A perturbation finite volume(PFV)method for the convective-diffusion integral equa- tion is developed in this paper.The PFV scheme is an upwind and mixed scheme using any higher-order interpolation and second-order in...A perturbation finite volume(PFV)method for the convective-diffusion integral equa- tion is developed in this paper.The PFV scheme is an upwind and mixed scheme using any higher-order interpolation and second-order integration approximations,with the least nodes similar to the standard three-point schemes,that is,the number of the nodes needed is equal to unity plus the face-number of the control volume.For instance,in the two-dimensional(2-D)case,only four nodes for the triangle grids and five nodes for the Cartesian grids are utilized,respectively.The PFV scheme is applied on a number of 1-D linear and nonlinear problems,2-D and 3-D flow model equations.Comparing with other standard three-point schemes,the PFV scheme has much smaller numerical diffusion than the first-order upwind scheme(UDS).Its numerical accuracies are also higher than the second-order central scheme(CDS),the power-law scheme(PLS)and QUICK scheme.展开更多
Historically,streamer-to-leader transition studies mainly focused on the rod-plane gap and low altitude analysis,with limited attention paid to the sphere-plane gap at high altitude analysis.In this work,sphere-plane ...Historically,streamer-to-leader transition studies mainly focused on the rod-plane gap and low altitude analysis,with limited attention paid to the sphere-plane gap at high altitude analysis.In this work,sphere-plane gap discharge tests were carried out under the gap distance of 5 m at the Qinghai Ultra High Voltage(UHV)test base at an altitude of 2200 m.The experiments measured the physical parameters such as the discharge current,electric field intensity and instantaneous optical power.The duration of the dark period and the critical charge of streamer-toleader transition were obtained at high altitude.Based on radial thermal expansion of the streamer stem,we established a modified streamer-to-leader transition model of the sphere-plane gap discharge at high altitude,and calculated the stem temperature,stem radii and the duration of streamer-to-leader transition.Compared with the measured duration of sphere-plane electrode discharge at an altitude of 2200 m,the error rate of the modified model was 0.94%,while the classical model was 6.97%,demonstrating the effectiveness of the modified model.From the comparisons and analysis,several suggestions are proposed to improve the numerical model for further quantitative investigations of the leader inception.展开更多
Convection and diffusion are the main factors affecting radon migration.In this paper,a coupled diffusion-convection radon migration model is presented taking into account turbulence effects.In particular,the migratio...Convection and diffusion are the main factors affecting radon migration.In this paper,a coupled diffusion-convection radon migration model is presented taking into account turbulence effects.In particular,the migration of radon is simulated in the framework of the k-εturbulence model.The model equations are solved in a complex 3D domain by the finite element method(FEM).Special attention is paid to the case study about radon migration in an abandoned air defense shelter(AADS).The results show that air convection in a confined space has a great influence on the radon migration and the radon concentration is inversely proportional to the wind speed.展开更多
In this study, the material is okra, a cucurbitaceous largely consumed in West Africa and South Asia. The influence of the external air parameters on food drying with different size, maturity, shape of the material is...In this study, the material is okra, a cucurbitaceous largely consumed in West Africa and South Asia. The influence of the external air parameters on food drying with different size, maturity, shape of the material is considered by convective drying. So, the okra was cut in several parts according to its three characteristic zones, the basis, the middle of the okra and the extremity because the three parts of the vegetable have not the same resistances in transfers by convective drying. The maturity of the okra also has an influence. The okra dries faster in its younger or older age. Okra dries slowly when its maturity is convenient to be consumed. The drying duration of okra with the age of 1, 2, 3, 4 and 5 days is respectively 580, 780, 990, 1200 and 850 min. When we consider the three (matters) constituent of the okra: the skin, the seeds and the central material, the central matter dries faster. The diffusion coefficient was identified in all cases in order to compare the influence of those intrinsic properties of that food.展开更多
基金The project supported by the National Natural Science Foundation of China(10272106,10372106)
文摘A perturbation finite volume(PFV)method for the convective-diffusion integral equa- tion is developed in this paper.The PFV scheme is an upwind and mixed scheme using any higher-order interpolation and second-order integration approximations,with the least nodes similar to the standard three-point schemes,that is,the number of the nodes needed is equal to unity plus the face-number of the control volume.For instance,in the two-dimensional(2-D)case,only four nodes for the triangle grids and five nodes for the Cartesian grids are utilized,respectively.The PFV scheme is applied on a number of 1-D linear and nonlinear problems,2-D and 3-D flow model equations.Comparing with other standard three-point schemes,the PFV scheme has much smaller numerical diffusion than the first-order upwind scheme(UDS).Its numerical accuracies are also higher than the second-order central scheme(CDS),the power-law scheme(PLS)and QUICK scheme.
基金supported by National Natural Science Foundation of China(Scientific Funds for Young Scientists)(No.52007064)。
文摘Historically,streamer-to-leader transition studies mainly focused on the rod-plane gap and low altitude analysis,with limited attention paid to the sphere-plane gap at high altitude analysis.In this work,sphere-plane gap discharge tests were carried out under the gap distance of 5 m at the Qinghai Ultra High Voltage(UHV)test base at an altitude of 2200 m.The experiments measured the physical parameters such as the discharge current,electric field intensity and instantaneous optical power.The duration of the dark period and the critical charge of streamer-toleader transition were obtained at high altitude.Based on radial thermal expansion of the streamer stem,we established a modified streamer-to-leader transition model of the sphere-plane gap discharge at high altitude,and calculated the stem temperature,stem radii and the duration of streamer-to-leader transition.Compared with the measured duration of sphere-plane electrode discharge at an altitude of 2200 m,the error rate of the modified model was 0.94%,while the classical model was 6.97%,demonstrating the effectiveness of the modified model.From the comparisons and analysis,several suggestions are proposed to improve the numerical model for further quantitative investigations of the leader inception.
基金supported by the National Natural Science Foundation of China[grant numbers 11705083]China Postdoctoral Science Foundation[grant number 2018M632975]+1 种基金National Natural Science Foundation of Hunan Province[grant number 2019JJ50488]Hunan Province Engineering Research Center of Radioactive Control Technology in Uranium Mining and Metallurgy&Hunan Province Engineering Technology Research Center of Uranium Tailings Treatment Technology,University of South China[grant number 2019YKZX1009].
文摘Convection and diffusion are the main factors affecting radon migration.In this paper,a coupled diffusion-convection radon migration model is presented taking into account turbulence effects.In particular,the migration of radon is simulated in the framework of the k-εturbulence model.The model equations are solved in a complex 3D domain by the finite element method(FEM).Special attention is paid to the case study about radon migration in an abandoned air defense shelter(AADS).The results show that air convection in a confined space has a great influence on the radon migration and the radon concentration is inversely proportional to the wind speed.
文摘In this study, the material is okra, a cucurbitaceous largely consumed in West Africa and South Asia. The influence of the external air parameters on food drying with different size, maturity, shape of the material is considered by convective drying. So, the okra was cut in several parts according to its three characteristic zones, the basis, the middle of the okra and the extremity because the three parts of the vegetable have not the same resistances in transfers by convective drying. The maturity of the okra also has an influence. The okra dries faster in its younger or older age. Okra dries slowly when its maturity is convenient to be consumed. The drying duration of okra with the age of 1, 2, 3, 4 and 5 days is respectively 580, 780, 990, 1200 and 850 min. When we consider the three (matters) constituent of the okra: the skin, the seeds and the central material, the central matter dries faster. The diffusion coefficient was identified in all cases in order to compare the influence of those intrinsic properties of that food.
