Automotive Engineering - December 2022 - BET10

Leak Testing
of orifices. Both distilled water and a
mixture of water and water/ethylene glycol
were used as these are typical automotive
coolants. In theory, as water/ethylene
glycol has a different viscosity than
distilled water, we expected that pressure
and the inner diameter of test capillaries
would produce significant differences.
1000
The first experiment looked at the numNumber
of drops in 69 minutes from glass capillaries with 30 mm
length and different capillary diameters @ 2.0 bar, 3.5 bar and
50 bar overpressure for 1:1 distilled water-glycol-solution
ber of droplets dripping off a glass capillary
during one hour in the system with
distilled water as the coolant at various
operating pressures at 20 °C. It can be seen
that the system pressure has a significant
influence on the number of drops, just like
the inner diameter of the capillaries.
It is also noticeable that with the 5μm
capillary, no drops fall off during the
measurement time and no visible droplet
emerges from the capillary tip. With the
10μm capillary, at an overpressure of 5
bar against the atmosphere, only one
drop drips off during the measuring time.
At 2 bar and 3.5 bar overpressure one
droplet develops at the capillary tip but
does not drip off.
The number of drops as a function of the
100
10
y = 4.0E-05x4.3E+00
y = 2.2E-05x4.3E+00
y = 2.7E-06x4.8E+00
1
Capillary diameter [μm]
Overpressure 5.0 bar
Overpressure 3.5 bar
Overpressure 2.0 bar
Data fit to overpressure 5.0 bar
Data fit to overpressure 3.5 bar
Data fit to overpressure 2.0 bar
Figure 3b: Number of drops in 60 minutes from glass capillaries with 30 mm length and different
capillary diameters @ 2.0 bar, 3.5 bar, and 5.0 bar overpressure for 1:1 distilled water-glycol-solution.
(Image: Inficon)
120
100
80
60
40
20
1
Water drops
Water-Glycol drops
Glycol drops
2
3 45 6
Overpressure cooling system [bar]
Data fit to water drops
Data fit to water-glycol drops
Data fit to glycol drops
Figure 4: Number of drops as a function of the pressure difference of a Ø25 μm diameter glass
capillary with 30 mm length. (Image: Inficon)
10
100
overpressure shows a good linear correlation
as expected from the Hagen Poiseuille
law for liquids. In a second experiment, the
dripping behavior of the various capillaries
with a solution of distilled water and ethylene
glycol in a mixing ratio of one-toone
at various operating pressures at 20° C
was investigated. It can be seen that the
number of drops has clearly decreased in
contrast to the previous measurement
with pure distilled water.
Here, within the measuring time of 60
minutes, not a drop fell from the 10μm
capillary for every pressure difference.
In the case of the 5μm capillary, no drop
formation could be determined visually.
Transferring the measurement
results
into a double logarithm scaled diagram
(Figures 3a and b), the dependence of
the drop rate to the fourth power of the
radius can also be seen in a good approximation,
just like the influence of the
pressure in the system which is described
in the theory.
Water has a particularly low dynamic
viscosity of 1.002 mPa/s and pure ethylene
glycol has a high dynamic viscosity
of 19.83 mPa/s at a temperature of 20° C.
A water-ethylene glycol solution of 1:1
(50 percent volume distilled water and
50 percent ethylene glycol) has a dynamic
viscosity of 4.1 mPa/s.
Summary and Conclusions
The measurements show very clearly
that the enumerated liquid droplets or
liquid leakage rate is linearly dependent
on the pressure difference, with the pressure
always being at atmospheric pressure.
This linear relationship is very clear
in Figure 4. In addition, it is easy to see in
the graph that the magnitude of the leak
rate decreases as the viscosity of the liquid
increases. The leakage rate for glycol
shows a factor of 10 times lower and for
the 50/50 water glycol mixture a factor of
Battery & Electrification Technology, December 2022
Number of drops in 60 minutes
Number of drops in 60 minutes

Automotive Engineering - December 2022

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