Evaporation Stage Research Articles

Infrared effects in the late stages of black hole evaporation

As a black hole evaporates, each outgoing Hawking quantum carries away some of the black holes asymptotic charges associated with the extended Bondi-Metzner-Sachs group. These include the Poincaré charges of energy, linear momentum, intrinsic angular momentum, and orbital angular momentum or center-of-mass charge, as well as extensions of these quantities associated with supertranslations and super-Lorentz transformations, namely supermomentum, superspin and super center-of-mass charges (also known as soft hair). Since each emitted quantum has fluctuations that are of order unity, fluctuations in the black hole’s charges grow over the course of the evaporation. We estimate the scale of these fluctuations using a simple model. The results are, in Planck units: (i) The black hole position has a uncertainty of sim {M}_i^2 at late times, where Mi is the initial mass (previously found by Page). (ii) The black hole mass M has an uncertainty of order the mass M itself at the epoch when M ∼ {M}_i^{2/3} , well before the Planck scale is reached. Correspondingly, the time at which the evaporation ends has an uncertainty of order sim {M}_i^2 . (iii) The supermomentum and superspin charges are not independent but are determined from the Poincaré charges and the super center-of-mass charges. (iv) The supertranslation that characterizes the super center-of-mass charges has fluctuations at multipole orders l of order unity that are of order unity in Planck units. At large l, there is a power law spectrum of fluctuations that extends up to l ∼ {M}_i^2/M , beyond which the fluctuations fall off exponentially, with corresponding total rms shear tensor fluctuations ∼ MiM−3/2.

Deviations from classical droplet evaporation theory.

In this article, we show that significant deviations from the classical quasi-steady models of droplet evaporation can arise solely due to transient effects in the gas phase. The problem of fully transient evaporation of a single droplet in an infinite atmosphere is solved in a generalized, dimensionless framework with explicitly stated assumptions. The differences between the classical quasi-steady and fully transient models are quantified for a wide range of the 10-dimensional input domain and a robust predictive tool to rapidly quantify this difference is reported. In extreme cases, the classical quasi-steady model can overpredict the droplet lifetime by 80%. This overprediction increases when the energy required to bring the droplet into equilibrium with its environment becomes small compared with the energy required to cool the space around the droplet and therefore establish the quasi-steady temperature field. In the general case, it is shown that two transient regimes emerge when a droplet is suddenly immersed into an atmosphere. Initially, the droplet vaporizes faster than classical models predict since the surrounding gas takes time to cool and to saturate with vapour. Towards the end of its life, the droplet vaporizes slower than expected since the region of cold vapour established in the early stages of evaporation remains and insulates the droplet.

Time evolution of GaAs(111) surface morphology and desorption rate during Langmuir evaporation: Monte Carlo simulation

The high-temperature GaAs annealing kinetics is studied by Monte Carlo simulation. The evaporation rate dependences on the annealing time are obtained for (111)A and (111)B substrate surfaces in a 800–1200 K temperature range. The surface morphology evolution and evaporation kinetics are shown to be dependent on the GaAs substrate orientation. The congruent evaporation of (111)A surface corresponds to the layer-by-layer evaporation mode, while, on the (111)B surface, multilayer vacancy islands are formed. At temperatures exceeding the congruent evaporation temperature, the initial evaporation stage before the gallium droplet formation agrees with the congruent evaporation mode. The appearance of Ga droplets on the surface, corresponding to the start of incongruent evaporation regime, results in a sharp fall of the GaAs evaporation rate. It is found that the Ga droplet on vicinal surfaces locally inverts the step movement direction.

Oscillatory Reversible Osmotic Growth of Sessile Saline Droplets on a Floating Polydimethylsiloxane Membrane

We report a cyclic growth/retraction phenomena observed for saline droplets placed on a cured poly (dimethylsiloxane) (PDMS) membrane with a thickness of 7.8 ± 0.1 µm floating on a pure water surface. Osmotic mass transport across the micro-scaled floating PDMS membrane provided the growth of the sessile saline droplets followed by evaporation of the droplets. NaCl crystals were observed in the vicinity of the triple line at the evaporation stage. The observed growth/retraction cycle was reversible. A model of the osmotic mass transfer across the cured PDMS membrane is suggested and verified. The first stage of the osmotic growth of saline droplets is well-approximated by the universal linear relationship, whose slope is independent of the initial radius of the droplet. The suggested physical model qualitatively explains the time evolution of the droplet size. The reported process demonstrates a potential for use in industrial desalination.

