In this work, we revised the expression of mixing intensity to describe the mixing output through a cross section in a flow system by considering heterogeneity of flow field, and carefully investigated the mixing proc...In this work, we revised the expression of mixing intensity to describe the mixing output through a cross section in a flow system by considering heterogeneity of flow field, and carefully investigated the mixing process along a straight tube with expanding/contracting cross section by simulation method. The simulation results show that a sudden expansion of cross section has remarkable mixing intensification effect within a limited period(on the sub-second scale) or tube-length(on the millimeter scale), corresponding to the generation of considerable local vortices determined by both the flow capacity and the ratio of cross section change; a sudden contraction of cross section has instantaneous but weak mixing intensification effect; through introducing a local expansion structure with proper length, as the combination of sudden expansion and sudden contraction, their mixing intensification effects could be superposed. Besides, the rationality and importance are experimentally verified to explore the time profile of mixing intensity and carry out the vortex analysis by simulation for enhancing the selectivity of a complicated reaction system. These progresses may lead to more meaningful quantitative description of mixing process in a flow microreactor for some specific chemical processes.展开更多
Considering the essential and influential role of centrifugal compressors in a wide range of industries makes most of engineers research and study on design and optimization of centrifugal compressors. Centrifugal com...Considering the essential and influential role of centrifugal compressors in a wide range of industries makes most of engineers research and study on design and optimization of centrifugal compressors. Centrifugal compressors are the key to part ofoil, gas and petrochemical industries as well as gas pipeline transports. Since complete 3D design of the compressor consumes a considerable amount of time, most of active companies in the field, are profoundly interested in obtaining a design outline before taking any further steps in designing the entire machine. In this paper, a numerical algorithm, named ACDA （adapted compressor design algorithm） for fast and accurate preliminary design of centrifugal compressor is presented. The design procedure is obtained under real gas behavior, using an appropriate equation of state. Starting from impeller inlet, the procedure is continued on by resulting in numerical calculation for other sections including impeller exit, volute and exit diffuser. Clearly, in any step suitable correction factors are employed in order to conclude in precise numerical results. Finally, the achieved design result is compared with available reference data.展开更多
Objective：To investigate the mechanism of nape cluster acupuncture in the treatment of acute cerebral infarction. Methods： Eighty patients with acute cerebral infarction were selected and randomly allocated to group...Objective：To investigate the mechanism of nape cluster acupuncture in the treatment of acute cerebral infarction. Methods： Eighty patients with acute cerebral infarction were selected and randomly allocated to group A and B. Group B was given routine treatment for acute phase and Group A was added with the nape cluster acupuncture based upon the treatment for Group B. The treatment was given twice daily, with 15 d as a course of the treatments, to observe the decreasing situation in the score of the nerve function defects and changes in plasma ET content. Results： There were significant differences in the score of the nerve function defects and plasma ET content before and after treatments in two groups （P〈 0.05）, but there was significant difference between Group A and Group B after treatment （P〈 0.05）, indicating the curative effect was better in Group A than in Group B.Conclusion： Nape cluster acupuncture can be used to effectively treat acute cerebral infarction and obviously decrease plasma ET content and reduce the score of the nerve function defects. The findings also proves that the therapeutic effect was obviously better than single medication, if nape cluster acupuncture was combined in the treatment of the acute cerebral infarction.展开更多
This paper introduces the influence factors of axial stiffness of tubular X-joints. The analysis model of tubular joints using plate and shell finite element method is also made. Systematic single-parameter analysis o...This paper introduces the influence factors of axial stiffness of tubular X-joints. The analysis model of tubular joints using plate and shell finite element method is also made. Systematic single-parameter analysis of tubular X-joints is performed using Ansys program. The influences of those factors, including ratio of brace diameter to chord diameter （β）, ratio of chord diameter to twice chord thickness （γ）, ratio of brace wall thickness to that of chord （τ）, brace-to-chord intersection angle （θ）, and chord stress ratio, ratio of another brace diameter to chord diameter, in-plane and out-of-plane moment of braces, etc., on stiffness of tubular X-joints are analyzed. Two non-dimensional parameters-joint axial stiffness factor ηN and axial force capacity factor ωN are proposed, and the relationship curve of the two factors is determined. Computational formulas of tubular X-joint axial stiffness are obtained by multi-element regression technology. The formulas can be used in design and analysis of steel tubular structures.展开更多
