Humberto Chaves

Humberto Chaves
Technische Universität Bergakademie Freiberg · Institute of Mechanics and Fluid Dynamics

Dr.

About

85
Publications
13,857
Reads
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1,127
Citations
Additional affiliations
October 1995 - present
Technische Universität Bergakademie Freiberg
Position
  • Lecturer
Description
  • Cavitation in transparent nozzles, development of new optical measurement techniques, e.g. correlation velocimetry, or self-mixing optical pressure sensor. Application of high power LEDs to visualization and measurement methods
June 1984 - November 1993
Max Planck Institute for Dynamics and Self-Organization
Position
  • Researcher
Description
  • Flow of retrograde fluids, evaporation waves, flash boiling of gasoline, cavitation in diesel injection nozzles, fuel deposition from sprays, splashing of drops
January 1984 - June 1984
Rensselaer Polytechnic Institute
Position
  • PostDoc Position
Description
  • Experiments in shock splitting in retrograde gases
Education
April 1980 - November 1983
Georg-August-Universität Göttingen
Field of study
  • Flow Physics
October 1974 - April 1980

Publications

Publications (85)
Chapter
Full-text available
This work is dedicated to the optimization of the inert gas atomization process applied for production of steel powders. One aim is the optimization of melt parameters with the target to reduce the particle size of atomized powder. A second aim is focused on the atomization equipment optimization. In order to study thermophysical properties of stee...
Conference Paper
Full-text available
We want to present proof-of-concept measurements for characterizing turbulent flows within a transparent replica of the upper human airways by means of an adopted Laser-Correlation-Velocimetry (LCV) measurement technique. So far, this measurement technique has only been employed for flow measurements of dense sprays. Our proposed approach utilizes...
Conference Paper
Full-text available
The waves produced by a submerged focusing shock wave generator, Piezoclast, EMS, Switzerland are observed using a pulsed LED (100ns) and backlit setup. The trigger source is inductively coupled with the high voltage pulse driving the piezoelectric generator. This allows a high repeatability and a temporal resolution of phase locked full size image...
Conference Paper
Full-text available
A high-speed liquid injector is used to simulate the jets produced by snapping shrimps. The injector uses the collision between an air-driven projectile with a piston that at the opposite end compresses water within a small cavity. The jet is ejected through a nozzle at the end of the cavity. Although, there is no valve, the water is compressed to...
Conference Paper
Full-text available
A more or less real size three hole (0.1 mm diameter) transparent injection nozzle was made with 120° betweenthe orifices and an inclination of 20° to the injector axis. The geometry is similar to that of a multi hole GDI injector. Experiments are performed using n-pentane and α-methyl-naphtalene mixtures in varying composition. The flow in the ori...
Article
The present paper reports on experimental observations performed on 2–6 mm low-density polystyrene particles rising freely in a water-glycerol mixture for the liquid at rest as well as with slow background rotation (axisymmetric solid body rotation around the vertical axis). Particle trajectories were studied in the Reynolds-numbers range of 200<Re...
Conference Paper
Full-text available
A first approach to the prediction of cavitation appearance in nozzles with rounded inlets and various pure fluids is presented. The method is direct optical observation of cavitation in real size transparent glass nozzles that have been polished at the inlet. Injection is performed into the atmosphere. As expected cavitation depends strongly on th...
Article
Full-text available
A novel vibrating finger viscometer for high-temperature measurement in liquid metals and alloys up to 1823 K was constructed. The dynamic viscosity (\(\eta \)) of the liquid fluid is measured as a product of \((\rho \cdot \eta )^{0.5}\) and the relative change of the field coil input for a constant amplitude recording at the resonant frequency of...
Conference Paper
Full-text available
Extracorporeal shock wave therapy is a method of transmitting pressure waves into human tissue by pressing a handset together with a gel for coupling onto the treatment area, e.g. shoulder. These devices work similar to a repetitive pneumatic hammer. The front piece of the handset first compresses the tissue. When the front piece retracts rarefacti...
