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Purpose – Very recently, driven by glassmakers and champagne houses, attention has been paid to the way to control effervescence and bubble nucleation. It was demonstrated that ascending bubbles act like many swirling motion generators in champagne glasses. It is the reason why a numerical modeling of flow dynamics induced by the effervescence in a glass of champagne has been carried out for the first time using the finite volume method by Computational Fluid Dynamics (CFD). The paper aims to discuss these issues. Design/methodology/approach – In order to define source terms for flow regime and to reproduce accurately the nucleation process at the origin of effervescence, specific subroutines for the gaseous phase have been added to the main numerical model. These subroutines allow the modeling of bubbles behavior based on semi-empirical formulas relating to bubble diameter and velocity or mass transfer evolutions. Findings – Details and development of the steps of modeling are presented in this paper, showing a good agreement between the results obtained by CFD simulations in a reference case of those from laser tomography and Particle Image Velocimetry experiments, validating the present model. Originality/value – A numerical modeling of flow dynamics induced by the effervescence in a glass of champagne has been carried out for the first time using the finite volume method by CFD.

Resume Ce travail concerne la theorie instationnaire de la convection naturelle sur plaque verticale chauffee a flux constant, developpee au moyen de l'approche integrale de Karman–Pohlhausen. Les difficultes liees a l'extension de cette methode aux regimes variables sont levees en supposant que l'epaisseur relative des couches limites thermique et dynamique est fonction uniquement du nombre de Prandtl durant la phase transitoire. Des comparaisons avec les resultats de la methode differentielle semblent valider le modele propose, developpe pour Pr>0,6.

This paper is inspired by the observation in the literature that there was a lack of data about the knowledge of semi-analytical solutions of steady thermal state applied to laminar boundary layer flows in the case of forced convection. Thus, we have made a complete analysis and synthesized the results on both the surface temperature and the surface flux problems, from the development of integral and differential methods, in the range 10−3 ≤ Pr ≤ 102. Moreover, it has been shown that the same ratio, δ T δ = 20 traduces the transition between boundary layer and slug flows, whatever the thermophysical considered case. Finally, we present a warning about the use of 2 and 3-order polynomial shapes by Pohlhausen method which induce a non-unicity of steady state thermal solutions.

Resume En utilisant une methode integrale, nous etudions l'evolution en regime variable d'une couche limite thermique a l'interface d'un ecoulement cisaille s'ecoulant sur une plaque plane, apres apport impulsif d'une densite de flux spatio-periodique sur la plaque. On montre, en considerant une plaque d'epaisseur nulle, et a partir de la solution analytique deduite en regime etabli, que le comportement de la couche limite thermique se trouve beaucoup plus influence par les phases locales de relaxation que par celles de rechauffement.

This study presents an analysis of the temperature evolution in a porous sample. Various situations have been examined: the porous solid is initially dry or water saturated, and the heating fluid is dry air or steam. This analysis showed experimentally the optimal phases of using steam to heat a material. Moreover, as humidity in the solid considerably modifies the heating kinetics, the study has also been carried out on a non-porous solid. The treatment of the temperature curves under an adimensionnal form shows a singular behaviour of those temperatures following the heating fluid nature and its temperature. Equations giving temperature versus time have been proposed. They are based on the definition of a time lag and a time constant, both being defined as a function of the single fluid temperature parameter. Finally, in the particular case of the non-porous solid heated by dry air, with additional approximations, it has been possible to check that the experimental time constant is very close to a fundamental time constant.

Based on the energy equation formulation, a numerical simulation for characterizing the transient heat exchange between a steady laminar boundary layer and a flat sample with no thickness is established. The unsteady behaviour is entirely due to the “thermal inertia” of the dynamical boundary layer generated after an impulsive heat flux step on the upper face of the plate. The time and space evolution of both the surface temperature and the heat exchange coefficient is evidenced. The results are compared to the steady solution deduced from the KARMAN-POLHAUSEN method. The feasibility to treat this kind of problem under a fully analytical form is studied.

