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Irreversibility Analysis of a Recuperative Heater during Undergoing the flowrate Impulsive Disturbance Transient Processes

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Energy Procedia 2019年 158卷 5311-5316页

作者： Chaoyang Wang Yongliang Zhao Zhu Wang Ming Liu Junjie Yan State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an 710049 China

The recuperative heater is widely used in the industrial production processes, and the irreversibility analysis on the heater during transients is scarce but necessary. Numerical method was adopted to model the recuperative heat exchanger to exhibit its dynamic behaviors during transient processes. The difference between the transient and stationary irreversibility can be called additional irreversibility. In this paper, the dynamic behaviors of the recuperative heater during transients are presented. With these thermal parameters, the irreversibility of a recuperative heater during hot and cold fluid flow rates impulsive disturbance transient processes was calculated and analyzed in detail. The calculation results show that: compared with steady-state corresponding value, the real-time irreversibility rate of the heater during transients is different. The total additional irreversibility values with impulsive disturbance in hot and cold fluid flow rates are obtained separately.

关键词： Recuperative heaters Irreversibility analysis Dynamic modeling Transisent processes

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Optimization of the radiation absorption for a scaled-up photocatalytic hydrogen production system

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SOLAR ENERGY 2018年 160卷 168-177页

作者： Yang, Yan Wei, Qingyu Liu, Haijun Zhao, Liang Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian Shaanxi Peoples R China

The effective absorption of photons by photocatalyst in the reactor is a challenge for scaled-up application of a photocatalytic hydrogen production system. The spatial distribution of radiation and photon absorption are proposed to be strongly dependent on the photocatalyst concentration and the structure of the solar collector. However, there have been few reports of the radiation absorption properties of a cylindrical reactor based on high power solar collector that is suitable for a large-scale photocatalytic hydrogen production system. In this study, the distribution of radiation in the reactor as represented by the local volumetric rate of photon absorption was determined by adopting the modified six-flux absorption scattering model based on the compound parabolic concentrator and the surface uniform concentrator. The explanations of the differences of radiation absorption properties were comprehensively analyzed by ray-tracking technique. The structure of the solar collector and the optimum catalyst concentration are recommended based on photon absorption efficiency. This work may serve as potential reference values for the optimal reactor operating parameters for large-scale application.

关键词： Photocatalytic hydrogen production system Solar collector Optimum catalyst concentration Photon absorption efficiency

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Flame morphology and self-acceleration of syngas spherically expanding flames

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INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2018年第36期43卷 17531-17541页

作者： Cai, Xiao Wang, Jinhua Zhao, Haoran Zhang, Meng Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

The self-acceleration of spherically expanding flames were investigated using a constant volume combustion chamber for CO/H-2/O-2/N-2 mixtures over a wide range of initial pressure from 0.2 to 0.6 MPa, CO/H-2 ratio from 50/50 to 10/90 and equivalence ratio from 0.4 to 1.5. The adiabatic flame temperature was kept constant by adjusting O-2/N-2 ratio at different equivalence ratios. Schlieren images were recorded to investigate the flame front evolution of spherically expanding flames. Local acceleration exponents were extracted using a proper equation to study the process of flame self-acceleration. Results show that the flame cells develop on the smooth flame fronts and finally reach fractal-like structures due to the hydrodynamic and diffusional-thermal instabilities, resulting in flame self-accelerative propagation. The critical Peclet number corresponding to the onset of self acceleration, Pe(cr) increases nonlinearly with the Markstein length, Ma. The observation further reveals that the onset of self-acceleration is mainly controlled by the diffusional-thermal effect. There exists two distinct flame propagation regimes in the self acceleration, namely quick transition accelerative and quasi self-similar accelerative regimes. The quick transition regime is controlled by the destabilization effect of hydrodynamic perturbation and stabilization effect of flame stretch. While the quasi self-similar regime is primarily affected by the cascading process of flame front cells controlled by hydrodynamic instability. The self-similar acceleration exponent, alpha(s) varies with the initial pressure and Lewis number, Le. The values of alpha(s) are measured to be 1.1-1.25 (smaller than 1.5), indicating the flame dose not attain self-turbulization. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