Preparation and properties of hydrotalcite microcapsules for coal spontaneous combustion prevention

Microcapsule materials are a new type of composite fire-extinguishing material that show good effects in preventing the spontaneous combustion of coal. In this paper, polyethylene glycol 6000 (PEG6000) was selected as the wall material, and hydrotalcite (LDHs) was selected as the core material. Microencapsulated LDHs samples with different core-to-wall ratios were prepared by melting dispersion and condensation. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR), thermogravimetry/differential scanning calorimetry (TG/DSC) and other experiments were used to characterize the surface morphology, dispersion, coating, pyrolysis and other characteristics of the microcapsules. On this basis, the microcapsules were mechanically mixed with a coal sample to prepare a chemically inhibited coal sample. Based on TG/DSC experiments, the effect of microcapsules with different core-to-wall ratios on the characteristics of coal spontaneous combustion was studied. Combined with thermokinetic parameters, the inhibition mechanism of the microcapsules with different core-to-wall ratios on coal spontaneous combustion was analyzed. The results showed that LDH-PEG6000 microcapsules were successfully prepared. The thermal reactivities and inhibition mechanism of microcapsules with different core-to-wall ratios were different, and the best effect was obtained when the core-to-wall ratio was 1:5. This microcapsule material can reduce the weight loss rate and heat release of coal, increase the critical temperature and maximum weight loss rate temperature by 8.8 °C and 33.6 °C, respectively, and increase the apparent activation energy of water evaporation and gas desorption stage by 13.42 kJ/mol and the thermal decomposition stage and combustion stage by 88.64 kJ/mol. Resistance microcapsules can effectively inhibit the coal spontaneous combustion reaction In addition, this research provides new ideas for solving the problem of coal spontaneous combustion in the goaf caused by the fully mechanized top coal caving technology and enriches the technical means of fire prevention.

The nascent coffee ring: how solute diffusion counters advection

We study the initial evolution of the coffee ring that is formed by the evaporation of a thin, axisymmetric, surface-tension-dominated droplet containing a dilute solute. When the solutal Péclet number is large, we show that diffusion close to the droplet contact line controls the coffee-ring structure in the initial stages of evaporation. We perform a systematic matched asymptotic analysis for two evaporation models – a simple, non-equilibrium, one-sided model (in which the evaporative flux is taken to be constant across the droplet surface) and a vapour-diffusion limited model (in which the evaporative flux is singular at the contact line) – valid during the early stages in which the solute remains dilute. We call this the ‘nascent coffee ring’ and describe the evolution of its features, including the size and location of the peak concentration and a measure of the width of the ring. Moreover, we use the asymptotic results to investigate when the assumption of a dilute solute breaks down and the effects of finite particle size and jamming are expected to become important. In particular, we illustrate the limited validity of this model in the diffusive evaporative flux regime.

Fast Preparation of Flexible Wet-Resistant and Biodegradable Films From a Stable Suspension of Xylan/Chitosan Polyelectrolyte Complexes

Novel hemicellulose-based films from polyelectrolyte complexes (PECs) of chitosan and xylan from sugar cane bagasse were prepared and characterized. PEC suspension from two different xylan to chitosan mass ratios (70/30 and 80/20) were considered. With the aim of shorten the whole film preparation process, PEC suspension was concentrated through a fast evaporation stage before casting. Results show that the concentration stage did not modify neither the size of the complexes, i.e., a size distribution with a mode at 450 nm and other at 5000 nm, nor the mechanical properties of the films. By the increment in xylan content from 70 to 80%, the strain at break was decreased (up to a value of 7%), the stress at break was increased (up to 22 MPa) and the swelling of the films was increased from 80 to 90%. After 25 days under aerobic burial conditions, degradation of the films was similar to cellulose.

