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Effects of surface wettability on boiling nucleation

Kung Cheng Je Wu Li Hsueh Pao/Journal of engineering Thermophysics 2016年第1期37卷 111-115页

作者： Zheng, Wen-Xiu Li, Si-Jie Bai, Bo-Feng State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

We established a gas-liquid-solid three phase pool boiling system from molecular dynamics insight, introducing the interactions between the wall and the fluid as an additional force. The effects of wall wettability on the boiling nucleation were studied from three aspects of the nucleation position, the average kinetic energy and the interface contact thermal resistance. The results show that strong surface wettability means strong constraint to the near surface molecules and gas nuclear position is farther from the surface. For stronger surface wettability, the molecular average kinetic energy for the molecules adjacent to the surface is significantly larger than that for the molecules far from the surface, for weaker surface wettability, molecular kinetic energy has a uniform distribution in the vertical direction of the wall. As increasing the surface wettability the interface contact thermal resistance increases and accordingly the boiling nucleation is weakened. © 2016, Science Press. All right reserved.

关键词： Nucleation

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Overexpressing F0/F1 operon of ATPase in Rhodobacter sphaeroides enhanced its photo-fermentative hydrogen production

Overexpressing F0/F1 operon of ATPase in Rhodobacter sphaero...

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作者： Zhang, Yang Yang, Honghui Feng, Jiali Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi'An Jiaotong University Xi'an710049 China Department of Environmental Science and Engineering Xi'An Jiaotong University Xi'an710049 China

The effect of atp genes overexpression in Rhodobacter sphaeroides HY01 on the amount of ATP, nitrogenase activity and hydrogen production were studied. The ATP content of ZTHF0 (F0 operon+), ZTHF1 (F1 operon+) and ZTHFF (F0 operon+, F1 operon+) was 6.5 ± 0.2 nmol/mL, 7.6 ± 0.2 nmol/mL and 8.3 ± 0.3 nmol/mL, respectively, which enhanced by 20.3%, 40.7%, and 53.7% compared with that of the control strain ZTH (pRK415+), respectively. However, the nitrogenase activities of ZTHF0, ZTHF1 and ZTHFF were 35.8 ± 0.5 nmol acetylene/(min·mg-dcw), 40.1 ± 0.7 nmol acetylene/(min·mg-dcw) and 29.3 ± 0.7 nmol acetylene/(min·mg-dcw), respectively, which increased by 18.2%, 32.3% and 0% compared with that of ZTH, respectively. The expression level of atp genes by real-time PCR showed that ZTHF0 or ZTHF1 only enhanced the expression of F0 operon or F1 operon, respectively, and ZTHFF enhanced the expression of both F0 and F1 operons. At the 5000 ± 200 lux with 10 mL culture, the hydrogen yields of ZTHF0 and ZTHF1 were 7636 ± 59 mL/L-culture and 8458 ± 76 mL/L, which increased by 10.5% and 27.8% compared with that of the control strain, respectively. Moreover, the maximum hydrogen evolution rate of ZTHF0 and ZTHF1 were 94.5 ± 4.1 mL/(Lh) and 103.1 ± 5.0 mL/(Lh), which enhanced by 15.4% and 20.6% compared with that of the control strain, respectively. The results suggested that overexpressing F0 operon or F1 operon could improve ATP content and hydrogen production performance in R. sphaeroides. © 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Hydrogen production

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Experimental Investigation on Heat Transfer Characteristics of Water in Inclined Downward Tube of a Supercritical Pressure CFB Boiler

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Journal of Thermal Science 2015年第5期24卷 478-487页

作者： WANG Siyang YANG Dong XIE Beibei WANG Long WANG Yongjie State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

