Mass Evaporation Rate Research Articles

Effect of Surface Evaporation on Steady Thermocapillary Convection in an Annular Pool

In order to understand the effect of surface evaporation on thermocapillary convection in an annular pool, a series of numerical simulation on thermocapillary convection of the fluids with Prandtl number from 0.01 to 50 in the pure vapor environment were carried out. The results show that thermocapillary convection is always coupled with the evaporation process on the free surface. With the increase of evaporation Biot number, the surface temperature decreases, and the evaporation mass flux near the hot wall increases obviously. However, near the cold wall, the evaporation mass flux increases first, and then decreases. When Marangoni number is small, the total evaporation mass rate at free surface increases with the increase of evaporation Biot number; when Marangoni number is larger, it increases first and then approaches a constant value. The aspect ratio of the annular pool has a positive influence on the thermocapillary convection strength and the total evaporation mass rate. With the increase of Prandtl number, the surface temperature rises gradually and the evaporative mass flux increases, and the thermocapillary convection cell moves gradually toward the outer wall and the free surface. This effect decreases with the increase of evaporation Biot number When evaporation Biot number is smaller, the total evaporation mass rate increases with the Prandtl number; when Biot number is larger, Prandtl number has little impact on the total evaporation mass rate.

On the Trigonometric Descriptions of Colors

<p class="1Body">An attempt is presented for the description of the spectral colors using the standard trigonometric tools in order to extract more information about photons. We have arranged the spectral colors on an arc of the circle with the radius R = 1 and the central angle θ = π/3 when we have defined cos (θ) = λ<sub>380</sub>/λ<sub>760</sub> = 0.5. Several trigonometric operations were applied in order to find the gravity centers for the scotopic, photopic, and mesopic visions. The concept of the center of gravity of colors introduced Isaac Newton. We have postulated properties of the long-lived photons with the new interpretation of the Hubble (Zwicky-Nernst) constant H<sub>0</sub> = 2.748… * 10<sup>-18</sup> kg kg<sup>-1 </sup>s<sup>-1</sup>, the specific mass evaporation rate (SMER) of gravitons from the source mass. The stability of international prototypes of kilogram has been regularly checked. We predict that those standard kilograms due to the evaporation of gravitons lost 8.67 μg kg<sup>-1</sup> century<sup>-1</sup>. The energy of long-lived photons was trigonometrically decomposed into three parts that could be experimentally tested: longitudinal energy, transverse energy and energy of evaporated gravitons. We tested the properties of the long-lived photons with the experimental data published for the best available standard candles: supernovae Type Ia. There was found a surprising match of those experimental data with the model of the long-lived photons. Finally, we have proposed a possible decomposition of the big G (Newtonian gravitational constant) and the small kappa κ (Einsteinian gravitational constant) in order to get a new insight into the mysterious gravitational force and/or the curvature concept.</p>

Evaporation of multicomponent liquid fuel droplets: Influences of component composition in droplet and vapor concentration in free stream ambience

Theoretical studies have been made to explore the coupling influences of droplet constituent compositions and free stream vapor concentrations on evaporation characteristics, namely, mass depletion rate and droplet temperature of a heptane-dodecane droplet (components with widely varying volatility) and methanol-ethanol droplet (components with close volatility) at lower and higher free stream temperatures. In case of heptane-dodecane droplet, temperature and mass depletion histories are controlled by the heavier component (dodecane). In case of methanol-ethanol droplet, the mass depletion history is controlled by the lighter component (methanol), while the droplet temperature history is controlled by the heavier component (ethanol). The presence of fuel vapors in free stream increases the droplet lifetime, and moreover, the influence is relatively more prominent with the presence of heavier component vapor alone at lower free stream temperature. The composition of component vapors for a fixed value of total vapor concentration in free stream has almost negligible influence on droplet lifetime. It is revealed that the well established empirical relation (Sh(1+Bm)0.7=2) for mass evaporation rate of a single component droplet can be used with reasonably fair accuracy in case of multicomponent droplet evaporation with logical modifications of mass transfer number and mass transfer coefficient for multicomponent system.

Experimental Assessment of Moisture Transfer in the Vertical Ventilated Channel

This article considers the moisture transfer phenomenon in the vertical ventilated channel. Also the article considers innovative structures for the vertical ventilated channel.The negative factors connected with moisture accumulation and excessive moistening of a heat insulation are given. Optimum design parameters for definition of the most intensive moisture transfer are discovered: systems with and without grooved lines. Influence that existence of technological gaps (grooved lines) has on the speed of air flows in a gap is investigated. Dependence of speed on width of the ventilated gap for a design with the opened and closed grooved lines is established empirically. The dehumidification properties of the vertical ventilated channel are described, as well as dependence of mass evaporation rate on time is established. Processes of drying-out in various conditions are compared.

