Aerosol formation from heat and mass transfer in vapour–gas mixtures

1985 ◽  
Vol 398 (1815) ◽  
pp. 307-339 ◽  
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Transport ◽  
Water Vapour ◽  
Formation Rate ◽  
Aerosol Size Distribution ◽  
Atmospheric Effects ◽  
Aerosol Formation ◽  
Pressurized Water ◽  
Small Diffusion

Heat and mass transfer equations and their coupling to the equation for the aerosol size distribution are examined for mixtures in which pressure changes are slow. Equilibrium between an aerosol and its surrounding vapour is shown to be generally fast so that vapour supersaturations are small. Diffusion and conduction control evaporation and condensation on aerosols so that the sign of the aerosol growth term can be determined by the ratio of their relative rates, given by the Lewis number, Le ; for example where Le < 1, as for water vapour–air mixtures, aerosols may evaporate as the mixture is cooled. A ‘condensation number’, Cn ( T ), representing the ratio of the rate of heat transport to that of latent heat by vapour diffusion, and which is a strong function of temperature, is introduced to describe the other main controlling physical effect in aerosol formation. Where Cn ≪ 1, as for high-temperature water vapour–air mixtures, the proportion of vapour that can condense as an aerosol is very small. For a fixed total heat transport rate, the maximum aerosol formation rate occurs near Cn ( T ) = 1, which is at T ≈ 4°C for water vapour–air mixtures at 1 atm pressure (101 325 Pa). Specific results in terms of Cn and Le are obtained for the proportion of vapour condensing as an aerosol during the cooling and heating of a mixture in a well-mixed cavity. The assumption of allowing no supersaturations, the validity of which is examined, is shown to lead to maximum aerosol formation. For water vapour–air mixtures predictions are made as to temperature regions in which aerosols will evaporate or not form in cooling processes. The results are also qualitatively applied to some atmospheric effects as well as to water aerosols formed in the containment of a pressurized water reactor following a possible accident. In this context the present conclusion that the whereabouts of vapour condensation is controlled by heat and mass transfer contrasts with previous assumptions that the controlling factor is relative surface areas.

Experimental and Numerical Research on Steam Direct Contact Condensation Process in Automatic Depressurization System of AP1000

2020 ◽  
Author(s):  
Yuhao Zhang ◽  
Li Feng ◽  
Zhimin Qiu ◽  
Jingpin Fu ◽  
Daogang Lu
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Direct Contact ◽  
Cfd Simulation ◽  
Condensation Process ◽  
Validation Data ◽  
Numerical Work ◽  
Pressurized Water ◽  
Temperature And Pressure ◽  
Contact Condensation

Abstract In the third generation pressurized water reactor AP1000 plant, the Automatic Depressurization System (ADS) is one of the most important passive safety system. However, the steam Direct Contact Condensation (DCC) microscopic mechanisms are very complicated, which are not very clear yet. Moreover, the high-pressure and high-temperature experiment is very expensive to be conducted for many different test conditions. So in the present work, both the experimental and numerical methods are employed to investigate the steam DCC behavior. The steam DCC experimental bench has been built up, and the key parameters including the flow patterns and steam core temperature distributions are measured to provide validation data for the numerical results. In aspect of the numerical work, CFD simulation on the steam condensation is conducted. The heat and mass transfer process is simulated through the three-dimension commercial software FLUENT 16.0. Some of the key heat and mass transfer correlations are added by User Defined Function (UDF). The key parameters including the condensation steam fraction, temperature, and pressure, etc. are analyzed, which reflect the major heat transfer characteristics. According to the results, the expansion-compression-steam tail could be observed in both the numerical and experimental results. In essential, the steam fraction, temperature, and pressure distributions are determined by the equilibrium and transformation between the thermal dynamic energy and kinetic energy. The results provide working references for the practical ADS steam spraying condensation process in AP1000 reactor.

scholarly journals Thermal effects of high energy and ultrafast lasers

2015 ◽  
Author(s):  
◽  
Nazia Afrin
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Heat Transport ◽  
Phonon Scattering ◽  
Heated Surface ◽  
High Energy ◽  
Electron Interaction ◽  
Energy Laser ◽  
High Energy Laser

Heat transfer describes the exchange of thermal energy, between physical systems depending on the temperature and pressure, by dissipating heat. The fundamental modes of heat transfer are conduction or diffusion, convection and radiation. Heat and mass transfer are kinetic processes that may occur and be studied separately or jointly. Studying them apart is simpler, but both processes are modeled by similar mathematical equation in the case of diffusion and convection. There are complex problems where heat and mass transfer processes are combined with chemical reactions, as in combustion. The resulting behavior of heat transport in microscale will be very different from macroscale heat transfer based on the averages taken over hundreds of thousands of grains (in space) and collision (in time). From the microscopic point of view, the process of heat transport is governed by phonon-electron interaction in metallic films and by phonon scattering in dielectric films, insulators and semi-conductors. For extremely heated surfaces by high energy laser pulse, it is very difficult to measure temperature of flux at the heated surface because of the unendurable capacity of the conventional sensors. Laser is the tool of choice when drill holes ranging in diameter from several millimeters to less than one micro-meter. Instead of having advanced melting and resolidification modeling process recently, the inherent uncertainties of the input parameters can directly cause unstable characteristics of the output results which means the parametric uncertainties may influence the characteristics of the phase change processes (melting and resolidification) which will affect the predictions of interfacial properties i.e., temperature, velocity and mainly the location of solid-liquid interface. All of those processes can be considered under high energy laser interaction with materials.

