Qianqian Di

Application of pore size analyzers in study of Chinese Angelica slices drying.

The objective of this article is to study the influence of pore size and distribution in plant tissue on drying behavior of plant materials using Chinese Angelica slices as an example. By using an automatic mercury injection apparatus and automatic surface area–porosity analyzer, the study compares the pore size distribution inside the matrix of a sample dried by 200 W microwave and 60°C hot air. The study also characterizes the matrix microstructure by scanning electronic microscopy (SEM) and discusses the drying dynamics of the sample, as well as the rehydration property of the dried sample. This work may be helpful for further investigation of the optimization of drying technology focused on micromechanisms and the quality of dried products.

Application of Automatic Mercury Injection Apparatus in Study of Astragalus Slices Drying

The objective of this article is to study the influence of pore size and distribution in plant tissue on drying behavior of plant materials using Astragalus slices as an example. By using an automatic mercury injection apparatus, the study compares the pore size distribution inside the matrix of sample dried by 200 W microwave power and hot air at 60°C. The study also characterizes the matrix microstructure by scanning electronic microscopy (SEM) and discusses the drying kinetics of the sample as well as the rehydration properties of the dried sample. Results show the advantage of automatic mercury injection apparatus over SEM to characterize the matrix microstructure of sample. This work may be helpful for further investigation on the optimization of drying process focused on micromechanisms and the quality of dried product.

Correlation between fractal dimension of matrix and extraction behavior of plant materials

This paper studies the correlation between fractal dimension of matrix microstructure of plant materials and extraction behavior using Astragalus root slices as examples. This work compared the yield of extracts on the conventional solvent soaking extraction of samples irradiated 3min by microwave 600W and 900W, respectively. Regarding to microwave treated samples, the area fractal dimensions (DL ) of aperture in shape were estimated by using the slit island method on the basis of SEM images analysis, the volume fractal dimensions (DV ) of pore size distribution inside matrix were also determined by the mercury injection method on the basis of measured results (6nm–40×105 nm) by automatic mercury injection apparatus. Our findings are that, 900W treated sample behaves higher yield of extracts than 600W. The values of DL and DV both increase with increasing of microwave power. The higher values of DL correspond to the much irregular and deformed shape of aperture, which seems un-benefit for the extraction of component inside matrix. However, the higher values of DV correspond to the less concentration of pore size distribution, implying better connectivity of pore or channel at multi-scale (including trachea 20μm–50μm, aperture 0.1μm–1μm and plasmodesma 1nm–10nm in size) and permeability inside matrix during extraction, higher yield of extracts. It demonstrates that combining the two fractal dimensions can present much more information for better understanding of mass transfer behavior and the knowledge of material properties.Copyright

Fractal Dimension of Pore Size Distribution Inside Matrix of Plant Materials and Drying Behavior

This paper studied the relationship between matrix microstructure of plant materials and drying behavior using Astragalus and Chinese Angelica root slices as examples. Astragalus and Chinese Angelica, two kinds of traditional Chinese Medicine Herb (CMH), are species of stem and root medicinal herb with the widely curative effects. Based on the measured results by using automatic surface area-porosity analyzer (at smaller scale ≤ 100nm), the volume fractal dimensions (DV ) were estimated to characterize the pore size distribution inside matrix of samples dried by different drying technologies, including microwave drying at 200W and conventional hot air drying at 60 °C. In cases studied in this paper, the values of DV are well related with drying time. As compared to hot air dried sample, DV of microwave dried sample increases by 5.9% for Astragalus, while 7.7% for Chinese Angelica. In comparison with hot air drying, the microwave drying time is reduced to 1/6 (30min/180 min) for Astragalus, while 1/16 (50min/810min) for Chinese Angelica. Combined the observation of SEM images of sample, our findings is that, higher fractal dimension, less concentration of pore size distribution, better connectivity of pore or channel with multi-scale characteristics (aperture about 0.1μm–1μm, plasmodesma about 1nm–10nm, or 10A–100A), much loose distribution of cytoplasm inside parenchyma cells, better permeability of moisture transfer path during drying process, shorter drying time. Our results demonstrate that the volume fractal dimension (DV ) of pore size distribution at smaller scale (≤ 100nm) could give a better understanding the mass transfer behavior of plant materials.Copyright

The Role of Aperture in the Extraction of Functional Components From Plant Materials

The extraction of functional components from natural plant is one of important processing in the development and further practical application of plant product. Microwave assisted extraction (MAE) has been widely used in the extraction of many samples for its unique heating mechanism, short extraction time and high yield of extract. Astragalus slice is a special and typical plant porous media. We describe an approach by scanning electronic microscope (SEM) to characterize the trachea and aperture of Astragalus slices irradiated 20 min by microwave at 600 W and 900 W, with the aim to analyze the effect of the microwave power on the extraction yield by SEM and discuss further the relationship between the microstructure characteristics of sample and mechanism on mass transfer in micro-scale. It is found that extract with the 20 min irradiation of microwave at 600 W is higher than that at 900 W because the apertures on the trachea wall remain open at 600 W, but shrink at 900 W. Moreover, we confirm the important role of the aperture in the extraction of plant materials. Therefore, this study has significant meanings to develop the optimized extraction technology of plant porous media and maintain or improve the quality of extract.Copyright

Mechanism on mass transfer in micro-scale during the microwave drying of plant porous materials