关键词： Spherically expanding flame Flame self-acceleration Self-acceleration regime Flame instability Acceleration exponent Syngas

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Investigation of the Heat Loss Effect on Cellular Flames via Proper Orthogonal Decomposition

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COMBUSTION SCIENCE AND TECHNOLOGY 2018年第5期190卷 803-822页

作者： Jin, Wu Wang, Jinhua Zhang, Weijie Cai, Xiao Nie, Yaohui Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

For better control of a lean premixed combustion system, it is necessary to understand the mechanism of unsteady cellular flame. The objective of the present study is to investigate how heat loss influences the cellular instability of lean premixed flame. The lean premixed CH4/H-2/air cellular flames generated on a McKenna burner were studied, and heat loss was responsible for the manifestation of unsteady cellular structure. A method of applying proper orthogonal decomposition in scale analysis is presented, which has proven helpful in characterizing the cellular flame. The multiple scale nature of unstable cellular flame was identified, and the small scales were found to act in the random movement of cells. The contribution of each scale is obtained. The energy distribution on modes indicates that the energy on higher-order modes, equivalently the contribution of smaller scales, is decreased with decreasing heat loss. Through analyzing the principal modes and temporal coefficients, heat loss is found to influence a flame's unstable behavior by promoting the oscillation of large scales, and the wrinkling factor is estimated. It is found that there is a cut-off length scale, below which the wrinkles make little contribution to the enhancement of combustion intensity.

关键词： Cellular flame Heat loss McKenna burner OH-PLIF Proper orthogonal decomposition

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Single and multi-objective optimizations of rotary regenerative air preheater for coal-fired power plant considering the ammonium bisulfate deposition

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INTERNATIONAL JOURNAL OF THERMAL SCIENCES 2019年 136卷 52-59页

作者： Wang, Limin Bu, Yufan Li, Dechao Tang, Chunli Che, Defu Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Xi An Jiao Tong Univ Sch Human Settlements & Civil Engn Dept Bldg Environm & Serv Engn Xian 710049 Shaanxi Peoples R China

Although much work has been done on the optimization of the recuperative heat exchangers, little attention has been paid to the optimization of rotary regenerative air preheater (RAPH) in coal-fired power plants. It is known that the ammonium bisulfate deposition (ABS) can adversely affect the safe operation of RAPH, so an improved Radian number was proposed to estimate the impact of ABS in the optimization of RAPH. The thermal hydraulic calculation program integrated with genetic algorithms was developed to conduct optimizations of RAPH. The design parameters included rotor radius, each fluid sector angle and each matrix layer height. The multi-objective optimization was carried out to maximize the effectiveness and to minimize the pressure drop from the perspective of users, while the single-objective optimization was performed to minimize the weight of the heat transfer elements from the perspective of manufacturers. The improved Radian number is more reasonable to reflect the ABS deposition compared with the original Radian number. The designer can estimate the ABS deposition status using the improved Radian number not only in the operating process but also in the design process of RAPH. The range of optimal solution becomes smaller but the rank of the Pareto solution stays unchanged with the decrease in the restriction of improved Radian number. The optimization with larger rotor radius restriction could obtain better Pareto results. The total weight of heat transfer elements could be reduced by at least 26.5% compared with that of the original design by using genetic algorithm.

关键词： Rotary air preheater Thermal-hydraulic performance Weight Optimization Ammonium bisulfate deposition

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Synthesis and applications of carbon quantum dots derived from biomass waste: a review

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ENVIRONMENTAL CHEMISTRY LETTERS 2023年第6期21卷 3393-3424页

