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Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio 被引量:5
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作者 YOO Geun-jong CHOI Hoon-ki DONG Wa-ryong 《Journal of Central South University》 SCIE EI CAS 2012年第2期471-476,共6页
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 12n. 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
关键词 spiral coiled tube heat exchanger Reynolds number curvature ratio secondary flow friction factor Nusselt number
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Theoretical and Experimental Study on Ground Coupled Heat Pump with Vertical Spiral Coil 被引量:4
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作者 李新国 周倩 +2 位作者 赵军 朱强 胡璟 《Transactions of Tianjin University》 EI CAS 2003年第2期123-126,共4页
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
关键词 ground coupled heat pump (GCHP) vert ic al spiral coil underground temperature distribution optimal operation ratio
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Comparison of three formulations for eddy-current problems in a spiral coil electromagnetic acoustic transducer
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作者 石文泽 吴运新 +3 位作者 龚海 赵志然 范吉志 谭良辰 《Journal of Central South University》 SCIE EI CAS CSCD 2016年第4期817-824,共8页
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 {I1 are based on inc... 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 {I1 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 Ili 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
关键词 electromagnetic acoustic transducer (EMAT) eddy current finite element method (FEM) skin and proximity effects spiral coil
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Experimental Verification to Estimate Ground Thermal Conductivity Using Spiral Coil Type Ground Heat Exchangers
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作者 Seok Yoon Min Jun Kim Gyu Hyun Go Seung Rae Lee 《Journal of Civil Engineering and Architecture》 2014年第4期425-429,共5页
This paper presents an experimental study on the evaluation of thermal response of a spiral coil type GHE (ground heat exchanger). This GHE was installed on partially saturated landfill ground that was composed of s... This paper presents an experimental study on the evaluation of thermal response of a spiral coil type GHE (ground heat exchanger). This GHE was installed on partially saturated landfill ground that was composed of silt and clay in the runway area of Incheon International airport. TRT (thermal response test) was conducted for more than 65 hours under continuous operation conditions. Ground thermal conductivity was derived based on line source theory, which has usually been found to be appropriate for line type GHEs such as U, W and 2U types. A reasonable method to derive ground thermal conductivity using the infinite line source theory for a spiral coil type GHE was introduced. Ground thermal conductivity from the TRT using spiral coil type GHE was compared with those from the analytical equivalent model of ground thermal conductivity. 展开更多
关键词 Ground thermal conductivity ground heat exchanger thermal response test spiral coil.
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Alternative flat coil design for electromagnetic forming using FEM 被引量:2
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作者 M.AHMED1 S.K.PANTHI +4 位作者 N.RAMAKRISHNAN A.K.JHA A.H.YEGNESWARAN R.DASGUPTA S.AHMED 《Transactions of Nonferrous Metals Society of China》 SCIE EI CAS CSCD 2011年第3期618-625,共8页
Electromagnetic forming (EMF) is a high velocity forming process that uses impulse magnetic force. Coil is an important component of EMF system which needs to be designed depending on application. Flat spiral coils ... Electromagnetic forming (EMF) is a high velocity forming process that uses impulse magnetic force. Coil is an important component of EMF system which needs to be designed depending on application. Flat spiral coils are generally used for electromagnetic forming of sheet metals. However, with this type of coil the central portion of the workpiece experiences marginal magnetic force. This leads to in-sufficient deformation at this portion and other problems like air entrapment. In this study, a conceptual design of flat coil was proposed for better distribution of magnetic forces over the workpiece. Comparative analysis of distribution of magnetic force, magnetic field and current density using the proposed and the existing coil designs were carried out using FEM. The result indicates that the proposed coil design produces comparatively better magnetic force distribution over the workpiece. Calculation of self-inductance of such coils was also carried out and was compared with FE simulation. 展开更多
关键词 electromagnetic forming flat spiral coil sheet metal forming FEM
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PIV EXPERIMENTAL RESEARCH OF FLOW STRUCTURE IN RECTANGULAR CHANNEL WITH TRANSVERSELY PLACED SPIRAL COIL INSERT 被引量:5
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作者 TANG Yu-feng TIAN Mao-cheng ZHANG Guan-min 《Journal of Hydrodynamics》 SCIE EI CSCD 2012年第4期518-525,共8页
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
关键词 Particle Image Velocimetry (PIV) spiral coil longitudinal vortices flow disturbance
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Reconfigurable Transmitter Coil Structure for Highly Efficient and Misalignment-insensitive Wireless Power Transfer Systems in Megahertz Range
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作者 Lihao Wu Bo Zhang 《Chinese Journal of Electrical Engineering》 CSCD 2019年第2期56-62,共7页
The structural optimization of coils is a key issue in wireless power transfer(WPT)applications owing to size limitations.In this study,a novel planar-spiral transmitter coil(TX-coil)with an outer-tight and inner-spar... The structural optimization of coils is a key issue in wireless power transfer(WPT)applications owing to size limitations.In this study,a novel planar-spiral transmitter coil(TX-coil)with an outer-tight and inner-sparse configuration is proposed to achieve a high quality factor(Q-factor)and uniform magnetic field,which ensures high efficiency and improves the misalignment tolerance for several-megahertz WPT systems.Furthermore,a closed-form expression for the Q-factor is provided and analyzed for coil optimization.By using this method,a TX-coil with an outer diameter of 100 mm and a wire diameter of 1.5 mm is designed and tested at 1 MHz.Finite element method simulations and experimental results demonstrate that the Q-factor is increased by about 8%in comparison with evenly spaced planar spiral coils,which is achieved while ensuring a relatively uniform magnetic field. 展开更多
关键词 High quality factor planar spiral coil structure optimization uniform magnetic field wireless power transfer
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