Patent
The invention relates to a device and a method for atomizing molten materials. To this end, molten material (6), which passes through a gap opening (5) in order to reach an outlet opening (2.1) that is flown through by propellant fluid, is sheared when contact occurs with the propellant fluid stream (3.1) along the inner wall of the flow channel (1...
Article
The free falling liquid steel jet behavior is numerically investigated using implicit large eddy simulations (ILES) and the volume of fluid (VOF) approach. The research is focused on primary breakup phenomena near the nozzle using the standard open-source computational fluid dynamics library OpenFOAM. To quantify the influence of process and constr...
Article
This paper addresses the measurement of the two-dimensional velocity distribution of ligaments and drops during melt atomization. The result of the atomization process is influenced by numerous parameters and is still not well understood. Also due to the high temperatures involved in the process, in situ measurements are very scarce. Due to the fac...
Patent
Die Erfindung betrifft eine Vorrichtung und ein Verfahren zum Zerstäuben von Schmelzen. Dabei wird Schmelzgut (6), das durch eine Spaltöffnung (5) in eine von Treibfluid durchströmte Auslassöffnung (2.1) gelangt, bei Kontakt mit dem Treibfluidstrom (3.1) entlang der Innenwand des Strömungskanals (10.2) geschert, wobei in einem in Strömungsrichtung...
Article
Full-text available
During the production of metal and alloy powders by melt atomization, the knowledge of the surface temperature distribution of drops is essential. This paper shows the application of low-cost industrial CCD-cameras in connection with advanced image processing techniques to measure the average two-dimensional surface temperature distribution of drop...
Patent
Die Erfindung betrifft ein Verfahren zur Bestimmung der Viskosität von Fluiden (16) im Hochtemperaturbereich mittels eines Vibrationskörperviskosimeters (8) und ein zugehöriges Vibrationskörperviskosimeter (8), wobei das Vibrationskörperviskosimeter (8) zumindest umfasst – einen Dämpfungskörper (1) zur Dämpfung von Eigenschwingungen, – ein Erregers...
Conference Paper
Full-text available
A Particle Tracing measurement technique is presented. Images of a rising particle are captured by a single camera equipped with a Plenoptic lens, consisting of a 3x3 doublet micro lens array in combination with a shadowgraphy technique. Aim of this setup is to triangulate the time resolute 3D position of the particle by using the small stereobasis...
Article
Full-text available
There is an increasing interest by doctors and patients in extracorporeal shock wave therapy (ESWT) for chronic plantar fasciopathy (PF), particularly in second generation radial extracorporeal shock wave therapy (RSWT). The present review aims at serving this interest by providing a comprehensive overview on physical and medical definitions of sho...
Article
Using a high-speed and high-resolution-camera system of droplets in glaze sprays and their impact on the surface of a green ceramic body based on silicate tiles have been characterized. The influence of the surface tension of the glaze slips on the droplet size distribution and their wetting behavior on contact with the green silicate body surface...
Article
Full-text available
The spitting cobra Naja pallida can eject its venom towards an offender from a distance of up to two meters. The aim of this study was to understand the mechanisms responsible for the relatively large distance covered by the venom jet although the venom channel is only of micro-scale. Therefore, we analysed factors that influence secondary flow and...
Data
Mesh information and equations of conservation of mass and momentum. (DOCX)
Article
An innovative pulsed reflection microscope (PRM) is used for optical in situ investigations of overload effects during fatigue crack growth in nodular cast iron. The optical system is based on the principle of a reflected-light microscope and can be integrated in any standard testing machines. Using the PRM the microstructural processes near the cr...
Article
Full-text available
The particle velocity and the particle temperature are two of the most important parameters influencing the deposition process of high-velocity oxy-fuel (HVOF) spraying. This article addresses the application of particle image velocimetry to the measurement of the 2D particle velocity distribution in the flame of an industrial burner in a spraying...
