Magnetofluidized Bed Research Articles

Continuous Production of Daidzein and Genistein from Soybean in a Magnetofluidized Bed Bioreactor

A magnetofluidized bed (MFB) bioreactor has been used for continuous production of daidzein and genistein from immobilized soybean culture for over 2 months. The MFB, which offers continuous, plug-flow biocatalyst throughput, is well suited for production of intracellularly stored plant metabolites. Soybean cultures were co-immobilized with ferritic stainless steel in calcium alginate spheres. Transport of biocatalyst through the column was controlled with a magnetic valve. Immobilized soybean concentrations reached over 10 g of dry tissue/L of biocatalyst. Daidzein and genistein concentrations ranged from 10 to 200 μg/g of dry soybean tissue. Biocatalyst microscopy suggested that oxygen diffusion in the biocatalyst was not rate limiting. Ampicillin, Timentin, and Benlate were found to have limited phytotoxicity at concentrations useful in preventing contamination in long-term, continuous bioreactor operation.

Phase holdup, liquid dispersion, and gas-to-liquid mass transfer measurements in a three-phase magnetofluidized bed

The gas holdup, ε g , liquid-phase axial dispersion coefficient, D ax, and volumetric gas-to-liquid mass transfer coefficient, k l a, have been measured for a three-phase magneto-fluidized bed (MFB) as a function of gas superficial velocity, liquid superficial velocity, and magnetic field strength. The solid phase consisted of 4 mm diameter calcium alginate spheres within which magnetite powder was entrapped. The liquid and gas phases were water and air, respectively. An axial, direct-current magnetic field having a magnitude between 0 and 300 G was applied by an external solenoid. Six different bed operating regimes were distinguished by visual inspection. Local values of ε g were measured using a fiber-optic probe, and the average values of ε g were measured using the valve technique. Average ε g values decreased by as much as 20% with increasing field strength due to bed contraction and the formation of preferred channels. Local ε g measurements correlated well with average measurements at low field strengths but became erratic at high field strengths due to bubble channeling. The liquid-phase axial dispersion coefficient was measured using a salt tracer. A fourfold decrease in D ax was observed in the channel regime. The volumetric oxygen mass transfer coefficient ( k l a) was determined from measurements of the steady-state oxygen profile across the reactor. A 30% increase in k l a was observed in the chain-channel regime. The experimental results for the MFB were compared to published correlations for conventional fluidized bed systems.

Heat transfer from a horizontal tube in a magnetofluidized bed

Heat transfer coefficient values are reported for a horizontal Nylon 24.1 mm diameter heated probe immersed in an iron shot bed of 1511 μm average diameter and exposed to an external uniform magnetic field collinear with the fluidizing air velocity. The electromagnet produces a maximum constant magnetic-field intensity of 27,850 A/m in a cylindrical central region, 152.4 mm in diameter and 152.4 mm in height, within a constancy of 1%. Total and local heat transfer coefficients are measured at different axial and angular positions over a range of air velocity (0.28–2.50 m/s) and magnetic-field intensity (0.0–19,974 properties, viz., minimum fluidization and bubbling velocities and mean bed voidage.

Heat transfer from an immersed surface in a magnetofluidized bed

Heat Transfer from an immersed horizontal cylindrical heat-transfer probe in an air-fluidized bed of iron shots exposed to an external magnetic field has been investigated. The probe is equipped to provide both total and local heat-transfer coefficients at different axial and angular positions. The fluidizing-air velocity and external magnetic-field intensities are varied to bring about different fluidization regimes starting from fixed-bed, magnetically stabilized-bed, partially stabilized-or bubbling-bed, and frozen-bed regimes. The nature of heat transfer is interpreted in all these regimes and conditions are identified where advantages of magnetic bed stabilization can be enjoyed without loss of heat-transfer rates.