Génie mécanique - Publications // Mechanical Engineering - Publications

Permanent URI for this collectionhttps://hdl.handle.net/10393/32278

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A software package for computing CJ-deflagrations propagating in vented tubes
(2023) Rakotoarison, Willstrong; Vilende, Yohan
This software package reflects the work done by the authors in their investigation on Chapman-Jouguet (CJ) deflagrations, propagating in vented tubes. In the studied configuration, tubes are open at their rear wall, where the flame originates. As a result, fast CJ deflagrations are expected to propagate with a shock wave ahead of them, which strength is directly dependent on the rear wall opening area. Assuming both the shock and the flame are discontinuities across which conservation of mass, momentum and energy applies, a simple double discontinuity problem can be posed. The present software solves this problem. It is coupled with the library CANTERA, to calculate the states across each discontinuities, accounting for realistic thermal and chemical gas properties. Details on the method are published under the authors name in Combustion and Flame (2023) : "Model for Chapman-Jouguet deflagrations in open ended tubes with varying vent ratio".
Pressure evolution from head-on reflection of high-speed deflagration in hydrogen mixtures
(2023) Yang, Hongxia; Wang, Wentian; Sow, Aliou; Radulescu, Matei
Our previous reported experiments revealed that the reflection of high-speed deflagrations in hydrogen-air and hydrogen-oxygen mixtures produces higher mechanical loading and reflected pressures than reflecting detonations. This surprising result was shown to correlate with the onset of detonation in the gases behind the reflected shock. We revisit these experiments with the aim of developing a closed-form model for the pressure evolution due to the shock-induced ignition and rapid transition to detonation. We find that the reflection condition of fast deflagrations corresponds to the chain-branching cross-over regime of hydrogen ignition, in which the reduced activation energy is very large and the reaction characteristic time is very short compared to the induction time. We formulate a closed-form model in the limit of fast reaction times as compared to the induction time, which is used to predict a square wave pressure profile generated by self-similar propagation of internal Chapman-Jouguet detonation waves followed by Taylor expansion waves. The model predictions are compared with Navier-Stokes numerical simulations with full chemistry, as well as simple Euler calculations using calibrated one-step, or two-step chain-branching models. Both simplified numerical models were found to be in good agreement with the full chemistry model. We thus demonstrate that the end pressure evolution due to the reflection of high-speed deflagrations can be well-predicted analytically and numerically using relatively simple models in this ignition regime, which is of primary interest for safety analysis and explosion mitigation. The slight departures from the square wave model are investigated based on the physical wave processes occurring in the shocked gases, controlling the shock-to-detonation transition. Using the two-step model, we study how the variations of the rate of energy release control the pressure evolution in the end gas, extending the analysis of Sharpe to very large rates of energy release.
Droplet Evaporator of Alcohol-Biodiesel Blends
(2022) Tanner, Alexis; Hallett, William
This work presents experimental data on the droplet evaporation of blends of biodiesel with 1-propanol and 1-pentanol and compares them to the results of numerical models of droplet evaporation. The phase equilibrium of the non-ideal mixture of alcohol with biodiesel was modelled using activity coefficients calculated from the UNIFAC method, which was shown to accurately reproduce experimental VLE data from the literature. Droplet evaporation experiments were performed for 1-propanol / biodiesel and 1-pentanol / biodiesel blends at temperatures of 450°C and 700°C. The numerical modelling compared two different liquid phase models: well-mixed and diffusion-limited. The diffusion-limited model was found to best represent the droplet evaporation process, particularly early in the droplet lifetime. Internal boiling and bubble formation were observed for all mixtures, driven by the large difference in boiling point between the components (around 200 ̊C). The diffusion-limited model was able to roughly predict the conditions under which bubble formation could occur.
Microfluidic blood vasculature replicas using backside lithography
(2019) Fenech, Marianne; Girod, Vincent; Claveria, Viviana; Meance, Sebastien; Abkarian, Manouk; Charlot, Benoit
Blood vessels in living tissues are an organized and hierarchical network of arteries, arterioles, capillaries, veinules and veins. Their sizes, lengths, shapes and connectivity are set up for an optimum perfusion of the tissues in which they deploy. In order to study the hemodynamics and hemophysics of blood flows and also to investigate artificial vasculature for organs on a chip, it is essential to reproduce most of these geometric features. Common microfluidic techniques produce channels with a uniform height and a rectangular cross section that do not capture the size hierarchy observed in vivo. This paper presents a new single-mask photolithography process using an optical diffuser to produce a backside exposure leading to microchannels with both a rounded cross section and a direct proportionality between local height and local width, allowing a one-step design of intrinsically hierarchical networks.