作者： Wu, Jiayu Chen, Tianyue Ge, Shengbo Fan, Wei Wang, Hui Zhang, Zhongfeng Lichtfouse, Eric Van Tran, Thuan Liew, Rock Keey Rezakazemi, Mashallah Huang, Runzhou Nanjing Forestry Univ Coll Mat Sci & Engn Coinnovat Ctr Efficient Proc & Utilizat Forest Res Nanjing 210037 Jiangsu Peoples R China Aerosp Kaitian Environm Technol Co Ltd Changsha 410000 Hunan Peoples R China Xian Polytech Univ Sch Text Sci & Engn Xian 710048 Shaanxi Peoples R China Donghua Univ Coll Environm Sci & Engn Shanghai 201620 Peoples R China Cent South Univ Forestry & Technol Coll Furniture & Art Design Changsha 410004 Hunan Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Shaanxi Peoples R China Nguyen Tat Thanh Univ Inst Appl Technol & Sustainable Dev 298-300A Nguyen Tat Thanh Dist 4 Ho Chi Minh City 755414 Vietnam Univ Malaysia Terengganu Higher Inst Ctr Excellence HICoE Inst Trop Aquaculture & Fisheries AKUATROP Terengganu 21030 Malaysia NV Western PLT 208B Second Floor Macalister Rd George Town 10400 Malaysia Shahrood Univ Technol Fac Chem & Mat Engn Water & Energy Solut Technol WEST Ctr Shahrood Iran

In the context of the circular economy and decreasing earth resources, waste should be converted into value-added materials such as carbon quantum dots, which are fluorescent nanomaterials with promising applications in sensing, biological imaging, energy storage, and photocatalysis. Here, we review carbon quantum dots with focus on their synthesis from biomass, factors controlling their performance, properties, and applications in energy, medicine, and environmental science. Applications include energy storage in batteries and supercapacitors, renewable energy, pollutant sensing and degradation, drug delivery, biosensing, and bioimaging.

关键词： Biomass waste Carbon quantum dots Synthesis Application Optical Energy Pollution Catalysis Medicine Quantum yield

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Oxidative degradation of quinazoline in supercritical water: a combined ReaxFF and DFT study

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MOLECULAR SIMULATION 2018年第18期44卷 1508-1519页

作者： Li, Guoxing Lu, Youjun Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian Shaanxi Peoples R China

Quinazoline (Qu) is a representative heterocyclic compound in chemical wastewater. In this work, the supercritical water oxidation of Qu is investigated using molecular dynamics simulations based on the ReaxFF reactive force field combined with density functional theory (DFT) method. The detailed reaction pathways, transformation routes of nitrogen element, and kinetic behaviours are systematically analyzed at the atomistic level. Simulation results show that the increment of temperature and O-2 molecule accelerates the reaction rate and facilitates the complete destruction of Qu. The pyrimidine ring in Qu can be attacked by the OH radical, O-2 molecule, and H2O molecule, thereby causing three main pathways for the pyrimidine ring-opening reaction. The aromatic ring undergoes a ring rearrangement process and opens under the attack of active O-2 molecules. DFT calculations demonstrate that the supercritical water cluster can decrease the cracking energy of chemical bonds and accelerate the degradation rate of Qu. In addition, the transformation routes of nitrogen element during reaction are described. NH3 is found to be the primary N-containing product after ring-opening reactions and is an intermediate for the production of N-2. Finally, the value of activation energy is obtained as 123.0 kJ/mol, which is reasonably consistent with the experimental results.

关键词： ReaxFF density functional theory reaction mechanism supercritical water oxidation quinazoline

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Numerical study on the spray and thermal characteristics of R404A flashing spray using OpenFOAM

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2018年 117卷 1312-1321页

作者： Zhou, Zhi-Fu Lu, Guan-Yu Chen, Bin Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Flashing spray is of great importance in a variety of engineering fields, which occurs as the pressurized liquid is released into a low-pressure environment below its saturation pressure. The initial stage close to the nozzle exit is furthest from thermodynamic equilibrium and the information of droplets is difficult to obtain by experimental ways due to the high density of droplets. This paper conducts a systematically numerical study on the spray and thermal characteristics of R404A flashing spray with high volatility and low saturation temperature, based on the open source tool OpenFOAM-2.4.0. key physics involved in the complex process, including droplet flash boiling, evaporation, droplet transport, breakup, heat transfer and interaction between droplet and gas phases are taken into consideration, through Reynolds Averaged Navier Stokes simulations (RANS) with Eulerian Lagrangian framework for the continuous phase and discrete phase respectively. The spray morphology and droplet diameter coincide reasonably with those in the experiment. It presents explosive atomization with large cone angle and quick expansion towards the radial direction near the nozzle exit. Droplet diameter and temperature undergoes a rapid reduction, while velocity accelerates in this region. A warm core with high droplet temperature exists in the spray central region, and droplet velocity is also larger than that at spray periphery. The ambient pressure significantly affects spray profile, penetration distance and velocity. The whole spray profile transforms to the expansion shape as the pressure increases above 0.5 MPa whereby it presents contractive one in low ambient pressure. Higher ambient pressure leads to lower droplet velocity but with longer penetration distance. These numerical results provide further insight into the mechanism of the flashing spray with volatile cryogens. (C) 2017 Elsevier Ltd. All rights reserved.

