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Mass Transfer Model (mass + transfer_model)
Selected AbstractsA hollow fiber membrane photo-bioreactor for CO2 sequestration from combustion gas coupled with wastewater treatment: a process engineering approachJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 3 2010Amit Kumar Abstract BACKGROUND: In the presence of light, micro-algae convert CO2 and nutrients to biomass that can be used as a biofuel. In closed photo-bioreactors, however, light and CO2 availability often limit algae production and can be difficult to control using traditional diffuser systems. In this research, a hollow fiber membrane photo-bioreactor (HFMPB) was investigated to: (1) increase the interfacial contact area available for gas transfer, (2) treat high nutrient strength (412 mg NO3, -N L,1) wastewater, and (3) produce algal biomass that can be used as a biofuel. RESULTS: A bench scale HFMPB was inoculated with Spirulina platensis and operated with a 2-15% CO2 supply. A mass transfer model was developed and found to be a good tool to estimate CO2 mass transfer coefficients at varying liquid velocities. Overall mass transfer coefficients were 1.8 × 10,6, 2.8 × 10,6, 5.6 × 10,6m s,1 at Reynolds numbers of 38, 63, and 138, respectively. A maximum CO2 removal efficiency of 85% was observed at an inlet CO2 concentration of 2% and a gas residence time (membrane-lumen) of 8.6 s. The corresponding algal biomass concentrations and NO3 removal efficiencies were 2131 mg L,1 and 68%, respectively. CONCLUSION: The results show that the combination of CO2 sequestration, wastewater treatment and biofuel production in an HFMPB is a promising alternative for greenhouse gas mitigation. Copyright © 2010 Society of Chemical Industry [source] A MODEL FOR TEMPERATURE AND MOISTURE DISTRIBUTION DURING CONTINUOUS MICROWAVE DRYING,JOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2005D. BOLDOR ABSTRACT A heat and mass transfer model of continuous drying of farmer stock (in-shell, uncured) peanuts (Arachis hypogaea L.) in a planar microwave applicator was developed and investigated. Transport phenomena equations previously developed for batch-type microwave drying were successfully adapted to account for the spatial variation of the electric field inside the applicator. The theoretical equations developed, together with experimental methods, were used to determine the effect of microwave power level and dielectric properties on the temperature profiles and reduction in peanuts' moisture content (mc). The temperature profiles from the solution of these equations matched the experimental ones determined using fiber optic temperature probes inserted into drying peanut pods. An exact theoretical determination of mc reduction during microwave drying was not possible due to the dependence of dielectric properties on mc. The surface temperature distribution of the peanut bed measured using infrared pyrometry was well correlated with internal temperature profiles. [source] Comparison of Selective Gas Phase- and Liquid Phase Hydrogenation of (Cyclo-)Alkadienes towards Cycloalkenes on Pd/Alumina Egg-Shell CatalystsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2006N. Wuchter Abstract The hydrogenation of dienes such as 1,3-butadiene, cyclooctadiene, and of acetylenic hydrocarbons on Pd catalysts shows high reaction rates and consequently, a strong influence of mass transfer on the selectivity of the intermediate alkene or cycloalkene product. 100,% selectivity towards (cyclo)-alkene hydrogenation is achieved for the gas phase when the Thiele modulus is , where L is the thickness of the active layer and Deff is the effective diffusion coefficient of the diene. The interdependencies expressed by this formula were studied in detail using model catalysts with regular pores of uniform length and diameter and perpendicular to the surface. These catalysts were prepared by anodic oxidation of aluminium wires and immobilization of the active Pd. For the liquid phase procedure of selective hydrogenation, a reaction mass transfer model has been derived in order to compare the gas phase and liquid phase procedures, in particular with respect to the selectivity. The hydrogenation of 1,3-cyclooctadiene and of 1,3-butadiene were studied for both procedures employing the same catalyst. The rate of hydrogenation can be represented for both cases by the identical kinetic equation r1,=,k1,cH2. This result is interpreted by assuming that the access of hydrogen to the surface through the dense layer of adsorbed diene is the rate determining step. [source] Hydrodynamics and Mass Transfer in Gas-Liquid-Solid Circulating Fluidized BedsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 12 2003Z. Liu Abstract Although extensive work has been performed on the hydrodynamics and gas-liquid mass transfer in conventional three-phase fluidized beds, relevant documented reports on gas-liquid-solid circulating fluidized beds (GLSCFBs) are scarce. In this work, the radial distribution of gas and solid holdups were investigated at two axial positions in a GLSCFB. The results show that gas bubbles and solid particles distribute uniformly in the axial direction but non-uniformly in the radial direction. The radial non-uniformity demonstrates a strong factor on the gas-liquid mass transfer coefficients. A local mass transfer model is proposed to describe the gas-liquid mass transfer at various radial positions. The local mass transfer coefficients appear to be symmetric about the central line of the riser with a lower value in the wall region. The effects of gas flow rates, particle circulating rates and liquid velocities on gas-liquid mass transfer have also been investigated. [source] | ||||||||||