Planar Laser Research Articles

Behavior of child droplets during micro-explosion and puffing of suspension fuel droplets: The impact of the component mixing sequence

The article provides experimental research findings on the behavior of micro-explosion and puffing of two-liquid droplets in different droplet formation schemes: liquid combustible component (rapeseed oil) as the shell with liquid incombustible component (water) as the core and vice versa. The experiments were conducted on fuel compositions that had not been pre-mixed; no coal particles had been added into them. These conditions aimed to reflect industrial production conditions with separate injection and blow-in of components into combustion chambers. Shadow Photography and Planar Laser Induced Fluorescence techniques were used in the experiments. An alcohol burner was used for heating droplets. The temperature of the heating medium was varied in the range of 850–1050 K by adjusting the vertical distance of the droplet from the burner bottom to match the conditions typical for industrial applications, specifically, composite fuel creation technologies and thermal/flame purification of liquids. Conditions have been determined under which droplets of combustible and non-combustible components are atomized during fragmentation thus producing polydisperse and monodisperse aerosols. Effects have been discovered whereby the fragmentation of combustible and noncombustible liquid components produces droplets of different sizes. Correlations between the size and component composition of child droplets with the heating temperature and mixing sequence of the liquids in the parent droplet have been established.

The Influence of AP Addition on the Combustion Characteristics of TKX‐50 with Concentrated Ignition

AbstractIn order to study the influence of ammonium perchlorate (AP) addition on the combustion reaction process of dihydroxylammonium 5,5’‐bistetrazole‐1,1’‐ diolate (TKX‐50), a concentrated ignition system was used to evaluate the ignition and combustion characteristics of the samples. The self‐luminescence characteristics and the OH concentration distribution in the flame of TKX‐50 and TKX‐50/AP composites were captured by a high‐speed camera and a planar laser induced fluorescence system (PLIF), respectively. The combustion products were then analyzed by a scanning electron microscope (SEM) and a X‐ray energy dispersive spectrometer (EDS). The results show that the reaction of TKX‐50 undergoes three stages with concentrated ignition, and a bright yellow color appears in the flame due to the formation of NH2α during the combustion process. When the materials of AP is added, there are pre‐ignition occurred for twice. The ignition delay time increases, and the reaction in the pyrolysis phase is more intense. Besides, the burning rate is faster and the flame brightness is significantly weakened due to the decrease of NH2α. During the combustion process, the high‐concentration OH signal of the two samples distribute on the two wings of the flames, and the peak signals are similar under the 10 Hz laser excitation. For the samples before and after the combustion reaction, the morphology is quite different, and the specific residue composition needs be further analyzed.

Experimental study on the aero-optical effects of a supersonic mixing layer controlled by the ramp vortex generator array.

As the main structure that induces aero-optical effects, the supersonic mixing layer is an essential structure in hypersonic flight vehicles with optical windows. The aero-optical effects of a Mc=0.17 supersonic mixing layer controlled by the ramp vortex generator array (RVGA) were investigated in detail using the nano-tracer-based planar laser scattering technique and ray tracing method. The incident locations and angles of the beam, and the mounting position of the RVGA, act as variables. In different cases, the optical path difference (OPD), Strehl ratio (SR), imaging displacement (ID), and bore sight error (BSE) are taken as evaluation parameters. Surprisingly, the length of the laminar section of the supersonic mixing layer varies little when the RVGA is applied. To reduce the aero-optical effects under our experimental conditions, the best incident angle is between 90º and 100º, and the position of the aperture should be carefully chosen to avoid the region of transition. A 10.75%-25.22% reduction of the average OPDrms and a 15.30%-33.99% reduction of the standard deviation of the OPDrms are achieved when the RVGA is applied, as well as an overall improvement of the SR, ID, and BSE. In our experimental circumstances, the supersonic mixing layer's aero-optical effects are suppressed to the full extent if the RVGA is mounted right at the trailing edge of the splitter.