关键词： R404A Flashing spray OpenFOAM Numerical simulation Spray and thermal characteristics

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Non-monotonic dependence of induced-charge electro-osmosis on ion concentration

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COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND engineering ASPECTS 2021年 622卷 126604-126604页

作者： Feng, Huicheng Zhao, Lingqi Zhong, Xin Lei, Xingfeng Wong, Teck Neng Northwestern Polytech Univ Unmanned Syst Res Inst Xian 710072 Peoples R China Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China Northwestern Polytech Univ Sch Chem & Chem Engn Xian 710072 Peoples R China Nanyang Technol Univ Sch Mech & Aerosp Engn 50 Nanyang Ave Singapore 639798 Singapore

Induced-charge electro-osmosis (ICEO) is an important phenomenon in microfluidics as it shows great potential for various microfluidic devices. However, many basic mechanisms of ICEO remain unclear. The effect of ion concentration on ICEO is controversial. Literature has reported that ICEO velocity either monotonically increases or decreases by increasing the ion concentration. In this paper, we experimentally captured that ICEO velocity increases at first and then decays as sodium chloride (NaCl) concentration increases, which covers the whole variation range in the existing literature. The NaCl concentration of peak ICEO velocity varies as the electric field strength increases. In addition, it is known that ICEO velocity achieves a maximum value upon increasing the electric field frequency, and the frequency of peak velocity is determined by the microfluidic chip geometry and the ion concentration based on the volumeless ion assumption. However, we found that it reduces as the electric field strength increases because of the steric effect of ions in real electrolyte solutions. Moreover, an inflowoutflow asymmetry is experimentally observed in ICEO vortex positions, which shows a dependence on the electric field and NaCl concentration. The vortices become close to the cylinder surface and the two vortices along the x axis tend to merge as NaCl concentration increases. The new findings could enrich the knowledge of ICEO.

关键词： Induced-charge electro-osmosis Ion concentration effect Inflow-outflow asymmetry

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A comparison study of cyclopentane and cyclohexane laminar flame speeds at elevated pressures and temperatures

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FUEL 2018年 234卷 238-246页

作者： Zhao, Haoran Wang, Jinhua Cai, Xiao Tian, Zemin Li, Qianqian Huang, Zuohua Xi An Jiao Tong Univ State Key Lab Multiphase Flow Power Engn Xian 710049 Peoples R China

Laminar flame speeds of cyclopentane/air and cyclohexane/air mixtures were determined at equivalence ratios of 0.7-1.6, initial pressures of 1-5 atm, and initial temperatures of 353-453 K using the spherically propagating flame method. Four recently published models of cyclopentane and cyclohexane were validated by current experimental data and showed a reasonable agreement, especially for JetSurF2.0 model and Tian model. A comparison of cyclopentane/air and cyclohexane/air laminar flame speeds was conducted over wide conditions. A comprehensive analysis was conducted through thermal, transport and chemical kinetic effects, and the reaction path analysis and sensitive analysis were employed to further investigate the chemical kinetic effects. The results showed that the laminar flame speed of cyclohexane/air mixture is larger than that of cyclopentane/air and the discrepancy increases with the initial pressure. The discrepancy mainly results from the chemical kinetic effects. Specifically, cyclopentane generates more methyl and allyl intermediates which can consume large amounts of H radicals and induce chain terminating reactions. While, cyclohexane generates a larger amount of ethyl and 1,3-butadiene intermediates which can further yield more vinyl, and the later can induce chain branching reactions and increase the overall burning rate. Thus, it is the different distribution of the cracked products in cyclopentane/air and cyclohexane/air flames that leads to the discrepancy of laminar flame speeds.

关键词： Laminar flame speeds Cyclopentane Cyclohexane Elevated pressures Elevated temperatures

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