Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
The three POEs showed good permittivity which decreased linearly with the increase in change length of the fatty acid chain (Figure 8). These permittivity results are higher than the permittivity of mineral oil, which is commonly used as dielectric fluid, but still in a very reasonable range, which allows the employment of PE-C6 as a dielectric fluid.
The thermal conductivity of the three molecules also resulted in being in a good range with PE-C6 having a significantly higher thermal conductivity compared to the other two esters (Figure 9). Thermal conductivity is a relevant parameter for refrigerant fluids, and these results indicate that PE-C6 would perform well.
Resistivity (C EI 60247) Figure 10:
Resistivity of PE-C5, PE-C6 and PE-C7
Dielectric dissipation factor (C EI 60247)
Thermal and oxidative stability results of the esters are also important for this study, as these are critical parameters affecting the performance of a base oil at high temperatures. The results of the thermal stability assessment are shown in Table 3 and Figure 12. All three esters performed well in this test both in terms of total sludge formation, which was significantly below the 25 mg /100 ml threshold, and in terms of visual evaluations. However, PE-C5 resulted in having a significantly higher total sludge weight compared to PE-C6 and PE-C7, which both produced less than 2 mg/100 ml.
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Positive results were achieved also in terms of electrical resistivity, with PE-C6 demonstrating a significantly higher resistivity compared to the other two esters (Figure 10). Another positive note is the fact that the dielectric dissipation factor of PE-C6 was significantly lower than the one of the other two esters (Figure 11).
By evaluating the performance of PE-C6 as a dielectric fluid we can suggest that this molecule would perform quite well as a dielectric and coolant. However, other parameters should be investigated to be able to conclude this, namely the breakdown voltage (also referred to as dielectric strength) and the heat capacity.
Table 3: Thermal stability results of PE-C5, PE-C6, and PE-C7 characterisation.
Figure 11: Dielectric dissipation factor of PE-C5, PE-C6 and PE-C7
It is worth noticing how the visual evaluation of the steel and copper rods for PE-C6 is very good as both rods of PE-C6 show almost no sludge residue.
LUBE MAGAZINE NO.186 APRIL 2025
37
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