In this study, experiments have been performed for an investigation on heat transfer of water in an inclined downward tube with an inner diameter of 20 mm and an inclined angle of 45° from the horizon, with the range of pressure from 11.5 to 28 MPa, mass flux from 450 to 1550 kg/(m2 s), and heat flux from 50 to 585 k W/m2. Based on the experimental data, the temperature distribution in the tube wall was derived. The heat transfer characteristics of inclined downward flow were compared with that of vertical downward flow. The effects of heat flux on wall temperature were analyzed and the corresponding empirical correlations were presented. The results show that heat transfer characteristics of water in the inclined downward tube are not uniform along the circumference from the top surface to the bottom surface. An increase in heat flux exacerbates the non-uniformity. At subcritical pressures, both dry-out and departure from nucleate boiling(DNB) occur at the top surface of the inclined downward tube; inversely, only dry-out takes place on the bottom surface of the inclined downward tube and in the vertical downward tube. At near-critical pressures, DNB and dry-out occur in the comparing tubes with greater possibility. At supercritical pressures, heat transfer gets enhanced in the pseudo-critical enthalpy region; in the high enthalpy region, the top surface temperature of the inclined downward tube decreases obviously.

关键词： inclined downward tube wall temperature circumferential non-uniformity heat transfer deterioration

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Industrialization prospects for hydrogen production by coal gasification in supercritical water and novel thermodynamic cycle power generation system with no pollution emission

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Science China(Technological Sciences) 2015年第12期58卷 1989-2002页

作者： GUO LieJin JIN Hui GE ZhiWei LU YouJun CAO ChangQing State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University

Energy conversion and utilization, particularly carbon-based fuel burning in air phase, have caused great environmental pollution and serious problems to society. The reactions in water phase may have the potential to realize clean and efficient energy conversion and utilization. Coal gasification in supercritical water is a typical carbon-based fuel conversion process in water phase, and it takes the advantages of the unique chemical and physical properties of supercritical water to convert organic matter in coal to H2 and CO2. N, S, P, Hg and other elements are deposited as inorganic salts to avoid pollution emission. The state key laboratory of multiphase Flow in power engineering has obtained extensive experimental and theoretical results based on coal gasification in supercritical water. Supercritical water fluidized bed reactor was developed for coal gasification and seven kinds of typical feedstock were selected. The hydrogen yield covers from 0.67 to 1.74 Nm3/kg and the carbon gasification efficiency is no less than 97%. This technology has a bright future in industrialization not only in electricity generation but also in hydrogen production and high value-added chemicals. Given the gas yield obtained in laboratory-scale unit, the hydrogen production cost is U.S.$ 0.111 Nm3 when the throughput capacity is 2000 t/d. A novel thermodynamic cycle power generation system based on coal gasification in supercritical water was proposed with the obvious advantages of high coal-electricity conversion efficiency and zero pollutant emission. The cost of U.S.$ 3.69 billion for desulfuration, denitration and dust removal in China in 2013 would have been saved with this technology. Five kinds of heat supply methods are analyzed and the rates of return of investment are roughly estimated. An integrated cooperative innovation center called a new type of high-efficient coal gasification technology and its large-scale utilization was founded to enhance the industrialization o

关键词： industrialization prospects hydrogen production supercritical water gasification power generation zero emission

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Ab Intio Calculations on Reaction Process of Piperazine Absorbing CO 2

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Energy Procedia 2017年 114卷 2121-2127页

作者： Tingting Zhang Yunsong Yu Guoxiong Wang Zaoxiao Zhang School of Chemical Engineering and Technology Xi’an Jiaotong University No.28 Xianning West Road Xi’an 710049 P.R. China State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University No.28 Xianning West Road Xi’an 710049 P.R. China School of Chemical Engineering University of Queensland Brisbane Qld. 4072 Australia

The increasing amount of CO 2 emitted to the atmosphere has a deep impact on the environment. It is urgent to take effective measures to reduce CO 2 emissions from its intensive emission source. Chemical absorption is an effective way to cover the large reduction of CO 2 , and piperazine (PZ) is one of the amines that have good performance on CO 2 capture. To make a deep understanding of the chemical mechanism of PZ absorbing CO 2 , computational studies on PZ chemically absorbing CO 2 are discussed in this work using Density functional theory (DFT). Possible reaction pathways of PZ absorbing CO 2 are analyzed. Due to the special chemical structure of PZ, the reaction processes can be divided into two parts, the process of (PZ+CO 2 )+PZ and (PZ+2CO 2 )+PZ. To make a good understanding of the reaction process, a comparison of that between PZ and MEA are discussed. The results show that PZ has lower forward and backward energy barriers than MEA in the zwitterion formation, but in the intermolecular hydrogen transfer process, PZ has higher forward and backward barriers than MEA. For the reaction process of PZ+2CO 2 , it can be stated as a two-step zwitterion formation with two transition states. For the following intermolecular hydrogen transfer of PZ(COO) 2 +PZ, the atom movements are similar to that of (PZCOO+PZ). All the discussions provide theoretical information of PZ chemical absorbing CO 2 .

