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Dynamics of capsules enclosing viscoelastic fluid in simple shear flow

JOURNAL OF FLUID MECHANICS 2018年 840卷 656-687页

作者： Luo, Zheng Yuan Bai, Bo Feng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Previous studies on capsule dynamics in shear flow have dealt with Newtonian fluids, while the effect of fluid viscoelasticity remains an unresolved fundamental question. In this paper, we report a numerical investigation of the dynamics of capsules enclosing a viscoelastic fluid and which are freely suspended in a Newtonian fluid under simple shear. Systematic simulations are performed at small but non-zero Reynolds numbers (i.e. Re = 0.1) using a three-dimensional front-tracking finite-difference model, in which the fluid viscoelasticity is introduced via the Oldroyd-B constitutive equation. We demonstrate that the internal fluid viscoelasticity presents significant effects on the deformation behaviour of initially spherical capsules, including transient evolution and equilibrium values of their deformation and orientation. Particularly, the capsule deformation decreases slightly with the Deborah number De increasing from 0 to O(1). In contrast, with De increasing within high levels, i.e. O(1-100), the capsule deformation increases continuously and eventually approaches the Newtonian limit having a viscosity the same as the Newtonian part of the viscoelastic capsule. By analysing the viscous stress, pressure and viscoelastic stress acting on the capsule membrane, we reveal that the mechanism underlying the effects of the internal fluid viscoelasticity on the capsule deformation is the alterations in the distribution of the viscoelastic stress at low De and its magnitude at high De, respectively. Furthermore, we find some new features in the dynamics of initially non-spherical capsules induced by the internal fluid viscoelasticity. Particularly, the transition from tumbling to swinging of oblate capsules can be triggered at very high viscosity ratios by increasing De alone. Besides, the critical viscosity ratio for the tumbling-to-swinging transition is remarkably enlarged with De increasing at relatively high levels, i.e. O(1-100), while it shows little change at

关键词： biological fluid dynamics capsule/cell dynamics

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Theoretical Study of Abstraction and Addition Reactions of 2,4,4-Trimethyl-1-pentene with H and O(³P) Radical

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ENERGY & FUELS 2018年第11期32卷 11831-11842页

作者： Yin, Geyuan Hu, Erjiang Li, Xiaojie Ku, Jinfeng Gao, Zhenhua Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

The calculation of rate constants of addition and abstraction reactions of 2,4,4-trimethyl-l-pentene with H and O(P-3) were conducted by conventional transition state theory (TST) and canonical variational transition state theory (CVT). Potential energy surfaces of reactions were calculated at the DLPNO CCSD(T)/cc-pVTZ//M06-2X/6-311G(d,p) as well as the CCSD(T)/6-311++G(d,p)//M06-2X/6-311(d,p) level. Moreover, quantum mechanical effects were determined by multidimensional small-curvature tunneling (SCT) and zero-curvature tunneling (ZCT) methods. 2,4,4-Trimethyl-l-pentene contains primary and secondary allylic, alkylic, and vinylic H atoms. It also contains addition reactions into central and terminal carbon atom channels. The results indicated that allylic H abstraction channels dominate the overall H abstractions resulting from the lower barriers. In addition, a radical added into terminal carbon dominates the addition reactions. The branching ratio is more than 72% above 1500 K for H abstraction and more than 90% below 500 K for H addition reactions.

关键词： Addition reactions Hydrogen abstraction Tunneling Energy Potential energy

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Condensation regime diagram for supersonic and subsonic steam jet condensation in water flow in a vertical pipe

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APPLIED THERMAL engineering 2018年 130卷 62-73页

作者： Xu, Qiang Ye, Shuyan Chen, Yanshuang Chen, Qiyu Guo, Liejin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

