Acetone Droplets Research Articles

A dual-height wick to improve capillary performance of vapor chambers

The wick performance is a crucial metric for ensuring the reliable and efficient operation of vapor chambers (VCs) away from dry-out. To enhance the performance of VC, a pitcher plant inspired enhanced wick characteristic dual-height microgrooves (DHMW) was fabricated on 6063 aluminum alloy by one-step picosecond laser texturing without chemical modification. This study describes the two-step capillary behavior of DHMW by high-speed camera and infrared camera. The effects of minor rib number, groove height ratio, length scale, and test liquids (water, acetone, ethanol) on the capillary performance were investigated. When using water as the working fluid, the DHMW achieved a K/Reff of 1.182 µm, which was about 71.3 % larger than that of normal microgroove wicks due to the liquid propagation effect and the flow resistance reduction effect. Furthermore, the maximum K/Reff could reach 1.819 µm of the sample with a minor rib depth of about 70 μm. However, the wetting results showed that the droplets of acetone and ethanol tend to spread laterally after contact with the surface, which is unfavorable for the formation of hierarchical transport in the DHMW. This study demonstrates that laser texturing is an effective and controllable method for the complex shaping of grooved aluminum wicks, with the potential to improve the heat transport capability of VCs.

Direct Numerical Simulation of Vortex Breakdown in Evaporating Dilute Sprays

AbstractThe effects of different vortex breakdown states on the evaporation process characterizing air-acetone vapor swirling jets laden with liquid acetone droplets in the dilute regime are discussed based on results provided by direct numerical simulations. Adopting the point-droplet approximation, the carrier phase is solved using an Eulerian framework, whereas a Lagrangian tracking of the dispersed phase is used. Three test cases are investigated: one with fully-turbulent pipe inflow conditions and two with a laminar Maxworthy velocity profile at different swirl rates. Consequently, turbulent, bubble-type, and regular conical vortex breakdown states are established. Following phenomenological and statistical analyses of both phases, a significant enhancement of the overall droplet evaporation process due to the onset of the conical vortex breakdown is observed due to the strongest centrifugal forces driving the entire liquid drops towards the low-saturation mixing layer of the jet. The effects of droplet inertia on evaporation are isolated through an additional set of simulations where liquid droplets are treated as Lagrangian tracers. While it is found that inertial effects contribute to enhanced vaporization near the mixing layer under bubble vortex breakdown conditions, droplet inertia plays a secondary role under both turbulent and conical vortex breakdown due to intense turbulent mixing and high centrifugal forces, respectively.

In–syringe homogenous liquid–liquid extraction combined with ionic liquid based dispersive liquid–liquid microextraction for the extraction of aflatoxin B1 from edible vegetable oil samples prior to HPLC-FLD analysis

Combination of in–syringe homogenous liquid–liquid extraction and ionic liquid based dispersive liquid–liquid microextraction has been employed for the extraction of aflatoxin B1 from edible vegetable oil samples. Firstly, a homogenous solution of oil sample containing the analyte and acetone (1.5 mL) is formed. Then, this homogenous state was broken by adding 100 µL of deionized water and the analyte was extracted into the produced fine droplets of acetone. In the following, acetone phase was taken and mixed with 65 µL of 1–hexyl–3–methylimidazolium tetrachloroferrate magnetic ionic liquid. The mixture was injected to sodium chloride solution (5 %, w/v) by a glass syringe. The ionic liquid droplets were collected by an external magnet and then, they were used for the determination step by high–performance liquid chromatography equipped with fluorescence detector. Under the optimum conditions, low limit of detection (13 ng kg−1) and quantification (44 ng kg−1), wide linear range (44–1 × 106 ng kg−1), acceptable extraction recovery (69 %), and good precision (relative standard deviations ≤ 4.0 %) were obtainable using the proposed method. These results verify the high capability of the proposed method for screening aflatoxin B1 in the various edible vegetable oil samples. Performing the method in syringe barrel provide easy collection of the extraction solvent without the need for centrifugation. Combination of homogenous liquid–liquid extraction with the microextraction procedure leads to obtain sensitive detection limits. The use of ionic liquid removed the necessity of centrifugation for separation of the extractant.