High repetition rate mapping of the interaction between a laser plasma and magnetized background plasma via laser induced fluorescence

The laminar coupling of energy between a laser-produced plasma and a background magnetized plasma was investigated via planar laser induced fluorescence diagnostic and magnetic flux probes. Experiments performed on the Large Plasma Device at the University of California, Los Angeles, mapped out the two-dimensional spatiotemporal evolution of the laser-plasma (debris) ion velocity distribution function (VDF) to assess debris-background coupling in a sub-Alfvénic regime. The acquisition of these data necessitates high repetition rate (1 Hz) as each dataset is the accumulation of thousands of laser shots, which would not be feasible in single-shot experiments. Fully kinetic, three-dimensional particle-in-cell simulations are compared to the measured VDFs to provide a framework in which we can understand the coupling of a sub-Alfvénic plasma flow through a preformed, magnetized plasma. The simulations display the same departure from the expected gyromotion of the debris plasma as observed in the experimental data, and in conjunction with the measured magnetic field traces, have led to the direct observation of the collisionless coupling via laminar fields.

Luminescent probe synthesis for oxygen visualization technique: Application to the effect of surfactant structure on oxygen mass transfer

Planar Laser Induced Fluorescence with Inhibition (PLIF-I) is a powerful technique for studying the local gas/liquid oxygen mass transfer from a single rising bubble. However, to track oxygen in the liquid phase, it is necessary to use an oxygen sensitive luminescent probe, which needs to be unreactive toward the liquid phase. This article presents the synthesis of a fluorophore, [Ru(dpp-diSO3)3]Na4, to be used in liquid phases containing anionic molecules. To avoid electrostatic interactions, the fluorophore and the component present in the liquid phase need to have the same charge. Thanks to the use of this new luminescent probe in PLIF-I application, the influence of the chain length of anionic surfactants (dodecyl sulfate sodium salt and tetradecyl sulfate sodium salt) on oxygen mass transfer has been studied at different concentrations (1.3 × 10-3-2.5 × 10-7 mol.L-1). Results show that, for a given bulk concentration, the longer the hydrophobic chain, the greater the decrease in velocity and mass transfer coefficient. These results are compared with those of a previous paper dealing with length of cationic and nonionic surfactants and a correlation is proposed, taking account of the intrinsic properties of surfactants and their concentration in the liquid phase.

Multi-dimensional modeling of mixture preparation in a direct injection engine fueled with gaseous hydrogen

With the recent advances of direct injection (DI) technology, introducing hydrogen into the combustion chamber through DI is being considered as a viable approach to circumvent backfire and pre-ignition encountered in early generations of hydrogen engines. As part of a broader vision to develop a robust numerical model to study hydrogen spark ignition (SI) combustion in internal combustion (IC) engines, the present numerical investigation focuses on mixture preparation in a hydrogen DI SI engine. This study is carried out with a single hole injector with gaseous hydrogen injected at 100 bar injection pressure. Simulations are carried out for high and low tumble configurations and validated against optical data acquired from planar laser induced fluorescence (PLIF) measurements. Varying mesh configurations are investigated for the impact on in-cylinder mixture distribution. A particular emphasis is placed on the effect of nozzle geometry and mesh orientation near the wall. Overall, the computational model is found to predict the mixture distribution in the combustion cylinder reasonably well. The results showed that the alignment of mesh with the flow direction is important to achieve good agreement between numerical analysis and optical measurement data.