An experimental research is performed to investigate the condensation regime diagram of supersonic and subsonic steam jet condensation in water flow in pipes. The original images of the jet plume are recorded using a visualization window and a high-speed camera. The jet condensation regimes are basically categorized into four types, including Chugging, Oscil-I, Oscil-II and Stable regimes, primarily based on the transient evolution of geometrical profile of the jet plume. And the average geometrical shape of the jet plume is found to shrink gradually with increase of ambient pressure. The stand deviation of pressure oscillation is highly correlated to jet condensation regimes, so it can be applied to quantitatively categorize different regimes. The steam mass flux, scaled by critical steam mass flux at different ambient pressure, is found to be irrelevant to the transitional lines among Chugging, Oscil-I, and "Stable or Oscil-II" regimes in the condensation regime diagram. Furthermore, the Oscil-II regime can be simply isolated from the "Stable or Oscil-II" regime via comparison of the standard deviation of pressure oscillation in this two regimes. Therefore, the jet condensation regime diagram obtained from low ambient pressure could be applied to conditions of elevated ambient pressure. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： Condensation regime diagram Regime classification Supersonic steam jet Pressure oscillation multiphase flow

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Nucleate boiling heat transfer model based on fractal distribution of bubble sizes

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2019年 128卷 1175-1183页

作者： Qi, Baojin Wang, Ya Wei, Jinjia Zhang, Yonghai Yu, Ting Xi An Jiao Tong Univ Sch Chem Engn & Technol Xian 710049 Peoples R China Xi An Jiao Tong Univ Suzhou Inst Suzhou 215123 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Scientifically and accurately predicting the distribution of the bubble sizes on the heating surface is a key step to improve the calculation accuracy of the boiling heat transfer model. In the present study, an ingenious nucleate boiling heat transfer model was developed on the basis of random fractal function of the bubble sizes distribution, and renormalization group theory was introduced to solve this distribution function. Compared to the previous correlations, the distribution function of bubbles for various sizes can be obtained by solving this random fractal distribution function with renormalization group method. Furthermore, the process of increasing the fractal dimension from 1 to 2 was first proposed in this paper to match the whole evolution of the heated liquid from natural convection to nucleate boiling, to transition boiling, and finally to film boiling. Therefore, the present model can reveal the nature of nucleate boiling more comprehensively and deeply. Through comparison, it can be found that the image of bubble distribution obtained from the random fractal model was very similar to the experimental photographs statistically, and the predictions heat transfer were in good agreement with the experimental data when the superheat AT is higher than 10 degrees C, and the deviation is less than 20%. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Bubble sizes distribution Fractal analyses Nucleate boiling Heat transfer model

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Peak shaving operational optimization of supercritical coal-fired power plants by revising control strategy for water-fuel ratio

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APPLIED ENERGY 2018年 216卷 212-223页

作者： Wang, Chaoyang Zhao, Yongliang Liu, Ming Qiao, Yongqiang Chong, Daotong Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Electricity generated from renewable energy source fluctuates heavily and can hardly be predicted. The peak shaving (or load cycling) operation of conventional thermal power plants is an effective means to mitigate the mismatch between electricity demands and supplies. Therefore, determining how thermal power plants can operate in a flexible and effective mode is an urgent issue that should be addressed. For thermal power plants, new methods and strategies need to be proposed to face the challenge of the integrating flexibility and energy saving into transient processes. Dynamic performances of thermal power plants during load cycling processes are affected by the coupling of the thermal system and the control system. Feasible approaches from optimizing the coordinated control system (CCS) may radically enhance the peak shaving capacity of thermal power plants. The heat storage in a coal-fired power plant, including heating surface metals and work media, varies with the load rate of the plant. During cycling load operations, the real-time heat storage value of one unit differs from that of the corresponding steady state load command rate. This difference hinders the flexibility of one unit and affects its economic performances during cycling processes. In this paper, a revised water fuel ratio (WFR) control strategy based on heat storage difference was proposed and tested on established coal-fired power plant models. Results show that the accumulation deviations of load rate command and real-time load rate are considerably reduced during load cycling processes when the proposed WFR control strategy is introduced. The revised WFR control strategy diminishes the difference between the target and the actual total power output. When the load cycling rate varies from 10 to 30 MW min(-1) between 50% and 100% THA, the standard coal consumption variation rate (Delta b(s),) decreases by 0.31-1,01 g kW(-1) h(-1) during loading up processes, and decreases by 0.26-1.69 g kW(-1)

