Evaporation Of Water Vapor Research Articles

Effect of non-equilibrium evaporation and condensation on bubble dynamics near the sonoluminescence threshold

The kinetic equation of evaporation and condensation of water vapour at the bubble wall is calculated numerically in order to investigate the non-equilibrium effect of evaporation and condensation. The liquid temperature at the bubble wall is also calculated as a function of time by estimating the heat flux at the bubble wall. Calculations are performed under a single-bubble sonoluminescence condition. It is clarified that the partial pressure of water vapour is identical to the saturated vapour pressure except at bubble collapse. At a strong collapse, the partial pressure of water vapour differs an order from the saturated vapour pressure of the heated liquid layer at the bubble wall. It is also clarified that most of all the vapour molecules (H 2O) undergo chemical reactions at the strong collapse.

Chemical Reactions in a Sonoluminescing Bubble

Rates of chemical reactions in an air bubble are calculated numerically under a condition of the single-bubble sonoluminescence (SBSL) and that of non-light-emission. In the calculations, effect of non-equilibrium evaporation and condensation of water vapor at the bubble wall and that of thermal conduction both inside and outside the bubble are taken into account. Numerical calculations reveal that appreciable amounts of OH, H 2 O 2 , HO 2 , O 3 , H 2 , H, and O molecules are created in a bubble under the condition of SBSL. The amounts of chemical products containing nitrogen such as NO x , NH x , and HNO x are much less than those of the above products at least in the first few acoustic cycles. Numerical calculations also reveal that no chemical reactions take place under a condition of non-light-emission. Connection with sonoluminescence is also discussed.

Large-Scale Atmospheric Moisture Cycling As Evaluated from NMC Global Analysis and Forecast Products

Abstract The broadscale aspects of the annual cycle of monthly mean global water vapor flux, flux divergence, evaporation, and precipitation derived from the National Meteorological Center (NMC) global analysis and forecast products were examined with two objectives in mind: 1) a critical evaluation of the usefulness of recent NMC products for descriptive and diagnostic studies of the global hydrological cycle and in the process and 2) to provide additional information on the behavior of the annual cycle of selected hydrological parameters over the globe in general and over the United States in particular. The 2-year period August 1991–July 1993, was chosen for study. The global-scale characteristics of the NMC vertically integrated vapor flux fields are described in terms of the rotational and divergent components of the stationary and transient parts of the vapor flux field. Values of the zonally averaged meridional vapor flux derived from the NMC analyses are broadly similar to those presented by Peixo...

Large-Scale Atmospheric Moisture Transport as Evaluated in the NCEP/NCAR and the NASA/DAO Reanalyses

Abstract Large-scale aspects of the atmospheric moisture transport and the overall moisture budget we studied using data from the National Centers for Environmental Prediction (NCEP) reanalysis. Our objective is to critically evaluate the usefulness of the reanalysis products for studies of the global hydrologic cycle. The study period is from January 1985 to December 1993. Monthly mean water vapor transport, evaporation, and precipitation are compared to the NASA Data Assimilation Office (DAO) reanalysis for roughly the same period and with satellite estimates and station observations. Comparisons of the moisture flux fields form the NCEP and the DAO reanalyses show general agreement in most aspects, but there are regional differences. Discrepancies in tropical moisture transport are largely due to uncertainties in the divergent winds. The DAO reanalysis shows a weaker Hadley circulation and weaker cross-equatorial flow, particularly during the Northern Hemisphere winter. Global patterns of evaporation f...

The Regional Particulate Matter Model: 1. Model description and preliminary results

The Regional Acid Deposition Model has been modified to create the Regional Particulate Model, a three‐dimensional Eulerian model that simulates the chemistry, transport, and dynamics of sulfuric acid aerosol resulting from primary emissions and the gas phase oxidation of sulfur dioxide. The new model uses a bimodal lognormal distribution to represent particles in the submicrometer size range. In addition to including the horizontal and vertical advection and vertical diffusion of the aerosol number concentration and sulfate mass concentration fields, the model now explicitly treats the response of the distribution parameters to particle coagulation within and between the modes, condensation of sulfate vapor onto existing particles, formation of new particles, evaporation and condensation of ambient water vapor in the presence of ammonia, and particle‐size‐dependent dry deposition. The model has been used to study how the degree of sulfuric acid neutralization by ambient ammonia affects the total aerosol concentrations and particle size distributions over eastern North America. Preliminary results for three representative locations, rural, near‐source, and nominal downwind of source, show that the effect is greatest for the rural and smallest for the near‐source regions, which corresponds with the largest and smallest values, respectively, of ammonium‐to‐sulfate molar ratios. The results indicate that the model could provide a tool for investigating the effects of various pollution control strategies, as well as new or alternative formulations of important aerosol processes.