Improving the thermal, productive, and environmental performance of a non-centrifugal cane sugar production module using a heat recovery system

Non-centrifugal cane sugar (NCS) is an unrefined sweetening product that has garnered growing interest in its commercialization for its nutritional attributes. However, NCS production modules present with thermal efficiency problems that may compromise the environmental and economic sustainability of the production process. Therefore, the objective of this study was to develop and implement a heat recovery system (HRS) within a traditional NCS production module to increase the production capacity and the overall thermal efficiency. A conceptual design of the system was carried out to recover residual heat from combustion gases. Later, a mathematical model was developed to predict the thermal performance of the HRS, and a techno-economic analysis was carried out as well. Finally, construction and experimental validation were carried out on an experimental NCS production module. The HRS consisted of a tube bank with staggered configuration and two coils located in the open exchangers (OEs) of the clarification and evaporation stages. The values predicted by the model, which represented average approximations of the experimental values, presented with a correlation coefficient of R 2 = 0.7378 and a mean relative error ≤8.13%. The implementation of the HRS achieved an increase in the capacity and overall thermal efficiency of the production module by 70% and 39%, respectively. Likewise, the emission rates of CO 2 and CO per unit of mass produced by NCS decreased by 28.23% and 29.14%, respectively. The economic analysis indicated that the internal rate of return on investment does not differ significantly between the traditional system and the HRS, which allowed the financial cost to be corrected in a period of time less than or similar to that required by the traditional system. • Mathematical model to predict the thermal performance. • Techno-economic analysis for two NCS production module Comparison. • Comparison of productivity, overall thermal efficiency and flue gases in two of NCS production module.

Combustion Characteristics and Kinetic Analysis of Biomass Pellet Fuel Using Thermogravimetric Analysis

Biomass pellet fuel is one of the development directions of renewable energy. The purpose of the article is to study the combustion characteristics of five kinds of biomass pellet fuel that can be used as biomass fuel and analyze their combustion kinetics. The thermogravimetric method (TG method) was used to analyze the combustion characteristics of five kinds of biomass pellet fuel and to calculate the index S of comprehensive combustion characteristic. The Arrhenius equation and the Coats–Redfern method were used to analyze the combustion kinetics of five kinds of biomass pellet fuel. The activation energy and pre-exponential factor were obtained according to different temperature ranges. Conclusions are as follows: The pyrolysis of five kinds of biomass pellet fuel mainly includes three stages: (1) water evaporation stage, (2) volatile component combustion stage, (3) fixed carbon oxidation stage. The TG curves of five kinds of biomass pellet fuel are roughly the same at the same heating rate. The peaks of thermal weight loss rate and maximum degradation rate are both in the high temperature range. The differential thermal gravity (DTG) curves of five kinds of biomass pellet fuel have an obvious peak. The peak temperature of the largest peak in the DTG curves is 280–310 °C. The first-order reaction equation is used to obtain the kinetic parameters in stages. The correlation coefficients are bigger than the value of 0.92. The fitting results are in good agreement with the experimental results. The activation energy of each sample is basically the same in each stage. The value in the volatile matter combustion stage is 56–542 kJ/mol, and the activation energy of the carbon layer slowly increases rapidly. The five kinds of biomass pellet fuels have good combustion characteristics and kinetic characteristics, and they can be promoted and applied as biomass pellet fuels in the future.

Evaporation Dynamics of a Sessile Droplet of Binary Mixture Laden with Nanoparticles.

We investigate the evaporation dynamics of a sessile droplet of ethanol-water binary mixtures of different compositions laden with alumina nanoparticles and compare with the no-loading condition at different substrate temperatures. Shadowgraphy and infrared imaging methods are used, and the experimental images are postprocessed using a machine learning technique. We found that the loading and no-loading cases display distinct wetting and contact angle dynamics. Although the wetting diameter of a droplet decreases monotonically in the absence of loading, the droplet with 0.6 wt % nanoparticle loading remains pinned for the majority of its lifetime. The temporal variation of the normalized droplet volume in the no-loading case has two distinct slopes, with ethanol and water phases dominating the early and late stages of evaporation, respectively. The normalized droplet volume with 0.6 wt % loading displays a nearly linear behavior because of the increase in the heat transfer rate. Our results from infrared imaging reveal that a nanofluid droplet displays far richer thermal patterns than a droplet without nanoparticle loading. In nanoparticle-laden droplets, the pinning effect, as well as the resulting thermo-capillary and thermo-solutal convection, causes more intense internal mixing and a faster evaporation rate. Finally, a theoretical model is also developed that satisfactorily predicts the evaporation dynamics of binary nanofluid droplets.

