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Wetting States and Departure Diameters of Bubbles on Micro-/Nanostructured Surfaces

LANGMUIR 2022年第10期38卷 3180-3188页

作者： Li, Junyang Gong, Shuai Zhang, Lenan Cheng, Ping Ma, Xiaojing Hong, Fangjun Shanghai Jiao Tong Univ Sch Mech Engn Shanghai 200240 Peoples R China MIT Dept Mech Engn Cambridge MA 02139 USA North China Elect Power Univ Beijing Key Lab Multiphase Flow & Heat Transfer L Beijing 102206 Peoples R China Suzhou Univ Sci & Technol Jiangsu Key Lab Micro & Nano Heat Fluid Flow Tech Suzhou 215009 Jiangsu Peoples R China

Wetting states for droplets have been extensively investigated in the past. As the counter phase of the droplets, bubbles' wetting states have rarely been systematically explored. The wetting state of a bubble is closely related to its departure diameter, which plays significant roles in bubble-generated processes in boiling heat transfer and gas-evolving reactions. Based on the principle of minimum surface energy, we explicitly define three equilibrium wetting states (hemi-wicking state, Wenzel state, and Cassie-Baxter state) for bubbles on micro-/nanostructured surfaces in this paper. We analyze the three-phase contact line profiles for bubbles under these wetting states and propose theoretical models for predicting departure diameters of hemi-wicking-state bubble and Wenzel-state bubble on micro-/nanostructured surfaces. We identify competing effects of bubble departure in Wenzel state: the augmentation of contact line length due to the roughness, which would delay bubble departure, and the decrease of contact line length due to the reduced apparent contact angle, which would facilitate bubble departure. We demonstrate that hemi-wicking-state bubble exhibits a much smaller departure diameter on the textured surfaces. These findings are supported by numerical simulations by the three-dimensional (3D) multiple-relaxation-time lattice Boltzmann method. It is found that the length of the outermost contact lines instead of all contact lines determines the departure diameter of hemi-wicking-state bubble based on bubble detachment processes captured by our 3D numerical simulations. This work offers an avenue for the accurate prediction and control of bubble departure behaviors from micro-/nanostructured surfaces, and therefore can guide optimal designs of micro-/nanostructured surfaces in a variety of applications in boiling, desalination, and hydrogen production by electrolysis.

关键词： Bubbles Contact angle Liquids Equilibrium Wetting

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Design and Simulation of a New Type of Fin-and-Tube heat Exchanger with Trapezoidal Slit Fins

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SSRN 2024年

作者： Zhang, Tianjiao Su, Mengyang Zhang, Hua Liu, Chuang Ouyang, Xinping School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai200093 China Key Laboratory of Thermo-Fluid Science and Engineering Ministry of Education Xi’an Jiaotong University Xi’an710049 China

Slit fin-and-tube heat exchangers are extensively utilized in industry, and optimizing the fin structure is conducive for improving energy efficiency and reducing energy losses. Therefore, a heat exchanger featuring trapezoidal slit fins was proposed in this study. To determine the structure of the slit fins, physical and mathematical models of the heat exchanger with a fin spacing Fp of 2.65 mm were established. We used a numerical simulation to investigate the structural parameters of the fin-and-tube heat exchanger, including the slit height Sh, slit width Sw, transverse tube spacing Pt, and longitudinal tube spacing Pl. Based on the simulation results, the effects of the four structural parameters on the comprehensive performance were evaluated. Additionally, the optimal parameter combination was determined through an orthogonal test, resulting in the following values: Sh = 1.47 mm, Sw = 4 mm, Pt = 42 mm, and Pl = 27.5 mm. This study provides significant theoretical and practical guidance. © 2024, The Authors. All rights reserved.

关键词： Energy dissipation

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Unraveling Reactive Nitrogen Emissions in Heavy-Duty Diesel Vehicles across Evolving Standards and Cheating Tactics

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ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024年第52期58卷 23180-23189页

作者： Ding, Xiang Huang, Cheng Huang, Dan Dan Hou, Yong Hu, Qingyao Lou, Shengrong Wang, Meng Zhou, Min Chen, Jun Yang, Huinan Huang, Rujin Fu, Qingyan Wang, Hongli Shanghai Acad Environm Sci Key Lab Format & Prevent Urban Air Pollut Complex Minist Ecol & Environm Shanghai 200233 Peoples R China Shanghai Acad Environm Sci State Environm Protect Key Lab Format & Prevent Ur Shanghai 200233 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China Chinese Acad Sci Inst Earth Environm Ctr Excellence Quaternary Sci & Global Change State Key Lab Loess & Quaternary Geol Xian 710061 Peoples R China Shanghai Environm Monitoring Ctr State Ecol & Environm Sci Observat & Res Stn Yangt Shanghai 200030 Peoples R China

