Gas absorption rates were experimentally determined for a number of tworphase gas-liquid systems in co-current horizontal flow through circular tubes. Sparingly soluble gases were used in order to determine the liquid phase resistance to mass transfer. A series of experiments was designed to separate the effects of gas density, liquid-phase diffusivity, viscosity, surface tension, and tube diameter, on the mass transfer rates. The gas-liquid systems employed, in a single tube 1.757 cm. in diameter, were CO₂-water, He-water, CO₂-ethanol, and CO₂-ethylene glycol. Two additional tube sizes, 1.228 and 2.504.cm. in diameter were employed with the C02-water system to determine the effect of tube diameter. The gas and liquid flow rates used produced four different flow regions, bubble, plug, slug, and annular flow. The gas, and liquid, superficial velocities ranged from 0.1 to 40 fps, and 0.5 to 3.6 fps, respectively. Two correlations were developed for predicting mass transfer rates in two-phase flow. The first, based on a theory that each bubble represents a "mixing stage", is applicable to the bubble and plug regions of flow, and correlates the experimental' data for a wide range of liquid physical properties, as well as gas and liquid flow rates, with a probable error of approximately 15%. The second correlation, applicable to slug flow, empirically correlates the data for this region, over the same wide range of physical properties and flow rates, with a probable error of approximately 10%. The surface renewal or "penetration theory" mechanism of transfer is shown to be consistent with the experimental results obtained in the bubble and plug regions. In the slug region, on the other hand, evidence is available to indicate that another mechanism (probably that proposed by Kishinevskii), becomes increasingly important as the degree of turbulence increases. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Photocatalysis is a green technology that has been widely used in wastewater treatment. In this work, mass transfer processes in corrugated photocatalytic reactors were characterized both experimentally and through computer simulations. For the experimental work, various drum rotational speeds, reactor liquid volumes and number of corrugations were studied to elucidate their effects on mass transfer phenomena. The mass transfer rate was found to increase with increasing rotational speed. Liquid volumes in the reactor significantly affect the mass transfer rate when 20% of the surface area of the drum was immersed. A higher mass transfer rate was found using the drum with 28 corrugations, which had the lowest mass transfer coefficient when compared to the drums with 13 and 16 corrugations. In the computer simulations, velocity and concentration fields within the corrugated reactors were modelled to explore the characteristics of mass transfer processes. The mass transfer coefficients predicted by the simulations were lower than those measured experimentally due to mass transfer limitations occurring between the corrugation volume and bulk solution in the simulations. Based on mass transfer characteristics, it was determined that the drum with 28 corrugations was the most efficient photocatalytic reactor, and had the lowest mass transfer coefficient among those studied.

<p>Radiative cooling is an approach that utilizes the material reflectance in solar spectrum to reflect solar irradiation and emit the energy to deep space (2.7K) through the transparent portion in atmosphere (8-13μm). Therefore, radiative cooling is a passive cooling method that can generate a large reduction in energy consumption in the cooling sector. Scientists have been researching on the best solution for passive radiative cooling, including the utilization of multi-layer techniques with a metallic base layer. However, the current solutions are usually not cost effective and thus limited in the commercial applications. We initially started with the experiment on single-layer cooling paints embedded with TiO₂nanoparticles, and we were able to achieve a partial daytime radiative cooling effect of 60Wm^-2 Built upon our lab’s success of full-daytime sub-ambient cooling based on BaSO₄-acrylic paints, we experiment with colored cooling paints based on BaSO₄ nanoparticles instead of TiO₂ nanoparticles. Our results show much enhanced solar reflectance while matching the color, indicating the potential for colored cooling paints, although outdoor tests have not shown significant temperature drop compared to commercial colored paints yet. At the same time, we also explore creatures with shells in nature for possible solutions. Seashells are collected and the microstructures and radiative properties are characterized. The results provide insights into bio-inspired radiative cooling solutions.</p>

QC 20110616

This study was performed to increase knowledge of oxygen mass transfer (kLa) and mixing times in the scale-up of disposable bioreactors.Results of oxygen mass transfer studies showed kLa to increase with increasing agitation and aeration rates. By maintaining a scale-up constant such as gassed power to volume or shear, an almost constant kLa was achieved during scale-up from 50 to 2000 L. Using the scale-up constant Pg/V resulted in statistically higher kLa values at greater reactor volumes. Mixing times were revealed to be significantly affected by agitation, but not by the aeration rates tested. No pattern was recognized in the mixing time data over an increase in volume. Commonly used methods for predicting kLa upon scale-up were compared to experimental data. New coefficients were determined to fit the historic models to the parameters of this study, namely the unique geometry and low agitation and aeration rates used in the single-use systems. Each of the resulting four models was found to have average error rates from 16-23%. Although the error rates are not statistically different, the Moresi and Patete model was determined to be most conceptually accurate. The Moresi and Patete model found kLa to be more dependent on aeration than on the power input. This finding was consistent with the results of the experimental studies. The results of this study were for aeration rates (0.02-0.04 vvm) and agitation rates (Pg/V range of 2-20 W/m3) that are commonly used in single-use bioreactor systems.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Bibliography : leaves 81-83. / M.S.

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<p> The rate of mass transfer from a series of bubbles, formed at constant frequency, rising through a quiescent liquid, was investigated at various times after bubble formation. The effect of surfactant on mass transfer was also studied. </p> <p> A decay from partially circulating to non-circulating conditions was found to occur in 7-8 seconds. The initial rate of mass ·transfer was appreciably reduced by the presence of surfactant. Mass transfer due to end effects was found to be 25-40% of the initial bubble mass. </p> / Thesis / Master of Engineering (ME)

A simplified model is developed to predict the heat and mass transfer between air and fallingilm liquid desiccant during dehumidification in a parallel-plate absorber. Compared to the second-order partial differential equations that describe fluid motion, first-order, non-coupled, ordinary differential equations are used to estimate the heat and mass transferred and explicit equations are derived from conservation principles to determine the exiting conditions of the absorber for different flow arrangements. The model uses a control volume approach that accounts for the change in desiccant film thickness and property values. The model agreed with a more complicated parallel flow model in literature. Using existing experimental data for a counterflow arrangement the model was validated over the range of input variables at the level of 8% for varying inlet desiccant flow rates and 10% for varying inlet air mass flow rates when an experimentally determined mass transfer coefficient was used in the model.