Conference Paper
Full-text available
Large Scale Particle Image Velocimetry is a further development of PIV dedicated to measure the surface velocity of flows, in particular of rivers under field conditions. This paper addresses the problem of illumination which is the bottleneck of the technique at the present time. Using a pulsed high efficiency LED together with adapted collimation...
Article
Full-text available
Measuring the void fraction distribution is still one of the greatest challenges in cavitation research. In this paper, a measurement technique for the quantitative void fraction characterization in a cavitating pipe flow is presented. While it is almost impossible to visualize the inside of the cavitation region with visible light, it is shown tha...
Article
A long distance microscope (LDM) is extended by a lens and aperture array. This newly formed channelling LDM is superior in high quality, high-speed imaging of large field of views (FOV). It allows imaging the same FOV like a conventional LDM, but at improved magnification. The optical design is evaluated by calculations with the ray tracing code Z...
Article
In this paper an innovative measurement system that has been developed to investigate the material properties of thin layers is presented. It is used to perform compression tests with small samples of polishing pads that are used for chemical-mechanical polishing of silicon wafers. The results show that a series connection of a Hookean spring and t...
Article
The Cranz-Schardin camera utilizes a Q-switched Nd:YAG laser and four single CCD cameras. Light pulse energy in the range of 25 mJ and pulse duration of about 5 ns is provided by the laser. The laser light is converted to incoherent light by Rhodamine-B fluorescence dye in a cuvette. The laser beam coherence is intentionally broken in order to avoi...
Chapter
In diseased lungs airway closure can occur due to the formation of liquid bridges. These can be caused e.g. by surface tension-driven instabilities. The airway closure leads to a blockage of gas exchange in the deeper part of the lung which in severe cases requires to apply mechanical ventilation and recruitment maneuvers. High-frequency ventilatio...
Conference Paper
Full-text available
Laser Doppler anemometry (LDA) is a widely used flow measurement technique for detecting flow velocity (see e.g. Albrecht et al. 2003). In addition to velocity also particle position measurements were performed with an extended LDA (Shirai et al. 2008). In the present work another extension is proposed. It is able to determine the velocity componen...
Conference Paper
Full-text available
In scanning PIV the light sheet is shifted rapidly perpendicular to the planes of observation of a high speed camera thus obtaining a 2 component 3 dimensional measurement of the flow velocity. It is desirable to use high aperture optics to collect as much scattered light as possible from the tracer particles. However, high aperture optics also hav...
Article
The convective transport of fluid within the human upper airways is investigated in a transparent model of the tracheobronchial tree. Oscillatory flow through the branching network with six generations was studied at varying Reynolds numbers between 400 and 2600 and Womersley numbers from 5.5 to 12.3 in the trachea representing clinical conditions...
Conference Paper
Full-text available
A new technique is presented for micro-PIV measurements in high velocity flows of small dimensions like injection nozzles or sprays at the nozzle exit. The technique requires only one pulsed incoherent light source of sufficiently short pulse duration. This duration limits the maximal resolved velocity since the image pair is not acquired with one...
Article
Today, nodular cast iron is intensively used in highly stressed components like wind turbine, machine and vehicle components, where variable cyclic loads are applied. In contrast to other common materials, where crack growth retardation is observed after overloads, crack growth acceleration was detected in fatigue crack growth experiments within no...
Article
The behaviour of two-phase gas-liquid flows in a stopper-rod controlled submerged entry nozzle (SEN) is investigated in water model experiments. The observed two-phase flow patterns can be classified into either bubble coring or bubbly slug. The scaling of the two-phase flows by means of similarity parameters is discussed. In the experiments, it is...
Article
Full-text available
In this article, we present a new imaging technique for multiple-segment microscopy at long working distances. In many applications, images of small structures might have to be taken simultaneously at widely separated points. At present, this is a problem because with a single lens it is possible to either take an image of one structure with high r...