关键词： Coal-fired power plant Transient processes Operational optimization Water fuel ratio Heat storage

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Evaluation of oxidation stability and engine behaviors operated by Prosopis juliflora biodiesel/diesel fuel blends with presence of synthetic antioxidant

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SUSTAINABLE ENERGY TECHNOLOGIES AND ASSESSMENTS 2022年第PartA期52卷

作者： Rajamohan, Sakthivel Gopal, Abbhijith Hari Muralidharan, Karthic Raja Huang, Zuohua Paramasivam, Baranitharan Ayyasamy, Tamilvanan Nguyen, Xuan Phuong Le, Anh Tuan Hoang, Anh Tuan Amrita Vishwa Vidyapeetham Amrita Sch Engn Dept Mech Engn Coimbatore Tamil Nadu India Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Natl Inst Technol Dept Prod Engn Trichy India Kongu Engn Coll Dept Mech Engn Perundurai India Ho Chi Minh City Univ Transport PATET Res Grp Ho Chi Minh City Vietnam Hanoi Univ Sci & Technol Sch Mech Engn Hanoi Vietnam HUTECH Univ Inst Engn Ho Chi Minh City Vietnam

This experimental study focuses on analyzing the oxidation stability, engine performance, and combustion characteristics of Prosopis juliflora biodiesel blended with synthetic antioxidants. In the first stage, four synthetic antioxidants such as Butylated Hydroxy Toluene, Propyl Gallate, Pyrogallol, Tert-Butyl-Hydroquinone (TBHQ) were selected to evaluate their oxidation stability. Resultantly, TBHQ was the best synthetic antioxidant with the highest induction period, corresponding to 10.19 h, among the above-mentioned synthetic antioxidants while it was added to the B20 blend (20% Prosopis juliflora biodiesel/80% diesel fuel). In the second stage, different concentrations of TBHQ (500, 1000, and 1500 ppm) were added to B20 sample for the test of performane, combustion, and emission characteristics of a 4-stroke diesel engine. Indeed, adding TBHQ to the B20 sample increased brake thermal efficiency and emissions of CO and HC, while it reduced brake-specific fuel consumption and emissions of NOx and CO2. Furthermore, it could be observed a decrease in peaks of in-cylinder pressure and heat release rate, and an increase in mass fraction burned as adding TBHQ. In general, the use of TBHQ antioxidant-included biodiesel for diesel engines could improve engine performance and emission, and enhance the fuel' oxidation stability.

关键词： Prosopis juliflora Biodiesel Antioxidant Oxidation stability Engine behavior

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Solute release from an elastic capsule flowing through a microfluidic channel constriction

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PHYSICS OF FLUIDS 2019年第12期31卷 121902-121902页

作者： Luo, Zheng Yuan Bai, Bo Feng Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

In recent years, microfluidic channels with narrow constrictions are extensively proposed as a new but excellent possibility for advanced delivery technologies based on either natural or artificial capsules. To better design and optimize these technologies, it is essential and helpful to fully understand the releasing behavior of the encapsulated solute from capsules under various flow conditions which, however, remains an unsolved fundamental problem due to its complexity. To facilitate studies in this area, we develop a numerical methodology for the simulation of solute release from an elastic capsule flowing through a microfluidic channel constriction, in which the tension-dependent permeability of the membrane is appropriately modeled. Using this model, we find that the release of the encapsulated solute during the capsule's passage through the constriction is enhanced with the increase in the capillary number and constriction length or the decrease in the constriction width. On the other hand, a large variation in the channel height, which is generally larger than the capsule diameter, generates little effect on the released amount of the solute. We reveal that the effects of the capillary number and constriction geometry on the solute release are generally attributed to their influence on the capsule deformation. Our numerical results provide a reasonable explanation for previous experimental observations on the effects of constriction geometry and flow rate on the delivery efficiency of cell-squeezing delivery systems. Therefore, we believe these new insights and our numerical methodology could be useful for the design and optimization of microfluidic devices for capsule-squeezing delivery technologies. Published under license by AIP Publishing.