Reactive nitrogen (Nr) emissions significantly affect air quality and the nitrogen cycle in ecosystems. Heavy-duty diesel vehicles (HDDVs), as major sources of these emissions, exhibit complex emission characteristics because of the combined effects of different driving conditions and aftertreatment technologies. This study first investigated the emission factors (EFs) of Nr species, including NO, NO2, HONO, N2O, and NH3, from HDDVs under different emission standards (China IV/V/VI) and cheating strategies, with a particular focus on the impact of selective catalytic reduction (SCR) systems. Vehicles employing water injection cheating present NO, NO2, and HONO EFs that are consistent with the China III standards, significantly undermining the effectiveness of Nr emission control. The evolution of SCR technology in China IV, V, and VI standards has generally led to substantial reductions in NO, NO2, and HONO emissions, yet the integration of ammonia slip catalysts (ASC) systems in China VI vehicles presents new challenges. While ASCs have successfully reduced NH3 slip to an average of 17 +/- 12 mg/km, they have also caused a 6-13-fold increase in N2O emissions compared with those of China IV and V vehicles, reaching levels of 205 +/- 85 mg/km. Additionally, China VI vehicles exhibit a marked increase in the HONO/NOx ratio, which increases from 0.9% in China V to 4.6%. These increases are attributed to high-temperature oxidation of NH3 within the ASC catalyst, leading to undesirable byproducts. The temporal dynamics of Nr emissions under real-world driving conditions further reveal that the effectiveness of aftertreatment technologies and their selectivity toward byproducts vary depending on the driving mode. This variability underscores the need for further optimization of the SCR and ASC technologies to balance the control of all the reactive nitrogen species effectively.

关键词： reactive nitrogen HDDV HONO N2O emission factors

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Large eddy simulation on the wake characteristics of linearly stratified flow past a sphere

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Scientific Reports 2025年第1期15卷 1-13页

作者： Xia, Tianci Wei, Na Shi, Liuliu School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai 200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering Shanghai 200093 China Key Laboratory of Power Machinery and Engineering of Ministry of Education Shanghai Jiao Tong University Shanghai 200240 China

In this study, Large Eddy Simulation (LES) has been employed to examine the influence of the Froude number (Fr) on the linearly stratified wake and internal waves behind a sphere at a subcritical Reynolds number of Re = 3700. Six distinct sets of models with varying Fr (Fr = 0.05, 0.25, 0.5, 1, 2, ∞) have been chosen to establish density linear stratification through the use of a User Defined Function (UDF). The analysis focuses on the impact of stratification on wake characteristics, velocity distribution, and the structure of internal waves within stratified flow. It is evident that density stratification plays a pivotal role in shaping wake structure. Notably, in stratified flows, wakes exhibit unique characteristics including the generation of internal waves, suppression of vertical velocity, and the emergence of oscillating wake patterns. The study reveals that a decrease in the Froude number leads to heightened vertical suppression of the wake and increased anisotropy of the velocity distribution. Furthermore, as the Froude number ascends from 0.05 to 2, the wake undergoes a transition from quasi-two-dimensional vortex shedding to three-dimensional turbulence. © The Author(s) 2025.

关键词： Froude number Internal wave Linearly stratified flow Wake

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Study of flow Pattern Transition Criterion and heat transfer Characteristics in Vertical Rectangular Narrow Channel for Steam heating

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SSRN 2023年

作者： Gu, Shengjie Tao, Leren Jin, Cheng Ju, Yiwei Zhao, Xiefei School of Energy and Power Engineering University of Shanghai for Science and Technology Shanghai200093 China Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power and Engineering University of Shanghai for Science and Technology Shanghai200093 China

To clarify the heat transfer characteristics of flow boiling in a narrow vertical rectangular channel at each stage and optimise the performance of the heat exchanger, an experimental study of the flow pattern and local heat transfer characteristics in a narrow vertical rectangular channel of steam heating with dimensions of 1400 mm × 250 mm × 2.75 mm (l × w × s) was carried out using deionized water as the working medium. Based on the mechanical model and the empirical formulas of the researchers, the preliminary derivation of the flow pattern transition criterion in the vertical rectangular narrow channel for steam heating is obtained. The effects of inlet temperature, mass flux and heating power on the local heat transfer characteristics were analyzed in conjunction with the flow patterns, and based on the parametric analysis of the experimental data, a new flow boiling heat transfer correlation formula was obtained which applies to the experimental conditions in this paper. The results show that the increase in inlet temperature has a positive effect on the nucleate boiling section, while the degree of effect on the local heat transfer coefficient is minimal after entering the churn flow phases. The increase in mass flux decreases the local heat transfer coefficient in the nuclear state boiling stage and enhances the local heat transfer coefficient in the evaporation zone of liquid film flow. The peak of the local heat transfer coefficient shows a tendency to shift to the left as the heating power increases. The new heat transfer correlation equation can well predict the local heat transfer coefficient of flow boiling in a vertical rectangular narrow channel heated by steam in this experimental condition. © 2023, The Authors. All rights reserved.

