Figure 2: Schematic of experimental setup.
A mixing tank is used to generate a mixture of bentonite powder with known concentration in water. Dried calcium bentonite powder was dispersed in water with the assistance of a mechanical stirrer. The bentonite powder was added at a ratio according to Eq (15) in section 3.2. Before the experiments, the suspension was stirred for 15 minutes. The homogeneous fluid mixture was then re-circulated by a progressive cavity pump in a closed loop for ultrasonic flow measurement. The pump motor speed was regulated by a variable frequency drive (VFD) via a speed potentiometer. A bellow was installed at the pump discharge side to minimize the piping vibration which may affect the meter accuracy.
The single path transit-time ultrasonic flowmeter utilized two piezoelectric transducers, which were clamped on the outside of the closed pipes at a specified distance from each other. The flowmeter measured fluid velocity by transmitting acoustic signals between the two transducers alternatively, first in the opposing direction of fluid flow, and then in the direction of flow. The differences between the transit times of the signals were directly proportional to fluid velocity. The flow output meter signal was then fed to the PC after being converted to an appropriate digital signal. The mud fluid was slowly pumped into 2-in (54.78 mm ID) stainless steel test section, which was controlled by the manual operated ball valve.
Experimentally, the output of transit-time ultrasonic flowmeter alone was insufficient, and a joint measurement with another reference method was normally required. Therefore, the desired flow was drained to an overhead tank for volumetric measurement. Video was recorded and the video images were processed by an algorithm to acquire the time series flow rate for comparison with the transit-time ultrasonic flowmeter readings.
After completion of all measurements, The experimental data were recorded in room temperature (27~33°C) were analyzed to obtain relationship between signal patterns in the ultrasonic sensors and bentonite concentration, flow speed and Reynolds number. Each experiment was conducted at unsteady flowing condition with flow accelerating from rest to 1.2 ~1.5 m/s, and next, decelerated to rest again, within a duration of 25~30 seconds.