分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： Based on the experiment of onset of nucleate boiling (ONB) in natural circulation and the nonequilibrium thermodynamics dissipative theory, the mechanism of ONB in narrow rectangle channels of natural circulation is proposed. It points out that the onset of nucleate boiling is influenced by the degree of superheat and the special conditions of narrow channels. Under the conditions of both density difference in natural circulation and narrow rectangle channels, the prediction model of ONB in natural circulation of narrow channels based on fluctuating is established. The experimental results show that the present model can be used to predict the heat flux of ONB in narrow rectangle channels. Features of ONB in natural circulation narrow rectangle channels are as follows: heating power is the incentive of the happen of ONB; the higher the heating power is, the higher the degree of superheat is, and the earlier the ONB will appear. With the pressurizing, the appearance of ONB will be delayed. The higher the degree of supercooling is, the later the ONB appears. The ONB will happen easier when there are noncondensable gases and roughness in the channels.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Li Yingjie
Xu Ye
Xu Jin-Long
Liu Dejian
Li Jingjing
Lin Zehao
Jiang Peng
Bian Shuaibo
Hao Chaojie
Chen Xiuhui
摘要： We observed the high-mass star-forming region G176.51+00.20 using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) with the 19-beam tracking observational mode. This is a pilot work of searching for neutral stellar winds traced by atomic hydrogen (i.e., HI winds) using the high sensitivity HI line toward high-mass star-forming regions where bipolar molecular outflows have been detected with high sensitivity by Liu et al. HI wind was detected in this work only in Beam 1. We find here that, similar to low-mass star formation, no matter how large the inclination is, the HI wind is likely sufficiently strong to drive a molecular outflow. We also find that the abundance of HI in the HI wind is consistent with that of the HI narrow-line self-absorption (HINSA) in the same beam (i.e., Beam 1). This implies that there is probably an internal relationship between HI winds and HINSA. This result also reinforces the assertion that HI winds and detected molecular outflows are associated with each other.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Li Yingjie
Xu Ye
Xu Jin-Long
Liu Dejian
Li Jingjing
Lin Zehao
Jiang Peng
Bian Shuaibo
Hao Chaojie
Chen Xiuhui
摘要： Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam tracking observational mode, high sensitivity and high-velocity resolution HI spectral lines have been observed toward the high-mass star-forming region G176.51+00.20. This is a pilot study of searching for HI narrow-line self-absorption (HINSA) toward high-mass star-forming regions where bipolar molecular outflows have been detected. This work is confined to the central seven beams of FAST. Two HINSA components are detected in all seven beams, which correspond to a strong CO emission region (SCER; with a velocity of $\sim$ $-$18 km s$^{-1}$) and a weak CO emission region (WCER; with a velocity of $\sim$ $-$3 km s$^{-1}$). The SCER detected in Beam 3 is probably more suitably classified as a WCER. In the SCER, the HINSA is probably associated with the molecular material traced by the CO. The fractional abundance of HINSA ranges from $\sim 1.1 \times 10^{-3}$ to $\sim 2.6 \times 10^{-2}$. Moreover, the abundance of HINSA in Beam 1 is lower than that in the surrounding beams (i.e., Beams 2 and 4--7). This possible ring could be caused by ionization of HI or relatively rapid conversion from HI to H$_2$ in the higher-density inner region. In the WCER (including Beam 3 in the SCER), the HINSA is probably not associated with CO clouds, but with CO-dark or CO-faint gas.
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