Blowoff of bluff body flames: Transient dynamics and three dimensional effects

This work examines the dynamics of confined bluff body flames in the process of lean blowoff (LBO) using simultaneous stereo-PIV (particle image velocimetry), OH PLIF (planar laser induced fluorescence) and formaldehyde (CH2O) PLIF. Flames at high density ratios blow off in at least two distinct stages: stage 1, where intermittent extinction occurs along the flame front, but the flame and flow remain qualitatively similar to stable conditions, and stage 2, where there is permanent downstream flame extinction and large-scale changes in dynamic flow characteristics. This paper particularly focuses on stage 2 processes, with the goal of understanding what ultimately leads to irrecoverable flame blowoff. A test facility was developed with the flexibility to achieve two goals: (1) approach LBO by keeping the parameters that influence its hydrodynamic stability approximately constant, particularly flow velocity (ubulk) and gas expansion ratio (σ), and (2) compare near-LBO dynamics under conditions where, well away from blowoff, the flame is globally stable (high σ case) and globally unstable (low σ case, where the Bénard-Von Karman, BVK, instability of the flow is present). The latter case was of particular interest as most prior detailed diagnostic studies of LBO have been performed at high σ, BVK-suppressed conditions. We find that the transient blowoff process remains largely unchanged in the high and low σ cases, apparently due to the fact that the BVK instability reappears in either case under conditions very close to LBO. In all cases, blowoff is preceded by permanent downstream extinction that moves progressively closer to the bluff body as LBO is approached. We also find that near-LBO dynamics are intrinsically three dimensional, due to both secondary instabilities of the shear layer and large out-of-plane motions believed to be due to confinement effects associated with bluff body-wall interactions. These three-dimensional structures often manifest themselves as burning reactant fingers which are caught in the backflow of the recirculation zone; under very near LBO conditions they impinge on the back of the bluff body and extinguish as well. At the very edge of blowoff, the recirculation zone is no longer composed of hot products and is unable to autoignite the oncoming reactant flow, leading to global extinction. The characteristic time associated with this feedback between downstream extinction and wake structure alteration that leads to blowoff is about two orders of magnitude larger than the characteristic flow time, D/ubulk. We also discuss several implications of these results on computations of LBO - in particular, LBO's intrinsically three-dimensionality and the need for many flow through times to capture it.

Temporal evolution of scalar modes in Richtmyer–Meshkov instability of inclined interface using high-speed PIV and PLIF measurements at 60 kHz

The current work presents simultaneous, high-speed measurements at 60,000 fields per second of velocity and mole fraction using particle image velocimetry (PIV) and planar laser induced acetone-fluorescence in a Richtmyer–Meshkov instability of an inclined interface (Atwood number, At = 0.22). Specifically, around 2 ms of temporal evolution of the vortex structures and their associated scalar modes immediately following the interface-reshock interaction is presented. Two initial interface conditions are discussed—(a) a sharp, inclined ‘single mode’ interface and (b) a ‘multi-mode’ interface where small perturbations are imposed on the single mode case. A 2D wavelet decomposition of the scalar flow field shows a highly intermittent distribution of small-scale variance throughout the interface even at late times. These are correlated strongly with the vortex structures and local turbulence intensity, where each small-scale scalar mode is sandwiched between two co-rotating vortex structures. This indicates that the interstitial regions between the vortices are significant hotspots of entrainment, which is then dispersed by the induced, counter-flow velocity fields. The multimode case demonstrates similar organization at large scales, while the scalar field is much more homogeneous at smaller scales. These observations highlight the importance of capturing the early time vortex evolution to accurately estimate any late time intermittency, especially where deposition of intense vorticity on sharp interfaces is present.

Study on fuel equivalence ratio range for supersonic premixed combustion mode to establish in a scramjet

With the tendency of high-speed flight and economic cruise, combustion mode in a scramjet engine will transfer from diffusion combustion mode to premixed combustion mode because of the decrease of Damköhler Number in combustor. In order to study the fuel equivalence ratio conditions for the establishment of premixed combustion mode and corresponding combustion mechanism, series of direct-connected experiments with gaseous ethylene as fuel were conducted. The total temperature of Mach 2.0 incoming flow ranged from 1200 K to 1700 K. Wall pressure of the combustor was collected to analyze related combustion mode and planar laser induced fluorescence (PLIF) was adopted to research combustion mechanism of corresponding combustion mode. Results showed that with the increment of fuel equivalence ratio ER, combustion mode transited from premixed combustion mode to partially premixed combustion mode and finally diffusion combustion mode. Bilateral injection scheme was more advantageous for premixed combustion to establish due to better fuel/air mixing and further downstream reaction position originating from diluted fuel in height position and corresponding low flame speed. Besides, total temperature of inflow had effect on the combustion characteristics in different aspects. On one hand, higher inflow total temperature brought lower lean fuel blow-off ER limit. On the other hand, the stabilization equivalence ratio range of premixed combustion mode would widen with the increment of inflow total temperature in the variation of 1200 K–1700 K which could be attributed to the coupling result of inflow temperature (affecting flame speed) and inflow velocity, indicating inevitability of appearance of premixed combustion mode in high-speed economic cruise with high inflow total temperature.