基金Supported by the National Natural Science Foundation of China(21176136,21422603)the National Science and Technology Support Program of China(2011BAC06B01)
文摘In this work, we revised the expression of mixing intensity to describe the mixing output through a cross section in a flow system by considering heterogeneity of flow field, and carefully investigated the mixing process along a straight tube with expanding/contracting cross section by simulation method. The simulation results show that a sudden expansion of cross section has remarkable mixing intensification effect within a limited period(on the sub-second scale) or tube-length(on the millimeter scale), corresponding to the generation of considerable local vortices determined by both the flow capacity and the ratio of cross section change; a sudden contraction of cross section has instantaneous but weak mixing intensification effect; through introducing a local expansion structure with proper length, as the combination of sudden expansion and sudden contraction, their mixing intensification effects could be superposed. Besides, the rationality and importance are experimentally verified to explore the time profile of mixing intensity and carry out the vortex analysis by simulation for enhancing the selectivity of a complicated reaction system. These progresses may lead to more meaningful quantitative description of mixing process in a flow microreactor for some specific chemical processes.
文摘Considering the essential and influential role of centrifugal compressors in a wide range of industries makes most of engineers research and study on design and optimization of centrifugal compressors. Centrifugal compressors are the key to part ofoil, gas and petrochemical industries as well as gas pipeline transports. Since complete 3D design of the compressor consumes a considerable amount of time, most of active companies in the field, are profoundly interested in obtaining a design outline before taking any further steps in designing the entire machine. In this paper, a numerical algorithm, named ACDA （adapted compressor design algorithm） for fast and accurate preliminary design of centrifugal compressor is presented. The design procedure is obtained under real gas behavior, using an appropriate equation of state. Starting from impeller inlet, the procedure is continued on by resulting in numerical calculation for other sections including impeller exit, volute and exit diffuser. Clearly, in any step suitable correction factors are employed in order to conclude in precise numerical results. Finally, the achieved design result is compared with available reference data.
文摘Objective：To investigate the mechanism of nape cluster acupuncture in the treatment of acute cerebral infarction. Methods： Eighty patients with acute cerebral infarction were selected and randomly allocated to group A and B. Group B was given routine treatment for acute phase and Group A was added with the nape cluster acupuncture based upon the treatment for Group B. The treatment was given twice daily, with 15 d as a course of the treatments, to observe the decreasing situation in the score of the nerve function defects and changes in plasma ET content. Results： There were significant differences in the score of the nerve function defects and plasma ET content before and after treatments in two groups （P〈 0.05）, but there was significant difference between Group A and Group B after treatment （P〈 0.05）, indicating the curative effect was better in Group A than in Group B.Conclusion： Nape cluster acupuncture can be used to effectively treat acute cerebral infarction and obviously decrease plasma ET content and reduce the score of the nerve function defects. The findings also proves that the therapeutic effect was obviously better than single medication, if nape cluster acupuncture was combined in the treatment of the acute cerebral infarction.
文摘This paper introduces the influence factors of axial stiffness of tubular X-joints. The analysis model of tubular joints using plate and shell finite element method is also made. Systematic single-parameter analysis of tubular X-joints is performed using Ansys program. The influences of those factors, including ratio of brace diameter to chord diameter （β）, ratio of chord diameter to twice chord thickness （γ）, ratio of brace wall thickness to that of chord （τ）, brace-to-chord intersection angle （θ）, and chord stress ratio, ratio of another brace diameter to chord diameter, in-plane and out-of-plane moment of braces, etc., on stiffness of tubular X-joints are analyzed. Two non-dimensional parameters-joint axial stiffness factor ηN and axial force capacity factor ωN are proposed, and the relationship curve of the two factors is determined. Computational formulas of tubular X-joint axial stiffness are obtained by multi-element regression technology. The formulas can be used in design and analysis of steel tubular structures.
