Commercial time-of-flight (TOF) ultrasonic flowmeters are rapidly expanding in the general industry. Among the different techniques that can be applied to determine the TOF of ultrasonic waves, the cross-correlation method presents numerous advantages, such as robustness for weak signals and noise suppression. However, the selection of an appropriate reference wave is presumably a key element in the precise measurement of TOF. In the present paper, an algorithm to compute an accurate TOF is proposed. The form of the electric signal received by the transducer is obtained from an acoustically-forced underdamped oscillator model, and the analytical solution of the model is proposed as a reference wave. In order to validate the effectiveness of this procedure, an ultrasonic flowmeter system is designed and tested in a flowmeter calibration test rig. It is demonstrated that the use of the presented scheme overcome the average method limitations, and turns out to be a convenient solution in a wide range of conditions. Robust measurements of near-zero flow values are acquired, which allow the achievement of a high dynamic range. The error curve of the proposed system have been obtained, revealing that the absolute value of the relative errors are lower than 2% within all the spectrum of flow rates considered (from 0.2 to 150 m 3 /h). Results demonstrate that the algorithm provides high-precision measurements within a wide dynamic range. The algorithm is portable and versatile: it can be adapted to different types of transducers without the need of additional measurements, allowing to adjust parameters on-the-fly for an optimal performance of the ultrasonic flowmeter system.
This work investigates the potential use of direct ultrasonic vibration as an aid to penetration of granular material. Compared with non-ultrasonic penetration, required forces have been observed to reduce by an order of magnitude. Similarly, total consumed power can be reduced by up to 27%, depending on the substrate and ultrasonic amplitude used. Tests were also carried out in high-gravity conditions, displaying a trend that suggests these benefits could be leveraged in lower gravity regimes.
The (Ba,Ca)(Zr,Ti)O3 ceramic system has received special attention in recent years because it may lead to promising lead-free piezoceramics. However, the stability of the functional properties of these materials is an important issue that requires greater attention. In this work, the (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 compound (BCZT) is taken as a reference material for evaluating the variation of the functional properties when an external stimulus (e.g., electric field or dynamical stress) is applied, which may constitute an important drawback of piezoceramics. The results show that BCZT exhibits a huge nonlinear behavior, which notably limits this leadfree material for transfer to applications. The instabilities manifest at considerably low amplitudes of the applied electric field or dynamical stress due to a large extrinsic contribution from the irreversible motion of domain walls. Understanding and controlling the physical phenomena related to the domain wall motion presents a fundamental challenge for achieving an effective enhancement of the functional property stability of this system.
We present an experimental study on the characteristics of liquid jets in different configurations. We consider jets injected perpendicular to gravity, jets injected parallel to gravity, and jets injected in a microgravity environment. We study the role played by gravity in the jet breakup length and in the dynamics of the droplets generated after breakup. We analyze droplets obtained in the dripping and jetting regimes, focusing the study on their size, trajectory, oscillation and rotation. The particularities of the considered injection configurations are analyzed. In normal gravity conditions, in the dripping and jetting regimes, the breakup length increases with the Weber number.The transition between these regimes occurs at We cr ≈ 3.2. Droplets are notably larger in the dripping regime than in the jetting one. In the latter case, droplet mean size decreases as the liquid flow rate is increased. In microgravity conditions, droplet trajectories form a conical shape due to droplet bouncing after collision. When a collision takes place, coalescence tends to occur at low modified Weber numbers (We m < 2), while bouncing is observed at higher values (We m > 2). The surface of a droplet oscillates after bouncing or coalescence events, following a damped oscillator behavior. The observed oscillation frequency agrees with theoretical predictions.
We present an experimental analysis of the effects of gravity level on the formation and rise dynamics of bubbles. Experiments were carried out with millimetre-diameter bubbles in the hypergravity environment provided by the Large Diameter Centrifuge of the European Space Agency. Bubble detachment from a nozzle is determined by buoyancy and surface tension forces regardless of the gravity level. Immediately after detachment, bubble trajectory is deviated by the Coriolis force. Subsequent bubble rise is dominated by inertial forces and follows a zig-zag trajectory with amplitude and frequency dependent of the gravity level. Vorticity production is enhanced as gravity increases, which destabilizes the flow and therefore the bubble path.PACS numbers: 47.55.dd, 47.20.Ky
An efficient long-term storage of cryogenic pro-1 pellants is a challenge for future space exploration missions.
2The vapour bubbles formed as a result of boil-off in the tank 3 walls can generate foam structures, which could be hazardous 4 in different operations in orbit. A recently proposed approach 5 to control the dynamics of bubbles is based on the generation 6 of an acoustic field by means of a piezoelectric transducer.7This technology needs to be validated at cryogenic tempera-8 tures in order to be applicable in space. In this perspective, 9 different piezoelectric elements and matching layer materials 10 have been tested at cryogenic temperatures to assess their 11 performance at such environmental conditions. We consider 12 the use of soft PZT piezoceramics coupled with an epoxy 13 resin as the matching layer. Experimental data reveal that 14 epoxy resin-based acoustic matching layers exhibit a linear 15 increase in the transmittance of the acoustic amplitude at 16 cryogenic conditions. The peak-to-peak amplitude increases 17 as temperature decreases up to a factor of 1.6. This result 18 opens the possibility of generating and transmitting acoustic 19 waves at cryogenic temperatures, which could be used in 20 the recently proposed technology to control the dynamics of 21 vapour bubbles in cryogenic fuel tanks.
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