The configuration, magnetic field calculation and field distribution of the birdcage RF coil is pre-sented. This type of coil can produce a circular Polarized magnetic field. It has been widely used in the MRIsystem f...The configuration, magnetic field calculation and field distribution of the birdcage RF coil is pre-sented. This type of coil can produce a circular Polarized magnetic field. It has been widely used in the MRIsystem for head and whole-body imaging which can achive nearly optimal RF field uniformity and signal-to-noise ratio(SNR). The rnagnetic field is evenly distributed over the coil. The features of the birdcage coil areanalyzed on the basis of numerical simulation and experimental studies.展开更多
Numerical method is used to investigate fully developed laminar flow in helically coiled circular tube in this paper.The non-dimensional parameter(secondary flow Reynolds number Se)based on absolute vorticity flux alo...Numerical method is used to investigate fully developed laminar flow in helically coiled circular tube in this paper.The non-dimensional parameter(secondary flow Reynolds number Se)based on absolute vorticity flux along the mainstream is used to indicate the intensity of secondary flow caused by the centrifugal effect in helically coiled circular tube.The relationship between the intensity of secondary flow and the intensity of laminar convective heat transfer is studied.The effects of curvature and torsion on the enhancement of heat transfer are also considered.The results reveal that the absolute vorticity flux along the mainstream can be used to indicate the local or averaged intensity of secondary flow;the non-dimensional parameter of the absolute vortex along the main flow determines the convective heat transfer and friction factor.The relationships of Nusselt number and friction factor with the Se are obtained.The effect of curvature on Nusselt number is obvious,but the effect of torsion on Nusselt number is less obvious.展开更多
文摘The configuration, magnetic field calculation and field distribution of the birdcage RF coil is pre-sented. This type of coil can produce a circular Polarized magnetic field. It has been widely used in the MRIsystem for head and whole-body imaging which can achive nearly optimal RF field uniformity and signal-to-noise ratio(SNR). The rnagnetic field is evenly distributed over the coil. The features of the birdcage coil areanalyzed on the basis of numerical simulation and experimental studies.
基金supported by the National Natural Science Foundation of China(No.51776093,No.52066009)Transformation of S&T achievements in Universities of Gansu Province of China(No.2019C-06)+1 种基金Major Special Projects of Gansu Province of China(21ZD4GA027)Young Scientists Fund of Lanzhou Jiaotong University(2020038)。
文摘Numerical method is used to investigate fully developed laminar flow in helically coiled circular tube in this paper.The non-dimensional parameter(secondary flow Reynolds number Se)based on absolute vorticity flux along the mainstream is used to indicate the intensity of secondary flow caused by the centrifugal effect in helically coiled circular tube.The relationship between the intensity of secondary flow and the intensity of laminar convective heat transfer is studied.The effects of curvature and torsion on the enhancement of heat transfer are also considered.The results reveal that the absolute vorticity flux along the mainstream can be used to indicate the local or averaged intensity of secondary flow;the non-dimensional parameter of the absolute vortex along the main flow determines the convective heat transfer and friction factor.The relationships of Nusselt number and friction factor with the Se are obtained.The effect of curvature on Nusselt number is obvious,but the effect of torsion on Nusselt number is less obvious.