Effects of thermal conduction on bubble dynamics near the sonoluminescence threshold

A simple model of bubble dynamics is constructed in which effects of thermal conduction and those of evaporation and condensation of water vapor are included. Results of numerical calculations when a bubble is irradiated by an ultrasonic wave reveal that the effect of thermal conduction is considerable. The calculated results fit with the experimental data of the radius–time curve much more satisfactorily than those by a model without thermal conduction. It is also concluded that a bubble transduces the energy of the acoustic wave into heat. Numerical calculations also reveal that the partial pressure of water vapor in a bubble differs considerably from the saturated vapor pressure especially at collapse of the bubble. Connection with sonoluminescence is also discussed.

Convective heat and mass transfer along an inclined heated plate with film evaporation

The purpose of this work is to investigate the heat and mass transfer characteristics along an inclined heated plate over which the water at room temperature flows downward as a film. To model the detailed transport processes special attention is drawn to the phase equilibrium and gas-liquid interface matching conditions. An implicit finite difference method is employed to solve the coupled governing equations for liquid film and gas flow together with the interfacial matching conditions. Evaporation of water vapor into the gas stream is examined for various conditions. The results clearly show the importance of the latent heat transport connected with film vaporization at the gas-liquid interface. In addition, it is found that an increase in inclined angle φ, inlet liquid film thickness δ or free stream velocity ϑ causes reductions in the wall and interfacial temperatures.

Identification of heat‐transfer processes during soil cooling, freezing, and thaw in central alaska

AbstractHourly time series of temperature and a surrogate measure of the soil water ionic (solute) concentration were obtained in the upper 50 cm of soil from two adjacent sites in central Alaska from August 1991 to May 1992. One site is located in a ground water seepage zone and is characterized by seasonal freezing of the upper soil. The other site is located over a body of permafrost. The time series, used simultaneously, display a unique signature diagnostic of the operative conductive and non‐conductive heat‐transfer process. During soil cooling in autumn, internal distillation (concurrent evaporation, vertical transport, and condensation of water vapour in soil column) moderates heat transfer in the active layer. A [zero curtain] develops in winter and persists for three months; maintenance of this isothermal layer is associated with water advection and internal distillation within the unfrozen zone. Conductive heat transfer is not possible in the isothermal layer during this period but dominates during late winter following soil freezing and closure of the zero curtain. Warming of the active layer in spring occurs nearly instantaneously and results from infiltration of snow cover meltwater and downward vapour migration. In contrast, water saturation of pore space at the seepage site inhibits vertical migration of vapour and water.

Microphysical modeling of cirrus: 1. Comparison with 1986 FIRE IFO measurements

We have used a one‐dimensional model of cirrus formation to study the development of cirrus clouds during the 1986 First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) intensive field observations (IFO). The cirrus model includes microphysical, dynamical, and radiative processes. Sulfate aerosols, solution drops, ice crystals, and water vapor are all treated as interactive elements in the model. Ice crystal size distributions are fully resolved based on calculations of homogeneous freezing nucleation, growth by water vapor deposition, evaporation, coagulation, and vertical transport. We have focused on the cirrus observed on November 1, 1986. Vertical wind speed for the one‐dimensional simulation is taken from a mesoscale model simulation for the appropriate time period. The mesoscale model simulation suggested that strong upward motions over Wyoming and subsequent horizontal transport of upper level moisture were responsible for the cirrus observed over Wisconsin on this date. We assumed that our one‐dimensional model could be used to represent a vertical column moving from Wyoming to Wisconsin over a period of several hours. Ice crystal nucleation occurs in our model in the 8 to 10‐km region as a result of the strong updrafts (and cooling) early in the simulation. Growth, coagulation, and sedimentation of these ice crystals result in a broad cloud region (5–10 km thick) with an optical depth of 1–2 after a few hours, in agreement with the FIRE measurements. Comparison with aircraft microphysical measurements made over Wisconsin indicates that the simulation generated reasonable ice water content, but the predicted ice number densities are too low, especially for radii less than about 50 μm. Sensitivity tests suggest that better agreement between simulated and observed microphysical properties is achieved if the nucleation rate is higher or stronger vertical mixing (perhaps associated with multidimensional motions) is present.