Experimental studies on combustion and atomization characteristics of aliphatic and aromatic hydrocarbons droplets

This study focused on how the properties of alcohols (ethanol, methanol, n-butanol), ketones (acetone), alkanes (hexane), esters (ethyl acetate), methyl benzenes (toluene), and ethers (diethyl ether) shape individual combustion and atomization behaviors. The experimentation conducted at the droplet scale involved suspending fuel droplets on a ceramic wire and subsequently igniting them for analysis. Experiments were recorded with a high-speed camera and a thermal camera with a spectral range of 7.5–14 μm. The results showed that the flame of the oxygenated fuel droplets, unlike non-oxygenated fuels, has a high non-luminous region seen throughout the combustion process. The diameter reduction of the fuel droplets during combustion tended to obey the D2-law. Single and multicomponent fuel droplets are hemispherical for preheating (Stage I) and hemispherical in droplet disruption mode for combustion and droplet diameter decrease (Stage II). Hexane, diethyl ether, and ethyl acetate were the fuels that were extinguished in the shortest time among the fuels studied here with extinction times of 1.021 s, 0.925 s, and 0.885 s, respectively. Hexane, diethyl ether, acetone, and diesel droplets had the minimum ignition delay times according to the experimental conditions in this study. In terms of maximum flame temperature, ethyl acetate exhibited the highest value among oxygenated fuel droplets, reaching 155 °C, while toluene demonstrated the highest maximum flame temperature of 244 °C among all fuel types, including non-oxygenated fuels.

Experiments on the breakup and evaporation of small droplets at high Weber number

Shock-driven multiphase mixing is present in numerous physical systems such as detonation-driven propulsion engines, liquid–vapor cloud explosions, and hypersonic flight droplet impacts. At the microscale, droplets experience deformation, breakup, and evaporation under extreme conditions (high Weber and Reynolds regimes). For small droplets, these phenomena are simultaneous and highly transient, making their interactions and interdependencies warrant further investigation. In this study, experiments are conducted in a shock tube facility to investigate these simultaneous droplet-scale phenomena. An interface consisting of small acetone droplets (⌀ 10–40 [μm]) is impulsively accelerated by a strong planar shock wave (Mach ∼2.09). The droplet size distribution is well-characterized in-situ utilizing a Phase Doppler Particle Analyzer (PDPA) and shadowgraphy. The development of child droplet clouds is captured through an ensemble of Mie scattering images. A simplified model is developed to interpret the experimental results, combining deformation, breakup, and evaporation models. The results indicate that the breakup of small droplets at high Weber numbers is likely dominated by the Rayleigh–Taylor (RT) mechanism, aligning with previous empirical models for low Weber numbers.

Similarity Analysis of Droplet Evaporation Trajectory in High-Temperature Gas Flow

In this study, a similarity analysis of droplet evaporation trajectory in high-temperature air crossflow based on numerical calculations was conducted. The procedure used for modeling the evaporation of a water droplet involved the use of a low boiling point liquid droplet. The trajectories of water and acetone droplets over an extensive temperature range of 695–1194 K were investigated, and the relationships for the corresponding parameters of the two different droplets, as well as the scale effect, were discussed. The results identify the existence of a comparative trajectory for different kinds of droplets, as well as the main dimensionless numbers governing the trajectory, by determining the Reynolds, Stokes, and Nusselt numbers. For each given gas flow Reynolds number, the droplet evaporation trajectory has a unique correspondence with the airflow temperature. Given this, a method of calculation to determine the modeling parameters of the droplet and crossflow was proposed. The applicability of the similarity modeling method of a single droplet to the spray droplets was examined, from which the spray structure in high-temperature crossflow was obtained.

