Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angl...Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12π. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.展开更多
The numeric al simulation study on the temperature distribution of underground field for the ground coupled heat pump (GCHP) with vertical spira l coil was carried out by using finite element. The distribution and rec...The numeric al simulation study on the temperature distribution of underground field for the ground coupled heat pump (GCHP) with vertical spira l coil was carried out by using finite element. The distribution and recovery of undergroun d field temperature under different operation ratio and the optimal operation ratio were simulated.The performance parameters, i.e. inlet and outlet temperature of the ground spiral coil in heating and cooling modes were tested, the heat extracted or emitted by the heat pump to the ground was calculated, and the coefficients of performance (COP) of GCHP at heat ing and cooling modes were analyzed.展开更多
Three differential equations based on different definitions of current density are compared. Formulation Ⅰ is based on an incomplete equation for total current density(TCD). Formulations Ⅱ and Ⅲ are based on incomp...Three differential equations based on different definitions of current density are compared. Formulation Ⅰ is based on an incomplete equation for total current density(TCD). Formulations Ⅱ and Ⅲ are based on incomplete and complete equations for source current density(SCD), respectively. Using the weak form of finite element method(FEM), three formulations were applied in a spiral coil electromagnetic acoustic transducer(EMAT) example to solve magnetic vector potential(MVP). The input impedances calculated by Formulation Ⅲ are in excellent agreement with the experimental measurements. Results show that the errors for Formulations Ⅰ& Ⅱ vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin & proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ⅲ to solve MVP when the coil diameter is less than twice the skin depth for Formulation Ⅰ is a low cost and high efficiency calculation method.展开更多
This paper elaborates on the magnetic forces between current carrying planar spiral coils. Direct and concentric rings methods are employed in order to calculate the magnetic force between these coils. The results obt...This paper elaborates on the magnetic forces between current carrying planar spiral coils. Direct and concentric rings methods are employed in order to calculate the magnetic force between these coils. The results obtained by two calculation methods show the efficiency of the replaced rings method in both simplicity and calculation time. Simula-tions using the Finite Element Method (FEM) are carried out to analyze the distribution of the magnetic flux density around the coils. Also, coils with precise size have been constructed and tested. The experimental results as well as the results obtained by FEM are used to validate the accuracy of the calculations.展开更多
The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry (PIV) measurements in both transverse and longitudinal sections. The experimental r...The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry (PIV) measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Com- pared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous dis- turbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the redu- ction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enha- nced in this area.展开更多
Objective.To compare the embolization effects of intracranial aneurysms with mechanical detachable spirals(MDS) and with Guglielmi detachable coils(GDC).Methods.One hundred and twenty cases with 125 intracranial aneur...Objective.To compare the embolization effects of intracranial aneurysms with mechanical detachable spirals(MDS) and with Guglielmi detachable coils(GDC).Methods.One hundred and twenty cases with 125 intracranial aneurysms were embolized in Beijing Hospital from March 1995 to July 1999.Sixty-six aneursms in 64 cases were embolized with MDS,51 in 48 with GDC, and 8 in 8 with both MDS and GDC.Clinical data includng sex,age,subarachnoid hemorrhage(SAH),Hunt & Hess grading,diameter and neck width of aneurysms,number and length of coils used per aneurysm,occlusive radio,and complications were compared between MDS and groups.Results.MDS and GDC groups were comparable(t-test or X^2 -test ,all P value>0.10) in terms of age,sex,diameter of aneurysms[(8.46±3.42)mm vs.(7.38±3.45)mm],neck width[(3.49±1.50)mm vs.(3.26±1.52)mm],coils number [(4.65±3.01)vs.(4.24±2.65)] and their length[(460.2±398.5)mm vs.(422.9±387.1)mm] used per aneurysm,occlusive ratio in aneurysms embolized≥80%[(95.00±6.32%)vs.(94.19%±7.63%)],mortality and permanent complications(7.8% vs.4.25)。Couclusions,MDS and GDC are all materials for embolization of intracranial aneurysms.MDS is less expensive,but more difficult to control and of propensity to complications while GDC is more compliant ,easier to be used,safer,and have many alternative types for use as well as more extensive indications.展开更多
基金supported by the Second Stage of Brain Korea 21 Projects,Korea
文摘Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12π. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.
文摘The numeric al simulation study on the temperature distribution of underground field for the ground coupled heat pump (GCHP) with vertical spira l coil was carried out by using finite element. The distribution and recovery of undergroun d field temperature under different operation ratio and the optimal operation ratio were simulated.The performance parameters, i.e. inlet and outlet temperature of the ground spiral coil in heating and cooling modes were tested, the heat extracted or emitted by the heat pump to the ground was calculated, and the coefficients of performance (COP) of GCHP at heat ing and cooling modes were analyzed.
