Evaporation Stage Research Articles

Production of a degenerate Fermi-Fermi mixture of dysprosium and potassium atoms

We report on the realization of a mixture of fermionic $^{161}$Dy and fermionic $^{40}$K where both species are deep in the quantum-degenerate regime. Both components are spin-polarized in their absolute ground states, and the low temperatures are achieved by means of evaporative cooling of the dipolar dysprosium atoms together with sympathetic cooling of the potassium atoms. We describe the trapping and cooling methods, in particular the final evaporation stage, which leads to Fermi degeneracy of both species. Analyzing cross-species thermalization we obtain an estimate of the magnitude of the inter-species $s$-wave scattering length at low magnetic field. We demonstrate magnetic levitation of the mixture as a tool to ensure spatial overlap of the two components. The properties of the Dy-K mixture make it a very promising candidate to explore the physics of strongly interacting mass-imbalanced Fermi-Fermi mixtures.

ІNTENSIVE AND ENERGY-SAVING EVAPORATORS WITH PLATE WARMING CHAMBER

The modern developments of the evaporators with plate warming chambers for manufactures related to the concentration of caustic soda solutions, phosphoric acid and chloride effluents utilization have been considered. The plate warming chambers different disposition within evaporator was presented. The plate warming chamber construction along with the evaporation sections consisting of three plates are considered. The plates composition and evaporator section are given. It is noted that due to a three special plates composition the section is formed. This section provides the solution overheating and boiling, separation of secondary steam and its direction to the next section heating, while partially evaporated solution flows to the next evaporation stage. The sequential combination of sections allows to develop the evaporator with reusable warming steam heat wherein the number of sections determines the warming steam heat multiplicity of use and its economy per unit of water being evaporated. A paper identifies the constructive decisions on the new intensive plate evaporators developing. They are able to significantly improve the solutions concentration processes taking into account their physico-chemical characteristics, corrosive aggressiveness and salt deposits on the heating surfaces. The technical approaches having constructive and material implementation, and manufacturing technology have been proposed.

Measuring the temperature of a rapidly evaporating water droplet by Planar Laser Induced Fluorescence

In this paper, we present the experimental research into the unsteady temperature fields of an evaporating water droplet with a 1–2 mm initial radius attached to a holder in a flow of air heated up to 1,000 °C. The limitations of Planar Laser Induced Fluorescence are established. We identify four distinct stages of droplet evaporation, in which the use and calibration of Planar Laser Induced Fluorescence differ significantly. Changes in the dye concentration in the droplet are found to result from the dye evaporation from the free surface of the droplet and its sedimentation onto the holder. A correction factor is introduced, based on the experimental results and dependent on a number of effects discussed. The factor is used to adjust the experimental measurements made via Planar Laser Induced Fluorescence and to obtain the reliable temperature fields of a rapidly evaporating water droplet.

Creation of an inflationary universe out of black hole space–time

We investigate the effect of a black hole as a nucleation site of a false vacuum bubble based on the Euclidean actions of relevant configurations. As a result we find a wormhole-like configuration may be spontaneously nucleated once the black hole mass falls below a critical value of order of the Hubble parameter corresponding to the false vacuum energy density. As the space beyond the wormhole throat can expand exponentially, this may be interpreted as creation of another inflationary universe in the final stage of the black hole evaporation.

Experimental study of evaporation of sessile droplets of the water-ethanol solution with different concentrations

The dynamics of the geometric parameters of droplets of a water-ethanol solution lying on a Teflon plate was investigated using high-speed microphotography. It was found that the evaporation of water droplets occurred with a constant contact line, and the evaporation of droplets of a water-ethanol solution was accompanied by its movement. At the initial stage of evaporation, the higher the concentration of ethanol in the drop was, the greater was the change in the contact spot diameter, corresponding to the change in the diameter of the spot of ethanol. Using the method of infrared thermography, three stages of temperature change of evaporating droplets were found. The first stage corresponds to the initial sharp decrease in temperature. The second stage is a process at a constant temperature. And finally, the third stage is the stage of its smooth growth to the ambient air temperature. A similar pattern with some features was observed for droplets with different concentrations of ethanol. At the initial stage of evaporation, the droplet temperature changed like the temperature of ethanol droplet, and then its behavior was similar to the temperature change of water droplets. The higher the ethanol concentration in the droplet was, the larger the change in temperature was, similar to the change in the temperature of the ethanol droplet.