Effect of biocrusts on profile distribution of soil water content and salinity at different stages of evaporation

In this study, the effect of biocrusts on daily variations of evaporation in soils of an arid rangeland was investigated during 142 days. Temporal and spatial variations of soil water and solute content were analyzed in three times of 17, 50 and 103 days, and four depths of 10, 20, 30 cm and 40 cm in six columns (20 cm diameter × 50 cm height) containing biocrusts (43 cm saline soil + 5 cm biocrusts) and four columns filled with bare soil (48 cm saline soil) respectively. Temporal variation of evaporation rate was supposed as a 3-stages process. Results showed that stage 1 and stage 2 are not distinguishable. We further found that, compared to bare soil, the biocrusts retarded water evaporation from soil surface (24 vs. 30 mm and 34 vs. 44 mm after 17 and 50 days respectively), and reduced solute accumulation in top soil, especially in the stage 2 of evaporation process (5 vs. 8 dS/m and 13 vs. 20 dS/m after 17 and 50 days respectively). The effect of biocrusts on the evaporation rate at the stage 3 of evaporation was not significant (9 vs. 9 mm after 103 days). Reduction of evaporation by biocrusts resulted in less soil salinity within entire soil profile. The effects of biocrusts on evaporation reduction are attributed to i) the biocrusts create mats on the soil surface, and swelling of mats blocks the soil pores in wet condition, and ii) the large pores of biocrusts disrupt the hydraulic connectivity between topsoil and subsoil, which minimizes the capillary rise. Since major part of water is evaporated during stage 2, and is controlled by water flow within the soil and at the surface, so conservation of the BSCs would be important for preserving hydrological functions advantage such as reducing evaporation and enhancing water retention in the salt affected and dry soils.

Enhanced flow boiling of HFE-7100 in picosecond laser fabricated copper microchannel heat sink

The enhanced flow boiling heat transfer of HFE-7100 in wavy copper microchannel heat sink was experimentally studied, which was fabricated with the picosecond laser technique. The micro porous structures were naturally formed on the sidewall and bottom of microchannel during the laser fabrication process, which increase the wall surface roughness. In single-phase flow region, the evaluation of performance evaluation criteria (PEC) proves the heat transfer enhancement overcomes the pressure-drop penalty in present wavy microchannel. In two-phase flow region, the flow patterns including bubbly flow, slug flow and annular flow were captured with the visualization technique, three heat transfer modes including heat convection, nucleate boiling and thin film evaporation were analyzed in detail. In wavy microchannel, the nucleate bubble on concave channel sidewall has a different apparent shape with a larger growth rate compared to that on convex one. In the thin film evaporation stage, the thickness of liquid film varies and it depends on the difference in curvatures between bubbles and sinusoidal channel sidewall. Compared to the straight channel, an increase of 28.89% for CHF can be achieved in wavy one, and the heat transfer coefficient enhancements of 60.76% and 52.71% are obtained in wavy one at the nucleate boiling stage and thin film evaporation stage, respectively.

Effect of Plasticizer on Mechanical and Thermal Properties of In Situ-Prepared Block Hydroxyl-Terminated Polyether Applied in Propellants

The relationship between the mechanical properties of in situ-prepared hydroxyl-terminated polyether (HTPE)/N-butyl-N-(2-nitroxyethyl)nitramine (Bu-NENA) binders and the plasticization ratio (pl/po), ranging from 0.4 to 1.2, was studied. The thermal properties and the very early stage of evaporation of Bu-NENA from an HTPE/Bu-NENA binder with a pl/po of 1.0 were also investigated. The results revealed that the pl/po ratio has a strong influence on the mechanical properties. When the pl/po ratio was 1.0, the mechanical properties of the in situ-prepared HTPE/Bu-NENA binder were satisfactory. The results showed that the Tg values of the in situ-prepared and traditional HTPE/Bu-NENA binder decreased as the plasticization ratio increased, and finally stabilized at approximately −75 and −78°C, respectively; moreover, the degree of phase mixing of the two soft segments of the in situ-prepared HTPE/Bu-NENA binder was greater than that of the traditional HTPE/Bu-NENA binder. The activation energy of the Bu-NENA evaporation from the in situ-prepared HTPE/Bu-NENA binder was close to that for the traditional HTPE/Bu-NENA binder, but the pre-exponential factor differed by an order of magnitude. Compared with the traditional HTPE propellant, the mechanical properties of the in situ-prepared HTPE propellant were greatly improved.

