Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat...Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.展开更多
Background The response of superheated emulsion detector with different halocarbons as active liquid to poly-energetic and mono-energetic neutrons has been carried out by different workers.The C_(2)H_(2)F_(4)detectors...Background The response of superheated emulsion detector with different halocarbons as active liquid to poly-energetic and mono-energetic neutrons has been carried out by different workers.The C_(2)H_(2)F_(4)detectors have not been explored much.This liquid has shown the potentiality of sensitivity to low-mass dark matter.The previous calibration of this liquid was carried out with the poly-energetic neutrons.Purpose In the present work,to better characterize the detector with neutrons,it is irradiated with quasi-mono-energetic neutrons and the results are compared with neutrons from ^(241)Am-Be.To run the detector for the dark matter search,it is required to calibrate it with neutrons,preferably with mono-energetic neutrons.But mono-energetic neutron is not available at all establishments;hence,it was calibrated with quasi-mono-energetic neutrons.Method The response of superheated emulsion consisting of the droplets of C_(2)H_(2)F_(4)has been studied using the quasi-mono-energetic neutrons.The superheated droplets have been fabricated in a visco-elastic gel matrix.The shock waves generated by the passage of the energetic particles are detected by the acoustic sensors coupled to the emulsion.The measurement has also been carried out for the blank target and beam-off conditions.Results and conclusion It is observed that the(P_(var))response of the emulsion in the low-frequency range is sharper for the quasi-mono-energetic neutrons from ^(7)Li(p,n)reaction and wider for the poly-energetic neutrons from ^(241)Am-Be.The fundamental frequency associated with bubble nucleation(FF values)is similar for the neutrons from ^(7)Li-target and ^(241)Am-Be source.The precise characterization of such detector is required for the application in neutron measurement as well as for the dark matter search experiment apart from the basic understanding of the radiation-induced bubble nucleation.展开更多
基金Supported by the National Natural Science Foundation of China （51106119, 81100707）, the Fundamental Research Funds for the Central University of China, Doctoral Fund of Ministry of Education （20110201120052） and the National Science and Technology Sur0orting Item （2012BAA08B03）.
文摘Multiple size group （MUSIG） model combined with a threedimensional twofluid model were em ployed to predict subcooled boiling flow of liquid nitrogen in a vertical upward tube. Based on the mechanism of boiling heat transfer, some important bubble model parameters were amended to be applicable to the modeling of liquid nitrogen. The distribution of different discrete bubble classes was demonstrated numerically and the distribu tion patterns of void fraction in the wallheated tube were analyzed. It was found that the average void fraction in creases nonlinearly along the axial direction with wall heat flux and it decreases with inlet mass flow rate and sub cooled temperature. The local void fraction exhibited a Ushape distribution in the radial direction. The partition of the wall heat flux along the tube was obtained. The results showed that heat flux consumed on evaporation is the leading part of surface heat transfer at the rear region of subcooled boiling. The turning point in the pressure drop curve reflects the instability of bubbly flow. Good agreement was achieved on the local heat transfer coefficient aalnst experimental measurements, which demonstrated the accuracy of the numerical model.
文摘Background The response of superheated emulsion detector with different halocarbons as active liquid to poly-energetic and mono-energetic neutrons has been carried out by different workers.The C_(2)H_(2)F_(4)detectors have not been explored much.This liquid has shown the potentiality of sensitivity to low-mass dark matter.The previous calibration of this liquid was carried out with the poly-energetic neutrons.Purpose In the present work,to better characterize the detector with neutrons,it is irradiated with quasi-mono-energetic neutrons and the results are compared with neutrons from ^(241)Am-Be.To run the detector for the dark matter search,it is required to calibrate it with neutrons,preferably with mono-energetic neutrons.But mono-energetic neutron is not available at all establishments;hence,it was calibrated with quasi-mono-energetic neutrons.Method The response of superheated emulsion consisting of the droplets of C_(2)H_(2)F_(4)has been studied using the quasi-mono-energetic neutrons.The superheated droplets have been fabricated in a visco-elastic gel matrix.The shock waves generated by the passage of the energetic particles are detected by the acoustic sensors coupled to the emulsion.The measurement has also been carried out for the blank target and beam-off conditions.Results and conclusion It is observed that the(P_(var))response of the emulsion in the low-frequency range is sharper for the quasi-mono-energetic neutrons from ^(7)Li(p,n)reaction and wider for the poly-energetic neutrons from ^(241)Am-Be.The fundamental frequency associated with bubble nucleation(FF values)is similar for the neutrons from ^(7)Li-target and ^(241)Am-Be source.The precise characterization of such detector is required for the application in neutron measurement as well as for the dark matter search experiment apart from the basic understanding of the radiation-induced bubble nucleation.