Experimental study of the evaporation of suspended droplets of a water-ethanol solution

The dynamics of the geometric parameters of droplets of a water-ethanol solution suspended on polypropylene filaments was investigated using high-speed microphotography. It was found that all suspended droplets had a spherical shape during the main time of evaporation. The higher the concentration of ethanol in the drop, the faster the droplet evaporates. The dynamics of the temperature of droplets of a water-ethanol solution suspended on polypropylene filaments was investigated using the method of infrared thermography. Three stages of temperature change of evaporating droplets of a water-ethanol solution were found. At the initial stage of evaporation, the droplet temperature changed like the temperature of an ethanol droplet, and then its behavior was similar to the temperature change of water droplets. The higher was the ethanol concentration in the droplet, the more similar was the temperature change with a change in the ethanol droplet temperature.

Nonisothermal Evaporation of Layers of Aqueous Salt Solutions

Evaporation of layers of aqueous solutions of salts (LiBr, CaCl2, NaCl, MgCl2, BaCl2, and CsCl) is studied experimentally. Experimental data are compared with evaporation of the water layer. The solution is placed on a horizontal surface of a cylindrical heating section. Experiments on surface crystallization of salts are carried out. For aqueous solutions of salts LiBr, LiCl, and CaCl2, there is an extremum for the heat transfer coefficient αl. For water and for solutions of salts NaCl and CsCl, the extremum is absent. The first factor is a decreasing function of time, and the second factor is an increasing function of time. For the water layer, both factors continuously increase with time, and the maximum evaporation rate corresponds to the final stage of evaporation. The heat balance for interface layer is made up. The role of the free gas convection in the heat balance strongly depends on the salt concentration and varies with the rise of evaporation time. For low salt concentrations the influence of free convection in the gas phase on heat transfer in the liquid phase can be neglected; however, for high concentrations this effect is comparable with other factors. The curves for the rate of crystallization have been built. More than two time differences between the experiment and the calculation are associated with the kinetics of dendritic structures.

Molecular dynamics simulation of characteristics of the nanodroplet evaporation

The molecular dynamics method is used to simulate the evaporation process of nanodroplets on heated substrates by LAMMPS software. The simulation process includes three stages: the relaxation of argon droplets at 84K, heating the substrates to 200 K, keeping the substrates temperature at 200 K to observe the evaporation of the droplet. By measuring the change of the whole morphology of the droplets during the evaporation process, the changes of the edge thickness are obtained. By analyzing the atomic velocity and displacement, the trajectories of the particles at the edge of the evaporation process are revealed and distribution of the temperature of the droplets are expressed. It is concluded that when the substrates at 200K, the whole droplet evaporation process is conclude four stages: fixed evaporation stage, the stick slip motion stage, once again into the fixed evaporation stage and fixed contact angle and the contact radius are decreasing the evaporation process until the end. Finally, the experimental platform was set up to verify the validity of the simulation. Without considering the influence of plate roughness, the height variation of the droplet obtained from the experiment has a high consistency with the simulation results.

Evaluation of Model Concepts to Describe Water Transport in Shallow Subsurface Soil and Across the Soil\u2013Air Interface

Soil water evaporation plays a critical role in mass and energy exchanges across the land–atmosphere interface. Although much is known about this process, there is no agreement on the best modeling approaches to determine soil water evaporation due to the complexity of the numerical modeling scenarios and lack of experimental data available to validate such models. Existing studies show numerical and experimental discrepancies in the evaporation behavior and soil water distribution in soils at various scales, driving us to revisit the key process representation in subsurface soil. Therefore, the goal of this work is to test different mathematical formulations used to estimate evaporation from bare soils to critically evaluate the model formulations, assumptions and surface boundary conditions. This comparison required the development of three numerical models at the REV scale that vary in their complexity in characterizing water flow and evaporation, using the same modeling platform. The performance of the models was evaluated by comparing with experimental data generated from a soil tank/boundary layer wind tunnel experimental apparatus equipped with a sensor network to continuously monitor water–temperature–humidity variables. A series of experiments were performed in which the soil tank was packed with different soil types. Results demonstrate that the approaches vary in their ability to capture different stages of evaporation and no one approach can be deemed most appropriate for every scenario. When a proper top boundary condition and space discretization are defined, the Richards equation-based models (Richards model and Richards vapor model) can generally capture the evaporation behaviors across the entire range of soil saturations, comparing well with the experimental data. The simulation results of the non-equilibrium two-component two-phase model which considers vapor transport as an independent process generally agree well with the observations in terms of evaporation behavior and soil water dynamics. Certain differences in simulation results can be observed between equilibrium and non-equilibrium approaches. Comparisons of the models and the boundary layer formulations highlight the need to revisit key assumptions that influence evaporation behavior, highlighting the need to further understand water and vapor transport processes in soil to improve model accuracy.

