Evaporation Of Binary Droplet Research Articles

Simulation of group of droplets evaporation

Droplet evaporation occurs in many natural phenomena and industrial processes; hence, several studies have been conducted on droplet evaporation. In many applications, a group of droplets evaporate and the interaction between them affects the evaporation process. In this paper, the front-tracking method is used to simulate the droplets groups evaporation. Since the front-tracking method uses a Lagrangian grid for each droplet, this method offers good accuracy in predicting the shape, the displacement and the evaporation rate of droplets. The numerical method has been developed to simulate the evaporation of binary droplets. The fluid surrounding the droplets is modeled as a gas mixture, so the numerical method can be used to simulate multiphase-multicomponent problems. The front-tracking method requires very fine grid resolution to simulate flows at high-density ratios; therefore, the method is rarely used at high-density ratios. In this paper, a two-step method is used to move the front at high-density ratios without requiring a very fine grid resolution. First, a static droplet evaporation is simulated, and the results are compared with the analytical solutions; evaporation of a Decane droplet is then simulated, and the results are compared with the experimental data. Subsequently, the evaporation of a binary droplet is modeled. The evaporation of a group of static droplets is also simulated, and the effect of droplets interaction is investigated. Next, the evaporation of three injected droplets is simulated, and the effect of some parameters on droplets interaction is probed. The evaporation rate and displacement of each droplet are calculated and compared with the single droplet. Finally, the evaporation of the groups of droplets is simulated, and the effect of different arrangements of droplets on the evaporation rate is studied. Understanding the droplets interactions is helpful in predicting droplet spray behavior and developing numerical methods. Thus, the presented results are useful to achieve a better understanding of the droplets interaction phenomenon, its outcomes, and the parameters affecting evaporation rate.

Optimization effect of propylene oxide (PO) on evaporation, combustion, and pollutant emissions of high-energy–density JP-10 fuel

JP-10 is a high-energy–density fuel that is widely used in aerospace propulsion systems due to its wide range of synthetic raw materials and low production costs. However, it faces challenges related to difficult ignition, low combustion efficiency and high pollutant emissions. To address this, blending JP-10 with propylene oxide (PO), a highly volatile substance, provides a practical solution. This study investigates the propagation and evolution characteristics of JP-10/PO binary fuel in large horizontal pipelines. The results demonstrate a synergistic enhancement effect achieved by the JP-10/PO hybrid fuel. PO, with its lower boiling point, quickly evaporates from the mixed droplets, creating a continuous primary flame. As the droplet temperature increases, JP-10, known for its high combustion heat, starts to evaporate, actively participating in the explosion process and forming a secondary flame that spreads in two directions. The combustion of the JP-10/PO mixed droplets involves both physical and chemical processes, including droplet evaporation and gaseous combustion. A binary droplet evaporation model is developed to quantitatively assess the impact of PO fuel ratio on spray evaporation. Additionally, the study examines steam explosion parameters and reaction product characteristics under different PO fuel ratios. It is observed that the evaporation of JP-10/PO mixed droplets occurs in three stages: transient heating, binary equilibrium evaporation, and single component equilibrium evaporation. Increasing the PO fuel ratio leads to a higher temperature rise rate of the droplets and an increased evaporation reaction rate constant. Moreover, the ignition delay time of JP-10/PO gas-phase mixture fuel decreases, while the adiabatic flame temperature gradually reduces. Furthermore, higher PO fuel ratios help reduce the emissions of unstable products in both mixed fuels due to the inherent oxygen content of PO molecules. The current research results can provide scientific references for the improvement of high-energy density fuels and the development of new propellants.

Analytical and experimental study on binary droplet evaporation: Inhibitory effect of adding mineral oil adjuvant to water

This work fundamentally explains the inhibitory effect of adjuvant on water droplet evaporation in pesticide application. An analytical droplet evaporation model coupled with the instantaneous distribution of temperature and species concentrations in the vapor film boundary layer accompanying with the droplet diameter decrease is developed to describe not only the droplet evaporation but also the surrounding boundary layer evolution process. Thermal and concentration boundary layer thicknesses as well as the property variations at the liquid-vapor interface are updated at each time step during the calculation. An adjuvant factor is defined to assess the inhibitory effect of the adjuvant on water droplet evaporation. The results show that adding a tiny amount of mineral oil adjuvant can inhibit water droplet evaporation. The analysis of droplet evaporation evolution demonstrates that the inhibitory effect is mainly controlled by mass diffusion where the concentration gradient surrounding the liquid-vapor interface dominates the overall phase change. A regression formula is introduced to express the dependence of droplet lifetime on temperature and humidity. The proposed model is proved to be suitable for the mixing condition with a tiny amount of adjuvant, which can be used to describe the mechanism of evaporation inhibition of pesticide adjuvant in plant protection.

