Development of High-pressure Viscometer for Lubricating Oils using Torsionally Oscillating Quartz Crystal.

点击翻译按钮获取中文摘要

X-cut quartz crystal rod having a diameter of 5mm and a length of 50mm was used as a sensor. four electrodes were made on its circumference by vacuum deposition of gold. This sensor was connected to an impedance analyzer for measuring equivalent circuit constants and change in resonant frequency of the crystal. The viscosity of the fluids can be calculated based on these values.The experiments were carried out under atmospheric pressure for investigating effects of several parameters, which seemed to be important when the measurements were carried out under a high pressure. The most important factor which should be clarified was maximum viscosity which can be measured by the apparatus. Because, the viscosity of the lubricating oils increases exponentially with pressure. Though the applied voltage should be increased if the maximum viscosity applicable for this measurement would be increased, the maximum voltage of the impedance analyzer used was found to be too low. Therefore, a new system consists of a frequency systhesizer and a digital multimeter was introduced, and the viscosity was calculated using difference in resonant frequency and equivalent resistance at resonating frequency. However, the impedance of the crystal was too high to measure equivalent resistance directly, therefore, twin crystal technique was introduced to measure viscosity.The maximum viscosity when the impedance analyzer was used was around 1000 cP. It is found that if the viscosity exceeds around 100 cP an elastic behavior was appeared and the fluids should be treated as an elasto-viscous fluid. The apparatus should be made more compact when it works under the high pressure.In addition, it is also found that the relaxization spectrum of the oil under the high pressure gives important informations of elasto-viscous property of the oil.