关键词： CO 2 absorption Piperazine Reaction mechanism DFT Energy barriers

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An experimental study of two-phase pressure drop of liquid nitrogen in circular horizontal channels 1

An experimental study of two-phase pressure drop of liquid n...

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1st International Conference IIR of Cryogenics and Refrigeration Technology, ICCRT 2016

作者： Chen, Xingya Zhang, Qiaoyu Xue, Rong Lai, Tianwei Hou, Yu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'an China School of Energy and Power Engineering Xi'an Jiaotong University No.28 Xianning West Road Xi'an China

ISBN: (纸本)9782362150173

Two-phase cryogenic flow are involved in many cooling systems. In order to study the mechanism of cryogenic two phase flow. Two-phase pressure drop of liquid nitrogen (LN2) in a circular horizontal channels was experimentally studied. A wide range of flow conditions: inlet pressure from 0.15 MPa to 0.30 MPa and mass flux from 120 kg/m2s to 320 kg/m2s, and tube diameters of 4 mm were performed in the experiment. The frictional pressure drop of two-phase LN2 in circular horizontal channel is estimated using two models, the homogeneous model and the separated flow model. In addition, the measured pressure drops are compared with those calculated from correlation models available for mini-scales. As a result, the homogeneous model with the Cicchitti et al. predict better than the other correlations mentioned in this study. © 2016, International Institute of Refrigeration. All rights reserved.

关键词： Two phase flow

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Aqueous Synthesis of Ultrathin Platinum/Non‐Noble Metal Alloy Nanowires for Enhanced Hydrogen Evolution Activity

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Angewandte Chemie 2018年第36期130卷

作者： Zhaojun Liu Jing Qi Moxuan Liu Shumeng Zhang Qikui Fan Hongpo Liu Kai Liu Haoquan Zheng Yadong Yin Chuanbo Gao Frontier Institute of Science and Technology and State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an Shaanxi 710054 China School of Chemistry and Chemical Engineering Shaanxi Normal University Xi'an Shaanxi 710119 China Department of Chemistry University of California Riverside CA 92521 USA

Although aqueous synthesis of nanocrystals is advantageous in terms of the cost, convenience, environmental friendliness, and surface cleanness of the product, nanocrystals of Pt and non‐noble metal alloys are difficult to obtain with controlled morphology and composition from this synthesis owing to a huge gap between the reduction potentials of respective metal salts. This huge gap could now be remedied by introducing a sulfite into the aqueous synthesis, which is believed to resemble an electroless plating mechanism, giving rise to a colloid of Pt‐M (M=Ni, Co, Fe) alloy nanowires with an ultrasmall thickness (ca. 2.6 nm) in a high yield. The sulfite also leads to the formation of surface M−S bonds and thus atomic‐level Pt/M–S(OH) interfaces for greatly boosted hydrogen evolution kinetics under alkaline conditions. An activity of 75.3 mA cm −2 has been achieved with 3 μg of Pt in 1 m KOH at an overpotential of 70 mV, which is superior to previously reported catalysts.

关键词： Dimetall-Legierungen Nanodrähte Platin Wasserstoffentwicklung Wässrige Synthesen

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Influence of wettability on motion of compound droplets on solid surface in microchannel flow

Influence of wettability on motion of compound droplets on s...