关键词： flow patterns

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Numerical study on the local heat transfer characteristic of supercritical CO2 in semicircular/circular channel under cooling condition

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INTERNATIONAL JOURNAL OF heat AND MASS transfer 2023年第1期209卷

作者： Zhong, Shaogeng Ren, Yan Wu, Weidong Yang, Yingying Yang, Qiguo Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

A mathematic-physical model was established to explore the local heat transfer characteristics of su-percritical CO2 in semicircular and circular channels under cooling condition, which was applied in the field of supercritical CO2 Brayton cycle. The numerical method was validated by the experimental data with the maximum error of 12.44%, meeting the accuracy requirement. And the operation pressure, cool-ing heat flux, inlet velocity and hydraulic diameter were 8 similar to 9 MPa, 10 similar to 14 kW center dot m -2, 1.2 similar to 5 m center dot s -1 and 1 similar to 2 mm, respectively. The results showed that the local heat transfer coefficient of SCO2 would increase at first and then decrease along the flow direction regardless of the semicircular channel and circular channel, and the peak value of the local heat transfer coefficient gradually decreased with increasing op-eration pressure and disappeared when the inlet velocity exceeded 3 m center dot s-1. Besides, the heat transfer performance of the horizontal semicircular channel was weaker than that of the circular channel due to the influence of the buoyancy effect. For the horizontal flow, the buoyancy effect was increased, while the heat transfer was decreased with increasing hydraulic diameter of the semicircular channel. Finally, the heat transfer correlation of the supercritical CO2 cooling process in the horizontal semicircular channel was modified by considering the influence of the dimensionless buoyancy effect and hydraulic diameter, and the prediction errors of 93.3% correlation calculation results were within +/- 13.5% after the modifica-tion. These results will provide some theoretical guidance on the design and optimization of the cooler for the supercritical CO2 Brayton cycle system. (c) 2023 Elsevier Ltd. All rights reserved.

关键词： SupercriticalCO 2 Semicircular channel Local heat transfer characteristic heat transfer deterioration Buoyancy effect

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A novel mass-heat exchange network analogy, regression, and synthesis method for mass exchanger networks

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HELIYON 2023年第10期9卷 e20574页

作者： Xiao, Yuan Cui, Guomin Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 20093 Peoples R China

Synthesis of mass exchanger network (MEN) is significant to save the material and reduce the pollution for process industries. Considering its small magnitude and concentration constraints, the optimized configuration of MEN can easily violate the concentration constraints, leading to a reduction in the structural diversity during the optimization process compared to that of a heat exchanger network (HEN) of the same size. Moreover, the constraint on the mass transfer driving force based on the equilibrium composition may also have major effects on the optimization process. To address these issues, this study presents a process-equipment-system analogy between the MEN and the HEN, proposing a novel mass-heat exchange network analogy, regression, and synthesis method. First, the generalized HEN was established by using an analogy considering the MEN based on either the original composition or the equilibrium composition. In this regard, a coordination coefficient was introduced to correct the deviation of the analogy relationship between the heat transfer and the mass transfer processes. Then, the generalized HEN was optimized by employing the random walk algorithm with compulsive evolution (RWCE). A regression method was proposed to regress the optimized HEN solution to the MEN expression, allowing the continuous optimization by using the RWCE with finer parameters. The final optimal solution obtained was found to be lower than those reported in the literature with enhanced structural diversity, demonstrating the effectiveness of the presented method and providing new ideas for further synchronous optimization of combined heat and mass exchanger networks.

关键词： Mass exchanger network heat exchanger network Mass -heat analogy Optimization

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Sensitively detection of ascorbic acid in orange samples with ionic liquid functionalized carbon dots and lanthanide complexes

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DYES AND PIGMENTS 2024年 227卷

作者： Li, Ying Xia, Ji-Ji Lu, Jia-Zhen Wang, Zi-Long Wang, Mi-Tang Univ Shanghai Sci & Technol Sch Mat & Chem Shanghai 200093 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

