1 Experimental apparatus and method
The PIV test apparatus for oils containing different particle sizes and
particle concentrations is shown in Fig. 1. 25# transformer oil is used
as the test fluid (colorless and transparent for the PIV test). First,
the oil is treated by a vacuum filter to obtain an initial oil sample.
Then, Cu, Fe and SiO2 powders with different particle
sizes are selected as the particulate matter. According to the ISO4406
standard of oil pollution degree, 0.02 g of Cu, Fe and
SiO2 powder are mixed with 1 L 25# transformer oil and
oscillated evenly in an ultrasonic oscillator for 8 h (temperature
30~60°C). Then, the mixed solution was separated using
filter paper having different pore diameters to obtain oil samples
having a medium diameter of 5 μm, 15 μm, 25 μm and 50 μm and a
concentration of 14.40 ppm. Next, the initial oil sample is added to the
oil sample at a certain volume ratio, and ultrasonic vibration is evenly
distributed over 8 h (temperature 30~60°C). Oil samples
containing particulates having a gradient concentration of 6.58, 4.57,
3.00, 0.971 and 0.648 ppm of different medium-diameter particles were
eventually obtained.
The pipeline containing granular oil is a square tube with a total
length of 500 mm and a section of 40×40 mm. The bottom and rear walls of
the pipe are made of steel plates, while the front and top walls are
made of transparent glass and are detachable for PIV laser incidence and
testing.