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Pressure transmitting fluid has many applications in wide variety of fields such as pressure measur-ing instruments, combustion engine, oil lubrication in gearboxes, compressors, pumps etc. Due to its wide variety of applications, it is utmost important to understand the rheological properties such as ultrasonic velocity of the pressure transmitting fluid. With this objective in mind, the present paper aims to determine the behavior of ultrasonic propagation velocity in one of the most commonly used pressure transmitting fluid, Sebacate oil (C18H34O4). To perform this experiment, first a high-pressure chamber was especially designed, developed and fabricated. During the design of the pressure chamber, stress analysis was performed using the finite element method (FEM). This analysis led to optimization of the design, as the stresses generated were within the safe limit, for the pressure range of (0-200) MPa. After optimization of the design, high-pressure chamber was fabricated using stainless steel material. To perform the experiment, this high-pressure chamber was assembled in a high-pressure line having hydraulic screw pump for pressure generation, oil reservoir of pressure transmitting fluid, pressure transducer for pressure measurement, ultrasonic transducer for ultrasonic propagation velocity measurement and high-pressure related accessories. Signals from the ultrasonic transducer was monitored with the help of ultrasonic flaw detector (UFD, Olympus: Epoch 1000) in terms of change in path length of two different echoes while assuming the velocity constant. The same process was repeated for the whole pressure range for both the increasing and decreasing pressure order. The ultrasonic propagation velocity in the Sebacate oil being used was measured with the help of ultrasonic interferometer facility available in the laboratory and was found as 1390 m/s at 25°C for the atmospheric pressure. It was observed that the decrease in the pathlength shown by the UFD is the evidence that the ultrasonic velocity increases with increase in the pressure in Sebacate oil and the velocity magnitude is almost same for the both increasing and decreasing order of pressure cycle with negligible hysteresis. It was also observed that the change in velocity with the change in pressure follows the same trend for both the echoes, which represents reproducibility of the measurement system.
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