Modeling comprehensive chemical composition of weathered oil following a marine spill to predict ozone and potential secondary aerosol formation and constrain transport pathways

AbstractReleases of hydrocarbons from oil spills have large environmental impacts in both the ocean and atmosphere. Oil evaporation is not simply a mechanism of mass loss from the ocean, as it also causes production of atmospheric pollutants. Monitoring atmospheric emissions from oil spills must include a broad range of volatile organic compounds (VOC), including intermediate‐volatile and semivolatile compounds (IVOC, SVOC), which cause secondary organic aerosol (SOA) and ozone production. The Deepwater Horizon (DWH) disaster in the northern Gulf of Mexico during Spring/Summer of 2010 presented a unique opportunity to observe SOA production due to an oil spill. To better understand these observations, we conducted measurements and modeled oil evaporation utilizing unprecedented comprehensive composition measurements, achieved by gas chromatography with vacuum ultraviolet time of flight mass spectrometry (GC‐VUV‐HR‐ToFMS). All hydrocarbons with 10–30 carbons were classified by degree of branching, number of cyclic rings, aromaticity, and molecular weight; these hydrocarbons comprise ∼70% of total oil mass. Such detailed and comprehensive characterization of DWH oil allowed bottom‐up estimates of oil evaporation kinetics. We developed an evaporative model, using solely our composition measurements and thermodynamic data, that is in excellent agreement with published mass evaporation rates and our wind‐tunnel measurements. Using this model, we determine surface slick samples are composed of oil with a distribution of evaporative ages and identify and characterize probable subsurface transport of oil.

Experimental Research of Moisture Evaporation Process from Biomass in a Drying Chamber

Presented mass evaporation rate hardwood (birch, aspen, maple, poplar) derived from experimental studies. The dependence of temperature on evaporation mass rate and calculated the accommodation coefficient for the respective temperature ranges are obtained. Analyzed the temperature of drying conditions relevant species hardwood.

The accommodation coefficient of the liquid at temperatures below the boiling

Are carried out experimental investigation of the laws of vaporization at temperatures below the boiling point. Is determined the mass rate of evaporation of distilled water in large intervals of time at different temperatures in order to sound conclusions about the stationarity of the process of evaporation of the liquid in the conditions of the experiments performed, and also studied the effect of temperature on the rate of evaporation. Accommodation coefficient is defined in the mathematical expression of the law of Hertz- Knudsen for standart substance used in the experiments.

Numerical study of heat and mass transfer during evaporation of a turbulent binary liquid film

This paper deals with a computational study for analysing heat and mass exchanges in the evaporation of a turbulent binary liquid film (water-ethanol and water-methanol) along a vertical tube. The film is in co-current with the dry air and the tube wall is subjected to a uniform heat flux. The effect of gas-liquid phase coupling, variable thermophysical properties and film vaporization are considered in the analysis. The numerical method applied solves the coupled governing equations together with the boundary and interfacial conditions. The algebraic systems of equations obtained are solved using the Thomas algorithm. The results concern the effects of the inlet liquid Reynolds number and inlet film composition on the intensity of heat and mass transfer. In this study, results obtained show that heat transferred through the latent mode is more pronounced when the concentration of volatile components is higher in the liquid mixture .The comparisons of wall temperature and accumulated mass evaporation rate with the literature results are in good agreement.

A theoretical study of the spheroidal droplet evaporation in forced convection

Abstract In many applications, the shape of a droplet may be assumed to be an oblate spheroid. A theoretical study is conducted on the evaporation of an oblate spheroidal droplet under forced convection conditions. Closed-form analytical expressions of the mass evaporation rate for an oblate spheroid are derived, in the regime of controlled mass-transfer and heat-transfer, respectively. The variation of droplet size during the evaporation process is presented in the regime of shrinking dynamic model. Comparing with the droplets having the same surface area, an increase in the aspect ratio enhances the mass evaporation rate and prolongs the burnout time.