Microphysical Effects on Cloud Water Acidity: A Case Study in a Nonprecipitating Cloud Event Observed at Mt. Mitchell, North Carolina

There is increasing recognition that deposition of cloud water may significantly contribute to the decline of forest. In this paper, chemical and microphysical data obtained at Mt. Mitchell, North Carolina during one orographic, non-precipitating cloud event are examined to investigate the relationship between temporal variation of cloud acidity and cloud microphysics. The cloud acidity was substantially higher than in precipitating cloud events. Sulfate, nitrate, ammounium and hydrogen ions were the major constituents. The results suggest that water vapor condensation and evaporation of cloud droplets are the dominant processes in determining the total concentration of cloud water. 18 refs., 6 figs.

Ice-forming nuclei in transvaal, Republic of South Africa

Concentrations of ice-forming nuclei (IFN) active by sorption and by condensation-followed-by-freezing were assessed during February and March, 1986 in Transvaal, Republic of South Africa. Concentrations were found to be very low; at S w just below 0% and at 2%, IFN concentrations below 10 m −3 at a temperature of −15°C were present on 44 and 28% of the days, respectively. Number concentrations and the rates of activation of IFN active through condensation-followed-by-freezing were found to be larger than those active by sorption. IFN active by condensation-followed-by-freezing usually nucleated ice at higher temperatures than the IFN active by sorption. The number concentration of IFN active through condensation-followed-by-freezing was found to be independent of water vapor supersaturation over liquid water in the range between 0 and 6% in the temperature range from −12° to −22°C. Evaporation and condensation of water vapor on IFN active through condensation-followed-by-freezing did not deactivate them.

Effects of wetted wall on natural convection heat transfer between vertical parallel plates

This study proposes to investigate the effects of latent heat transfer, in association with the water vapor evaporation from the wetted channel wall, on the natural convection heat transfer. Major nondimensional groups identified areGr T ,Gr M ,Pr, Sc andφ. Results are especially presented for an air-water system under various heating conditions. The influences of channel length, wetted wall temperatures and the relative humidity of the moist air in the ambient on the heat and mass transfer are examined in great detail. Tremendous enhancement in heat transfer due to the exchange of the latent heat of vaporization is clearly demonstrated.

Physics in The Field

One of the earliest and most important contributions of physics to agriculture was in defining how water evaporates from crops – of considerable importance in planning the amounts and timing of irrigation requirements. Some 40 years ago H L Penman of Rothamsted Experimental Station combined the concepts of energy-driven evaporation (considering the solar and thermal radiation balance) and diffusion of water vapour down a humidity gradient from crop to atmosphere.

Organic films on atmospheric aerosol particles, fog droplets, cloud droplets, raindrops, and snowflakes

Surface‐active organic molecules are common constituents of atmospheric aerosol particles, raindrops, and snowflakes. If these compounds are present as surface films, transfer of gases into the atmospheric water systems could be impeded, evaporation could be slowed, and the aqueous chemical reactions could be influenced. To investigate these possibilities, we have reviewed the chemical literature pertaining to organic films on aqueous surfaces: their composition, structure, properties, and effects. We then review the surface‐active organic compounds in atmospheric water. We report the results of new measurements of surface tension of aqueous solutions of common atmospheric organic compounds (β‐pinene, n‐hexanol, eugenol, and anethole) and demonstrate that the compounds produce films with properties similar to those of the more well known surfactants. We conclude that organic films are probably common on atmospheric aerosol particles and that they may occur under certain circumstances on fog droplets, cloud droplets, and snowflakes. If present, they will increase the lifetimes of aerosol particles, fog droplets, and cloud droplets, both by inhibiting water vapor evaporation and by reducing the efficiency with which these atmospheric components are scavenged. The presence of the films will not cause a significant reduction of solar radiation within the aqueous solution. It appears likely, however, that the transport of gaseous molecules into and out of the aqueous solution will be impeded by factors of several hundred or more when organic films are present. Since incorporated gas molecules provide much of the oxidizing potential of atmospheric water droplets, the organic films will play a major role in droplet chemistry by strongly inhibiting solution oxidation.

Chemical Composition of Acid Fog

Fog water collected at three sites in Los Angeles and Bakersfield, California, was found to have higher acidity and higher concentrations of sulfate, nitrate, and ammonium than previously observed in atmospheric water droplets. The pH of the fog water was in the range of 2.2 to 4.0. The dominant processes controlling the fog water chemistry appear to be the condensation and evaporation of water vapor on preexisting aerosol and the scavenging of gas-phase nitric acid.

