Evaporation of pure and binary liquid droplets is of interest in thermal sprays and spray drying of food, ceramics and pharmaceutical products. Understanding the rate of heat and mass transfer in any drying process is important not only to enhance evaporation rate or vapor-gas mixing, but also to predict and control the final morphology and microstructure of the precipitates. Acoustic levitation is an alternative method to study micron-sized droplets without wall effects, which eliminates chemical and thermal contamination with surfaces. This work uses an ultrasonic levitation technique to investigate the vaporization dynamics under radiative heating, with focus on evaporation characteristics, precipitation kinetics, particle agglomeration, structure formation and droplet stability. Timescale and temperature scales are developed to compare convective heating in actual sprays and radiative heating in the current experiments. These relationships show that simple experiments can be conducted in a levitator to extrapolate information in realistic convective environments in spray drying. The effect of acoustic streaming, droplet size and liquid properties on internal flow is important to understand as the heat and mass transfer and particle motion within the droplet is significantly controlled by internal motion. Therefore, the droplet internal flow is characterized by Particle Image Velocimetry for different dropsize and viscosity. Nanosuspension droplets suspended under levitation show preferential accumulation and agglomeration kinetics. Under certain conditions, they form bowl shaped structures upon complete evaporation. At higher concentrations, this initial bowl shaped structure morphs into a ring structure. Nanoparticle iv migration due to internal recirculation forms a density stratification, the location of which depends on initial particle concentration. The time scale of density stratification is similar to that of perikinetic-driven agglomeration of particle flocculation. The density stratification ultimately leads to force imbalance leading to a unique bowl-shaped structure. Chemically active precursor droplet under acoustic levitation shows events such as vaporization, precipitation and chemical reaction leading to nanoceria formation with a porous morphology. The cerium nitrate droplet undergoes phase and shape changes throughout the vaporization process followed by formation of precipitate. Ex-situ analyses using TEM and SEM reveal highly porous morphology with trapped gas pockets and nanoceria crystalline structures at 70oC. Inhomogeneity in acoustic pressure around the heated droplet can induce thermal instability. Short wavelength (Kelvin-Helmholtz) instability for diesel and bio-diesel droplets triggers this secondary atomization, which occurs due to relative velocity between liquid and gas phase at the droplet equator. On the other hand, liquids such as Kerosene and FC43 show uncontrollable stretching followed by a catastrophic break-up due to reduction in surface tension and viscosity coupled with inhomogeneity of pressure around the droplet. Finally, a scaling analysis has been established between vaporizing droplets in a convective and radiative environment. The transient temperature normalized by the respective scales exhibits a unified profile for both modes of heating. The analysis allows for the prediction of required laser flux in the levitator experiments to show its equivalence in a corresponding heated gas stream. The theoretical equivalence shows good agreement with experiments for a range of droplet sizes.

Lopez Lake Reservoir is the primary source of potable water for the Cities of Arroyo Grande, Grover Beach, Pismo Beach, and to the Community Service Districts of Oceano and Avila Beach. In this study, a water balance and sediment yield analysis model was developed for the reservoir’s watershed. The model was used to estimate evaporation from the lake and to examine the effects of a wildfire on the reservoir. Evaporation and wildfire are dependent on variables that change on a spatial and temporal scale, making modeling challenging. The County of San Luis Obispo uses pan coefficients to estimate evapotranspiration losses from the reservoir. In this study, a water balance model was developed using a watershed model known as Soil and Water Assessment Tool, SWAT. Evaporation loss from the lake was calculated using the inflows simulated by the model, and other fluxes (e.g., water released for consumption to Arroyo Grande Creek, precipitation) that were obtained from the County of San Luis Obispo. The evaporation values estimated by the pan coefficient model were significantly higher than the water balance and the Penman-Monteith predictions. The Penman-Monteith method estimates seem more reasonable for the lake. SWAT was also used to simulate effects of a wildfire on sediment inflow and sediment yield into the reservoir for a year after a simulated fire. Results showed that sediment inflow rates increased by a factor of 3 following the simulated wildfire. Lopez Lake Reservoir’s capacity would be significantly affected by a wildfire. To improve the evaporation estimates it is recommended that the County of San Luis Obispo install streamflow gauges to measure the inflow into the reservoir. Using the streamflow gauges the reservoir evaporation could be calculated using the water balance method. Adding climate gauges at the reservoir would increase the accuracy of the Penman-Monteith method. Sediment gauges in the watershed would provide a calibration data source for the model as well as data collection points in the event of an actual wildfire.

