The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average s...The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average shear rate in the whole tank but also the local value in the vicinity of impeller increases linearly with impeller speed.Furthermore,the shear coefficient(Ks,imp)at the impeller outlet is linearly related to the impeller flow number(Nq)and decreases with the increase of Nq in general at the constant power consumption per unit volume(Pv).During scale-up based on the constant Pv and geometric similarity,CFD results show that the volume-averaged shear rate(cavg)for RDT decreases faster than that of other impellers with the impeller tip velocity(Utip).The novel multi-blade combined(MBC)impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate at the same Pv after scale-up.These studies provide a data basis for selecting the impeller types and improving the shear rate environment in the large-scale stirred tank.展开更多
The temperature distribution under shear with a high strain rate and the cooling rate of the shear bands of Al, Cu and 0.06C steel have been calculated using a computer. The results show that the temperature of shear ...The temperature distribution under shear with a high strain rate and the cooling rate of the shear bands of Al, Cu and 0.06C steel have been calculated using a computer. The results show that the temperature of shear band increases with the increase of the average strain rate (_o). When _o is in the range 8×10~5 to 10~6 1/s, the structure of the adiabatic shear band in a 0.06C steel is martensite but it becomes metallic glass if _o=10~6 1/s. As to A1 and Cu, the structure of the adiabatic shear bands can also be of metallic glass if _o is greater than 1.8×10~6 and 5.5×10~7 1/s respectively. It explains that Cu tends most difficultly to form adiabatic shear band, while 0.06C steel most readily among the three metals.展开更多
Following a sticky particle model and its computer simulation scheme proposed in the previous papers, the motions of particles in both 2-and 3-dimensional shear flow fields are simulated. At a steady state of clusteri...Following a sticky particle model and its computer simulation scheme proposed in the previous papers, the motions of particles in both 2-and 3-dimensional shear flow fields are simulated. At a steady state of clustering process, the radial distribution functions are calculated to precisely describe the microstructure of aggregates in dispersions, and the configuration of particles is displayed,which gives a direct view of microstructure. It is found that (1) the kind of the microstructure transforms from compact clusters to a loose network as the concentration of particles increases; (2) the microstructure is independent of shear rate which only dominates the size of clusters formed at steady state.展开更多
基金National Key Research and Development Program (2020YFA0906800)the National Natural Science Foundation of China (21808221, 91934301, 21961160745)+2 种基金External Cooperation Program of BIC, Chinese Academy of Sciences (122111KYSB20190032)the Key Research Program of Nanjing IPE Institute of Green Manufacturing Industry (No. E0010719)Innovation Academy for Green Manufacture, Chinese Academy of Sciences (IAGM2020C06)
文摘The main spatial distribution features of shear rate in a stirred tank operated with five different radial and axial flow impellers were presented with particle image velocimetry(PIV)experiments.Not only the average shear rate in the whole tank but also the local value in the vicinity of impeller increases linearly with impeller speed.Furthermore,the shear coefficient(Ks,imp)at the impeller outlet is linearly related to the impeller flow number(Nq)and decreases with the increase of Nq in general at the constant power consumption per unit volume(Pv).During scale-up based on the constant Pv and geometric similarity,CFD results show that the volume-averaged shear rate(cavg)for RDT decreases faster than that of other impellers with the impeller tip velocity(Utip).The novel multi-blade combined(MBC)impeller with the increased height-to-diameter ratio of the stirred tank is able to more effectively improve the distribution uniformity of shear rate at the same Pv after scale-up.These studies provide a data basis for selecting the impeller types and improving the shear rate environment in the large-scale stirred tank.
文摘The temperature distribution under shear with a high strain rate and the cooling rate of the shear bands of Al, Cu and 0.06C steel have been calculated using a computer. The results show that the temperature of shear band increases with the increase of the average strain rate (_o). When _o is in the range 8×10~5 to 10~6 1/s, the structure of the adiabatic shear band in a 0.06C steel is martensite but it becomes metallic glass if _o=10~6 1/s. As to A1 and Cu, the structure of the adiabatic shear bands can also be of metallic glass if _o is greater than 1.8×10~6 and 5.5×10~7 1/s respectively. It explains that Cu tends most difficultly to form adiabatic shear band, while 0.06C steel most readily among the three metals.
文摘Following a sticky particle model and its computer simulation scheme proposed in the previous papers, the motions of particles in both 2-and 3-dimensional shear flow fields are simulated. At a steady state of clustering process, the radial distribution functions are calculated to precisely describe the microstructure of aggregates in dispersions, and the configuration of particles is displayed,which gives a direct view of microstructure. It is found that (1) the kind of the microstructure transforms from compact clusters to a loose network as the concentration of particles increases; (2) the microstructure is independent of shear rate which only dominates the size of clusters formed at steady state.
