Effect of liquid condition on moisture saturation coefficients in synthetic and natural esters

The liquid specific moisture saturation coefficients A and B are required for accurate use of thin film capacitance moisture sensors. These have been previously produced and evaluated for new liquids including synthetic and natural esters. In-use synthetic and natural esters have not yet been evaluated. This paper aims to demonstrate the difference in results of aged esters compared to new, as well as demonstrating the effect on results which can be caused by using improper methods in these liquids. The results highlight the importance of using liquids with high enough initial moisture content and also demonstrate that the moisture saturation curve is mostly unchanged by changing the temperatures used in calculation. The results also show that ageing the synthetic ester in different ways did not significantly affect the moisture saturation curve, however ageing the natural ester open to air led to an increase in measured saturation limit at all temperatures when it was heavily oxidised. It is hypothesised that this is due to the presence of oxidation products other than acid in the natural ester.