Spatial evolution of multi-scale droplet clusters in an evaporating spray

Evaporative sprays are encountered in a wide range of engineering applications. Since clustering of droplets in sprays leads to strong inhomogeneity in the spatial distribution of droplet concentration that impacts mass, momentum, and energy exchange between the spray and the surrounding flow, a detailed investigation of droplet clustering in evaporating sprays is important. In the current research work, we experimentally investigate the spatial evolution of droplet cluster characteristics in an evaporating acetone spray injected from an air-assist atomizer. The droplet size and velocity are measured using Interferometric Laser Imaging for Droplet Sizing technique. In detail, characterization of the droplet clusters is achieved by the application of Voronoi analysis to particle image velocimetry images of the spray droplets. This approach not only identifies the droplet clusters but also provides area, length scale, and local droplet number density within the clusters. The identified droplet clusters are multi-scale and could be classified into either large- or small-scale clusters, which scale with spray half-width and Kolmogorov length scale, respectively. Experiments are also conducted in water spray under the same operating conditions. Despite the similarity in the droplet clustering process between the two sprays at small scales of air turbulence, some distinct trends are observed for the large-scale clusters in the acetone spray. This is attributed to the higher evaporation rate of acetone droplets, which promotes preferential accumulation of droplets.

Prediction of turbulent flow characteristics and heat transfer in a dilute droplet-laden flow over a backward-facing step

We present numerical investigation of the influence of the thermophysical properties of droplets on turbulence modification, scattering of droplets, and heat transfer augmentation in a two-phase mist flow over a backward-facing step. Predictions are made for droplets of water, ethanol, acetone, and glycerol, with droplet diameters in the range d 1 =1–100 μm and mass fractions in the range ML 1=0.01–0.1 at the inlet. The RANS approach is used to simulate the gaseous phase, and the motion and heat transfer of the dispersed phase are computed using Eulerian model. Carrier phase turbulence is predicted using a second moment closure model. The effect of attenuation of the gas phase turbulent kinetic energy is shown to be minimal for acetone droplets (more than 7%), whereas the largest effects are seen for glycerol and water droplets (up to 15%). Heat transfer enhancement is shown to reach a maximal value with the use of ethanol (more than twice as high as for single-phase flow over the backward-facing step), while minimal intensification is obtained for the evaporation of acetone droplets (up to 25%).

Feasibility Analysis On Transient Speed Of Sound Investigations Using Laser-Induced Thermal Acoustics In Evaporating Droplets

The development of combustion processes to achieve higher efficiencies has led to a continuous increase in operating pressures that exceed the critical point of the injected fluids. Especially for supercritical atmospheric conditions with respect to the injected fluid, the fundamental physics of the occurring mixing and evaporation processes are not fully understood. In particular, quantitative data for the validation of numerical simulations as well as analytical models remain sparse. Laser-induced thermal acoustic (LITA) is a seedless, non-intrusive measurement technique capable of detecting speed of sound data within these mixing processes. Until now, the feasibility of time-resolved LITA measurements in complex fluid dynamic processes has not been proven. Therefore, a feasibility analysis on transient speed of sound investigations using laser-induced thermal acoustics in evaporating droplets has been conducted. LITA has hereby been applied in the wake of a free-falling acetone droplet evaporating in a nitrogen atmosphere at nearcritical conditions. To the authors’ best knowledge, this is the first-time transient LITA measurements investigating macroscopic fluid phenomena, such as fluid injection and evaporation processes, have been conducted. The evaporation of the droplet has been simultaneously visualised using shadowgraphy, whereas time-resolved speed of sound data have been directly detected by a high-speed LITA system with a high-repetition rate excitation laser source.