Evaluations of the preferential evaporation of binary droplet by rainbow technique and simulation

The evaporation behavior of the ethanol and heptane binary droplets was investigated using both, experimental and simulation methods. Droplets with three compositions of ethanol/heptane and three initial diameters were tested at ambient temperatures of 373 and 473 K, respectively. The preferential evaporation behavior of the individual components inside the binary droplet was obtained and confirmed by both, the numerical and experimental results. The heavier component undergoes prior evaporation when the lighter component dominates the liquid mixture. A systematic comparison between the experimental measurements and simulation results was made with respect to the normalized diameter and refractive index. The spatial and temporal dependences of the refractive index on the temperature and composition were obtained. The composition of the liquid phase has a decisive effect on the variation of refractive index near the droplet surface. Temperature controls the refractive index during the initial stage. Furthermore, the experimental results validate the accuracy of the non-ideal equilibrium model for predicting the diameter, temperature, and concentration of binary droplets for the first time. A linear fitting between the refractive index gradient in the liquid phase and the deviations of the equivalent refractive index from the refractive index at the droplet center has been proposed.

Photothermally Caused Propylene Glycol–Water Binary Droplet Evaporation on a Hydrophobic Surface

Photothermal effect has shown great promise in manipulating the droplet evaporation. In this work, the evaporation of a propylene glycol–water binary droplet on the hydrophobic surface induced by the photothermal effect of a focused infrared laser with a wavelength of 1550 nm was experimentally investigated. Dynamic evaporation behaviors were discussed through the visualization method and image processing technique. Experimental results showed that the photothermally induced evaporation of such a binary droplet could be divided into two stages: the first stage dominated by the evaporation of water with more volatility represented by rapid variations of the droplet volume and geometric parameters and the second stage dominated by the evaporation of propylene glycol with less volatility represented by a smaller slope. Correspondingly, the binary droplet evaporation first experienced the mixed mode greatly related to the more volatile component, and then the constant contact radius mode greatly related to the less volatile component. In addition, the effects of the initial composition and input laser power were also discussed. This work provides a deep understanding of the photothermal effect of a focused light-caused evaporation behaviors of the propylene glycol–water binary droplets and a potential route to accommodate various applications using the evaporation of the binary droplet.

A Review on the Evaporation Dynamics of Sessile Drops of Binary Mixtures: Challenges and Opportunities

The wetting and evaporation dynamics of sessile droplets have gained considerable attention over the last few years due to their relevance to many practical applications, ranging from a variety of industrial problems to several biological systems. Droplets made of binary mixtures typically undergo complex dynamics due to the differential volatility of the considered components and the ensuing presence of thermocapillary effects. For these reasons, many research groups have focused on the evaporation of binary droplets using a variegated set of experimental, numerical, and purely theoretical approaches. Apart from reviewing the state-of-the-art about the existing experimental, analytical, and computational techniques used to study the evaporation dynamics of binary sessile droplets, we also provide some indications about possible future research directions in this specific area.

Effect of sessile binary droplet evaporation at different ambient temperatures on interfacial profile near the triple line

Heat and mass transfer near the triple line of an evaporating droplet contains complex physics, while the mechanisms of evaporation influenced by the ambient temperature remain unclear. This paper describes an experimental study of interfacial profile near the triple line during evaporation of pure water and binary mixtures including dilute aqueous ethanol and n-butanol solutions at different ambient temperatures. The difference of interfacial profile between single and multi-component sessile evaporative droplets were experimentally demonstrated. The result shows that the thin film evaporation of the binary droplets is greatly suppressed when the ambient temperature drops. The thin film thickness reduces with the time under various ambient temperature conditions which are below 25 °C. The thickness difference at between 0 s and 40 s decreases in the order of water, ethanol solution and n-butanol solution. For water droplet, the critical thin film thickness at which the evaporation mode changes decreases with increasing ambient temperature, which is opposite to the binary droplets. Meanwhile, the rate of change of thin film thickness increases with increasing ambient temperature for water or ethanol solution, while it decreases with increasing temperature for n-butanol solution, which is attributed to the contact line energy barrier that decreases with increasing ambient temperature.

