Finite element simulation of nonlinear convective heat and mass transfer in a micropolar fluid-filled enclosure with Rayleigh number effects

A mathematical model is presented to study the double-diffusive convective heat and mass transfer of a micropolar biofluid in a rectangular enclosure, as a model of transport phenomena in a bioreactor. The vertical walls of the enclosure are maintained at constant but different temperatures and concentrations. The conservation equations for linear momentum, angular momentum, energy and species concentration are formulated subject to appropriate boundary conditions and solved using both finite element and finite difference numerical techniques. Results are shown to be in excellent agreement between these methods. Several special cases of the flow regime are discussed. The distributions for streamline, isotemperature, isoconcentration and (isomicrorotation) are presented graphically for different Lewis number, buoyancy parameter, micropolar vortex viscosity parameter, gyration viscosity parameter, Rayleigh number, Prandtl number and micro-inertia parameter. Micropolar material parameters are shown to considerably influence the flow regime. The flow model has important applications in hybrid aerobic bioreactor systems exploiting rheological suspensions e.g. fermentation

Paraffin oil as a "methane vector" for rapid and high cell density cultivation of Methylosinus trichosporium OB3b

Slow growth and relatively low cell densities of methanotrophs have limited their uses in industrial applications. In this study, a novel method for rapid cultivation of Methylosinus trichosporium OB3b was studied by adding a water-immiscible organic solvent in the medium. Paraffin oil was the most effective at enhancing cell growth and final cell density. This is at least partially due to the increase of methane gas transfer between gas and medium phases since methane solubility is higher in paraffin than in water/nitrate minimal salt medium. During cultivation with paraffin oil at 5% (v/v) in the medium, M. trichosporium OB3b cells also showed higher concentrations of the intermediary metabolites, such as formic acid and pyruvic acid, and consumed more methane compared with the control. Paraffin as methane vector to improve methanotroph growth was further studied in a 5-L fermentor at three concentrations (i.e., 2.5%, 5%, and 10%). Cell density reached about 14 g dry weight per liter with 5% paraffin, around seven times higher than that of the control (without paraffin). Cells cultivated with paraffin tended to accumulate around the interface between oil droplets and the water phase and could exist in oil phase in the case of 10% (v/v) paraffin. These results indicated that paraffin could enhance methanotroph growth, which is potentially useful in cultivation of methanotrophs in large scale in industry