BACKGROUND-ORIENTED SCHLIEREN FOR FLOW AND THERMAL SYSTEMS: PRINCIPLES OF IMAGE FORMATION AND APPLICATIONS

Imaging fluid flow and transport phenomena has gained considerable attention in the recent past. The imaging techniques are not only limited to visualization tools but, when coupled with suitable data reduction algorithms, can lead to the generation of the complete whole field quantitative data of flow and transported properties. In this direction, the technique of background-oriented schlieren (BOS) is one of the latest developments that has garnered significant attention among the research community. The present article reviews the plausible configurations of the BOS system, including principles of image formation and its applications in the domain of flow and thermal systems. Particular attention is paid to various constraints that one faces while configuring the imaging technique correctly from its first principles and those associated with the development of data reduction methodologies for BOS image analysis. Various modifications affected in the standard BOS, since the time it was proposed by Meier et al. (2002, 2013), for mapping the flow and transported properties as well as thickness variations of liquid surfaces are reviewed. Following an extensive review of the available literature, the potential of BOS in imaging single- as well as two-phase heat transfer phenomena is demonstrated by setting up lab-based test configurations that include natural convection over a heated vertical flat plate and horizontally placed circular cylinder, and the evaporation dynamics of impinging acetone droplet(s). The recorded BOS images are quantitatively analyzed to retrieve the field distribution of parameters of interest in each of the configurations studied.

Multi-objective optimization of acetone droplet impingement on phase change material in direct-contact discharge method

Improving the discharge process of phase change materials (PCMs) is of great importance and can be effective for thermal energy storage (TES) systems. In this research, the direct-contact method for acetone droplet on molten paraffin is optimized to enhance the efficiency of the discharge process of PCMs and TES systems working with intermediate boiling fluid (IBF). In order to improve the storage rate and increase the freezing rate in the system, the NSGA-II algorithm is used. When the acetone droplet hits, owing to its low boiling point relative to the temperature of molten paraffin, the acetone evaporates, causing the creation of solidified paraffin area. The main goal of the current investigation is to maximize the solid volume, which depends on two parameters: the Weber acetone droplet and the temperature of the molten paraffin. Furthermore, maximizing this volume is equivalent to increasing the freezing rate and decreasing the melting rate. For better discernibility, the relative sensitivities of solidified paraffin area and maximum crater depth to the variations in the dimensionless parameters of paraffin surface temperature and Weber number are obtained. In this regard, the experimental results are fitted by exponential functions. Two-objective optimization with the solidified paraffin area and maximum crater depth as cost functions are performed to be maximized. Moreover, uncertainties and tolerances are considered through performing a robust triple optimization. By using final decision makings (FDMs), the results are achieved from Pareto front through two methods, LINMAP (We = 1699.428, θ = 1.188) and TOPSIS (We = 1699.325, θ = 1.202). Based on the results, the solidified paraffin areas obtained by LINMAP and TOPSIS methods are 168.616 mm2 and 155.101 mm2, respectively.

The effect of fine droplets on laminar propagation speed of a strained acetone-methane flame: Experiment and simulations

In this study, we investigate the effect of the presence of fuel droplets, their size and concentration, on stretched laminar flame speeds. We consider premixed strained methane/air mixtures, with the addition of small acetone droplets, and compare the flame velocity field behaviour to that of the fully vaporized mixture. An impinging stagnation flame configuration is used, to which a narrowly distributed polydisperse mist of acetone droplets is added. Total acetone molar concentrations between 9% and 20% per mole of methane are used, corresponding to 18.6% and 41.4% of the total fuel energy. The Sauter Mean Diameter (SMD) of acetone droplets is varied from 1.0 to 4.7 μm by carefully tuning the air flow rate passing through an atomizer. The droplet size distribution is characterized by a Phase Doppler Anamometry (PDA) system at the outlet of the burner. The flame propagation speed is measured using Particle Image Velocimetry (PIV) for overall equivalence ratios ranging from 0.8 to 1.4 at various strain rates, and the result is compared with a reference case in which acetone was fully vaporized. Unlike the fully vaporized flame, a two-stage reaction flame structure is observed for all droplet cases: a blue premixed flame front followed by a reddish luminous zone. Comparison of the results between gas-only and droplet-laden cases shows that the mean reference burning velocity of the mixture is significantly enhanced when droplets are present under rich cases, whereas the opposite is true for stoichiometric and lean cases. The mean droplet size also changes the relationship between flame speed and strain rate, especially for rich cases. The result suggests that with typical conditions found in laminar strained flames, even for the finest droplets that may have been vaporized before reaching the flame front, the resulting inhomogeneities may lead the flame to behaves differently from the well-premixed gaseous counterpart. Simulations at similar conditions are performed using a two-phase counterflow flame model to compare with experimental data. Model results of reference velocities do not compare well with observations, and the possible reasons for this behaviour are discussed, including the difficulties in determining the pre-vaporization process and thus the boundary conditions, as well as the fidelity of the current point-source based 1D model.