关键词： Microfluidics

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Experimental study of liquid nitrogen spray characteristics in atmospheric environment

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APPLIED THERMAL engineering 2018年 142卷 717-722页

作者： Xue, Rong Ruan, Yixiao Liu, Xiufang Chen, Liang Zhang, Xingqun Hou, Yu Chen, Shuangtao Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

A comprehensive understanding of the spray characteristics at the macroscopic and microscopic levels is crucial for taking advantage of a liquid nitrogen spray. In this study, an open cycle system is developed for investigating the liquid nitrogen spray characteristics of two fine fog nozzles with different outlet diameters in an atmospheric environment. The effect of the injection pressure and nozzle orifice diameter on the mass flow rate, discharge coefficient, spray field pattern, and spray cone angle are obtained, as well as the droplet spatial distribution. The correlation between these parameters could benefit the selection of spray nozzles in a cryogenic spray cooling system.

关键词： Liquid nitrogen spray Mass flow rate Spray field Spray cone angle Droplet spatial distribution

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Numerical analysis of heat transfer to water flowing in rifled tubes at supercritical pressures

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APPLIED THERMAL engineering 2018年 133卷 704-712页

作者： Shen, Zhi Yang, Dong Li, Yaode Liang, Ziyu Wan, Li Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

Heat transfer to supercritical water flowing in vertical upward rifled tubes are studied. The shear stress transport turbulence model was applied to numerical analysis and was validated with experimental data. Results of numerical simulation showed that the present model could provide a satisfactory prediction with enough accuracy. According to the results, inner wall temperature varies periodically in circumferential direction. It peaks at the intersection of the root and the leeward side and reaches the minimum at the intersection of the crest and the windward side. The circumferential distribution of inner wall heat flux is similar to that of the inner wall temperature. However, at the root the variation of inner wall heat flux is contrast to that of inner wall temperature and the rotational flow caused by the screw thread may contribute to this result. Heat transfer enhancement occurs where the boundary layer is filled with fluid of large specific heat and the effect of kinetic energy is not dominant. The structural parameters of screw thread affect heat transfer in rifled tubes. The increase of thread height significantly improved the performance of heat transfer, but the effects of pitch, lead angle and thread form are negligible.

关键词： Supercritical water Heat transfer Rifled tube Numerical simulation

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Experimental investigation on heat transfer characteristics in circulatory flash vaporization of aqueous NaCl solution

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DESALINATION 2018年 446卷 12-20页

作者： Wang, Yu He, Qi Li, Gen Yang, Qingzhong Yan, Junjie Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China

In this work, a series of experiments on circulatory flash vaporization of 10% and 20% NaCl solution was performed. The heat transfer characteristics in circulatory flash vaporization under different experimental conditions were presented. The non-equilibrium fraction of circulatory flash vaporization (NEF) was adopted to describe the extent of flash vaporization process completion. A volumetric heat transfer coefficient of circulatory flash vaporization (h(v)) was introduced in the present study to evaluate the heat flux evolution from per unit volume of liquid pool under unit superheat degree. Moreover, the influences of superheat degree, pressure of flash evaporator, initial liquid level, circulating flow rate and concentration of NaCl solution on the volumetric heat transfer coefficient were also analyzed. Results suggested that the volumetric heat transfer coefficient increased with the superheat degree and flash chamber pressure. Lowering the initial liquid level and brine concentration promoted the heat transfer intensity. And Nusselt number of circulatory flash vaporization Nu(A) was proposed to describe the heat transfer performance of circulatory flash vaporization according to the definition of volumetric heat transfer coefficient. Moreover, a correlation between Nusselt number of circulatory flash vaporization and dimensionless parameters was obtained with the relative error between -31.1% and 32.8% for 1.5 <= Delta T <= 20 K, 400 <= Q <= 1200 L h(-1), 7.4 <= P-f <= 31.2 kPa and 0.05 <= f(m) <= 0.2.

关键词： Circulatory flash vaporization Volumetric heat transfer coefficient Non-equilibrium fraction Aqueous NaCl solution

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