In the food industry, ascorbic acid (AA) is widely used as an antioxidant. However, the concentration of AA is influenced by various factors, including temperature, time, and pH value during food preparation and storage, leading to its instability in content. This makes the accurate detection of AA content particularly important. Precise determination of AA content in food and pharmaceuticals is crucial for ensuring the adequate intake of essential vitamins and maintaining good health. Herein, we have developed a successful preparation method of an imidazole-based ionic liquid functionalized CDs hybrids APM-CDs. A novel photo functional hybrid probe Eu3+@APM-CDs was obtained via an ion-exchange reaction between APM-CDs and lanthanide complex Eu (DPA)3. The obtained hybrid probe was extensively characterized in detail. What's more, the results show that the fluorescent intensity of Eu3+@APM-CDs has a good linear response to AA concentrations in the range of 25-500 mu M (R-2 = 0.99), with a detection limit of 80 nM. The fluorescence probe demonstrates good selectivity and sensitivity toward AA and has the potential for significant application in AA detection by simplifying procedures and reducing interference from impurities.

关键词： Lanthanide probe Ionic liquid C-dots Fluorescence sensor Ascorbic acid

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Study on the heat and Mass transfer Characteristics of Humidifiers in Humidification-Dehumidification Desalination Systems

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ENERGIES 2023年第24期16卷 8006页

作者： Zhu, Qundong Wu, Weidong Ren, Yan Wang, Fengxian Han, Yipeng Krzywanski, Jaroslaw Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai 200093 Peoples R China Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

The humidifier plays a key role in a humidification-dehumidification (HDH) desalination system;it directly affects both the freshwater production efficiency and energy consumption ratio of the system. In this study, for a humidifier in an HDH system, a heat-mass coupled differential equation model of spray water and air on the surface of the packing material was established, and the effects of parameters such as the spray water temperature (tw), mass flow rate of spray water (mw), air temperature (ta), and air mass flow rate (ma) on the humidification performance of humidifiers composed of eight different types of packing materials were investigated. The results show the following: (1) Under the same inlet spray water and air conditions, the humidification performance of different packing materials from good to bad is as follows: cellulose paper, polypropylene, hackettes, saddles, snowflakes, wooden slats, polyvinyl chloride, gunny bag cloth. (2) Increasing the tw can significantly improve the humidification performance. To achieve higher humidification energy efficiency, it is recommended to increase the tw to above 80 degrees C. (3) With the increase in the mw, although the humidification efficiency (epsilon(hum)) decreases slightly, the (hum)idification rate (m(hum)) increases, and the specific humidification energy ratio (eta(hum)) decreases accordingly. To maintain a high m(hum) and a low eta(hum), it is advisable to control the mw at not less than 0.5 kg/s. (4) Increasing the (hum)idifier inlet ta can improve the m(hum), epsilon(hum), and eta(hum), although not as effectively as increasing tw. (5) Increasing the ma can improve m(hum) and epsilon(hum). However, it simultaneously increases the eta(hum). The results of this study can provide theoretical guidance for the selection of efficient packing materials and the optimization of humidifier operating conditions in HDH desalination systems.

关键词： humidification-dehumidification (HDH) desalination humidifier packing material heat and mass transfer

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The limitation mechanisms on the discharge behavior of Li-O2 batteries

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JOURNAL OF ELECTROANALYTICAL CHEMISTRY 2024年 955卷

作者： Wang, Yuanhui Hao, Liang Yanshan Univ Sch Vehicle & Energy Qinhuangdao 066004 Peoples R China Univ Shanghai Sci & Technol Sch Energy & Power Engn Shanghai Key Lab Multiphase Flow & Heat Transfer P Shanghai 200093 Peoples R China

A comprehensive model for lithium-oxygen (Li-O2) batteries is proposed and the discharge performance across varying cathode thickness, porosity, and pore structural evolution modes is thoroughly investigated. The results reveal that the cathode surface passivation restricts the discharge capacity but promotes the uniform distribution of lithium peroxide (Li2O2), especially near the O2 side. The electrode thickness of 255 mu m serves as the boundary point between the two limiting mechanisms, with thicker electrodes primarily governed by O2 diffusion and thinner ones by surface passivation. In addition, a novel hybrid model is proposed with the morphological change of the cathode pore structure, which can predict the discharge performance made of different carbon materials, proving its superiority over the commonly used Single model. The maximum discharge capacities of carbon nanoparticle (CNP)- and carbon nanotube (CNT)-based cathodes are obtained at the radius of CNP and CNT of 30 nm and 20 nm, respectively. The superiority of discharge performance of the CNP-based cathode over the CNT-based cathodes becomes more pronounced as the carbon material radius increases. The evolution of the cathode pore structure morphology needs to be considered for the cathode made of small-sized CNP or CNT, such as rCNP = 10 nm and rCNT = 20 nm.

关键词： Li -O 2 battery Oxygen diffusion Surface passivation Pore structure morphology

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