A rationally based model applicable for heat pump tumble dryer

The present study proposes a rationally based heat pump clothes dryer model which is capable of handling transient behaviors of both air-side and refrigerant side. The model can take into account the geometrical variation of the heat exchangers. Yet the proposed model is free from extra constraints that were normally imposed by previous studies. The simulation shows that there exist three stages in a typical drying process, including a preheat stage, followed by a constant evaporation stage, and finally a falling drying rate period. The calculation indicates that the variation of the clothes temperature and the system suction/discharge pressure show an appreciable rise in the first stage, remain nearly unchanged at the second stage, and increase again at the final stage of drying process. Also, the corresponding maximum specific moisture extraction rate (SMER) peaks at the end of the second stage while the corresponding coefficient of performance (COP) drops continuously. The simulation also indicates that increasing the air volumetric flowrate yields a lower discharge/suction pressure, a higher COP value, and a shorter drying time. The results also suggested that a good strategy to maximize COP is initiated by a low volumetric rate during the preheat stage, increasing it during the second stage and lowering it to an intermediate flowrate at the end of the drying period. Increasing heat exchanger size, either by increasing heat exchanger width or the number of tube row, results in a lower suction/discharge pressure and a shorter drying time. Although both approaches adopt larger surface area to promote overall performance, it is found that increasing the width of heat exchanger yields more effective results.

Transient Heat Transfer Characteristics of Supercritical Fluid during Rapid Depressurization Process

A combination of experimental studies and numerical simulations is employed to probe into the transient heat transfer phenomenon during rapid depressurization of supercritical fluid in a cylindrical vessel connected to atmosphere via a sudden valve on the top. The effects of initial conditions on heat transfer characteristics are studied, and the morphological characteristics of supercritical fluid are analyzed. Results show: (i) there is a strong re-circulation inside the supercritical fluid with a sudden pressure drop. The heat transfer process is divided into four stages: the initial depressurization stage, the rapid evaporation stage, the nucleate boiling stage and the surface evaporation stage; (ii) under the subcritical state, a higher temperature contributes to a faster temperature drop rate and a shorter fast evaporation time. Moreover, a higher initial pressure leads to a lower equilibrium temperature and a shorter time it takes to reach the equilibrium temperature; (iii) differences are presented in terms of the effect of initial pressure in subcritical and supercritical zones on temperature drop rate with a turn near the critical point. A higher initial pressure gives rise to a higher equilibrium temperature, a slower temperature drop rate and the gradual increasing fast evaporation time; (iv) the experimental data are in good agreement with the calculated results, with a maximum error of 10%.

Creation of an inflationary universe out of a black hole

We discuss a two-step mechanism to create a new inflationary domain beyond a wormhole throat which is created by a phase transition around an evaporating black hole. The first step is creation of a false vacuum bubble with a thin-wall boundary by the thermal effects of Hawking radiation. Then this wall induces a quantum tunneling to create a wormhole-like configuration. As the space beyond the wormhole throat can expand exponentially, being filled with false vacuum energy, this may be interpreted as creation of another inflationary universe in the final stage of the black hole evaporation.

The stage analysis and countermeasures of coal spontaneous combustion based on "five stages" division.

