Influence of ultrasonic waves on viscosity of edible natural esters based liquid insulation

In many of the high voltage apparatus, liquid insulation is used as the coolant and isolating medium between conducting parts. Petroleum based mineral oil is utilized as one of the liquid insulation in most of the applications such as transformers, oil bushing and etc. Recently many research works are engaged in the development of alternate liquid insulation with vegetable oil based natural esters. Major concern with natural esters is their higher viscosity which influences in the cooling characteristics of liquid insulation. With the aim of reducing the viscosity, the edible natural esters are treated with ultrasonic waves of 100 W ultrasonic power at a fixed frequency of 30 kHz. This work is carried out with edible natural esters such as sunflower oil (SFO), palm oil (PO) and sesame oil (SO). Further analysis on the impact of ultrasonic wave for different exposure conditions, the natural esters are exposed to ultrasonic waves for different time period of 15 minutes to 60 minutes with different temperatures of 30, 60 and 90°C in ultrasonic wave treatment setup. This process results in the reduction of viscosity of natural esters after ultrasonic treatment. The influence of ultrasonic waves on viscosity is studied by measuring the values of viscosity of treated natural esters after 24 and 720 hours for analyzing the retention of reduction in viscosity after treatment. This investigation reveals that the ultrasonic waves have impact on the reduction of viscosity of natural esters. Also the outcome of the ultrasonic treatment is derived as the mathematical model to estimate the viscosity values for different processing temperature and exposure time.