The Interaction Between In-Cylinder Flow And Flame Propagation In An Optical SI Engine Measured By High-Speed PIV

The relationship between the flow field and flame propagation is essential in determining the dynamics and effects of turbulent flow in an optical SI engine. In this study, the high-speed PIV technique was applied to evaluate the incylinder velocity and turbulence distribution under firing condition. The simultaneous measurement technique of incylinder flow and flame propagation characterized the relationship between flow field and flame propagation in the same cycle. A 500 cc single-cylinder optical engine was used for this experiment. The bore diameter and stroke length were 86 mm and 86 mm respectively, and compression ratio was 10.4. The flame front configuration was extracted from the PIV image based on planar laser tomography method. The strong contrast between the intensity of burned and unburned region in the captured images due to low gas and seed density of the former was utilized to derive this flame front. In order to evaluate the interaction between flame and flow with high resolution, the interrogation area was set to 16 × 16 pixels. This corresponds to 0.75 × 0.75 mm. The spatial filter of 6 mm was used to separate the instantaneous flow velocity into a low frequency component and a high frequency component. The engine speed was 1200 rpm and absolute intake pressure was 60 kPa. The equivalence ratio was stoichiometry condition. The ignition timing were set to 19 deg.BTDC. The characteristic cycles in the same test condition were extracted and discussed. The bulk flow with the large scale as large as the size of the combustion chamber influences the overall shape of the flame propagation, and the state of the flame propagation greatly fluctuates from cycle to cycle. The flame propagates with enhancing the large scale existing tumble flow that exists in earlier crank angle locations. Focusing on the local flame structure, the high-frequency velocity component was strong near the local flame peak and weak near the local flame valley. The flame at the local peak region propagates while pulling the valley region.

Investigation of CN in the Reacting Boundary Layer of Ablating Graphite using PLIF

Planar Laser Induced Fluorescence (PLIF) of CN is used to study graphite ablation during exposure to an atmosphericpressure, high-temperature air flow. The 5000 K to 6000 K air flow is produced by the 50 kW Inductively Coupled Plasma (ICP) Torch at The University of Texas at Austin. Temporally- and spatially- resolved PLIF imaging is used to offer insight into reaction layer behavior. Two-line LIF thermometry in the reaction layer is also used, where the temperature is inferred from the ratio of signal intensities resulting from pumping two rotational lines, while collecting the broadband fluorescence. PLIF results are compared to s imultaneously-collected optical emission spectra. This work represents a first s tep towards building a better understanding of the thermo-chemical environment and the chemical kinetics of high-temperature material ablation, and provides insights into the production of CN during the ablation of carbon-based ablators in hypersonic applications.