The “three stages” division of coal spontaneous combustion is fuzzy and lacks adequate risk and warning levels corresponding to its divisions; additionally, the targeted prevention measures for each stage have not been described. To address the shortcomings of the “three stages” division, the “five stages” division was proposed to more clearly analyze the stage changes of the spontaneous combustion of coal. The “five stages” method divides the process of the spontaneous combustion of coal into five stages, including: the latent stage, heat accumulating stage, evaporation stage, active stage, and hypoxic stage. The critical point of each stage was determined using adiabatic oxidation experiments and programmed heat experiments. As the critical point of the latent stage, the temperature of zero activation energy is approximately 55–70°C. In the heat accumulating stage, the critical point is the temperature (approximately 90°C) where the external moisture of coal evaporates violently while the internal moisture of coal has not yet fully evaporated. During the evaporation stage, the temperature (approximately 105°C) where the internal moisture has evaporated completely represents the end of this stage and the start of the active stage (105–170°C). When the oxygen concentration drops to 5%, the spontaneous combustion of coal enters the hypoxic stage. Thus, an oxygen concentration of 5% represents the critical point of the start of the hypoxic stage (above 170°C). After the analysis of each stage, risk and warning levels were determined. Considering the major prevention measures of the spontaneous combustion of coal, a staged warning and disposal table was created.

Influence of the noncondensable component on the characteristics of temperature change and the intensity of water droplet evaporation

The removal of vapor molecules from a droplet surface is an important stage of evaporation in a vapor–gas mixture. In this work, with the evaporation of a water droplet in a vapor–gas medium as the example, the influence of the noncondensable component on the intensity of the evaporation process and the characteristics of the temperature change is examined. The heat supplied to an interface is often assumed to be entirely utilized for evaporation, with the formed vapor removed from the evaporation surface through diffusion. However, the diffusion flux develops at a distance of some mean free paths of vapor molecules away from the evaporation surface, that is, in the Knudsen layer. In this layer, because of intermolecular collisions, the molecule–velocity distribution undergoes substantial changes, which are calculated using the methods of physical kinetics. Herein, the system of two Boltzmann kinetic equations for a vapor–gas mixture is used for calculating mass flux density of the evaporating substance near the evaporation surface. The calculation results are then compared with published experimental data.

Evaporation From Confined Porous Media Due to Controlled IR Heating From Above

We report an experimental study of evaporation due to controlled infrared (IR) heating from above from an initially saturated confined porous medium consisting of nearly ‘mono-disperse’ particles which has been rarely used earlier. We have used three diagnostic tools simultaneously, evaporation rate measurements using a precision weighing balance, surface temperature measurements using IR imaging, and fluorescein dye mixed with water to visualize the drying front and the evaporation sites. IR images show that the first stage, so-called constant rate period (CRP), was maintained due to films of water reaching the top surface from the saturated region below. Gradually reducing evaporation rate in stage 1 is shown to be related to ‘shrinking evaporating patches’ on the top surface, clearly revealed as lower-temperature regions in the IR images. End of CRP coincides with disappearance of the low-temperature patches. We give end of CRP in terms of the average depth (Lcap) of the liquid level from the top surface at that time. Lcap and duration of CRP are strong functions of the porous medium bead size, transition to stage 2 happening earlier for coarser spheres. The obtained Lcap values deviated from the predictions of Lehmann et al. (Phys Rev E 77(5):056309, 2008) which we show is due to a small range of pore sizes in the current experiments. For both water and highly volatile n-pentane, we show that Lcap normalized by a length scale derived from gravity-surface tension force balance goes like Bo0.20, for Bo varying from 2.0E − 04 to 1.0E − 01; Bo is the Bond number. Fluorescein dye imaging shows a different view of the evaporation stages. During CRP, highly concentrated deposits of the fluorescein dye particles, orange in colour, are seen in the top few bead layers. These orange deposits represent the sites on the beads surfaces where the evaporation has taken place. Even with external heating, evaporation from such a porous medium is limited to a finite depth from the evaporating end, similar to the observation by Lehmann et al. (2008) for isothermal evaporation in Hele-Shaw cell.