Numerical simulation of effect of acetone droplets injection on methane/air laminar premixed flame behavior

Numerical simulation of effect of acetone droplets injection on methane/air laminar premixed flame behavior

A method for measuring droplet evaporation in a shock-driven multiphase instability

Experimental measurements of bulk droplet evaporation within a shock-driven multiphase instability, or SDMI, were studied using advanced imaging diagnostics. Specifically, droplet evaporation was quantified by determining the rate of acetone vapor produced from liquid acetone droplets. The extent of the acetone vapor produced was measured using quantitative planar laser-induced fluorescence (Q-PLIF). In addition to vapor concentration, Q-PLIF also accounts for the effects of pressure and temperature on the fluoresced acetone. Concurrently performed with Q-PLIF were particle image velocimetry (PIV) measurements as the means to gather data on the acetone droplet’s velocities as well as the particle fields morphology throughout its development. By using these two diagnostic techniques, two successive data points of the acetone droplets evaporation rate throughout the development of the SDMI were obtained. Although these first two data sets were not adequate to fully prescribe an accurate evaporation rate model, they were a sufficient corrigendum to the commonly-utilized D-squared evaporation law. Overall, the previous techniques have been demonstrated that acetone droplet evaporation can be measured quantitatively, enabling prediction of evaporation enhancement due to the strong hydrodynamic mixing within the SDMI.

Numerical analysis of swirling turbulent droplet-laden flow and heat transfer in a sudden pipe expansion

The effect of swirling intensity on the structure and heat transfer of a turbulent gas–droplet flow after a sudden pipe expansion has been numerically simulated. Air is used as the carrier phase, and water, ethanol, and acetone are used as the dispersed phase. The Eulerian approach is applied to simulate the dynamics and heat transfer in the dispersed phase. The gas phase is described by a system of Reynolds-averaged Navier-Stokes (RANS) equations, taking into account the effect of droplets on mean transport and turbulent characteristics in the carrier phase. Gas phase turbulence is predicted using the second-moment closure. A swirling droplet-laden flow is characterized by an increase in the number of small particles on the pipe axis due to their accumulation in the zone of flow recirculation and the action of the turbulent migration (turbophoresis) force. A rapid dispersion of fine droplets over the pipe cross-section is observed without swirling. With an increase in swirling intensity, a significant reduction in the length of the separation region occurs. The swirling of a two-phase flow with liquid droplets leads to an increase in the level of turbulence for all three types of liquid droplets investigated in this work due to their intensive evaporation. It is shown that the addition of droplets leads to a significant increase in heat transfer in comparison with a single-phase swirling flow. The greatest effect of flow swirling on heat transfer intensification in a two-phase gas-droplet flow is obtained for the droplets of ethanol and water and smallest effect is for the acetone droplets.

Non-invasive, spatially averaged temperature measurements of falling acetone droplets in nitrogen atmosphere at elevated pressures and temperatures

Mean temperatures of acetone, millimeter-sized, freely falling droplets in a nitrogen atmosphere are studied at two different locations downstream a capillary-type injector. Injection and ambient temperatures have been varied independently between 433 and 513K and pressures from 2 to 6MPa. The ratio of simultaneously measured laser-induced phosphorescence (LIP) and fluorescence (LIF) is shown to be a suitable approach for measuring temperatures in the given conditions. Cumulated uncertainties (2σ) of mean droplet temperatures of ±3K are estimated. The temperatures measured in this study are partly compared to results of previous investigations where droplet temperatures have been estimated by an extrapolation of temperature mixture fraction data in the gas phase obtained from spontaneous Raman scattering. Overall a reasonable agreement has been observed which indicates the applicability of the previous approach for estimations based on the adiabatic mixing assumption and the extrapolation of the Raman-measured data.