Fuel-rich hetero-/homogeneous combustion of C3H8/O2/N2 mixtures over rhodium

The catalytic (heterogeneous) and gas-phase (homogeneous) combustion of C3H8/O2/N2 mixtures over rhodium was investigated experimentally and numerically at 5 bar and at fuel-rich equivalence ratios φ = 2.0-3.5 relevant to propane Catalytic Partial Oxidation (CPO). In situ spatially-resolved Raman measurements of major gas-phase species concentrations and Planar Laser Induced Fluorescence (PLIF) of formaldehyde were applied in an optically accessible channel-flow reactor to monitor the catalytic and gas-phase processes, respectively, while accompanying 2D simulations were carried out with detailed hetero-/homogeneous chemical reaction mechanisms. Due to the high gas-phase reactivity of propane, homogeneous chemistry could not be ignored over most of the reactor's oxidation zone length (upstream zone where the deficient reactant oxygen is not fully consumed). The presence of gas-phase chemistry deteriorated the otherwise high catalytic syngas (H2 and CO) selectivities over the oxidation zone. Raman measurements of major gas-phase species concentrations over the restricted oxidation zone length without appreciable gas-phase chemistry showed that the catalytic reaction mechanism slightly underpredicted (overpredicted) the H2 (CO) formation. The same behavior was also attested over the remaining length of the oxidation zone where combined catalytic and gas-phase chemistry was present. The production of considerable amounts of H2 at the highest investigated equivalence ratio of 3.5 accelerated the onset of homogeneous ignition and the formation of strong flames. The discrepancies between measured and predicted homogeneous ignition distances were less than 6.8% in all cases, illustrating the validity of the employed hetero-/homogeneous kinetic schemes. Contrary to past methane CPO studies, the contribution of gas-phase chemistry and the formation of strong flames in propane CPO was detrimental to syngas production.

Comparison between sonic jets with one jet orifice and two opposite orifices into a Ma-3.0 supersonic crossflow through circular ducts

Large-eddy simulations and nanoparticle-based planar laser scattering experiments are conducted to investigate various physical aspects of transverse sonic jets injected into a Ma-3.0 supersonic crossflow through a circular pipe. Configurations with one jet and two opposite jets are compared. For the single jet, a separation shock is generated by the recirculation zone on the opposite wall, and this intersects with the jet shear layer to push several jet plumes into the near-wall region. For the two jets, the bow shocks interact with each other, forming an oblique shock train. All of the shocks promote vortex breakage in jet wakes. A counter-rotating vortex pair is generated in the jet near-field region, enhancing the local mixing. A near-wall region in the jet lee between the counter-rotating vortex pair branches exhibits a low fuel mass fraction. The jet fluid in the downstream near-wall region is entrained by the crossflow upstream of the jet. The interaction between the bow shocks and shear layers of the two jets induces recirculation zones in the lee of the jet, which enhance the fuel mixing. This explains the phenomenon whereby the total pressure recovery coefficient and mixing efficiency of two jets are higher than those of the single jet.

Planar cw N2O laser with RF excitation

The article presents the results of studying and optimizing the output power and spectral characteristics of radiation of a sealed-off continuous wave (cw) planar N2O laser depending on the input radio frequency power and the size of the interelectrode gap in the discharge, on the composition and pressure of the working gas mixture N2O:N2:He:Xe, on the time of continuous operation of the laser. The effect of adding carbon monoxide CO to the working gas mixture is discussed. The maximum values of the output power—17.5 W and the efficiency—7.3% were obtained in a sealed-off cw N2O laser, which significantly exceed the known values. When N2 was replaced by air in the gas mixture: N2O:Air:He:Xe = 2.3:2.3:5:0.4, the laser output power was 10.6 W. The radiation powers of N2O and CO2 lasers are 13.1 W and 18.6 W, respectively, when the working mixture in the emitter is replaced and the same operating conditions are applied—the input power is 180 W and the pressure of the working gas mixture is 30 Torr.

Delaying hypersonic boundary layer transition using forward-facing step arrays: An experimental work

Our previous research has demonstrated that a single forward-facing step (FFS) could delay the hypersonic boundary layer transition on a cone [Xu et al., “Influences of steps on the hypersonic boundary-layer transition on a cone,” AIAA J. 59, 439–446 (2021)]. This paper aims to further this study by investigating the control effects of FFS arrays on the hypersonic boundary layer transition on a 7° half-angle sharp cone. Experiments are conducted in a Mach 6 wind tunnel using nano-tracer-based planar laser scattering techniques and high-frequency pressure sensors. Cases with smooth surfaces, single FFS, or FFS arrays with different spacing and step heights are studied for comparison. The results show that FFS arrays present a better performance on stabilizing the second mode wave and delaying the transition than a single FFS. Notably, the spacing and height between and of the steps also play an important role in the delay effect. For the cases studied, a better control effect can be achieved using FFS arrays spaced at a larger distance or with step height increasing along the flow direction. Moreover, FFS arrays could restabilize the second mode wave that has been amplified by the upstream backward-facing step.

