represents the momentary
thermal flux [W.m−2] from the probe surface which must
be removed into cooling oil. The transient temperature
field in the body of the probe is described by FourierKirchhoff´s differential equation of heat conduction in the
cylindrical coordinate system [5].
3. EXPERIMENT
The experimental equipment (Fig.1) consisted of
electrical resistance furnace of LM 212.10 type, cylindershaped experimental probe oil Isorapid 277HM, portable
USB-based DAQ for thermocouples NI USB 9211 for
digital record of measured temperatures, personal
computer and pneumatically manipulator for probe
moving.
For each probe was carried out six measurements of time
changes in temperature at the center of the probe.
Temperatures were recorded with a time step 0.2 s.
Geometrical and initial conditions of the experiment were
based on the quenching Wolfson's test [1]. The initial
probe temperature was 850 °C and the probe was
*Correspondence Author’s Address: Slovak University of Technology in Bratislava, Faculty of Materials Science and Technology,
Institute of Production Systems and Applied Mechanics, Department of Applied Mechanics, Trnava, Slovak Republic,
stefan.hajdu@stuba.sk
Štefan Hajdu, Ján Španielka, Bohumil Taraba: Exploration of the Effect of Material Probe on the Parameters of Cooling Process
by the Wolfson´S Test into Oil Isomax 166; Machine Design, Vol.3(2011) No.4, ISSN 1821-1259; pp. 247-250
immersed vertically into unagitated oil with constant
temperature of 60 °C. Oil temperature 60 °C was selected
based on the results of experiments [7] which have used
oil quenching highest cooling effect. Cooling process was
captured by a digital camera.
Characteristics of oil: Isomax 166 is intensive quenching
oil with low viscosity, which is primarily used for
hardening carbon, alloy, thermally modified and hardened
steel. It allows a high degree of hardened even for large
components. It is resistant to evaporation. Recommended
operating temperature range is 40 to 70 °C, coefficient of
kinematic viscosity at 40 °C is 12.5e−6 m2.s−1.
a)
b)
c)
Fig.3. Cooling copper probe STN 42 3001, a) vapor
phase at the time 3.9 s, b) The beginning of boiling phase
oil at the time 7.4 s, c) boiling oil at the time of 9.6 s
Fig.3 shows the process of cooling of the copper probe.
Both figures provide visualization of the instantaneous
state of the cooling probe on its surface: a) gas packaging
phase, b) boiling point at the bottom of the probe,
c) boiling oil in the place of the thermocouple location.
Time data for Fig.2 and 3 were subtracted from the
digitized video.
4. NUMERICAL SIMULATION
Fig.1. Experimental device: 1 electrical resistance
furnace, 2. personal computer, 3. probe with
thermocouple, 4. NI USB 9211 converter, 5. cooling
medium + heater, 6. record of temperature curve, 7.
pneumatic manipulator
60
Isomax 166 belongs to the type of quenching oils with
very intense cooling effect and the characteristic value of
HP (Hardening Power) is 942 [8]. Figure 2 is recorded on
cooling of the steel probe STN 41 7255 at selected times
after initiation of cooling.
Numerical simulation of the cooling probe process was
calculated using engineering and scientific computer code
ANSYS [9]. Simulation model of the probe was twodimensional and geometrically replaced half of the
cylindrical probe in longitudinal section (Fig.4).
Axisymetric linear elements were used and they were
switched to the acceptance of surface temperature.
Computational procedures were transient and nonlinear.
φ 12,5
a)
b)
c)
Fig.2. Cooling steel probe STN 41 7255, a) vapor phase
at time 1 s, b) the beginning of boiling oil at the time
2.8 s, c) boiling oil at the time of 6.3 s
248
Fig.4. Probe geometry and geometrical model with
generated mesh
In the simulation model were considered thermophysical
properties of materials listed in Table 1 [10, 11, 12].
Štefan Hajdu, Ján Španielka, Bohumil Taraba: Exploration of the Effect of Material Probe on the Parameters of Cooling Process
by the Wolfson´S Test into Oil Isomax 166; Machine Design, Vol.3(2011) No.4, ISSN 1821-1259; pp. 247-250
Table 1. Thermophysical material properties of the probe
Thermal
conductivity
coefficient
λ[W. m−1.K−1]
STN STN
Temp.
