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
A new ultrasonic transducer with multi-belts coil for generating and receiving longitudinal guided wave in ferromagnetic material pipes is proposed.The theory backgrounds and transduction principle of the proposed tra...A new ultrasonic transducer with multi-belts coil for generating and receiving longitudinal guided wave in ferromagnetic material pipes is proposed.The theory backgrounds and transduction principle of the proposed transducer are presented and ana- lyzed.To verify the performance of the transducer,several experiments are performed.The performance of inspecting crack, frequency-tuned characteristic,effect of bias static magnetic field and dynamic magnetic field,lift-off effect and effect of the period number of the exciting current are investigated.The results show that the proposed coils not only could tune the center frequency but also could improve the amplitude and signal-to-noise(SNR)of the detected signals.Bias static magnetic field and dynamic magnetic field are two important factors influencing the amplitude of the longitudinal guided wave.The amplitude of the longitudinal guided wave is exponentially decreased versus the lift-off distance of the transmitter and receiver.Period number of excitation signal could influence the amplitude and wave width of the ultrasonic wave.The proposed transducer could easily control the wave modes and would be a better choice for pipes’monitoring and inspection compared to traditional single-belt coil transducer.展开更多
Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the unifo...Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material （PCM） temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperaalre distribution was also confirmed by simulation results.展开更多
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 {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.
基金supported by the National Natural Science Foundation of China(Grant No.10974115)
文摘A new ultrasonic transducer with multi-belts coil for generating and receiving longitudinal guided wave in ferromagnetic material pipes is proposed.The theory backgrounds and transduction principle of the proposed transducer are presented and ana- lyzed.To verify the performance of the transducer,several experiments are performed.The performance of inspecting crack, frequency-tuned characteristic,effect of bias static magnetic field and dynamic magnetic field,lift-off effect and effect of the period number of the exciting current are investigated.The results show that the proposed coils not only could tune the center frequency but also could improve the amplitude and signal-to-noise(SNR)of the detected signals.Bias static magnetic field and dynamic magnetic field are two important factors influencing the amplitude of the longitudinal guided wave.The amplitude of the longitudinal guided wave is exponentially decreased versus the lift-off distance of the transmitter and receiver.Period number of excitation signal could influence the amplitude and wave width of the ultrasonic wave.The proposed transducer could easily control the wave modes and would be a better choice for pipes’monitoring and inspection compared to traditional single-belt coil transducer.
基金supported by the National Natural Science Foundation of China(Grant No.51576187)Fundamental Research Funds for the Central Universities(Grant No.WK2090130016)
文摘Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material （PCM） temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperaalre distribution was also confirmed by simulation results.
