Study On Microwave Enhancing Flowing And Mass Transfer Inside Matrix Of Plant Porous Materials

The solvent extraction of medicinal herb, water flowing during plant materials drying and membrane separation processing in porous structure of membrane are all complicated mass and energy transfer process for its un-homogeneity, un-stability and coupling with the biological physics and chemistry properties. Microwave Assisted Extraction (MAE) is a kind of green extraction technology.This paper studied the effect of microwave on the mass transfer process of plant porous materials from the points of the micro-structure of porous media and molecular weight distribution of water extracts or the particle size distribution of suspension, by using scanning electronic microscope(SEM), automatic mercury injection apparatus, automatic surface area-porosity analyzer, micro and ultro filtration membranes, laser particle size analyzer, atomic force microscope(AFM) and high performance liquid chromatograph(HPLC). Astragalus and Angelica slices are a kind of root and sterm meidcinal herb, also a typical of plant porous materials. This work choose Astragalus and Angelica slices, micro and ultro-filtration membranes, as the objects of study, combinng the experimental research with theoretical analysis, our findings indicate that: (1) MAE technology is obviously better than traditional reflux technology on the fast extraction of valid components with bigger molecule weight and the avoiding of invalid extracts; (2) Microwave radiation could make the degradation of biological macro-molecular, resulting the variation of the characteristics of aggregation state of extracts processed by microwave assisted technology; (3) Trachea and aperture characteristics of plant porous materials play an important role in the mass transportation of porous medium. A suitable microwave power level is helpful for maintaining or improving the permeability of transportation tissue in materials and promoting the fast dissolution of effective components; (4) Microwave drying technology behaves significant advantages in decreasing drying time of root and stem plant porous materials, especially which contain more glutinous component; (5) Compared to hot air dried sample, microwave dried Chinese angelica slices have the faster absorption rate and the lower capacity of re-hydration, which may be attribute to their the larger average pore diameter, the lower porosity, the smaller total pore volume. However, microwave dried Astragalus slices behaves faster the absorption rate and higher the capacity of re-hydration, which may be due to that larger the average pore diameter, higher the porosity, larger the total pore volume; (6) Microwave assisted filtration could considerably enhance the processed volume of suspension with micro-particle; (7) Microwave assisted technology is also helpful for cleaning fouling on the surface of membrane and inside the pores of membrane, and preventing from the declining of the membrane flux during the process of solution ultra-filtration. It can be suggested that the microwave assisted technology is benefit to promote the mass transfer process during the membrane operation; (8) The fractal scaling law of box counting method is not suitable for the apertures on the wall of trachea inside matrix. The Slit island method and the mercury injection method are better. A smaller fractal dimension at 600W presented that borderline of the apertures is smoother than that of 900W, which is in favor of functional components flowing; (9) The fractal dimension of pore size distribution inside materials matrix correlated well with both the drying behavior and re-hydration property. The higher the fractal dimensions of sample, results in higher porosity and the better the connectivity of moisture transfer path. This work have important meanings in theory to enrich the research fields of heat transfer and mass transfer, promote the creativity in theory and the break-up in technology of relative fields of application and research.