標題: Bubble dynamics in evaporation flow of R-134a in narrow annular ducts due to flow rate oscillation
作者: Chen, C. A.
Lin, T. F.
Ali, Hafiz Muhammad
Amani, Pouria
Yan, Wei-Mon
機械工程學系
Department of Mechanical Engineering
關鍵字: Time periodic evaporation flow;R-134a refrigerant;Bubble dynamics;Flow rate oscillation
公開日期: 1-一月-2019
摘要: This article aims to investigate the influence of imposed flow rate oscillation on the bubble behaviors of evaporative flow of R-134a in horizontal narrow annular ducts. Particularly, the effects of amplitudes and periods of the oscillating flow rates along with the vapor quality of the R-134a on the bubble characteristics are examined in details. Moreover, the R-134a flow photos captured at the middle axial location are presented to illustrate the shift between the annular two-phase flow pattern and the bubble nucleation at different operating conditions and time instances. The observations reveal that the imposed mass flow rate oscillation results in the fluctuation of bubble departure diameter and frequency along with the density of active nucleation sites with the same frequencies. The larger amplitudes and longer periods of the mass flow rate oscillation lead to the stronger fluctuations in bubble dynamics. Furthermore, it is found that the bubble nucleation on the heating surface is the dominant mechanism at the low vapor quality of 0.05. However, the annular two-phase flow prevails over a relatively large portion of the periodic cycle at the dryness fraction of 0.5 and over the entire cycle at the dryness fraction of 0.95. Finally, the evaporative heat transfer of R-134a subject to the flow rate oscillation is correlated as a function of the mass flow rate and the vapor quality.
URI: http://dx.doi.org/10.1016/j.icheatmasstransfer.2018.12.012
http://hdl.handle.net/11536/148856
ISSN: 0735-1933
DOI: 10.1016/j.icheatmasstransfer.2018.12.012
期刊: INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
Volume: 100
起始頁: 27
結束頁: 34
顯示於類別:期刊論文