In cycling, the gross efficiency (GE, %), defined as the ratio of the power output to the metabolic power (total energy expended according to the time), is one of the main determinants of the perfo...

Legend has it that the Benedictine monk Dom Pierre Perignon discovered the Champagne method for making sparkling wines more than 300 years ago. As it happens, a paper pre‐ sented to the Royal Society in London described the Champagne production method in 1662, six years before Perignon ever set foot in a monastery. In fact, Perignon was first tasked with keeping bubbles out of wine, as the effervescence was seen as vulgar at the time. But then tastes changed and fizz became fashionable, so Perignon’s mandate was reversed; he went on to develop many advances in Champagne production, including ways to in‐ crease carbonation. In any case, the process was not regularly used in the Champagne re‐ gion of France to produce sparkling wine until the 19th century. Since that time, Champagne has remained the wine of celebration, undoubtedly because of its bubbling behavior.

International audience; A numerical modeling of bubble-driven flow patterns in a glass of champagne has been carried out for three champagne temperatures, by using the finite-volume method by CFD (computational fluid dynamics). In order to define source terms for flow regime and to reproduce accurately the bubble nucleation process responsible for champagne effervescence, specific subroutines for the gaseous phase have been added to the main numerical model. These subroutines allow the modeling of bubbles behavior based on semiempirical formulas relating to bubble diameter, mass transfer, velocity, and drag force. Both ascending bubble dynamics and bubble-driven flow patterns dynamics were examined, respectively, 60 s, 180 s, and 300 s after pouring champagne into the glass. Details and development of the various steps of modeling are presented in this paper, showing that the bubble-driven flow patterns velocities of the liquid phase significantly vary with the champagne temperature.

International audience; A theoretical model based on the integral formalism approach for laminar external natural convection in the vicinity of a vertical wall is used to be extended to nanofluids. Two kinds of thermal boundary conditions including uniform wall temperature (UWT) and uniform heat flux (UHF) are used for this modeling. Two different nanofluids are tested, namely, Cu/water and CuO/water nanofluids for which both viscosity and thermal conductivity were determined using Brownian motion-based models. A close attention is focused on the influence due to increasing the volume fraction of nanoparticles on both the heat transfer and dynamic parameters. Results are presented only for particle volume fractions up to 4% to ensure a Newtonian behavior of the mixture. It has been found that natural convection heat transfer increases with the volume fraction for a fixed Grashof number, whatever the nanofluid is. Nevertheless, the enhancement of heat transfer is more pronounced in the case of Cu/water than for the CuO/water nanofluid. Moreover, this trend is also confirmed regarding the dynamical parameters such as the maximum velocity value within the dynamical boundary layer and the corresponding boundary layer thickness.

A simple glass of champagne or sparkling wine may seem like the acme of frivolity to most people, but in fact, it may rather be considered as a fantastic playground for any fluid physicist or physicochemist. In this chapter, results obtained concerning various steps where the CO₂ molecule plays a role (from its ingestion in the liquid phase during the fermentation process to its progressive release in the headspace above the tasting glass) are gathered and synthesized to propose a self-consistent and global overview of how gaseous and dissolved CO₂ impact champagne and sparkling wine science. Some recent investigations, conducted through laser tomography techniques, on ascending bubbles and ascending-bubble-driven flow patterns found in champagne glasses are reported, which illustrate the fine interplay between ascending bubbles and the fluid around under standard tasting conditions. The simultaneous monitoring of gaseous CO₂ and ethanol in the headspace of both a flute and a coupe filled with champagne was reported, depending on whether or not the glass shows effervescence. Both gaseous CO₂ and ethanol were found to be enhanced by the presence of ascending bubbles, thus confirming the close link between ascending bubbles, ascending-bubble-driven flow patterns, and the release of gaseous CO₂ and volatile organic compounds.

International audience; This study deals with recent researches undertaken by the authors in the field of hydrodynamics of human swimming. The aim of this numerical study was to investigate the flow around the entire swimmer's body. The results presented in this article focus on the combination of a 3D computational fluid dynamics code and the use of the k-ω turbulence model, in the range of Reynolds numbers representative of a swimming level varying from national to international competition. Emphasis is placed on the influence of a postural change of the swimmer's head in hydrodynamic performances, which is directly related to the reduction of overall drag. These results confirm and complete those, less accurate, of a preliminary 2D study recently published by the authors and allow the authors to optimise the swimmer's head position in underwater swimming.