Contact angle study of blood dilutions on common microchip materials
(2013) Pitts, K L; Abu-Mallouh, S; Fenech, M
Biocompatible polymers are commonly used to fabricate microfluidic channels for the study of biological flows such as blood microflows. The most common of these materials is polydimethylsiloxane (PDMS) which is very hydrophobic. Oxygenated plasma is advocated to treat the PDMS with reported decreases in contact angle i.e. increase the hydrophilicity of the material in order to make the liquid flow easily. All contact angle studies have been reported with water. Here the contact angles of blood suspensions, in saline and native plasma, are compared to each other and water on common microfluidic chip materials. The hydrophilic effect of plasma-treatment on PDMS is not found to be as significant with blood suspensions as it is with water. Red blood cells suspended in native plasma are found to have a greater contact angle than those suspended in saline.
Reversibility of artifacts of fluid volume measurements by bioimpedance caused by position changes during dialysis
(2002) Fenech, M; Jaffrin, M Y; Malmen, U
The effect of temporary position changes, sitting up from supine, on extracellular (ECW) and intracellular (ICW) resistances and fluid volumes calculated from whole body bioimpedance using a Xitron 4200 impedancemeter was investigated on 8 patients during dialysis for a total of 11 tests. It was found that ECW resistance decreased instantaneously by an average of 2.3% when the patient sits up, due to plasma and interstitial fluid shift into the legs which decreases leg resistance, the major contributor to total resistance. This drop in resistance is incorrectly interpreted by the device as an increase in ECW volume which averages 235 ml. But this effect is completely reversible and both ECW resistance and fluid volume rapidly resume their normal course when the patient returns to his initial position. No significant variation in ICW resistance was observed in any of the patients at the position change. We conclude that segmental impedance, which has been proposed to minimize this artifact, is not advisable in dialysis monitoring and that it is simpler to ignore or switch off measurements during the position change so that later data are not affected by it.
Effects of red blood cell aggregation on microparticle wall adhesion in circular microchannels
(2019) Stroobach, Mark; Haya, Laura; Fenech, Marianne
The wall adhesion of 1 µm microparticles in human blood was studied in circular microchannels. The level of particle wall adhesion was measured for varying levels of shear rate and varying degrees of red blood cell aggregation, which was modulated by the addition of macromolecule dextran 500. The blood preparations were injected into PDMS microfluidic devices that were modified to have circular channels, better matching the geometry of physiological microcirculation compared to square channels or Couette flow systems. The circular walls of the microchannels were embedded with biotinylated phospholipids to which marginating microspheres coated with streptavidin bound. The particle wall adhesion was evaluated by counting the particles adhering to the channel wall after flushing the channel. Blood preparations of five dextran concentrations (including baseline case of 0%) were tested for four flow velocities, to quantify the effects of aggregation for varying shear rate. It was found that the level of particle wall adhesion was positively correlated with the level of RBC aggregation, particularly at low shear rates, when aggregation was enhanced. The particle adhesion was especially enhanceat aggregation levels in the range of physiological aggregation levels of whole blood, suggesting that RBC aggregation plays an important role in the dynamic of platelets and leukocytes in vivo.
Experimental Characterization of Brushless DC Motors and Propellers for Flight Application
(2016-06-26) Muzar, Dominic; Lanteigne, Eric
Although there exist a number of accurate UAV thruster models, these models require precise measurements of several motor and propeller characteristics. This paper presents simple motor and propeller models based solely on data provided by manufacturers. The theoretical performance predictions for the motors and propellers are computed and then compared to experimental results obtained in static thrust tests. The objective is to confirm the accuracy of the models and facilitate the selection of appropriate brushless DC motor and propeller combinations for flight applications.
Development of Compact Self-Balancing Robot with Self-Standing and Stair-Climbing Capability
(2013-05-13) Robillard, Dominic; Lanteigne, Eric
Self-balancing robots can turn on the spot using differential steering with better efficiency than tracked or four-wheel drive robots, and they can be many times their width in height. However they have two major limitations: they cannot stand-up on their own and cannot climb stairs. In this paper, a novel design is proposed to address these issues. A single degree of freedom is added to the center of a four-wheel drive robot. This arm allows the robot to climb stairs and stand-up on its own. A model and simulation of the balancing and the stair-climbing process are derived and the stair-climbing is compared against experimental results with a prototype. It was shown that the model closely follows the trend of the experimental results and provides a basis for future studies on the concept.

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