Physical bases of freezing point measurement using ... - Boschung

Proceedings of the 9 th SIRWEC Conference 15-17 March 1998, Luleå, Sweden 281
Let us consider now a road where a salt content of 20 g/m 2 has been spread. Table 2
gives the freezing temperatures for different thicknesses of the solution. From -13.9 °C for a
thickness of 0.1 mm, the freezing temperature increases very quickly to -2.3 °C for a
thickness of 0.5 mm!
e [mm] Ts [°C]
0.1 -13.9
0.2 -6.1
0.3 -3.9
0.4 -2.9
0.5 -2.3
Table 2 : dependence of the freezing temperature on the thickness of the solution
for a salt content of 20 g/m 2 .
Freezing temperatures are reported versus the thickness of the solution for different salt
contents in figure 6. When e increases, the phase diagram of figure 5 is gone through from the
right to the left, or in other words, in the direction of decreasing NaCl concentrations.
T s [°C]
0
-5
-10
-15
-20
-25
5 g/m 2
e [mm]
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
10 g/m 2
20 g/m2
30 g/m 2
40 g/m 2
Figure 6 : dependence of Ts on the thickness of the solution for different salt contents.
For a given salt constant, the thickness eopt of the solutions which gives the best
protection of the road, i.e. the NaCl concentration of the eutectic, is given by :
e
opt [mm]
ν ( 0. 233)
⋅ s
-3
=
= 3.73⋅10 s 2 . (12)
[ g/m ] 0. 233