A dynamical study of the flow in an asymmetrically heated vertical plane channel has been conducted experimentally. Experiments were carried out in water for three aspect ratios and for a range of modified Rayleigh numbers corresponding to the boundary layer flow regime. The flow dynamics were characterized by means of visualization techniques based on laser tomography using discrete and continuous tracers. Flow visualizations were carried out in the plane of symmetry of the channel along its entire height. The investigations focused more specifically on the influence of the aspect ratio and the modified Rayleigh number on the flow structure both in steady-state regime and during the transitional phase occurring just after the start of the heating. An upward boundary layer flow is found near the heated wall, accompanied by a reverse flow developing on the opposite side from the top open-end of the channel. In steady state, the reverse flow takes the form of an elongated eight-shaped structure with two main recirculation cells. The length of the upper cell of the eight-shape structure decreases with increasing aspect ratio. For a fixed aspect ratio, the increase in modified Rayleigh number results in a decrease in the penetration of the reverse flow. During the transient the flow structure is shown to evolve from a single cell to a final eight-shaped structure.

The origin of infrared thermography comes in 1800 when William Herschel discovered thermal radiation, the invisible light later called infrared, but only in the mid-sixties infrared thermography became a technique of temperature cartography. He proved that this radiation, called infrared, followed the same law as visible light. Later, this phenomenon was connected with the laws of Planck and Stefan. The first detectors for this type of radiation, based on the principle of the thermocouple and thermopile called, were developed around 1830. In 1970, the first cameras appeared for commercial. The first models were made up of a technology-based pyroelectric tube with an optical IR instead of the classical elements. Today, these concepts have been improved with new technologies in electronics and computing. Infrared acquisition systems can arrive at very high frame rates. The major argument is whether infrared thermography can determine thermal variations to enable sufficient quantitative analyses. The creation of computerized systems using complex statistical data analysis, which ensure high quality results, and the enhancement of thermal sensitivity have increased the development of technology of infrared thermography.

International audience

A simple glass of champagne or sparkling wine may seem like the acme of frivolity to most people, but in fact, it may rather be considered as a fantastic playground for any fluid physicist or physicochemist. In this chapter, results obtained concerning various steps where the CO 2 molecule plays a role (from its ingestion in the liquid phase during the fermentation process to its progressive release in the headspace above the tasting glass) are gathered and synthesized to propose a self-consistent and global overview of how gaseous and dissolved CO 2 impact champagne and sparkling wine science. Some recent investigations, conducted through laser tomography techniques, on ascending bubbles and ascending-bubble-driven flow patterns found in champagne glasses are reported, which illustrate the fine interplay between ascending bubbles and the fluid around under standard tasting conditions. The simultaneous monitoring of gaseous CO 2 and ethanol in the headspace of both a flute and a coupe filled with champagne was reported, depending on whether or not the glass shows effervescence. Both gaseous CO 2 and ethanol were found to be enhanced by the presence of ascending bubbles, thus confirming the close link between ascending bubbles, ascending-bubble-driven flow patterns, and the release of gaseous CO 2 and volatile organic compounds.

International audience; This paper aimed to study the feasibility of application of infrared thermography to detect osteoarthritis of the knee and to compare the distribution of skin temperature between participants with osteoarthritis and those without pathology. All tests were conducted at LACM (Laboratory of Mechanical Stresses Analysis) and the gymnasium of the University of Reims Champagne Ardennes. IR thermography was performed using an IR camera. Ten participants with knee osteoarthritis and 12 reference healthy participants without OA participated in this study. Questionnaires were also used. The participants with osteoarthritis of the knee were selected on clinical examination and a series of radiographs. The level of pain was recorded by using a simple verbal scale (0-4). Infrared thermography reveals relevant disease by highlighting asymmetrical behavior in thermal color maps of both knees. Moreover, a linear evolution of skin temperature in the knee area versus time has been found whatever the participant group is in the first stage following a given effort. Results clearly show that the temperature can be regarded as a key parameter for evaluating pain. Thermal images of the knee were taken with an infrared camera. The study shows that with the advantage of being noninvasive and easily repeatable, IRT appears to be a useful tool to detect quantifiable patterns of surface temperatures and predict the singular thermal behavior of this pathology. It also seems that this non-intrusive technique enables to detect the early clinical manifestations of knee OA.