Experimental study on the coupled behavior of dynamic cracking and moisture-heat evolution of a clay under evaporation

A clay is prone to shrinkage and cracking under evaporation, which can cause vast hazards in geotechnical and geo-environmental engineering. Knowledge of the coupled behavior of dynamic cracking and moisture-heat evolution is helpful for better understanding the mechanical performance of a clay under evaporation. An evaporation experiment was conducted on a clayey soil specimen in this study, accompanied by observation of shrinkage and cracking and monitoring of moisture-heat. In this way, the fully coupled behavior of shrinkage, cracking, and moisture-heat evolution of the clay under evaporation was investigated. The results show that the clay loses most of its water and achieves most of the shrinkage before the latter evaporation stage. Especially in the intermediate evaporation stage, the soil saturation has a quick reduction, the soil suction has a linear increase, and the soil temperature has a sharp rise. Because of this moisture-heat evolution, both the degree of the nonuniform shrinkage and the increased rate of the crack ratio and the crack depth reach the maximum values. Along with the crack developing downward and bringing new air-entry channels, the actual evaporation front also moves downward. The evaporation from the surface-exposed crack can significantly affect the moisture-heat evolution of the clay. The crack can develop further to the width and the depth owing to the nonuniform shrinkage existing at the different locations and the different depths of the clay. The nonuniform shrinkage may be attributed to the heterogeneity of the soil properties, the inhomogeneous evaporation environment, and the huge difference of moisture-heat characteristics of the clay.

Effects of evolving salt precipitation on the evaporation and temperature of sandy soil with a fixed groundwater table

AbstractThe effects of salt precipitation on water and heat transport in soil have garnered considerable attention. However, salt precipitation growth on the soil surface and its influence on soil evaporation and temperature under a fixed groundwater table are not well understood. Therefore, the objective of this study was to investigate the impact of the evolution of salt precipitation on evaporation and temperature in sandy soils with a fixed groundwater table depth (20 cm). The laboratory experiment consisted of two treatments for sand columns: one with fresh groundwater, and the other with saline groundwater. Regions with salt precipitates expanded laterally and vertically whereby a salt crust was formed that disconnected from the soil. The lateral growth of salt precipitation had a minor impact on evaporation as the soil remained wet, while mostly being covered by the salt crust. However, the elevated salt crust caused a sharp decrease (>60%) in the evaporation rate. Therefore, a new stage of saline soil evaporation was determined; the evaporation rate was further reduced by the elevated salt crust. Moreover, the soil profile temperature decreased when the soil was covered by the salt crust, which is likely attributable to the increased albedo and the formation of a layer of air owing to the elevated salt crust. Therefore, we suggest that the upward growth of salt precipitation should be comprehensively studied because it can cause significant reductions in evaporation rates and soil temperature.

Ethanol Evaporation Characteristics of the Blends of Fatty Acid Methyl Ester and Ethanol

The evaporation characteristics of fatty acid methyl ester (FAME) mixed with four concentrations of ethanol at 873K and normal atmospheric pressure are studied herein. FAME is used as base oils, and ethanol mass fractions vary from 10%, 20%, 30% to 40%. The experimental results show that the evaporation process of the binary component droplets of FAME-ethanol can be divided into two stages: a fluctuation evaporation stage, and an equilibrium evaporation stage. In these four concentration gradients, micro-explosions occur in the droplet evaporation process. The fluctuation evaporation stage is divided into two stages: a strong fluctuation stage and a weak fluctuation stage. After the micro-explosion, there is still a small amount of ethanol in the droplet. Due to the surface tension of the droplet, a small amount of ethanol cannot make the droplet violently fluctuate. The results show that the earlier the droplet micro-explosion occurs, the more intense it is, and the shorter the lifetime of the droplet is. Different concentrations of ethanol have different improvements in droplet evaporation characteristics. Generally, the higher the ethanol concentration is, the shorter the lifetime of the droplet is. However, increasing the ethanol concentration from 20% to 30% has the most obvious effect on the lifetime of the droplet.

