Tools for creating LaTeX-integrated graphics and animations under GNU/Linux

This paper describes how to easily create graphics and animations that can be included in LATEX documents. This article discusses three kinds of figures: plots, schematics, and pictures. The tools presented here can quickly generate plots, and are based on simple gnuplot and bash scripts that display the final result on the screen. Ipe is an excellent program to deal with complex figures and schematics, and the animate package is used to make a series of figures change over time to simulate a movie. All the programs used in this article are free software.Peer ReviewedPostprint (published version

Effects of gravity level on bubble formation and rise in low-viscosity liquids

We present an experimental analysis of the effects of gravity level on the formation and rise dynamics of bubbles. Experiments were carried out with millimeter-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 on the gravity level. Vorticity production is enhanced as gravity increases, which destabilizes the flow and therefore the bubble path.Peer ReviewedPostprint (published version

Effects of gravity level on bubble detachment, rise, and bouncing with a free surface

Bubble detachment, rise, and bouncing upon impact with a free surface is studied experimentally in variable gravity conditions. Previous investigations focused on the effects of fluid properties such as viscosity or surface tension on the rise and bouncing dynamics. Gravity force is a crucial factor in the detachment, rise and bouncing processes. However, the effect of different gravity levels has never been studied experimentally. In this paper we analyze the role of gravity in the detachment, rise velocity and bouncing motion of millimetric bubbles colliding with a free surface. Single air bubbles in ethanol are detached from a nozzle by the buoyancy force. After reaching a terminal velocity, the rising bubble interacts with the free surface in a bouncing process prior to coalescence. The equivalent bubble diameter at detachment decreases as the gravity level increases, in agreement with the theoretical prediction. An expression for the terminal velocity as a function of gravity is proposed. The terminal velocity is found to increase with the gravity level, although bubbles are smaller at higher values of gravity. The bouncing process has been modelled by a damped oscillator, in which the free surface acts as an elastic membrane. An expression for the frequency of bouncing as a function of gravity has been obtained, showing a good agreement with the experimental results. The motion of the bubble during the bouncing process can be approximated by an underdamped oscillator even if viscosity is negligible. Therefore, viscosity is not the main responsible for damping, which is probably due to energy transfer from the bubble to the fluid in the form of vortex and surface waves generation.Peer ReviewedPostprint (author's final draft

Low Weber number jet collision regimes in microgravity

The outcome of the collision between two liquid jets depends on the liquid properties, jet velocity, and impact angle. So far studies on liquid jet impingement have been carried out in normal gravity conditions. In microgravity, jets are not accelerated and can show a different behavior than on ground. We perform an experimental analysis of the injection of liquid jets in microgravity, focusing in the jet impingement at different velocities and impact angles at low Weber numbers. Several regimes are obtained, some of which are not observable on ground. Other regimes take place at different parameter ranges than in normal gravity. A map of the observed regimes is proposed in terms of the Weber number and the impact angle.Peer ReviewedPostprint (author's final draft

Bouncing of bubbles impacting at a free surface

Peer ReviewedPostprint (published version

On ground study of bubble jets collision

Collisions of bubble jets have been experimentally studied in a normal gravity environment. Jets are introduced into a cavity full of liquid by means of a microbubble injector [1]. The experimental set-up, designed for a future use in low gravity conditions, allows the control of the impact angle between jets [2], bubble size and velocity. Individual bubble properties and the whole jet structure are analyzed from the images recorded. We present results on the role played by the impact angle and the distance between injectors on the structure of the final jet. A systematic study for different gas and liquid flow rates has been carried out in order to compare the results obtained in normal gravity with those to be obtained in a future campaign at INTA drop tower

Bubbly jet impingement in different liquids

The impingement of bubbly jets in distilled water and ethanol has been experimentally studied on ground. An experimental apparatus for the study of jet impingement on ground and inmicrogravity has been designed. The opposed-jet configuration with changeable orientation is used in order to study which is the better disposition to achieve an efficient mixing process. The impact angle between jets that can be changed from 0◦ (frontal collision) up to 90◦ (perpendicular collision). The impinging jets are introduced into a test tank full of liquid by means of two bubble injectors. The bubble generation method, insensitive to gravity level for low Bond numbers, is based on the creation of a slug flow inside a T-junction of capillary tubes of 0.7 mm of diameter. Bubble velocities at the injector outlet and generation frequencies can be controlled by changing gas and liquid flow rates. Individual bubble properties and coalescence events, as well as the whole jet structure are analyzed from the images recorded by a high speed camera. Bubble velocities are compared with the velocity field of a single-phase jet. Rate of coalescence between bubbles is found higher in ethanol than in water, creating a higher dispersion in bubble sizes.Peer ReviewedPostprint (published version

Experimental analysis of bubble jets collision

Peer ReviewedPostprint (published version

High-precision time-of-flight determination algorithm for ultrasonic flow measurement

© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Commercial time-of-flight (TOF) ultrasonic flowme- ters 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.Peer ReviewedPostprint (author's final draft

Experimental study of bubbles behaviour

Peer Reviewe