The steady equilibrium conditions for a mixed gas of neutrons, protons, electrons, positrons and radiation fields （abbreviated as npe^± gas） with or without external neutrino flux are investigated, and a genera...The steady equilibrium conditions for a mixed gas of neutrons, protons, electrons, positrons and radiation fields （abbreviated as npe^± gas） with or without external neutrino flux are investigated, and a general chemical potential equilibrium equation μn = μp ＋ Cμe is obtained to describe the steady equilibrium at high temperatures （T 〉 10^9 K）. An analytic fitting formula of coefficient C is presented for the sake of simplicity, when neutrinos and antineutrinos are transparent. It is a simple method to estimate the electron fraction for the steady equilibrium npe^± gas that adopts the corresponding equilibrium condition. As an example, we apply this method to the GRB accretion disk and confirm that the composition in the inner region is approximately in equilibrium when the accretion rate is low. For the case with external neutrino flux, we calculate the initial electron fraction of neutrino-driven wind from the proto-neutron star model M15-l1-r1. The results show that the improved equilibrium condition makes the electron fraction decrease significantly more than the case μn = μp ＋ μe when the time is less than 5s post bounce, which may be useful for r-process nucleosynthesis models.展开更多
Numerical simulation was carried out to study the centrifugally-driven flow and heat transfer inside rotating metallic porous disk subjected to local heat flux. The effects of rotational speed, solid thermal conductiv...Numerical simulation was carried out to study the centrifugally-driven flow and heat transfer inside rotating metallic porous disk subjected to local heat flux. The effects of rotational speed, solid thermal conductivity and porosity on heat transfer were analyzed. The thermal transport coefficient, defined as the ratio of local heat flux to maximum temperature difference on the disk, was introduced to evaluate the thermal transport capacity in rotating porous disk. For convenience, the conjugation between convective heat transfer inside the rotating porous disk and convective heat transfer over the rotating disk surface was decoupled in the present study. Firstly, the convective heat transfer over the free rotating disk surface was investigated indi-vidually to determine the heat transfer coefficient over the disk surface to the ambient air. Then the convective heat transfer over a rotating disk surface was treated as the thermal boundary condition for the computation of convective heat transfer in-side rotating porous disk. Under the present research conditions, the results show that the centrifugally-driven flow is enhanced significantly with the increase of rotational speed. Consequently, the maximum temperature on the disk surface is decreased and the temperature distribution tends to be uniform. The thermal transport capacity in rotating porous disk is also enhanced with the increase of solid thermal conductivity or the decrease of solid porosity. In the rotating porous disk, the solid phase heat transfer is clearly the dominant mode of heat transport and the fluid phase makes an incremental contribution to the total heat transfer.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 10733010, 10673010 and 10573016)the National Basic Research Program of China (2009CB824800)+2 种基金the Scientific Research Funds of Sichuan Provincial Education Department (10ZC014, 2009ZB087)China West Normal University(09A004)Graduate Innovation Funds of USTC
文摘The steady equilibrium conditions for a mixed gas of neutrons, protons, electrons, positrons and radiation fields （abbreviated as npe^± gas） with or without external neutrino flux are investigated, and a general chemical potential equilibrium equation μn = μp ＋ Cμe is obtained to describe the steady equilibrium at high temperatures （T 〉 10^9 K）. An analytic fitting formula of coefficient C is presented for the sake of simplicity, when neutrinos and antineutrinos are transparent. It is a simple method to estimate the electron fraction for the steady equilibrium npe^± gas that adopts the corresponding equilibrium condition. As an example, we apply this method to the GRB accretion disk and confirm that the composition in the inner region is approximately in equilibrium when the accretion rate is low. For the case with external neutrino flux, we calculate the initial electron fraction of neutrino-driven wind from the proto-neutron star model M15-l1-r1. The results show that the improved equilibrium condition makes the electron fraction decrease significantly more than the case μn = μp ＋ μe when the time is less than 5s post bounce, which may be useful for r-process nucleosynthesis models.
基金supported by the National Natural Science Foundation of China (Grant No. 51076063)
文摘Numerical simulation was carried out to study the centrifugally-driven flow and heat transfer inside rotating metallic porous disk subjected to local heat flux. The effects of rotational speed, solid thermal conductivity and porosity on heat transfer were analyzed. The thermal transport coefficient, defined as the ratio of local heat flux to maximum temperature difference on the disk, was introduced to evaluate the thermal transport capacity in rotating porous disk. For convenience, the conjugation between convective heat transfer inside the rotating porous disk and convective heat transfer over the rotating disk surface was decoupled in the present study. Firstly, the convective heat transfer over the free rotating disk surface was investigated indi-vidually to determine the heat transfer coefficient over the disk surface to the ambient air. Then the convective heat transfer over a rotating disk surface was treated as the thermal boundary condition for the computation of convective heat transfer in-side rotating porous disk. Under the present research conditions, the results show that the centrifugally-driven flow is enhanced significantly with the increase of rotational speed. Consequently, the maximum temperature on the disk surface is decreased and the temperature distribution tends to be uniform. The thermal transport capacity in rotating porous disk is also enhanced with the increase of solid thermal conductivity or the decrease of solid porosity. In the rotating porous disk, the solid phase heat transfer is clearly the dominant mode of heat transport and the fluid phase makes an incremental contribution to the total heat transfer.