The application of additives to base liquids in the sole aim to increase the heat transfer coefficient is considered as an interesting mean for thermal systems. Nanofluids, prepared by dispersing nanometer-sized solid particles in a base-fluid (liquid), have been extensively studied for more than a decade due to the observation of an interesting increase in thermal conductivity compared to that of the base-fluid (Xuan & Roetzel, 2000; Xuan & Li, 2000). Initially, research works devoted to nanofluids were mainly focussed on the way to increase the thermal conductivity by modifying the particle volume fraction, the particle size/shape or the base-fluid (Murshed et al., 2005; Wang & Mujumdar, 2007). Using nanofluids strongly influences the boundary layer thickness by modifying the viscosity of the resulting mixture leading to variations in the mass transfer in the vicinity of walls in external boundary-layer flows. Then, research works on convective heat transfer, with nanofluids as working fluids, have been carried out in order to test their potential for applications related to industrial heat exchangers. It is now well known that in forced convection (Maiga et al. 2005) as well as in mixed convection, using nanofluids can produce a considerable enhancement of the heat transfer coefficient that increases with the increasing nanoparticle volume fraction. As concerns natural convection, the fewer results published in the literature (Khanafer et al. 2003; Polidori et al., 2007; Popa et al., 2010; Putra et al. 2003) lead to more mixed conclusions. For example, recent works by Polidori et al. (2007) and Popa et al. (2010) have led to numerical results showing that the use of Newtonian nanofluids for the purpose of heat transfer enhancement in natural convection was not obvious, as such enhancement is dependent not only on nanofluids effective thermal conductivities but on their viscosities as well. This means that an exact determination of the heat transfer parameters is not warranted as long as the question of the choice of an adequate and realistic effective viscosity model is not resolved (Polidori et al. 2007, Keblinski et al. 2008). It is worth mentioning that this viewpoint is also confirmed in a recent work (Ben Mansour et al., 2007) for forced convection, in which the authors indicated that the assessment of the heat transfer enhancement potential of a nanofluid is difficult and closely dependent on the way the nanofluid properties are modelled. Therefore, the aim of this paper is to present theoretical models fully describing the natural and forced convective heat and mass transfer regimes for nanofluids flowing in semi-infinite geometries, i.e. external boundary layer flows along

In champagne and sparkling wine tasting, the concentration of dissolved CO 2 is indeed an analytical parameter of high importance since it directly impacts the four following sensory properties: (i) the frequency of bubble formation in the glass, (ii) the growth rate of rising bubbles, (iii) the mouth feel, and (iv) the nose of champagne, i.e., its so-called bouquet . In this state-of-the-art review, the evolving nature of the dissolved and gaseous CO 2 found in champagne wines is evidenced, from the bottle to the glass, through various analytical techniques. Results obtained concerning various steps where the CO 2 molecule plays a role (from its ingestion in the liquid phase during the fermentation process to its progressive release in the headspace above the tasting glass) are gathered and synthesized to propose a self-consistent and global overview of how gaseous and dissolved CO 2 impact champagne and sparkling wine science.

International audience

In the present work, a theoretical model based on the integral formalism approach for both laminar and turbulent external natural convection is extended to nanofluids. By using empirical models based on experimental data for computing viscosity and thermal conductivity of water–alumina and water–CuO suspensions, a close attention is first focused on the influence due to increasing the volume fraction of nanoparticles on the heat transfer and then to the transition threshold between laminar and turbulent regimes. The heat transfer is shown to strongly depend on the flow regime and on particle volume fraction. A clear degradation of heat transfer is observed using nanofluids while compared to that of the base-fluid. Moreover, the fact of increasing the particle volume fraction tends to delay the occurrence of the flow transition to turbulence.