scholarly journals Numerical and experimental investigation of heat and mass transfer within bio-based material

2019 ◽  
Vol 23 (1) ◽  
pp. 23-31 ◽  
Author(s):  
Mounir Asli ◽  
Frank Brachelet ◽  
Alexis Chauchois ◽  
Emmanuel Antczak ◽  
Didier Defer
Keyword(s):  
Mathematical Model ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Water Vapour ◽  
Test Facility ◽  
Good Prediction ◽  
Vapour Permeability ◽  
Hygroscopic Properties ◽  
Good Concordance ◽  
The Mathematical Model

In this paper, the coupled heat and mass transfer within porous media has been studies. First, the studied materials have been characterized experimentally and than evaluated their thermal properties, namely thermal conductivity and specific heat in different states (dry-wet). The hygroscopic properties, namely water vapour permeability, water vapour sorption. At second time, we present and validate the mathematical model describing heat and mass transfer within bio-based materials, by the confrontation with the experimental results. The materials properties obtained from the characterisation part are used as model?s input parameters. Moreover, a test facility is mounted in the laboratory in order to compare the numerical and experimental data. The founded results show a good concordance between the simulated and measured data. According to this results the mathematical model of Philip and de Vries gives a good prediction of hygrothermal behaviour of bio-based material. This model will allow us to save money and time of the experimental part in the future.

scholarly journals Static Conversion of a Salinity Difference into a Temperature Difference: A Heat and Mass Transfer Investigation

2017 ◽  
Author(s):  
Matteo Morciano ◽  
Matteo Fasano ◽  
Pietro Asinari ◽  
Eliodoro Chiavazzo
Keyword(s):  
Mass Transfer ◽  
Sodium Chloride ◽  
Heat And Mass Transfer ◽  
Heat Transport ◽  
Salinity Gradient ◽  
Ambient Pressure ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Chloride Water ◽  
Salinity Difference

In this work, we experimentally investigate mass and heat transport phenomena ina modular device while converting a solution salinity difference into a temperature difference.Operations occur under fixed total ambient pressure and without mechanical moving parts, thusrealizing a fully static conversion. Provided that a constant salinity gradient can be imposed, theproposed device is able to generate a steady cooling capacity. Here, we purposely operate withenvironmentally benign and easily accessible sodium chloride water solutions only. A numericalmodel is finally elaborated, validated and used to explore a wider range of possible deviceconfigurations and operating conditions.

scholarly journals Validation of the heat and mass transfer models within a pressurized water reactor containment using the International Standard Problem No. 47 data

2012 ◽  
Vol 33 (2) ◽  
pp. 23-46 ◽  
Author(s):  
Tomasz Bury ◽  
Jan Składzień ◽  
Adam Fic
Keyword(s):  
Experimental Data ◽  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Pressurized Water Reactor ◽  
Two Phase ◽  
Pressurized Water ◽  
Water Reactor ◽  
International Standard ◽  
Standard Problem ◽  
Transfer Models

Abstract A lumped parameter type code, called HEPCAL, has been worked out in the Institute of Thermal Technology of the Silesian University of Technology for simulations of a pressurized water reactor containment transient response to a loss-of-coolant accident. The HEPCAL code has been already verified and validated against available experimental data, which in fact have been taken from separate effect tests mainly. This work is devoted to validation of the latest version of the HEPCAL code against experimental data from more complex tests. These experiments have been performed on three different test rigs (called TOSQAN,MISTRA and ThAI) and a part of them became the basis of the International Standard Problem No. 47 (ISP-47) dedicated to containment thermal-hydraulics. Selected experiments realized within the framework of the ISP-47 project have been simulated using the HEPCAL-AD code. The obtained results allowed for drawing of some important conclusions concerning heat and mass transfer models (especially steam condensation), two-phase flow model and buoyancy effects.

Paper 5: Direct Contact Heat and Mass Transfer Studies with Water Droplets in a Water Vapour–Air Mixture

1969 ◽  
Vol 184 (7) ◽  
pp. 1-5
Author(s):  
A. Porteous
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Water Vapour ◽  
Direct Contact ◽  
Droplet Diameter ◽  
Experimental Information ◽  
Water Droplets ◽  
Contact Heat ◽  
Process Industries ◽  
Mass Transfer Studies

The design of cooling and dehumidification towers is important for many process industries. This paper reports the results of a theoretical and experimental investigation on the direct contact heat and mass transfer characteristics of water droplets in counter-current flow through a water vapour-air mixture which simulates the stream to be dehumidified. The range of temperatures and dew points studied was 250–410°F and 85–112°F respectively. The effect of parameters such as contact path length, water droplet to water vapour-air mass ratios, droplet diameter, and entrainment are studied. The experimental information is then utilized in the design of a dehumidification tower.

Sign in / Sign up

Export Citation Format

Share Document