Experimental study of flow and mass transport in the near-wake region of a rigid planar metal net panel

Aquaculture cages constructed from rigid material have become increasingly popular in recent years due in part to the continuous expansion of the aquaculture industry offshore, where cages need to withstand much harsher ocean conditions. Most previous studies of hydrodynamic interactions with aquaculture cages have explored the impacts of more traditional flexible cage net panels on wake flow fields and mass transport properties. In the current experimental study, Particle Image Velocimetry and Planar Laser Induced Fluorescence techniques were used to measure flow and concentration fields in the near wake region of a steady current through a rigid metal net panel to analyze both the flow patterns and mass transport processes. The results indicated that, similar to a flexible polyethylene net panel, the time-average velocities and turbulence characteristics in the near wake region were highly inhomogeneous and anisotropic, with the turbulent intensity following a short-range, power-law decay downstream of the panel. In direct comparison with a flexible net panel of similar net solidity, the rigid net panel was found to slightly enhance the lateral spreading of the plume, with cross-sectional profiles of the mean concentration and concentration fluctuation shown to exhibit self-similar Gaussian distributions. The rigid net panel also resulted in a lower flow blockage, as measured by a velocity reduction coefficient, with the corresponding turbulent intensity also reduced compared to the flexible panel due to an overall reduction in the drag force. In addition, the rigid panel tended to create larger wake eddies than the flexible panel, leading to enhanced scalar mixing and, hence, faster rates of concentration decay in the near-wake region. These experimental findings have potential implications for cage-based aquaculture operations, where rigid fish cages are comparatively more likely to generate favorable environments for fish growth, as well as helping to reduce negative impacts on the surrounding aquatic environment.

On the physical nature of the turbulent/turbulent interface

The existence of a turbulent/turbulent interface (TTI) has recently been verified in the far wake of a circular cylinder exposed to free-stream turbulence (Kankanwadi & Buxton, J. Fluid Mech., vol. 905, 2020, p. A35). This study aims to understand the physics within the TTI. The wake boundary, approximately 40 diameters downstream of a circular cylinder subjected to grid-generated turbulence, was investigated through simultaneous cinematographic, stereoscopic particle image velocimetry and planar laser induced fluorescence experiments. With no grid placed upstream of the cylinder, the behaviour of the resultant interface, our closest approximation to a turbulent/non-turbulent interface, exactly matched what is observed in existing literature. When background turbulence is present, viscous action is no longer the only method by which enstrophy is transported to the background fluid, unlike for turbulent/non-turbulent interfaces. The presence of rotational fluid on both sides of the TTI allows the vorticity stretching term of the enstrophy budget equation to be the dominant actor in this process. The role of viscosity within a TTI is greatly diminished as the vorticity stretching term takes over responsibilities for enstrophy production. The turbulent strain rate normal to the TTI was found to be enhanced in the interfacial region. Decomposing the vorticity stretching term into components aligned with the three principal strain-rate directions, it was found that the term most aligned with the interface-normal direction contributed to the largest share of enstrophy production. This indicates that better ‘organised’ vorticity on the wake side of the interface yields the enstrophy amplification leading to the previously discovered enstrophy jump across the TTI by Kankanwadi & Buxton (J. Fluid Mech., vol. 905, 2020, p. A35).