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2016年大连国际微流控和芯片实验室大会

作者： Xinglong Shang Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

To understand droplet motion on solid surfaces is very important for many applications such as enhanced oil recovery（Freitas et al.2011）,droplet spreading,manipulation and fabrication of droplets in microfluidic devices（Worner et al.2012）.Solid surface wettability affects significantly the movement of the contact line and hence dominants the motion of droplets on solid surfaces,especially when the flow is confined to ***,the compound droplets are often common with the applications mentioned above（e.g.,water-in-oil-in-water and oil-in-water-in-oil type compound droplet）.Furthermore,the wettability of solid surfaces is often heterogeneous that make the drop motion more *** aim of this work is to investigate the influence of solid surface wettability（e.g.,solid surface wettability gradient and contact angle hysteresis） on the motion of compound droplets in microchannel *** this end,we develop a three-dimensional model by combining the front tracking method for drop surface motion and the generalized Navier boundary condition（Qian et al.2003） for contact line *** front tracking method to model the deformation and motion of compound droplets surrounded by elastic interfaces has been developed and validated in our previous work（Bai et al.2012;Luo et al.2015）.The presence of inner droplet significantly influences the deformation and motion of compound droplets on solid *** to the results from previous two-dimensional front tracking methods（Huang et al.2004） and other numerical methods（Ding et al.2010）,the pattern of ripples is observed in our simulations on the drop *** effects of dimensionless numbers including the Reynolds number,the capillary number and the volume ratio of the inner to the outer droplet are ***,it is demonstrated that the gradient of solid surface wettability and the hysteresis of contact angle have a remarkable effect on the deformation and motion of compound droplets.

关键词：

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Recent advances in nanoporous graphene membrane for gas separation and water purification

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Science Bulletin 2015年第21期60卷 1807-1823页

作者： Chengzhen Sun Boyao Wen Bofeng Bai State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

Graphene is a one-atom-thick sheet of graphite comprising sp2-hybridized carbon atoms arranged in the hexagonal honeycomb lattices. By removing the honeycomb lattices and forming nanopores with specific geometry and size, nanoporous graphene has been demonstrated as a very high-efficiency separation membrane, due to the ultrafast molecular permeation rate for its one-atom thickness. This review focuses on the recent advances in nanoporous graphene membrane for the applications of gas separation and water purification, with a major emphasis on the molecular permeation mechanisms and the advanced fabrication methods of this state-of-the-art membrane. We highlight the advanced theoretical and experimental works and discuss the gas/water molecular transport mechanisms through the graphene nanopores accompanied with theoretical models. In addition, we summarize some representative membrane fabrication methods, covering the graphene transfer to porous substrates and the pore generation. We anticipate that this review can provide a platform for understanding the current challenges to make the conceptual membrane a reality and attracting more and more attentions from scientists and engineers.

关键词： Nanoporous graphene Gas separationWater purification Molecular permeationmechanism Membrane fabrication

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Movement of Oil-Water-Solid Three-Phase Contact Line under Velocity Gradients

Movement of Oil-Water-Solid Three-Phase Contact Line under V...

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2016年大连国际微流控和芯片实验室大会

作者： Wenxiu ZHENG Chengzhen SUN Bofeng BAI State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University

The movement of three-phase contact line which formed in the oil-water-solid three-phase area is of great importance in a number of applications,such as oil recovery,groundwater remediation,decontamination and *** process of oil droplets/film migration and detachment,which are controlled by the moving contact line,has shown its great significance in oil *** are various factors which can drive the contact line to move,such as pressure and electrical driving forces,etc,which will generate a velocity gradient for the flow near the *** this paper,we dedicate to investigate the moving rule of contact line under a velocity gradient from molecular dynamics(MD) ***,MD simulations are implemented by the FORCITE module in the Material Studio software to obtain the microscopic view of the moving contact *** size of the system is about 14 nm×3 nm×50 nm,including 2880 oil molecules and 33080 water *** interatomic interactions are described by COMPASS force field,for which van der Waals interaction is described by 9-6 Lennard-Jones potential and electronic interaction is described by Coulombic potential *** water and oil molecules are arranged on a silica substrate and the velocity gradient is generated by moving the upper *** water molecules we used SPC/E *** cutoff radius is 1.25 nm to the short-range intermolecular *** long-range Coulombic interactions are handled with the Ewald *** on the MD simulations,the configuration of water and oil molecules shows us the morphology of the contact line and variations of the contact angle at different velocity *** results exhibit that the contact line will move only when the velocity gradient is larger than a certain *** force inside the contact line region such as friction force and shear stress are calculated to make a deep understanding of the moving contact *** property of water/oil molecules and velocity profile

关键词： Movement of Oil-Water-Solid Three-Phase Contact Line under Velocity Gradients Velocity

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