E. Otto

FORMATION OF SULPHURIC ACID AEROSOLS AND CLOUD CONDENSATION NUCLEI: AN EXPRESSION FOR SIGNIFICANT NUCLEATION AND MODEL COMPRARISON

Abstract A new analytical expression has been derived to predict atmospheric conditions where homogeneous water–sulphuric acid nucleation will have a significant effect on aerosol and cloud condensation nuclei population. In the expression, the condensational sink due to pre-existing aerosol particles and source due to chemical production of sulphuric acid have been taken into account. The analytical expression has been derived using a sectional aerosol dynamic model including nucleation, condensation, coagulation, deposition and sulphuric acid formation in the gas phase. In the present study we have also compared the sectional model with modal and monodisperse models. All models may be used for predicting the onset of significant new particle formation. However, the computationally more efficient models—monodisperse, modal, and sectional with low number of sections—over- or underpredict particle formation in some situations.

The log-normal size distribution theory of brownian aerosol coagulation for the entire particle size range : part I analytical solution using the harmonic mean coagulation kernel

Abstract Brownian aerosol coagulation was studied theoretically using the moment method of log-normal size distribution functions. An analytic solution to the size distribution of a coagulating aerosol was derived. In order to cover the entire size range the harmonic mean of the near-continuum and the free-molecule coagulation coefficient were applied. Therefore, the analytic solution is valid for the entire particle size range, i.e. covering from the free-molecule regime, via both the transition and the near-continuum regimes, to the continuum regime. The present work represents the first analytical solution to the Brownian aerosol coagulation problem that addresses the entire particle size range.

Thermophoretical and diffusional particle transport in cooled laminar tube flow

Abstract A highly accurate dimensional and a less accurate non-dimensional model to describe particle transport due to combined convection, diffusion and thermophoresis in cooled laminar tube flows are presented. To verify the dimensional model, an experimental setup was built. Results determined by applying the model to describe the particle transport in the experimental setup are compared with the experimental data gained. The influences of different fluid mechanical and aerosol dynamical effects (e.g. temperature dependence of the material properties, particle diffusion, particle concentration profiles) on particle deposition are discussed. Applying the less accurate non-dimensional model a new thermophoretic parameter was found and a simple approximation formula to calculate the total thermophoretic deposition efficiency is suggested. Results for axial deposition profiles considering particle transport due to convection and thermophoresis as well as convection, diffusion and thermophoresis are presented.

Brownian coagulation of submicron particles

Individual particles suspended in a fluid collide by various mechanisms such as random Brownian motion of particles, differential settling velocities, flow turbulence and by differential velocity gradients in laminar flow. Among these mechanisms, coagulation due to Brownian motion is an important particle growth mechanism in situations where small aerosol particles at a high concentration (as in flame reactors) or long-term behavior of suspended particles (as in the atmosphere) are concerned. In this paper the dynamical aerosol process—Brownian coagulation—is reviewed. The most often used formulas for describing the collision rate over the entire particle size regime are presented in a general form. Numerical modeling techniques used to describe the changes of the size distribution due to the coagulation process are described and discussed. Available analytical solutions are summarized.

Particle transport in sampling lines used in fire detection systems

Abstract For certain application areas in fire detection, air sampling systems are used which sample at different locations. The sampled air is transported to one fire detector. The aerosol coming from a starting fire, transported to at least one of the openings of the pipe system, is modified mainly because of non-representative sampling at the intake, particle losses in the pipe and dilution by sampled air from other openings. These changes of the aerosol during transport for a model system designed using design rules given by the manufacturer, are calculated. The main goal of this article is to give information regarding which particle size range a sampling is possible for, to impart α feeling about problems which may occur. For very small particles ( 5 μm, the particle losses become important. However, dilution is the most important factor. The reduction in concentration by using a multiple sampling system can be counteracted if the alarm level of the detector is reduced correspondingly. In order to guarantee the same detection level, the alarm level for the investigated model system has to be reduced to less than 1·8% of the alarm level without a sampling pipe system.