The border effect on urban land expansion in China: The case of Beijing-Tianjin-Hebei region

Since the seminal contribution of McCallum (1995), border study has been introduced to broader fields. However, it’s still a puzzle that how administrative boundaries affect the process of urban land expansion. In this study, we develop the Stage Model of Border Effect on urban land expansion based on Core-Periphery Theory and divide the evolutive process of border effect into four stages: the invisibility stage of administrative boundaries, the differentiation stage of administrative boundaries, the channelization stage of administrative boundaries and the evaporation stage of administrative boundaries. In the model, urban land distribution of different cities in urban agglomeration is in high-level balance after the evolution which is from low-level equilibrium to none-equilibrium state during the invisibility stage and the evaporation stage. Then, Beijing-Tianjin-Hebei region is fully studied based on conditionalβconvergence analysis. Research results show that the model is well adapted to empirical study and evolutive process of border effect on urban land expansion in the region experienced the invisibility stage of administrative boundaries, the differentiation stage of administrative boundaries and the channelization stage of administrative boundaries from 1990 to 2010. We also find that the wider the gap between cities of different administrative ranks is, the larger the border effect tends to be. When border effects of different cities are equal and measure results are “1″, process of urban land expansion enter the evaporation stage of administrative boundaries. Additionally, impact of boundaries on urban land expansion is a long-term and cumulative process. The longer the research period is, the more significant the border effect tends to be. These findings can serve as basis of theoretical support and policy recommendations in breaking restriction of boundaries, delimiting the urban growth boundary and contributing to the rational expansion of urban land.

Unitized Power and Heat Generating Steam–Gas Plant

This paper considers the prospects of creating steam–gas thermoelectric plants for power supply to microdistricts and towns remote from centralized power plants. We propose a new type of thermoelectric plants with a waste heat boiler of medium steam parameters and an afterburner section located between its evaporation stages. It has been shown that fuel afterburning increases electric and thermal power and the specific electric power production at heat consumption.

On the viability of regular black holes

The evaporation of black holes raises a number of conceptual issues, most of them related to the final stages of evaporation, where the interplay between the central singularity and Hawking radiation cannot be ignored. Regular models of black holes replace the central singularity with a nonsingular spacetime region, in which an effective classical geometric description is available. It has been argued that these models provide an effective, but complete, description of the evaporation of black holes at all times up to their eventual disappearance. However, here we point out that known models fail to be self-consistent: the regular core is exponentially unstable against perturbations with a finite timescale, while the evaporation time is infinite, therefore making the instability impossible to prevent. We also discuss how to overcome these difficulties, highlighting that this can be done only at the price of accepting that these models cannot be fully predictive regarding the final stages of evaporation.

Heat transfer of aqueous salt solutions during evaporation on a structured heated wall

Evaporation and heat transfer of the layers of water and aqueous salt solutions (H2O/LiBr, H2O/CaCl2, H2O/LiCl) have been studied experimentally. Evaporation rate is greater for a structured wall than for a smooth one. When simulating droplet evaporation and heat transfer, it is necessary to take into account free convection of air and vapor. There is a change of the heat transfer coefficient for salt solutions layers on the structured surface with the presence of an extremum. The largest value of the heat transfer coefficient α on the structured surface corresponds to water for the final stage of evaporation. For salt solutions, α is lower than that of water. The maximum excess of heat transfer coefficient of micro-structured wall above the smooth wall (20–25%) corresponds to the maximum height of the liquid layer for the initial period of evaporation. With increasing time, the excess is reduced.

Transient and local two-phase heat transport at macro-scales to nano-scales

Two-phase cooling has become a promising method for improving the sustainability and efficiency of high energy-density and power-density devices. Fundamentally, however, two-phase thermal transport is not well understood for local, transient processes, especially at critical to near-critical heat fluxes at the macro, micro, and nano-scales. Here we report spatiotemporal characterization of the single-bubble ebullition cycle in a hot-spot heating configuration with heat fluxes approaching 3 kW cm−2. In particular, we experimentally reconstruct the spatiotemporal heat transfer coefficient in terms of its proportionality at both the macro-scale (l >> 1 μm) and the micro-to-nanoscale (l < 1 μm). We show that the maximum rates of heat transfer occur during the microlayer evaporation stage of the ebullition cycle, corresponding to critical maxima in the heat transfer coefficient of ~160 ± 40 kW m−2 K−1 and ~5300 ± 300 kW m−2 K−1 at the macro-scale and micro-to-nanoscale, respectively.