Browsing by Author "Li, Bingxi"

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Heat performances of a thermosyphon as affected by evaporator wettability and filling ratio
(2018-01-25)
Xu, Zhi
;
Zhang, Yaning
;
Li, Bingxi
;
Wang, Chi-Chuan
;
Ma, Qin
A thermosyphon is considered an efficient heat dissipation device in engineering fields due to its low thermal resistance. The heat transfer mechanisms for thermosyphons at different evaporator wettability and filling ratios are not well detailed. A model considering evaporator wettability in terms of a contact angle is developed to detail the phase change process to explore the heat transfer mechanism for a thermosyphon in this study. The effects of evaporator wettability and filling ratio on the heat performances of a thermosyphon charged with water are investigated. It is observed that the simulated absolute temperatures with a contact angle are in better agreement with the experimental results with an average relative error of 0.15% than the simulation results without a contact angle (0.28%). The results show that a hydrophilic surface causes bubbles to easily depart the evaporator wall, thereby increasing the heat performance, whereas a hydrophobic surface causes bubbles to adhere to the evaporator wall, decreasing the heat performance. Further study shows that a low filling ratio of 12% will result in drying out, but a high filling ratio of 40% will prevent large bubbles from reaching the liquid surface, thereby decreasing the heat performance. The heat performance is best at filling ratios of 20-30% for an evaporator with a hydrophilic surface. (C) 2017 Elsevier Ltd. All rights reserved.
Miscible density-driven flows in heterogeneous porous media: Influences of correlation length and distribution of permeability
(2019-01-04)
Li, Qian
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Cai, Weihua
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Li, Feng-Chen
;
Li, Bingxi
;
Chen, Ching-Yao
A random process and highly accurate pseudospectral method associated with compact finite differences are incorporated to evaluate effects of permeability heterogeneity to gravity-driven miscible porous media flows. Flows in heterogeneous permeability fields, based on multiple sets of random realizations with identical statistical characteristics, are simulated to elucidate the global trend of mean quantities and local variations. The presence of heterogeneity provokes more prominent fingering competition and greater variation of fingers' widths, hence the mean values of interested quantitative measures, i.e., breakthrough time, amount of fluid volumes transported, and normalized mixing effectiveness, are generally reduced. Resonant effects, whose influences on the flow fields are the most significant, are verified to occur in an intermediate correlation length, in which the widths of fingers are slightly less than the correspondent correlation length. Nevertheless, under the resonant conditions these measures are the most widely scattered between different random realizations associated with the same control parameters. The widest scatterings are mainly because of the enhancing sensitivity of flow path selections under such resonant conditions, especially in a few realizations whose high or low permeability regions align along with or transverse to the main flow direction. The significant scatterings of these quantitative measures, which had drawn little attention previously, suggest more cautious treatments for practical implementations in the regime of resonant effects.
The impact of heterogeneous anisotropy of porous media on density-driven convection
(2019-09-26)
Li, Qian
;
Cai, Weihua
;
Tang, Xiaojing
;
Chen, Yicheng
;
Li, Bingxi
Purpose The aim of this study is to numerically simulate the density-driven convection in heterogeneous porous media associated with anisotropic permeability field, which is important to the safe and stable long term CO2 storage in laminar saline aquifers. Design/methodology/approach The study uses compact finite difference and the pseudospectral method to solve Darcy's law. Findings The presence of heterogeneous anisotropy may result in non-monotonic trend of the breakthrough time and quantity of CO2 dissolved in the porous medium, which are important to the CO2 underground storage. Originality/value The manuscript numerically study the convective phenomena of mixture contained CO2 and brine. The phenomena are important to the process of CO2 enhanced oil recovery. Interesting qualitative patterns and quantitative trends are revealed in the manuscript.
The influences of the inclination angle and evaporator wettability on the heat performance of a thermosyphon by simulation and experiment
(2018-01-01)
Xu, Zhi
;
Zhang, Yaning
;
Li, Bingxi
;
Wang, Chi-Chuan
;
Li, Yongji
A model considering evaporator wettability in terms of the contact angle is developed in this study. In addition, experiments are conducted using a copper thermosyphon with a length of 240 mm and internal and external diameters of 22.2 mm and 25.4 mm. The influences of the inclination angle and evaporator wettability on the heat performance of a thermosyphon charged with water are investigated. It is observed that simulated temperatures agree well with experimental data with a relative error of 0.12% for a modified thermosyphon. The results show that bubbles attaching to the wall of the evaporator decrease as the inclination angle increases from 15 degrees to 90 degrees, which decreases thermal resistance by 59.5%. As the heating power increases from 10 W to 14 W, thermal resistance reduces more significantly (44.1% decrease) for an evaporator with a hydrophilic surface than for an evaporator with a hydrophobic surface (20.6% decrease) because the bubble emission frequency of a hydrophilic surface rises more sharply (265% increase) than that of a hydrophobic surface (100% increase) at an inclination angle of 90 degrees. (C) 2017 Elsevier Ltd. All rights reserved.