Conference Paper
Full-text available
A new type of optical pressure sensor / microphone is presented. The transduction of pressure to the mechanical deflection of a membrane is basically the same as for capacitance transducers. The pressure varies linearly the curvature of the membrane for small deflections. A reflective membrane is used, thus acting as an active optical mirror with a...
Article
In this paper we present a new technique to measure the wall-shear-stress named mirror PTV (MPTV). The basic principle is the use of a reflective coated surface to record the flow in the very near wall region in such way, that the original particle and its mirror image are detected. The distance between the original particle image and its correspon...
Conference Paper
Full-text available
A new type of laser two focus (L2F) velocimeter is presented. It utilizes the self-mixing effect of laser diodes for amplification of the backscattered light coming from each focus. The light from two laser diode packages placed close to each other (5.6 mm for standard packages) is focused by a lens forming the two foci. Their separation depends on...
Article
Argon injection is widely used to reduce nozzle clogging during continuous casting, but its effects on the flow in the submerged entry nozzle are not yet fully understood. Therefore, the gas liquid flow in a stopper rod controlled submerged entry nozzle is Investigated experimentally and numerically. First single-phase liquid flow is studied. Numer...
Conference Paper
Full-text available
The difficulties of PIV measurements in high speed flow measurements in small orifices are discussed. A backlit micro PIV system was developed to measure the flow within real size transparent VCO nozzle with orifices of 150 μm in diameter. Using refractive index matching the resolution of the PIV images reaches almost the diffraction limit. Larger...
Chapter
IntroductionExperimental Set-UpResults Regimes of drop fragmentationNucleate boiling in the liquid filmConvection in the liquid filmConclusions AcknowledgementsReferences Regimes of drop fragmentationNucleate boiling in the liquid filmConvection in the liquid film
Article
We present in this paper test results of flexible micro-pillars and pillar arrays for wall shear stress measurements in flows with fluctuating wall shear stress such as unsteady separated flows or turbulent flows. Previous papers reported on the sensing principle and fabrication process. Static calibrations have shown this sensor to have a maximum...
Article
An oscillating pipe flow with a free surface is investigated numerically and experimentally. The pipe diameter is 12mm. Due to this small diameter capillary forces play an important role. Therefore special attention has to be paid to the flow field near the free surface. The numerical model is based on the fundamental flow equations. The free surfa...
Conference Paper
Full-text available
A new optical method for velocity measurement is presented that functions well in optically dense sprays. It is basically a modified Laser-Two-Focus velocimeter with the difference that the data is evaluated by cross-correlation and not by time of flight analysis. This renders the method insensitive to a low signal to noise ratio. The optical set-u...
Conference Paper
Full-text available
The onset and development of cavitation in an injection nozzle is strongly dependent on the nozzle geometry. The length to diameter ratio, the curvature of the inlet to the nozzle hole, the angle of the hole axis relative to the sac hole axis are some of the geometric parameters that influence the location and appearance of cavitation. In the prese...
Article
The measurement of velocities in dense sprays with standard methods (laser Doppler anemometry, LDA, or phase Doppler anemometry, PDA) is difficult because of the high particle number density. Therefore, a laser two-focus method was developed with a modified data evaluation algorithm using cross-correlation. This method allows us to measure velociti...
Conference Paper
Full-text available
The knowledge of the temporal and spatial variations of the spray velocity is a necessary requirement for the development of models and CFD codes simulating the atomization processes in engines. For measurements of the spray velocity originating from a fuel nozzle a cross-correlation method is developed. This method allows data acquisition in the o...
Conference Paper
Full-text available
The present study has been performed to obtain a better understanding of the atomization process. The strategy is first to minimize stochastic perturbations by generating a laminar jet and to reduce all other perturbations produced by the injection system to a minimum. In a second step well defined periodic velocity fluctuations are imposed on the...