Measurements of CO(2) fluxes outgassing from glasses containing a standard Champagne wine initially holding about 11.5 g L(-1) of dissolved CO(2) were presented, in tasting conditions, during the first 10 min following the pouring process. Experiments were performed at room temperature, with a flute and a coupe, respectively. The progressive loss of dissolved CO(2) concentration with time was found to be significantly higher in the coupe than in the flute, which finally constitutes the first analytical proof that the flute prolongs the drink's chill and helps it to retain its effervescence in contrast with the coupe. Moreover, CO(2) volume fluxes outgassing from the coupe were found to be much higher in the coupe than in the flute in the early moments following pouring, whereas this tendency reverses from about 3 min after pouring. Correlations were proposed between CO(2) volume fluxes outgassing from the flute and the coupe and their continuously decreasing dissolved CO(2) concentration. The contribution of effervescence to the global kinetics of CO(2) release was discussed and modeled by use of results developed over recent years. Due to a much shallower liquid level in the coupe, bubbles collapsing at the free surface of the coupe were found to be significantly smaller than those collapsing at the free surface of the flute, and CO(2) volume fluxes released by collapsing bubbles only were found to be approximately 60% smaller in the coupe than in the flute. Finally, the contributions of gas discharge by invisible diffusion through the free surface areas of the flute and coupe were also approached and compared for each type of drinking vessel.

An experimental investigation was performed to study the heat transfer performance of a 36 nm-Al2O3-particle–water nanofluid in a confined and submerged impinging jet on a flat, horizontal and circular heated surface. The tests were realized for the following ranges of the governing parameters: the nozzle diameter is 3 mm and the distance nozzle-to-heated-surface was set to 2, 5 and 10 mm; the flow Reynolds number varies from 3800 to 88 000, the Prandtl number from 5 to 10, and the particle volume fraction is ranging from 0 to 6%. Experimental data, obtained for both laminar and turbulent flow regimes, have clearly shown that, depending upon the combination of nozzle-to-heated surface distance and particle volume fraction, the use of a nanofluid can provide a heat transfer enhancement in some cases; conversely, for other combinations, an adverse effect on the convective heat transfer coefficient may occur. Within the experimental parameters used, it has been observed that highest surface heat transfer coefficients can be achieved using an intermediate nozzle-to-surface distance of 5 mm and a 2.8% particle volume fraction nanofluid. Nanofluids with high particle volume fractions, say 6% or higher, have been found not appropriate for the heat transfer enhancement purpose under the confined impinging jet configuration. On the other hand, for a very small and a large distance of nozzle-to-heated-surface, it has been observed that the nanofluid use does not provide a perceptible heat transfer enhancement and has, for some particular cases, produced a clear decrease of the convective heat transfer coefficient while compared to that obtained using distilled water.

The so-called effervescence process, which enlivens champagne and sparkling wines tasting, is the result of the fine interplay between CO(2)-dissolved gas molecules, tiny air pockets trapped within microscopic particles during the pouring process, and some liquid properties. This critical review summarizes recent advances obtained during the past decade concerning the physicochemical processes behind the nucleation, rise, and burst of bubbles found in glasses poured with champagne and sparkling wines. Those phenomena observed in close-up through high-speed photography are often visually appealing. Let's hope that your enjoyment of champagne will be enhanced after reading this fully illustrated review dedicated to the deep beauties of nature often hidden behind many everyday phenomena (51 references).

Laser tomography techniques were used to capture the dynamics of bubbles released from particles (arbitrarily called fliers) freely floating in traditional flutes poured with champagne. By use of long exposure time photography, the trajectories of bubbles released by fliers were found to leave very elegant and characteristic "prints" as they crossed a section of champagne illuminated with a 1 mm thick laser sheet. This characteristic print was made with a succession of lighting filaments. Fine analysis of these prints left by fliers enabled us to deduce the bubbling frequency of each flier (which ranged from about 4 bubbles/s up to about 22 bubbles/s a few seconds after pouring), as well as its velocity through the liquid medium (which ranged from about 0.8 mm/s to about 7.6 mm/s). Finally, this flow visualization technique, very recently applied to the science of champagne and sparkling wines, also proved to be a useful technique to underscore fliers' bubbling instabilities along their rather erratic way through the liquid medium.

