COAGULATION AND DEPOSITION OF ULTRAFINE AEROSOLS IN TURBULENT PIPE FLOW

The primary objective of this thesis is to perform a theoretical and experimental study of the simultaneous coagulation and diffusion of ultrafine particles (diameter < 0.02 (mu)m) in turbulent pipe flow. As part of this study a systematic investigation of the aerosol measuring instruments used has been undertaken. The instruments studied include a condensation nucleus counter, a screen diffusion battery, and a sample extraction dilution system.; In Chapter 2 calibration data for the TSI continuous flow condensation nucleus counter are given with a recommendation to improve the counting efficiency in the single particle counting mode. Data for particle diameters from 0.0020 to 0.50 (mu)m are given and used to support discussion of the instrument behavior. Experimental results are compared to theory and the discrepancies discussed.; In Chapter 3 a diffusion battery constructed of layers of metal screens is described. Metal screens are used because they are readily available in a variety of mesh sizes. In this chapter an expression for calculating aerosol penetration through screens is presented. Experimental data supporting this expression are then presented. The theoretical expression for aerosol penetration through the screens as a function of particle size may be used for designing screen diffusion batteries.; Metal screen diffusion batteries are compact, versatile, and relatively easy to construct. For these reasons, a number of recent studies have focused on the design of and interpretation of data from these instruments. In this chapter a screen diffusion battery is designed using the theoretical expression presented.; Chapter 4 describes an aerosol sample extraction and dilution system. In gas and aerosol measurement, dilution of a sample is often necessary to bring a high initial particle concentration to within the range of the measuring instrument or to quench chemical reactions or stop particle agglomeration. This chapter describes a sample extraction and dilution system (SEDS) designed to sample a high concentration (10('10) particles/cm('3)) of ultrafine particles (particle diameters less than 0.02 (mu)m) with low characterized particle losses and minimal change in the size distribution due to coagulation. While designed with ultrafine aerosol sampling in mind, the SEDS can also be used for sampling larger particles and gasses as well.; For ultrafine aerosol sampling, dilution ratios are limited by allowable particle losses and residence times in the SEDS. With the present design the sample can be diluted by a factor ranging from 260:1 to 4380:1. Calibration with 0.035 (mu)m and 0.100 (mu)m aerosol has confirmed the flow based dilution ratios.; In Chapter 5 a simplified model for simultaneous Brownian coagulation and diffusional deposition of a free molecule aerosol in turbulent tube flow is presented. Experimental data supporting the simpified model are also presented. The model specifically addresses the case where the effects of both coagulation and deposition are important and the simplifying assumption of pure coagulation or pure deposition cannot be made. The range of coagulation--deposition regimes is well represented by the experimental data which were taken with a diffusion battery and condensation nucleus counter.; The dimensional analysis performed in deriving the model produces a dimensionless parameter which determines the relative importance of coagulation and deposition. Based on initial conditions, this dimensionless parameter indicates when either coagulation or deposition may be ignored.; The model is shown to describe the observed results very well. Experimental results illustrate the importance of intermolecular forces in coagulation.