Responses to drought were studied on greenhouse grown plants of Sphaeralcea grossulariaefolia (Hook. & Arn.) Rydberg. A pressure bomb was modified to measure leaf water potential (ψ). Leaf water potentials varied from -2 to -80 bars. Matric potential proved negligible. Low osmotic potentials indicated that turgor pressure remained positive. Photosynthesis decreased linearily with leaf water potential decreases. At about -32 bars ψ net photosynthesis became zero and around -45 bars ψ all photosynthesis ceased. Dark respiration decreased below about -18 bars proportionally to leaf water potential decrease until becoming minute at -60 bars. A very rapid rise in CO2 equilibrium concentration occurred as leaf water potential decreased below -18 bars. Abscission of leaves began at -6 bars ψ. At -32 bars ψ only about 15 percent of initial leaf area remained. A close balance between transpiration and soil moisture absorption was maintained by stomatal closure and leaf area abscission. Upon watering, rapid regeneration of foliage following severe drought was especially notable. Growth characteristics related to drought and possible indexes of physiological vitality were discussed.

<p> Evaporation was calculated for a subarctic beach ridge, near Churchill, Manitoba, using the energy balance approach. Energy balance calculations for the measurement season revealed an average Bowen ratio, β, of 0.68, with a value of 1.00 representing α' (the evaporability parameter). Fifty-seven percent of the net radiation was utilized by the evaporative heat flux over this tundra surface. Regressions were used to determine the most likely combination of environmental variables responsible for the behaviour of evaporation. Surface soil moisture remained relatively constant throughout the summer measurement period and soil temperatures appeared to be unrelated to evaporation. Air temperature proved to be insignificant to the evaporation flux, and net radiation alone could only account for 54% of the variability. The combination of the net radiation and the wet and dry bulb temperature depression at 1 m accounted for 88% of the variability of the evaoorative heat flux. The mean α' for a site is assumed to be controlled by the surface type in simplified variations of the combination model. The conclusion has been drawn from this study that the variability of α' can be accounted for by variable atmospheric humidities as well as net radiation. The importance of this atmospheric control on the rate of evaporation is emphasized.</p> / Thesis / Master of Science (MSc)

<p> In 1978, the water balance of a small lake near Resolute, N.W.T. was studied. Using measured water inputs and water outputs, the change in storage term was calculated. A positive net change in storage was partitioned between storage in the active layer and storage in the lake.</p> <p> A comparison of the magnitudes of the various components of the water balance equation shows that i) for the snow-dammed lake, outflow is most important for the few days following the breakup of the channel, ii) evaporation is an important process, removing almost as much water as summer precipitation received by the basin, and iii) depending on the condition of the active layer during freeze-up, considerable amounts of water may be held in storage at the end of summer.</p> / Thesis / Bachelor of Arts (BA)

<p> Energy-budget calculations and equilibrium model estimates of evaporation from a lichen-dominated upland site in the Hudson Bay low-lands are presented. The energy budget calculations reveal that the lichen surface is relatively resistant to evaporation with an average of only 54 percent of the daily net radiation being utilized in the evaporative process. Equilibrium estimates of evaporation consistently overestimate actual evaporation by 5 and 8 percent for hourly values and daily totals respectively. A simple model, a function of the equilibrium model, is derived from a comparison of actual and equilibrium evaporation. The only inputs required for the model are net radiation, soil heat flow and screen temperatures. Tests of the model indicate that it will predict actual evaporation within 5 percent and that it can probably be applied to any high latitude surface which exhibits a relatively large resistance to evaporation.</p> / Thesis / Master of Science (MSc)

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