Laser tomography techniques were used in order to make visible the flow patterns induced by ascending bubbles in flutes poured with champagne. The stability of flow patterns was investigated in flutes showing natural (without any specific surface treatment) as well as artificial effervescence (i.e., engraved at their bottom), all along the first 15 min after pouring. Engravement conditions were found to strongly influence the kinetics and the stability with time of the mixing flow phenomena found in champagne glasses.

The aim of this numerical work is to analyze the effect of the position of the swimmer's head on the hydrodynamic performances in swimming. In this initial study, the problem was modeled as 2D and in steady hydrodynamic state. The geometry is generated by the CAD software CATIA and the numerical simulation is carried out by the use of the CFD Fluent code. The standard k-epsilon turbulence model is used with a specific wall law. Three positions of the head were studied, for a range of Reynolds numbers about 10(6). The obtained numerical results revealed that the position of the head had a noticeable effect on the hydrodynamic performances, strongly modifying the wake around the swimmer. The analysis of these results made it possible to propose an optimal position of the head of a swimmer in underwater swimming.

The present paper investigates a numerical study of flow instabilities in transient mixed convection in a vertical pipe. At the entrance of the pipe, the flow is suddenly submitted to a temperature step. The convection heat transfer on the outer surface of the pipe is taken into account. The governing equations are solved using a finite difference explicit scheme. The numerical results show that the time development of streamlines and isotherms is strongly dependent on the inlet temperature steps. For positive temperature steps, the unsteady vortex is significant in the vicinity of the wall and the reversal flow appears below the wave instability. In the case of negative temperature steps and especially for the low Reynolds number, the reversal flow appears on top of the wave instability. During the transient, the apparition of the vortical structures along the wall leads to the wall boundary layer instability. This phenomenon is due to the transient mixed convection flows. The temperature step effects on the heat transfer of the flow are presented in our paper.

This study deals with skin-friction drag analysis in underwater swimming. Although lower than profile drag, skin-friction drag remains significant and is the second and only other contribution to total drag in the case of underwater swimming. The question arises whether varying the thermal gradient between the underwater swimmer and the pool water may modify the surface shear stress distribution and the resulting skin-friction drag acting on a swimmer's body. As far as the authors are aware, such a question has not previously been addressed. Therefore, the purpose of this study was to quantify the effect of this thermal gradient by using the integral formalism applied to the forced convection theory. From a simplified model in a range of pool temperatures (20-30 degrees C) it was demonstrated that, whatever the swimming speeds, a 5.3% reduction in the skin-friction drag would occur with increasing average boundary-layer temperature provided that the flow remained laminar. However, as the majority of the flow is actually turbulent, a turbulent flow analysis leads to the major conclusion that friction drag is a function of underwater speed, leading to a possible 1.5% reduction for fast swimming speeds above 1m/s. Furthermore, simple correlations between the surface shear stress and resulting skin-friction drag are derived in terms of the boundary-layer temperature, which may be readily used in underwater swimming situations.

A theoretical approach is proposed to investigate the transient dynamic behaviour of a free convection boundary layer-type flow. The set of continuity, momentum and energy equations are solved with the classical Boussinesq approximation using the Karman–Pohlhausen integral method. Applying a step variation of the uniform heat flux on a vertical wall, the boundary layer thickness and velocity profiles within the viscous layer, streamline patterns and volumetric flow rate are evaluated as a function of time. In addition, corresponding fully analytical asymptotic solutions are derived to be readily used in engineering applications.