41
42
Τ [°C]
7255 3001
0
14.8
395
100
15.8
392
300
18.4
382
500
22.0
376
700
25.7
371
900
29.4
365
Specific heat
capacity
c [J.kg−1.K−1]
STN
41
7255
455
475
508
550
602
630
STN
42
3001
385
396
416
437
458
469
Density
ρ [kg.m−3]
STN
41
7255
7940
7911
7830
7745
7662
7578
STN
42
3001
8960
8916
8823
8723
8618
8508
4.1. Inverse-numeric-correlation method (INC)
Inverse-numeric-correlation method (INC) was proposed
by authors of this article and the INC method is applied to
solution of direct inverse problems. Through the iterative
INC method can find a result which it is very likely and
useful for computer prediction of thermal treatment
processes. Task solution by the INC method must meet
the following criteria: relative error for measured and
calculated temperature in i-time must be less than 0.01
relative error for cooling rates derived of measured and
calculated temperature must be less than 0.05.
the effect of boiling oil is more intensive with a sharp
transition to free convection. Cooling rates at the center of
gravity of the probe are obtained by derivation of cooling
curves from Fig.5. The comparison of both cooling rate
curves can you see on Fig.6. Figure 7 shows the
dependence of combined heat transfer coefficient of
surface temperature probes which were obtained by INC
method. The maximum values of the combined heat
transfer coefficients are comparable. Maximum combined
heat transfer coefficient for copper is 4752 Wm−2.K−1 and
for steel 4253 Wm−2.K−1. The noticeable difference exists
between surface temperature values where expires vapor
phase and starts boiling phase. Clearly defined
Leidenfrost´s temperature is 674 °C at start of boiling for
steel probe. In the cooling process of copper occurs
boiling phase at the surface temperature less than 620 °C.
Boiling phase is ending at temperature of surface 297 °C
in both tests.
5. OBTAINED RESULTS
Cooling curves for both materials probes were obtained
from as statistical processing of measured temperatures
files using software Origin 8.
Fig.6. Cooling rates of the probes in relation to measured
temperature
Fig.5. Cooling curves for austenitic steel STN 41 7288
and for copper STN 41 3001
The obtained cooling corves are showed in Fig.5. The
Figure 5 explains that the processes of cooling copper and
steel probe are quantitatively different. During cooling
process of copper probe exist vapor phase longer. The
transition vapor phase into boiling phase is smoothed and
Fig.7. Dependences of combined heat transfer coefficients
as function of surface temperature
249
Štefan Hajdu, Ján Španielka, Bohumil Taraba: Exploration of the Effect of Material Probe on the Parameters of Cooling Process
by the Wolfson´S Test into Oil Isomax 166; Machine Design, Vol.3(2011) No.4, ISSN 1821-1259; pp. 247-250
ACKNOWLEDGEMENT
This article was realized with the support of grants VEGA
1/0364/11 and VEGA 1/1041/11
REFERENCES
Fig.8. Dependence of heat flux from the surface probe
into the oil in relation to the cooling time
Effect of the material probe on the process of heat transfer
from probe surface into the oil is evident in Fig.8 on
which can you see values of heat flux for two different
materials in dependence on the cooling time. The time
difference between maximum values of heat flux is 3.7 s.
By comparing Fig.8 with Fig.2 and 3 can be monitored
very good relation between both photos and numerical
obtained data.
6. CONCLUSIONS
1) Material of the probe STN 42 3001 does not on a heat
transfer into the unagitated cooling oil basic influence
although has to standard material probe nearly twenty
times higher coefficient of thermal conductivity.
2) After comparing the obtained results it is possible to
argue that the main parameter for the emergence of
boiling oil Isomax 166 is not surface temperature but the
heat flux. The boil is beginning on probe surface if the
heat flux into the cooling oil falls to level that can no
longer to recover vapor phase of the evaporating oil.
According to the obtained results vapor phase ceases
when value of the heat flux is less than 293 kW.m−2.
3) The maximum heat flux from the probe into the
unagitated oil Isomax 166 is for steel 1.96 MW.m−2 and
for copper is 1.91 MW.m−2.
4) Cooling rate with using copper probe was increased
only about 47.2 %. The maximum value of the cooling
rate is for steel 108 K.s−1 and for copper 159 K.s−1.
5) The most important conclusion is the fact that for the
quantification of cooling media properties is the probe
material adequate according to standard ISO 9905. The
limiting factors of heat transfer from the probe into the
cooling oil are the thermal properties of the tested oils.
250
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