High-intensity laser therapy of patients with atrophic scars: results of a comparative prospective interventional cohort study

BACKGROUND: Scars of various sizes and localization are formed in more than 100 million patients annually. Atrophic scarring defects of the skin are verified in more than 80% of patients with acne and in 30% of patients with other injuries. Different skin remodeling technologies have different effectiveness, which actualizes the search for optimal methods of scar correction. The most promising of them are combinations of high-intensity laser radiation.
 AIMS: Determination of therapeutic effects of high-intensity laser therapy in patients with atrophic skin scars.
 MATERIALS AND METHODS: A prospective interventional cohort comparative study of the therapeutic effects of high-intensity laser therapy in patients with atrophic skin scars was conducted. In patients with emerging scars, a combination of homogeneous photothermolysis by long-pulse Nd:YAG laser radiation (l=1.064 microns) followed by fractional ablative photothermolysis of CO2 laser (l=10.6 microns) was used, and in patients with mature scars, a combination of homogeneous photothermolysis of long-pulse Nd:YAG laser (l=1.064 microns) and planar laser photodestruction of CO2 laser (l=10.6 microns).
 115 patients with the diagnosis of "atrophic scars" (ICD-X, Class XII "Diseases of the skin and subcutaneous tissue", L90.5) were examined, among which groups with emerging (49 patients) and mature (66 patients) scars were identified. Empirical research methods ― clinical, instrumental, and medico-sociological ― have been applied. The analysis of the obtained data was carried out using the methods of descriptive, parametric and multifactorial statistics with the determination of the specific weight of the studied features.
 RESULTS: The improvement of the clinical status, pronounced remodeling of the skin in the area of atrophic scars, under the influence of various combinations of high-intensity laser therapy was revealed. An increase in the quality of life indicators according to the Skindex-29 and Dermatology Life Quality Index (DLQI) scales was determined, more pronounced in the groups of patients with atrophic scars in comparison with the group of patients with mature scar deformities. Combinations of high-intensity laser therapy have a favorable safety profile, are characterized by a high degree of compliance and satisfaction with the results of treatment. The effectiveness of variant high-intensity laser therapy in patients with atrophic scars is 8690%.
 CONCLUSIONS: Combinations of high-intensity laser therapy in patients with developing atrophic scars cause dermoplastic and fibromodeling therapeutic effects, in patients with mature ones ― reepithelizing, fibrocorrecting therapeutic effects.

Turbulent mass transfer near gas-liquid interfaces in water and shear-thinning dilute polymer solution

Turbulence is known to enhance gas-liquid mass transfer and mixing of high Schmidt number dissolved gases in water by deforming the concentration boundary layer that develops at the interface. Fundamental mechanisms of surface renewal and injection have been progressively evidenced throughout the last decades, via fundamental experiments of low mean shear turbulence interacting with flat interfaces in water. However, and despite the obvious influence of non-Newtonian behaviours on gas liquid mass transfer in industrial and environmental applications, not such study exists (to the best of the author’s knowledge) on whether and how these mechanisms apply in shear-thinning dilute polymer solutions (DPS). Following a previous work on near surface hydrodynamics, turbulent mass transfer and mixing is studied in a weakly shear-thinning fluid, and compared to the Newtonian, water case. Stereoscopic Particle Image Velocimetry (SPIV) and Inhibited Planar Laser Induced fluorescence are used simultaneously to measure the local liquid phase velocity and dissolved gas concentration fields respectively. Coupled measurements are used to estimate the turbulent mass fluxes, which are interpreted using a conditional quadrant analysis. Results show that in DPS as well as in water, surface renewal is the most frequent mechanism, but injection events are the most efficient in terms of mass transfer. Even at a low concentration, the polymer significantly modifies the signature of those mass transfer events, by enhancing scalar stretching and injection mass transfer outside of the viscous sub-layer, altering classical gradient models.

1.14 kW peak power mid-infrared Er:YAG planar waveguide MOPA laser.

We report on a quasi-continuous Er:YAG planar waveguide laser operated at 2.94 µm based on the major oscillator power amplification configuration. With the total pump peak power of 32.01 kW, a maximum output peak power of 1.14 kW was obtained at the seed injection peak power of 184.4 W operated at 400µs, 40 Hz. Furthermore, the numerical simulation results indicate that better performance of the laser could be obtained with the higher injected seed laser power. To the best of our knowledge, this is the first experimental demonstration of 2.94 µm planar waveguide laser with an Er doped host material.