The Influence of Droplet Dispersity on Droplet Vaporization in the High-Temperature Wet Gas Flow in the Case of Combined Heating

The change in the thermal and energy state of the water droplet is defined numerically. The influence of droplet dispersity on the interaction of the transfer processes was evaluated. In influence of the Stefan flow was considered as well. The internal heat transfer of the droplet was defined by the combined heat transfer through effective conductivity and radiation model. The results of the numerical modeling of heat and mass transfer in water droplets in a wet flue gas flow of 1000 °C highlight the influence of the variation in heat transfer regimes in the droplet on the interaction of the transfer processes in consistently varying phase change regimes. The results of the investigation shows that the inner heat convection diminishes intensively in the transitional phase change regime because of a rapid slowdown of the slipping droplet in the gas. The radiation absorption in the droplet clearly decreases only at the final stage of equilibrium evaporation. The highlighted regularities of the interaction between combined transfer processes in water droplets are also valid for liquid fuel and other semi-transparent liquids sprayed into high-temperature flue gas flow. However, a qualitative evaluation should consider individual influence of dispersity that different liquids have.

Correlations between emission events in Rainbow Gravity

In this work, we study emission correlations in Rainbow Gravity (RG) black holes known to have black hole remnants. Non-thermal corrections are responsible for generating non-zero correlations between particle emission events during the black hole evaporation process. With this in mind, we calculate the temperatures considering back-reaction effects. Then, we obtain the correlations between emission events for a RG metric proposed by Magueijo and Smolin. We also discuss through a numerical analysis the emission correlations behavior in the last stages of evaporation of the black hole.

Auto-selection of quasi-components/components in the multi-dimensional quasi-discrete model

A new algorithm for the auto-selection of quasi-components and components (QC/Cs) in the ‘multi-dimensional quasi-discrete’ model is suggested. This algorithm is applied to the analysis of heating and evaporation of multi-component fuel droplets. It allows one to automatically select QC/Cs and update the initial selection during droplet evaporation. The new algorithm is expected to be applicable to the analysis of a wide range of fuels and fuel blends. It can be directly implemented into CFD codes with minimal intervention by end-user. Using this algorithm, the effects of transient diffusion of species on droplet lifetimes are investigated for mixtures of Diesel and E85 (85% vol. ethanol and 15% vol. gasoline) fuels. It is shown that the new algorithm can reduce the analysis of the E85-Diesel fuel droplets, taking into account the contributions of up to 119 components at the initial stage of heating and evaporation, to that based on 5 QC/Cs, near the end of droplet evaporation, with up to 1.9% errors in predicted droplet temperatures and radii. The CPU time needed to perform calculations using the new algorithm is shown to be 80% less than that when considering the full composition of fuel.

Two-Stage Evaporative Inlet Air Gas Turbine Cooling

Gas turbine inlet air-cooling (TIAC) is an established technology for augmenting gas turbine output and efficiency, especially in hot regions. TIAC using evaporative cooling is suitable for hot, dry regions; however, the cooling is limited by the ambient wet-bulb temperature. This study investigates two-stage evaporative TIAC under the harsh weather of Riyadh city. The two-stage evaporative TIAC system consists of indirect and direct evaporative stages. In the indirect stage, air is precooled using water cooled in a cooling tower. In the direct stage, adiabatic saturation cools the air. This investigation was conducted for the GE 7001EA gas turbine model. Thermoflex software was used to simulate the GE 7001EA gas turbine using different TIAC systems including evaporative, two-stage evaporative, hybrid absorption refrigeration evaporative and hybrid vapor-compression refrigeration evaporative cooling systems. Comparisons of different performance parameters of gas turbines were conducted. The added annual profit and payback period were estimated for different TIAC systems.