Investigation of Evaporative Mass Transfer with Turbulent-Forced Convection Air Flow over Roughness Elements

AbstractThe effect of obstruction in the form of creation of additional turbulence caused by roughness elements on evaporation rates and hence on the convective mass transfer coefficient has been investigated under varying conditions of air velocities and water temperatures. The respective ranges of flow Reynolds number and water temperature for this study were 20,000–120,000 and 30–50°C, respectively. The range of relative roughness height was 0.011–0.075. It has been found that there is a significant effect of the presence of roughness elements, and this effect is a strong function of flow Reynolds number and the relative roughness height of its obstructions. An empirical correlation has been developed to relate Sherwood number as a function of Reynolds number and relative roughness height to facilitate prediction of mass transfer and evaporation rate under varying Reynolds number and relative roughness height.

Development of parallel miniature bubble column bioreactors for fermentation process

AbstractBACKGROUNDIn recent years, bioprocess development has been used scaled down bioreactors, parallel operation and on‐line monitoring. In this study novel miniature bubble column bioreactors (MBCRs) have been developed. Reproducibility of the bioreactors, the effect of operational parameters and scale up to a conventional STR were studied.RESULTSFermentations in the parallel MBCRs were reproducible under the same conditions. Increasing the aeration rate had an insufficient effect on the specific growth rate (μ) of E. coli, but it led to an increase in the volumetric mass transfer coefficient (KLa) and evaporation rate. The oxygen uptake rate (OUR) remained constant at different aeration rates as well as μ. Increasing the temperature resulted in a significant increase in μ, KLa, evaporation rate and OUR. Control of the pH had a slight but sufficient effect on KLa. Scale up results with an equal KLa demonstrated good agreement between the MBCR and a conventional STR. According to the Damköhler number, the biochemical reaction was rate‐limited.CONCLUSIONHigh achievable KLa in the MBCRs and successful scale‐up suggested the present system was an efficient alternative to the stirred or shaken devices for high throughput cultivations. © 2014 Society of Chemical Industry

A simplified method on thermal performance capacity evaluation of counter flow cooling tower

Abstract The thermal performance capacity of a wet cooling tower is dominated by weather conditions, particularly ambient wet-bulb temperature. In this paper, the tower performance was predicted by a simplified model which was characterized by specification of a mass evaporation rate equation. The purpose of this study was to present a calculation that was accurate and simple to implement, and could be applied to evaluate acceptance tests for new towers, to monitor changes in tower performance as an aid in planning maintenance, and to predict tower performance under changed operating conditions. The results were validated and showed good agreement with experimental measurements. The results were also presented in simple formats that were easy to use and understand. These allowed reduction of test data and comparison of test results to design data. The method held a practical advantage for predicted tower thermal performance capability to which it was best suited when both flow rate and temperature of inlet water were near design conditions since it required neither the measurement of air flow rate nor the calculation of tower characteristic ( h mass A / L ) . The expected results of this study will make it possible to incorporate cooling tower design and simulation to evaluate and optimize the thermal performance of power plants for example.

Dependence of Spectral State Transition and Disk Truncation on Viscosity Parameter $\alpha $

Abstract A wealth of Galactic accreting X-ray binaries has been observed in both the low/hard and high/soft states. The transition between these two states has often been detected. Observations show that the transition luminosity between these two states is different for different sources, ranging from 1% to 4% of the Eddington luminosity $L_{\rm Edd}$. Even for the same source, the transition luminosity at different outbursts can be different. The transition can occur at luminosities from 0.0069 to 0.15 $L_{\rm Edd}$. In order to investigate the underlying physics, we study the influence of viscosity parameter $\alpha $ on the transition luminosity on the basis of the disk-corona model for black holes. We calculate the mass-evaporation rate for a wide range of viscosity parameters such as 0.1 $\le$$\alpha $$\le$ 0.9. Fitting the numerical results, we obtain fitting formulae for both the transition accretion rate and the corresponding radius as a function of $\alpha $. We find that the transition luminosity is very sensitive to the value of $\alpha $, $L/L_{\rm Edd}\propto\alpha^{2.34}$. For 0.1 $\le$$\alpha $$\le$ 0.6, the transition luminosity varies by two orders of magnitude, from 0.001 to 0.2$L_{\rm Edd}$. Comparing with observations, we find that transition luminosity can be fitted by adjusting the value of $\alpha $, and the model-determined values of $\alpha $ are mostly in the range of observationally inferred values. We also investigate the truncation of the disk in the low/hard state for some luminous sources. Our results agree roughly with the observations.