This paper deals with experimental modeling of the unsteady junction flow features in the vicinity of an isoflux heated wall with mounted insulated rectangular ribs representing three distinctive ribbed test geometries. Both flow visualizations and surface temperature distributions show that the blockage effect upstream of the ribs, as well as the presence of complex eddy structures inside the open cavities, significantly affect the heat transfer process. All the configurations indicate degraded heat transfer performance in the area close to the ribs and an enhancement just downstream from the last rib.

International audience; An experimental study has been made of the influence of different convective atmospheres on the thermal behaviour of materials in a rectangular cavity. The atmospheres can be dry air, humid air, or superheated steam. Two kinds of materials are studied: porous and nonporous. The comparisons show a benefit in using humid atmospheres to reach the saturation temperature in a minimum of time. Afterwards the behaviours tend to those obtained with dry air. The presence of humidity within the material modifies the heating kinetics as well under dry air as under steam. By normalising the central temperature, predictive models have been proposed, giving the central temperature history for each material under the kinds of convective atmospheres.

In champagne tasting, gaseous CO(2) and volatile organic compounds progressively invade the headspace above glasses, thus progressively modifying the chemical space perceived by the consumer. Simultaneous quantification of gaseous CO(2) and ethanol was monitored through micro-gas chromatography (μGC), all along the first 15 minutes following pouring, depending on whether a volume of 100 mL of champagne was served into a flute or into a coupe. The concentration of gaseous CO(2) was found to be significantly higher above the flute than above the coupe. Moreover, a recently developed gaseous CO(2) visualization technique based on infrared imaging was performed, thus confirming this tendency. The influence of champagne temperature was also tested. As could have been expected, lowering the temperature of champagne was found to decrease ethanol vapor concentrations in the headspace of a glass. Nevertheless, and quite surprisingly, this temperature decrease had no impact on the level of gaseous CO(2) found above the glass. Those results were discussed on the basis of a multiparameter model which describes fluxes of gaseous CO(2) escaping the liquid phase into the form of bubbles.

Flow visualization techniques1,2,3 were employed to investigate vortex instabilities in free convection plumes (Fig. 1) as well as in the interaction of opposite buoyancy-induced flows (Figs 2,3). Visualizations were carried out by means of laser tomography combined with the electrolytic precipitation method2 (Figs 1,3) and the dye fluorescent technique4 (Figs 3(a,b)). The opposite flows consist in an ascending boundary layer developing along a uniformly and periodically heated vertical plate and a descending plume generated by a constantly cooled horizontal cylinder placed near the wall4 (Fig. 2). The electrolytic method and the dye technique were used simultaneously for part of the investigation of the opposite buoyancy-induced flows (Figs 3(a,b)) in order to distinguish the boundary-layer development (electrolytic method) from that of the plume (dye technique). Figure 1 highlights the usual development of a mushroom-like vortex above a heated horizontal cylinder while Figure 3 shows some singular structures developing at the plume/boundary layer interface during the interaction of the opposite flows. The wall heating results in the formation of a mushroom-type vortex (not shown here), that is transported along an axis oblique with respect to the wall. Then, the wall thermal relaxation phase leads to an interfacial instability in the form of a KelvinHelmholtz instability (Fig. 3a). This instability becomes the source of three-dimensional small-scale structures resulting in a large three-dimensional spiral motion (Fig. 3b). Finally, the flow is reattaching at the wall in the form of multiple counter-rotating vortices (Fig. 3c) originating from the opposition of the descending plume and the ascending boundary layer.

The so-called effervescence process, which enlivens champagne and sparkling wines tasting, is the result of the fine interplay between CO(2)-dissolved gas molecules, tiny air pockets trapped within microscopic particles during the pouring process, and some liquid properties. This critical review summarizes recent advances obtained during the past decade concerning the physicochemical processes behind the nucleation, rise, and burst of bubbles found in glasses poured with champagne and sparkling wines. Those phenomena observed in close-up through high-speed photography are often visually appealing. Let's hope that your enjoyment of champagne will be enhanced after reading this fully illustrated review dedicated to the deep beauties of nature often hidden behind many everyday phenomena (51 references).

Cycling science has undergone a great revolution in recent years. During individual time-trials, racing events in which cyclists race against the clock are not permitted to ride behind other cyclis...