Astragalus slice is one species of stem and root medicinal herb with the widely curative effects, also a special and typical plant porous material, and the drying operation is one of important processing technologies in its storage and further practical application. This paper characterizes the microstructure of Astragalus slices dried by microwave technique at 200 W by using scanning electronic microscope (SEM). The study also compares Astragalus slices dried by microwave with those untreated and discusses the drying mechanism. Result shows that as compared to the untreated sample, the microwave dried sample behaves much shorter drying time with more and larger pore and open structure on the surface layer of matrix, but without significant change about the distribution status of cytoplasm inside parenchyma cells. Further analysis suggests that the vapor diffusion is the dominant mode of moisture transfer inside matrix during the microwave drying process of sample, resulting in the well-preserved structures of sample, including parenchyma cell and trachea. This is also helpful for maintaining the distribution status of cytoplasm, particularly avoiding the agglomeration of biological macro-molecular, which is benefit to improving the permeability of moisture transfer path, leading to the rapidly dehydration of moisture. This work seems to be helpful for developing the optimized drying technology of plant porous material focused on micro-mechanism and the quality of dried products.Copyright

Effect of Biological Macro-Molecular Flow on the Hot Air Drying of Astragalus Slices

Astragalus slice is one species of stem and root medicinal herb with the widely curative effects, also a special and typical plant porous material, and the drying operation is one of important processing technologies in its storage and further practical application. By using scanning electronic microscope (SEM), we mainly characterize the micrographics of parenchyma cell, trachea and aperture of Astragalus slices dried by hot air at 60°C, with the aim to discuss the relationships among the microstructure of sample, macro-drying property and drying mechanism in micro-scale. Results show that in hot air dried sample, the distribution status of cytoplasm inside parenchyma cells appears obvious different with that of untreated sample, behaving agglomeration and leaving wide space with cell wall. Furthermore, we find that in comparison with the untreated sample, the shape of aperture in hot air dried sample basically maintains un-changed, but most of apertures are fully filled with some perceived substance. It is demonstrated that the flow phenomenon of cytoplasm occurs inside matrix accompanied by the moisture diffusion in the mode of liquid water, particularly biological macro-molecular, which directly influence the permeability of moisture transfer path inside matrix and the quality of dried products. Hence, this study has significant meanings to develop the optimized drying technology of plant porous material focused on micro-mechanism and the quality of dried products.© 2009 ASME

Experimental Study on Micro-scale Flow of Compounds During Microwave Assisted Extraction of Astragalus Slices

An experimental study is performed on the matrix microstructure and size of transport compounds during the process of microwave assisted extraction (MAE) of Astragalus slices. By using membrane separation technology, we analyze the size distribution of compounds in Astragalus water extracts. We also characterize the variation of matrix microstructure by scanning electronic microscope (SEM). The study indicates that the diffusion process of transport compounds inside matrix is strongly nonhomogeneous and anisotropic, and has a multiscale characteristic. This work may give some inspiration for scientists and engineers in the fields of micro- and nanoscale.

Fractal Characterization of Astragalus Slices Under Various Microwave Assisted Extraction Conditions

Microwave has been widely used in the extraction of many samples for its unique heating mechanism, short extraction time and high yield of extract. The microstructure characteristics of plant materials are closely related with macro-property and mechanism on mass transfer within matrix. Fractal geometry, with the ability to describe irregular objects provides a new language. Astragalus slice is a special and typical plant porous media. We characterize the microstructure of Astragalus slices irradiated by microwave at 600 and 900 W by using fractal dimension, with the aim to analyze the effect of the microwave power on the extraction yield and discuss further the relationship between the fractal dimensions and microstructure changes of sample during microwave assisted extraction process. It is found that the fractal scaling law of box counting method is not suitable for the apertures on the wall of trachea inside matrix, and Slit Island and mercury injection method may be used. Fractal dimensions of samples at microwave 600 W are smaller than that at 900 W. The smaller fractal dimension is in favor of effective components dissolution inside the slices, which led to extract with the 20 min irradiation of microwave at 600 W is higher than that at 900 W.Copyright

Preliminary Study on the Dynamic Stability of TiO2-Water Based Nanofluids Flow in Circular Tube

The preparation of nanofluids with good suspending stability is an important premise for further scientific research and engineering application. However, previous studies mainly focused on the stability of nanofluids in static situation without any flow, and seldom discussed the suspending stability of nanofluids in flow. The objective of this study is to investigate the suspending stability of nanofluids in flow using TiO2 -water nanofluids flowing through a circular tube as an example. The study uses the centrifugal sedimentation weight of supernatant suspending solution to characterize the stability of nanofluids. The bigger centrifugal sedimentation weight represents the better stability. This study also characterization of particle size distribution of nanofluids by Malvern laser particle size analyzer. In the present experiment conditions, TiO2 -water nanofluids with the mass fraction of 0.5% are driven by a peristaltic pump and flows through a circular tube with 4.8 mm inner diameter. In the present experimental conditions, the volume flow rate of TiO2 -water nanofluids is slightly lower than that of pure water. The size distribution of nanoparticle in fluid after circulating flow 2 hours behaves more uniformly than that in a fluid after maintaining static situation 2 hours. with the increasing of Reynolds number of fluid in circulating flow, the suspending stability of nanofluids in circulating flow is significantly higher that that in static situation. When the Reynolds number is up to 2000, the suspending status of nanoparticles in the base fluid is nearly the same as the initial status of sample before circulating. Despite its preliminary, this work demonstrates that the flow pattern is one of influence factors on the suspending stability of nanofluids, which should not be ignored in the study of the suspending stability and heat transfer performance of nanofluids. This study may give some inspiration for further research on relative fields such as the preparation of nanofluids for heat transfer enhancement and so on.© 2009 ASME