Heat Transfer Characteristics in an Evaporating Thin Film and Intrinsic Meniscus in a Binary Fluid Sessile Droplet

ABSTRACTThe evaporation of binary droplets containing a mixture of two species with completely different physicochemical properties is important in many applications. This paper describes a numerical study of the heat transfer characteristics of a thin liquid film and an intrinsic meniscus in a sessile droplet of a binary fluid, 5.0wt% aqueous n-butanol solution, to analyze the influence of various factors on the heat transfer. The thin film was longer than for a water droplet and the heat and mass fluxes were greater. The droplet contact radius, wall superheat, contact angle, and the air in a closed environment can affect the contribution of the heat transfer in the thin film region on the overall heat transfer. The wall superheat has the greatest effect on the heat transfer followed by the droplet size, surface wettability, and non-condensable gas. These four significant effects can be efficiently combined to enhance the heat transfer in applications involving binary droplet evaporation.

Kinetics of picoliter binary droplet evaporation on a substrate at reduced pressure

The effects of different factors on the time of evaporation of a single picoliter droplet of a water-alcohol solution on a metal substrate with a high thermal conductivity have been studied in the free molecular regime. It has been experimentally shown that the evaporation of such droplets occurs in the pinning mode. The evaporation times have been measured for droplets of water-alcohol solutions of different concentrations on the substrate at a reduced pressure. The calculations performed in terms of a one-dimensional mathematical model have shown that the rates of evaporation of pico- and femtoliter droplets of water-alcohol solutions nonlinearly depend on alcohol concentration, initial droplet height, and substrate temperature.

EXPERIMENTAL STUDY ON BINARY DROPLET EVAPORATION AT ELEVATED PRESSURES AND TEMPERATURES

The evaporation characteristics of single and multicomponent droplets hanging at the tip of a quartz fiber are studied experimentally at the different environmental conditions under normal gravity. Heptane and Hexadecane are selected as two fuels with different evaporation rates and boiling temperatures. At the first step, the evaporation of single component droplet of both fuels has been examined separately. At the next step the evaporation of several blends of these two fuels, as a binary component droplet, has been studied. The temperature and pressure range is selected between 400 and 700°C, and 0.1 and 2.5 MPa, respectively. A high-temperature environment was provided by a falling electrical furnace. The initial diameter of droplet was in the range of 1.1 and 1.3 mm. The evaporation process was recorded by a high-speed CCD camera. The results of binary droplet evaporation show the three-stage evaporation. In the first stage the more volatile component evaporates. The droplet temperature rises after an almost non-evaporative period and, in the third stage, a quasi-linear evaporation takes place. The evaporation of the binary droplet at low pressure is accompanied with bubble formation and droplet fragmentation and leads to incomplete microexplosion. The component concentration affects the evaporation behavior of the first two stages. The bubble formation and droplet distortion does not appear at high environment pressure.

Comparisons of uncoupled, film theoretical and exact solutions for binary droplet evaporation and condensation

The model for evaporation or condensational growth of a monodisperse binary droplet population is presented. Three methods for estimating steady state gas phase mass fluxes are compared. The uncoupled model neglects the coupling between mass transfer rates; the film theoretical model is based on an approximate approach and it is simpler to use than the exact model. The most significant discrepancies were found between the results given by the uncoupled and the more exact models for an ammonia-water droplet evaporating in helium atmosphere. The film theoretical model seems to predict the mass fluxes reliably when these are in different directions. The exact model is verified by comparisons with experimental literature data for the condensation of n-propanol-water droplets and the agreement is good.

A model for binary droplet evaporation and condensation, and its application for ammonia droplets in humid air

We present the results of theoretical investigations concerning the quasistationary evaporation of freely falling droplets in the continum regime. The drople is contained in humid air, and evaporation is accompanied by simultaneous condensation of water vapour at the droplet surface. The mathematical model is based on simultaneous numerical solution of equations governing mass and heat transfer outside the droplet. Numerical results show the influence of the relative humidity on the evaporation rate and on the deposition of liquid ammonia

Binary droplet evaporation in the presence of an inert gas: An exact solution of the Maxwell-Stefan equations

The mass transfer rates for the evaporating binary droplet in the continuum regime is considered. Exact solutions for concentrations profiles in the gas phase have been derived from the Stefan-Maxwell equations. The mole fraction profiles are given as functions of mass fluxes, which are solved numerically from a set of two nonlinear equations. The solution represents a definite improvement over the approximate and the purely numerical solutions previously available: numerical methods are needed only in solving the set of nonlinear algebraic equations.

Condensation and evaporation of binary droplets with internal mass transfer

The condensation and evaporation of binary droplet have been theoretically and numerically investigated. The evaluation of the mole fractions at the droplet surface is based on the model, where a thin, well-stirred liquid film is allowed to mix with the droplet by diffusion. The evaporation of ammonia-water droplet is numerically predicted. The effect of small liquid phase diffusitivies seems to cause the surface composition to differ from the bulk. However, the effect on the evaporation rate is reduced due to coupling with the droplet temperature.