The absorption and evaporation of tritiated water vapor by soil and grassland

The absorption and loss of tritiated water (HTO) vapor at bare soil and grass surfaces were studied in laboratory and field experiments. The exchange involves turbulent mixing in the air and diffusion within the soil. In short exposures it was found that uptake by moist soil was controlled by atmospheric mixing and was described by an exchange velocity of about 1 cm s−1. The exchange velocity was a little smaller for air-dried soil and grass surfaces. For exposure times exceeding a few minutes re-evaporation reduced the rate of net uptake, but the total amount deposited continued to increase as the HTO diffused deeper into the surface. The diffusion coefficient for HTO in soil was investigated in the laboratory and a simple equation was derived to predict the effective diffusion coefficient. Tritiated water, absorbed during a brief exposure, evaporated during several weeks. Its behavior was described by the diffusion equation, but unexplained discrepancies were found in apparent diffusion coefficients in field conditions. Rain washed the activity into the soil and impeded evaporation. Most of the HTO vapor interacts with the surface within two or three days following a low level release. The effect of the surface exchange on the distribution of dose following a release of HTO vapor may be large, but will depend on the weather over a period of weeks and is difficult to foresee.

V.H.F and u.h.f. field-strength variations corresponding to river beds

The mechanisms of propagation over land and over sea, respectively, are reviewed to detect the causes of the field-strength maximum in the afternoon, in the former case, and of the corresponding minimum in the latter case. The analysis of the received power for two transhorizon links over land along a river bed indicates an effect of the river bed on the afternoon field-strength rise, and a three-part nocturnal trend of field strength. These properties are explained in terms of evaporation and condensation processes of water vapour near the ground, and also by-the superposition of the continental and oceanic types of diurnal variations of field strength. They are in agreement with fading characteristics on line-of-sight links along river beds.

The dynamics and energetics of mature tropical cyclones

Rapid progress toward the understanding of tropical cyclones has been made during the past 10 years, largely as a result of the development of numerical models. The dynamics and energetics of the mature tropical cyclone are reviewed in this article. First, the pressure, wind, temperature, and moisture structures of the hurricane are summarized. Then a scale analysis is applied over four separate regions of the hurricane domain to emphasize the most important dynamic processes in each region. The energetics of the tropical cyclone is examined in detail. The storm is shown to be a self‐sustaining quasi‐steady thermodynamic heat engine that is driven primarily by latent heat release. The relationship between latent heating and production of kinetic energy is discussed from the available potential energy viewpoint. The possibility of a steady state axisymmetric hurricane in a closed domain is considered. Although such a model appears possible from an energetic viewpoint, angular momentum considerations reveal that a steady axisymmetric closed system is impossible on any scale. For small domains (radius ∼500 km), in which axisymmetric circulations are possible, the system must be open in order that angular momentum be imported from the environment. For larger domains, axisymmetric circulations are unrealistic. The water vapor budget of the hurricane is examined to indicate the relative importance of evaporation and horizontal transport of water vapor in maintaining the moisture supply. Evaporation is shown to be an important percentage of the precipitation in the mature storm. Finally, the numerical modeling of tropical cyclones is summarized. An important problem in the development of hurricane models is the treatment or parameterization of the cumulus cloud scale and the hurricane scale interactions. The implications of the concept of conditional instability of the second kind on hurricane modeling are discussed. Results from several axisymmetric (two‐dimensional) hurricane models, including attempts to simulate hurricane modification experiments, are summarized. Some recent results from a time‐dependent three‐dimensional hurricane model are presented.

Mass and heat transfer relations in evaporation through porous membranes

AbstractThis study concerns rates of evaporation and mass transfer of water vapor from a heated salt solution through a water repellent porous membrane to a cooled water condensate. This transfer is a result of temperature differences and corresponding vapor pressure differences across the membrane. Three groups of experiments were carried out which indicate that the major factor influencing the rates of transfer is diffusion through a stagnant gas in the membrane pores. However, an equation considering film heat transfer coefficients, membrane thermal conductivity, and an empiricial correction based on temperature driving force appears to be necessary for representing all the data. The empirical correction appears to be related to internal condensation and possibly diffusion along surfaces.

A NUMERICAL EXPERIMENT ON THE DEVELOPMENT OF A TROPICAL CYCLONE

Abstract A model of a tropical cyclone is constructed which is based upon conservation of momentum, mass,water vapor and heat in the hydrostatic system. The horizontal and vertical eddy-exchange processes for momentum, moisture and heat are included in the equations in order to incorporate the planetary frictional (Ekman) layer into the model. The effects of the surface boundary (Prandtl) layer are simulated by the boundary conditions for the equations, which permit the evaluation of surface stress, the sensible heat transport and the evaporation of water vapor from the earth surface. The energy sources of the model are the latent heat of condensation released during the ascent of moist air and the sensible heat transported from the ocean surface. The formulation of the finite-difference equations for the axially-symmetric case is presented, together with an examination of the computational stability. By means of a high-speed computer, two independent computations with and without the supply of latent hea...