Article
The measurement of velocities in dense sprays with standard methods (LDA, PDA) is difficult because of the high particle number density. Therefore, a Laser-Two-Focus method was developed with a modified data evaluation algorithm using cross-correlation. This method allows to measure velocities within the dense core of a spray near the nozzle exit a...
Conference Paper
Full-text available
Due to the complex geometry of “valve covers orifice” (VCO) nozzles, details of the cavitation process in real size nozzles are very difficult to observe. For that purpose the tip of a standard VCO nozzle was replaced in the present investigation by a glass prism which has a conical recess for the needle tip and two opposing holes of about 1 mm in...
Conference Paper
Full-text available
By grinding a standard VCO single hole nozzle for a large Diesel engine and the subsequent gluing of a transparent glass nozzle (4mm x 4mm with a hole of 1 mm in length and 0.2 mm diameter) on the injector it was possible to observe the flow within and outside the nozzle hole for a real size injector geometry in the same way Arcoumanis et al. did f...
Conference Paper
Full-text available
By modulating the pressure upstream of a nozzle trains of drops are produced which impact the thin layer of liquid formed by the spreading of the previous drops on a glass block. The spreading flow was observed from below through the glass block with a CCD camera. For certain conditions a very regular production of bubbles is observed. The origin o...
Conference Paper
Full-text available
It is well known that the atomization of a liquid exiting a nozzle is strongly influenced by the interaction with the surrounding air. This aerodynamic interaction of the jet with the air has been studied extensively both theoretically (linear stability analysis) and experimentally. However, the atomization process is initiated by finite perturbati...
Article
Full-text available
Progress in Diesel spray modelling highly depends on a better knowledge of the instantaneous injection velocity and of the hydraulic section at the exit of each injection hole. Additionally a better identification of the mechanisms which cause fragmentation is needed. This necessitates to begin with a precise computation of the two-phase flow which...
Conference Paper
Full-text available
Cavitation, which occurs in diesel injection nozzles, is experimentally investigated in real size transparent nozzles. It is shown that even in the case of a sharply edged inlet cavitation can disappear for a short time interval (in the order of ten microseconds) provided the pressure rises sufficiently fast, i.e., within a time comparable to the t...
Conference Paper
Full-text available
The atomization of a liquid jet exiting a nozzle is initiated by perturbations of the jet coming already from the nozzle flow (swirl, flow separation, cavitation, turbulence) which are not well quantified and in most cases stochastic. The subsequent process of atomization is completed by the interaction between the perturbed jet and the surrounding...
Conference Paper
Full-text available
The atomization of a liquid jet exiting a nozzle is initiated by perturbations of the jet which are generated already within the nozzle (swirl of the flow due to asymmetries of the inlet, flow separation, cavitation, turbulence etc.). Then the subsequent process of actual spray formation is completed by the interaction between the modulated and per...
Article
When liquid drops impinge on a wall heated up above the boiling temperature of the liquid, bubbling and convection are observed in the emerging film which spreads along the wall. Experimental investigations of these processes and of the connected evaporation of the liquid are aimed at an improved understanding of the underlying mechanisms important...
Conference Paper
Full-text available
Highly reproducible structures occur in a diesel spray for an appreciable part of the injection duration immediately after the opening transient of the needle. They were observed by using the signal of a pressure transducer placed in the tip of the injector 4 mm upstream of the nozzle hole as a trigger for high speed stroboscopic pictures of the sp...
Conference Paper
Full-text available
The measurement technique presented relies on the large image magnification (46 times) of a real size transparent diesel injection nozzle (0.2 mm in diameter and 1mm in length). In the image plane two light fibres collect the light and guide it to two photomultipliers. The position of the measuring volumes relative to the nozzle in the object plane...
Article
Under diesel engine conditions the exit velocity of diesel fuel out of an injection nozzle depends on the temporal increase of the supply pressure. Therefore, heading 'slow' fuel elements are caught up by 'fast' elements leaving the nozzle at a later time. Similar processes occur in modulated flow. This kind of interaction ("collision") of liquid e...