Chemical and Biomolecular Engineering Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2751

Browse

Now showing 1 - 3 of 3

FLUID AND PARTICLE DYNAMICS IN AN AEROSOL VIRTUAL IMPACTOR
(2004-05-03) Charrouf, Marwan; Calabrese, Richard V; Chemical Engineering
The collection and characterization of chemical and biological aerosols is essential to many areas of particle research such as toxicological studies, pollutant sampling, and biohazard assessment. This work presents the simulation of a low cutpoint, high volume aerosol sampling device known as the "virtual impactor". A steady state, three dimensional RANS type calculation is done using the FLUENT(TM) computational fluid dynamics code to predict the turbulent flow field inside the device. Particle collection efficiency and wall losses are then obtained by solving the particle equation of motion governed by drag for mono-dispersed samples of spherical particles in the 0.1-0.4 micro-meter diameter range. Predictions of the mean fluid velocity field with the incompressible Reynolds stress model and the compressible k-epsilon turbulence model are relied upon for conducting particle tracking calculations. FORTRAN 90 computer code is developed to solve the particle equation of motion using an implicit second order accurate time integration scheme. In addition, a multi-variate, scattered point interpolation method is implemented to obtain the fluid velocity at a position away from an Eulerian mesh point. It is found that "adaptive" drag law models are necessary to correctly account for slip and compressibility. The results indicate the trends observed in the experiments, and a 50% cutpoint diameter between 0.250 and 0.275 micro-meter. Recommendations for improved modeling in future work are made.
Mixed Organic Surfactant Effects on Cloud Condensation Nuclei
(2021) Mitchell, Ian Wallace; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Atmospheric aerosols affect Earth’s radiative budget through direct and indirect effects. The direct effects are well understood but the indirect effects have large uncertainty associated with them. Uncertainty is so great that even the sign of the radiative forcing associated with indirect effects is questioned. This work examines aerosol indirect behavior by assessing surfactant effects on the activation of aerosol particles into cloud droplets. Szyszkowski-Langmuir surface tension models are applied to Köhler theory to capture surfactant effects on aerosol activation behavior. Surfactant aerosols tested are succinic acid and sodium dodecyl sulfate (SDS). Results suggest that a small addition of surface active material (like SDS) to organic carboxylic acids (like succinc acid) can significantly change droplet activation behavior.
REAL-TIME COMPARISON OF PHYSICAL AND CHEMICAL AEROSOL MEASUREMENT METHODS
(2019) OYEBANJO, FRANCIS; Asa-Awuku, Akua; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Atmospheric aerosols are major contributors to air pollution. Overexposure to these particles can cause severe respiratory and cardiovascular impairments. Aerosols also affect the planet's climate through radiative forcing. Various techniques exist to monitor the physical and chemical characteristic of aerosols but few allow for real-time analysis. In this thesis, real-time field measurements of aerosol particles were compared with values reported by state regulatory agencies. These values were also compared to mass concentrations of PM2.5 in order to determine if a correlation exists between the two. Lastly, the relationship between particle mobility-size and chemical characterization using Raman spectroscopy is explored in an effort to obtain quantitative semi-continuous spectral data. This study found no variation between local and regional particulate matter measurements and no discernable correlation between PM2.5 mass and particle number concentration. The relationship between particle size and Raman intensity remains unknown due to the non-uniformity of mobility-size selected particles.