基金Project(2014BAF12B01)supported by the Key Projects in the National Science&Technology Pillar Program during the Twelfth Five-year Plan Period,ChinaProject(51405520)supported by the National Natural Science Foundation of ChinaProject(2012CB619505)supported by National Basic Research Program of China
文摘Three differential equations based on different definitions of current density are compared. Formulation Ⅰ is based on an incomplete equation for total current density(TCD). Formulations Ⅱ and Ⅲ are based on incomplete and complete equations for source current density(SCD), respectively. Using the weak form of finite element method(FEM), three formulations were applied in a spiral coil electromagnetic acoustic transducer(EMAT) example to solve magnetic vector potential(MVP). The input impedances calculated by Formulation Ⅲ are in excellent agreement with the experimental measurements. Results show that the errors for Formulations Ⅰ& Ⅱ vary with coil diameter, coil spacing, lift-off distance and external excitation frequency, for the existence of eddy-current and skin & proximity effects. And the current distribution across the coil conductor also follows the same trend. It is better to choose Formulation I instead of Formulation Ⅲ to solve MVP when the coil diameter is less than twice the skin depth for Formulation Ⅰ is a low cost and high efficiency calculation method.
文摘This paper elaborates on the magnetic forces between current carrying planar spiral coils. Direct and concentric rings methods are employed in order to calculate the magnetic force between these coils. The results obtained by two calculation methods show the efficiency of the replaced rings method in both simplicity and calculation time. Simula-tions using the Finite Element Method (FEM) are carried out to analyze the distribution of the magnetic flux density around the coils. Also, coils with precise size have been constructed and tested. The experimental results as well as the results obtained by FEM are used to validate the accuracy of the calculations.
基金the Shangdong Province Key Scientific and Technological Project (Grant No.2008GG10007009)the Independent Innovation Foundation of Shandong University (GrantNo. 2009TS051)the Graduate Independent Innovation Foundation of Shandong University (Grant No.31380071613059)
文摘The flow field in a rectangular channel with a transversely placed spiral coil insert is investigated by Particle Image Velocimetry (PIV) measurements in both transverse and longitudinal sections. The experimental results show that multi-longitudinal vortices are induced downstream of the spiral coil and are distributed as a symmetrical vortex array along the horizontal central line of the transverse section. Along the mainstream, due to the spiral motion of the longitudinal vortices, the velocity fluctuates in a manner of the damped sinusoidal curve and the velocity component in the wall normal direction is improved in the channel. Com- pared with the flow field in a smooth channel it is found that the movement of the longitudinal vortices can cause a continuous dis- turbance near the channel walls and thus enhances the fluid velocity in the near wall region, which consequently leads to the redu- ction of the velocity gradient and a more uniform velocity distribution. With the increase of the Reynolds number, the induced longitudinal vortices gain strength and become straighter and closer to the channel walls, thus the turbulence intensity is further enha- nced in this area.
基金This work was originally published in the Chinese Journal of Neuro-surgery (2001 17(2): 87-90) in Chinese.
文摘Objective.To compare the embolization effects of intracranial aneurysms with mechanical detachable spirals(MDS) and with Guglielmi detachable coils(GDC).Methods.One hundred and twenty cases with 125 intracranial aneurysms were embolized in Beijing Hospital from March 1995 to July 1999.Sixty-six aneursms in 64 cases were embolized with MDS,51 in 48 with GDC, and 8 in 8 with both MDS and GDC.Clinical data includng sex,age,subarachnoid hemorrhage(SAH),Hunt & Hess grading,diameter and neck width of aneurysms,number and length of coils used per aneurysm,occlusive radio,and complications were compared between MDS and groups.Results.MDS and GDC groups were comparable(t-test or X^2 -test ,all P value>0.10) in terms of age,sex,diameter of aneurysms[(8.46±3.42)mm vs.(7.38±3.45)mm],neck width[(3.49±1.50)mm vs.(3.26±1.52)mm],coils number [(4.65±3.01)vs.(4.24±2.65)] and their length[(460.2±398.5)mm vs.(422.9±387.1)mm] used per aneurysm,occlusive ratio in aneurysms embolized≥80%[(95.00±6.32%)vs.(94.19%±7.63%)],mortality and permanent complications(7.8% vs.4.25)。Couclusions,MDS and GDC are all materials for embolization of intracranial aneurysms.MDS is less expensive,but more difficult to control and of propensity to complications while GDC is more compliant ,easier to be used,safer,and have many alternative types for use as well as more extensive indications.