Application of computational fluid dynamics for LNG vapor dispersion modeling: A study of key parameters

The increased demand for Liquefied Natural Gas (LNG) has led to the construction of several new LNG terminals in the United States (US) and around the world. To ensure the safety of the public, consequence modeling is used to estimate exclusion distances. For LNG industry, the purpose of identifying these exclusion distances is to protect the public from being reached by flammable vapors during a release and they are determined by one-half of the Lower Flammability Limit (half LFL, 2.5% v/v). Since LNG vapors are heavier-than-air when released into atmosphere, it goes through several stages, which are respectively characterized as negative, neutral, and positively buoyant as it dilutes. To address this complex phenomenon, several simple models were developed and tested against large scale experimental data for the past three decades. This paper was derived from the development of design and safety specifications for LNG facilities based on experimental and theoretical research at Mary Kay O'Connor Process Safety Center (MKOPSC). Medium-scale LNG tests were performed at the Brayton Fire Training Field (BFTF), Texas A&M University to provide data for this specific research. Computational fluid dynamics (CFD) was used to perform consequence modeling for LNG release. The CFD code showed good agreement with the data collected during the November 2007 test performed at BFTF. This paper showed the simulation setup and the comparison with data collected for two scenarios: release on water and on dry concrete. Once the model was tuned against experimental data, it was used in a sensitivity analysis on parameters to assess the effects on the LFL distance and the concentration levels. Furthermore, three turbulence models were compared. The source term was composed of turbulence intensity at the source, LNG pool geometry, mass evaporation rate, and LNG pool area. The vapor dispersion parameters were wind velocity, sensible heat flux, and obstacles effects. It was concluded that at low wind velocity, the source term parameters strongly influenced the LFL distance and the concentration level. On the other hand, at high wind velocity, the source term parameter had a slight effect on the LFL distance and the concentration levels.

Effects of variable density for film evaporation on laminar mixed convection in a vertical channel

A numerical investigation was conducted to study mixed convection in a vertical parallel-plate channel with evaporation of thin liquid films on wetted walls. Air–water vapor and air–hexane vapor mixtures, assumed as ideal gases, are considered under various boundary conditions. Steady laminar, two-dimensional flows are examined in detail for large mixture density changes between the inlet and outlet sections of the channel. Comparisons with the usual problem formulations based on the Boussinesq approximation are discussed. The elliptic flow model used allow to predict flow reversal as well as recirculation cells in the entrance region. The evaporation of water and hexane into a downward laminar stream of dry air leads to various flow structures according to the interfacial mass fraction, W v,w , and differences in the molecular weights of the species. For water evaporation, the thermal and solutal forces are opposing. In the entrance region, evaporation produces a significant increase in axial velocity at the core region in comparison with pure forced flow. For W v,w larger than ≈0.2, upward velocities may be observed in the wall regions due to solutal buoyancy forces near the wetted surfaces. For hexane evaporation, the solutal force acts downward. Mass diffusion produces both a strong flow acceleration in the boundary layers and flow recirculations at the channel center for large mass evaporation rates.

THE X-RAY SPECTRAL ANALYSIS OF DWARF NOVA WZ Sge OBSERVED WITH ROSAT IN QUIESCENCE

X-ray spectral parameters were determined for WZ Sge observed with the ROSAT PSPC. The raw data were fitted with various spectral models and the best fit spectral models are found to be that of Raymond–Smith and Thermal Bremsstrahlung. The best fit temperature was estimated to be kT ~ 2.17 keV while the column density was found to be NH ~ 2.8 × 1020 cm -2. The estimated 0.1–2.4 keV flux was in the range of log F = -12 ergs cm -2 s -1. WZ Sge stars show long outburst recurrence times and weak X-ray emissions during the quiescence states. It is possible to lengthen repetition cycles by decreasing the viscosity parameter (α); however there still remains the question why α is so small, specifically for these objects. The Coronal Siphon Model of Meyer and Meyer–Hofmeister1 can explain these phenomenons successfully. For this reason, the equations of this model were applied to the results of spectral analysis. Using this model, the mass accretion rate, mass evaporation rate in corona and the radius of the corona were calculated to be 1014.48 gr yr-1, 10-5.4 gr cm-2 s-1 and 109.7 cm, respectively. The obtained values suggest that the corona model can indeed operate in WZ Sge system.

A cool disk in the Galactic Center?