Direct Numerical Simulations of the Evaporation of Dilute Sprays in Turbulent Swirling Jets

The effects of swirled inflows on the evaporation of dilute acetone droplets dispersed in turbulent jets are investigated by means of direct numerical simulation. The numerical framework is based on a hybrid Eulerian–Lagrangian approach and the point-droplet approximation. Phenomenological and statistical analyses of both phases are presented. An enhancement of the droplet vaporization rate with increasing swirl velocities is observed and discussed. The key physical drivers of this augmented evaporation, namely dry air entrainment and swirl-induced centrifugal forces acting on the droplets, are isolated with the aid of additional simulations in which the inertial properties of the droplets are neglected. The correlation between swirl and dry air entrainment rate is found to be responsible for the increase of the global evaporation rate and the spray penetration length reduction, while swirl-induced centrifugal forces are found to be effective only in the jet shear layer, close to the injection orifice, for the analyzed cases.

Super-fast discharge of phase change materials by using an intermediate boiling fluid

The low thermal conductivity of phase change materials (PCM) results in the slowdown in the discharging process of PCM which limits the usability of these materials in the field of Thermal Energy Storage (TES). In this research, an innovative solution is proposed to significantly accelerate the solidification speed, up to two orders of magnitude greater than conventional methods. Using acetone as the intermediate boiling fluid (IBF), the paraffin discharge rate as a phase-change material is significantly improved which is known as super-fast discharge (SFD) in this article. In this method, liquid acetone takes the heat by boiling in liquid paraffin and causes it to solidify. As the liquid acetone boils, the acetone vapor reaches the condenser and condenses by losing heat, Condensed acetone droplets then fall into the molten paraffin. This process continues until the whole paraffin solidifies. It is shown that the paraffin solidification time is decreased from 2 h using conventional methods to 39 s by using IBF. In addition to the proof-of-concept and the achievement of super-fast discharging, this research, studies the effect of different ratios of paraffin mass to acetone volume on solidification rate experimentally, to determine the best ratio in terms of discharging time. The results show that for a given paraffin mass, there is an optimal volume for acetone, use of which minimizes the solidification time.

The effect of droplets thermophysical properties on turbulent heat transfer in a swirling separated mist flow

The numerical investigation of the effect of the swirl number and the thermophysical properties of water, ethanol, and acetone droplets on the particle scattering, turbulence modification and heat transfer in a droplet-laden flow is carried out. The set of 3D steady-state Reynolds-averaged Navier–Stokes (RANS) equations for the two-phase flow is utilized. The dispersed phase is modeled by the Eulerian approach. The flow swirling significantly shortens the length of the recirculation zone (up to two times in comparison with non-swirling flow at swirl number S = 0.5) for all types of the studied liquids. The highest value of heat transfer rate is obtained for the ethanol droplets (up to 10%), and the lowest one is obtained for the acetone droplets (up to 50%), both in comparison with water droplets. The swirling of the turbulent mist flow causes heat transfer enhancement (more than 1.5 times in comparison with the non-swirling droplet-laden flow). In the swirling flow, the value of the volume fraction of the dispersed phase has a maximum in the axial region of the pipe, and further in the direction of the wall its value is very small. The effect of heat transfer enhancement weakens with increasing Reynolds number of the flow. A region without droplets appears in the wall zone of the swirling two-phase flow, and the region is largest for acetone droplets.

Microfluidic mid-infrared spectroscopy via microresonator-based dual-comb source.

Over the past decade, microresonator-based soliton combs based on photonic integration have broadened the scope of applications in sensing, ranging, and imaging. The large comb line spacing on the order of hundreds of gigahertz allows for rapid acquisition of absorption spectra in the condensed matter phase without aliasing via a dual-comb interferometer. We present a proof-of-principle demonstration of high-throughput label-free microresonator-based dual-comb spectroscopy in a microfluidic chip that dynamically probes the linear absorption of liquid acetone in the mid-infrared wavelength regime. We measure the flow dynamics of an acetone droplet with a spectral acquisition rate of 25kHz (40μs per spectrum) covering a spectral range from 2900 to 2990nm. Combining microfluidics and silicon-photonic technology would potentially enable a compact time-resolved spectroscopy system for a wide range of applications such as chemical synthesis, biological cell-sorting, and lab-on-a-chip.