We study the possibility of a cool disk existing in the Galactic Center in the framework of the disk-corona evaporation/condensation model. Assuming an inactive disk near the gravitational capture distance left over from an earlier evolutionary stage, a hot corona should form above the disk since there is a continuous supply of hot gas from stellar winds of the close-by massive stars. We study the interaction between the disk and the corona. Whether the cool disk can survive depends on the mass exchange between disk and corona which is determined by the energy and pressure balance. If evaporation is the dominant process and the rate is larger than the Bondi accretion rate in the Galactic Center, the disk will be depleted within a certain time and no persistent disk will exist. On the other hand, if the interaction results in hot gas steadily condensing into the disk, an inactive cool disk with little gas accreting towards the central black hole might survive in the Galactic Center. For this case we further investigate the Bremsstrahlung radiation from the hot corona and compare it with the observed X-ray luminosity. Our model shows that, for standard viscosity in the corona (), the mass evaporation rate is much higher than the Bondi accretion rate and the coronal density is much larger than that inferred from Chandra observations. An inactive disk can not survive such strong evaporation. For small viscosity () we find condensation solutions. But detailed coronal structure computations show that in this case there is too much X-ray radiation from the corona to be in agreement with the observations. From this modeling we conclude that there should be no thin/inactive disk presently in the Galactic Center. However we do not exclude that the alternative non-radiative model of Nayakshin ([CITE]) might instead be realized in nature and shortly discuss this question.

Study of interaction in spray between evaporating droplets and turbulence using second order turbulence RANS modelling and a Lagrangian approach

The objective of this work is to analyse the interaction between evaporating droplets and the turbulent flow of the carrier gas using a second order turbulence RANS modelling in an Euler-Lagrangian approach including two-way coupling. The analysis is performed in a vertical isopropanol polydispersed spray issuing into a co-flowing, heated air stream. The results mainly display the turbulence modulation effects besides the turbulent dispersion of evaporating droplets: 1) The influence of droplet diameter and interface transport on the gas phase turbulence as well as 2) The effect of the droplet evaporation on the mass and heat transfer processes are compared with experimental data. 3) The reciprocal influence of the modification of interface transport by turbulence, i.e., the influence of the turbulent fluctuations of different quantities (such as velocity, temperature, etc.) on the droplet evaporation (through the mass and heat evaporation rates, the droplets diameter distribution) are computed and discussed.

X-RAY SPECTRAL ANALYSIS OF SU UMa TYPE DWARF NOVAE OBSERVED WITH ROSAT

X-ray spectral parameters were determined for eight SU UMa type Dwarf Novae observed with the ROSAT PSPC. The raw data were fitted with various spectral models and the best fit spectral models are found to be that of Raymond–Smith and Thermal Bremsstrahlung. The best fit temperatures were estimated to be between kT ~ 1.1-1.8 keV while the Column Densities were found to be between NH ~ 2.4×1020-4.1×1020 cm -2. The estimated 0.1-2.4 keV fluxes were in the range of log FX=-13 to -11 ergs cm-2 s-1. FX/F UV and FX/F opt rates were calculated to be between ~0.09 and ~0.37. This shows that most of the energy is radiated in the Optical and Ultraviolet band from the accretion disk in the quiescent state. Many of the SU UMa type Dwarf Novae show an Ultraviolet lag in their outburst spectrum, the Coronal Siphon Flow Model of Meyer and Meyer-Hofmeister may explain this phenomenon. This model proposes a corona at the boundary layer of a system when it is a quiescent state and suggests that some parts of the X-rays come from the corona. For these reasons, the equations of this model were applied to the results of the spectral analysis. Using this model, the mass accretion rates, the mass evaporation rates, and the radii of the coronas were calculated to be ~10-12.3-10-11.3 M⊙ yr -1, ~10-6.5-10-5.5 g cm -2 s -1 and ~109.1-109.9 cm , respectively. The pressures in the coronas were less than ~1200 g cm -2 s -1 for (z) up to ~10×109 cm . The obtained values suggest that the Corona model can indeed operate in SU UMa type Dwarf Novae.

Two‐Temperature Coronal Flow above a Thin Disk

We extended the disk corona model to the inner region of galactic nuclei by including different temperatures in ions and electrons as well as Compton cooling. We found that the mass evaporation rate, and hence the fraction of accretion energy released in the corona, depend strongly on the rate of incoming mass flow from the outer edge of the disk, a larger rate leading to more Compton cooling, less efficient evaporation, and a weaker corona. We also found a strong dependence on the viscosity, with higher viscosity leading to an enhanced mass flow in the corona and therefore more evaporation of gas from the disk below. If we take accretion rates in units of the Eddington rate, our results become independent of the mass of the central black hole. The model predicts weaker contributions to the hard X-rays for objects with higher accretion rate like narrow-line Seyfert 1 galaxies, in agreement with observations. For luminous active galactic nuclei, strong Compton cooling in the innermost corona is so efficient that a large amount of additional heating is required to maintain the corona above the thin disk.