Journal of University of Chinese Academy of Sciences

Experimental study on three-fluid spray characteristics of glycerol/water/compressed air

BAI Feilong, JING Qing, ZHOU Zhifu, WANG Rui, YANG Tao, CHEN Bin

2017, 34 (2): 129-134. DOI: 10.7523/j.issn.2095-6134.2017.02.001

Twin-fluid atomization by gas and liquid has been widely used in the modern industry. Few studies have been conducted on the three-fluid atomizer. A test rig using a nozzle was constructed to explore the atomization characteristics of glycerol/water/compressed air spray. Spray patterns were captured by a high-speed camera, while droplet diameter and particle velocity were measured by a phase Doppler particle analyzer (PDPA). The relationships between the air-liquid ratio (ALR) and the atomization spatial properties, including droplet Sauter diameter and mean velocity, were investigated. It is found that droplet Sauter diameter varies slightly with ALR in the range from 0.327 to 0.518. Droplet diameter and velocity show strong non-uniformity in the spray field. Near the nozzle exit droplet diameter decreases rapidly while droplets are accelerated leading to higher droplet velocity. At different axial positions, the atomization effects show a similar trend that the atomization is finer in the center area of the spray than in the margin.

Effect of non-condensable gas on pressure oscillation of submerged steam jet

CONG Yuelei, WANG Yingchun, CHEN Weixiong, CHONG Daotong, YAN Junjie

2017, 34 (2): 135-140. DOI: 10.7523/j.issn.2095-6134.2017.02.002

Abstract ( 303 ) PDF (KB) ( 2 )

Effect of non-condensable gas on pressure oscillation of submerged steam jet is studied experimentally. With the presence of non-condensable gas, the pressure oscillation intensity reduces significantly compared with that of pure steam. As the air mass fraction increases, the axial position of pressure oscillation peak shifts downstream. The oscillation intensity peak value increases with the air mass fraction when the water temperature is below 45℃, while it decreases when the water temperature is higher than 50℃. When the water temperature is within the range between 45 and 50℃, the peak value of oscillation intensity is almost invariant with the air mass fraction. Furthermore, the oscillation frequency decreases with the increase of the air mass fraction, steam mass flux, and subcooled water temperature.

Experimental studies on the flow and wall temperature distribution of solar cavity receiver under non-uniform heat flux

HAO Yun, WANG Yueshe, HU Tian, WEI Yuqing

2017, 34 (2): 141-145. DOI: 10.7523/j.issn.2095-6134.2017.02.003

Abstract ( 293 ) PDF (KB) ( 2 )

On account of one-target focus type of the heliostats in the tower solar power technology, the heat flux in the cavity receiver is non-uniform in time and space, which may lead to the panels burst or ablation due to the local over-heat in some extreme situation. In this work, an electrical heated evaporating experimental loop, including five parallel vertical tubes, is set up to evaluate the hydrodynamic characteristics of evaporation panels in a solar cavity receiver under various non-uniform heat fluxes. The influence of the heat flux concentration ratio, total flow rate, and system pressure on the flow distribution of parallel tubes is discussed. The hydrodynamic characteristics of working fluid in the heated surface of cavity receiver are obtained by performing experiments. This work offers information for development of large-capacity, high-efficiency, and large-scale cavity receivers.

Theoretical and numerical analyses of interphase forces in dilute particle-laden channel turbulence

LI Zhenzhong, WEI Jinjia, YU Bo

2017, 34 (2): 146-152. DOI: 10.7523/j.issn.2095-6134.2017.02.004

Abstract ( 438 ) PDF (KB) ( 2 )

We investigated the relative importance of interphase forces using theoretical method and direct numerical simulation, respectively. The particle motion was described by Basset-Boussinesq-Oseen equation, and the lift force and Magnus force were also considered. It was found that the frequency analysis and dimensional analysis appropriately predicted the importance of the interphase forces relative to the drag force. In these analyses, the parameters of particle-laden flow were within the scope of the calculation formula for different forces. In the streamwise and spanwise directions, Basset force, drag force, and gravity were important. However, drag force, lift force, and Basset force were significant in the wall-normal direction.

Instability mechanism of interfacial waves in swirling annular gas-liquid flow

LIU Li, BAI Bofeng

2017, 34 (2): 153-159. DOI: 10.7523/j.issn.2095-6134.2017.02.005

Abstract ( 280 ) PDF (KB) ( 2 )

To reveal the mechanism of interfacial wave instability in swirling annular gas-liquid flow, a theoretical model for interfacial waves is established based on the Kelvin-Helmholtz instability theory and the two-fluid model. The dispersion equation is derived, and the interfacial stability criterion is obtained and verified analytically. Results indicate that the interplay of aerodynamic, centrifugal, and surface tension forces gives rise to interfacial instability. Specially, the centrifugal force acting on the interface has triple effects on the stability, depending on the relative magnitudes of gas/liquid dynamic pressures. Effects of gas velocity, swirl intensity, and cylinder curvature on the growth characteristics of the interfacial waves are examined in detail.

Breakup and atomization of annular flow jet in crossflow

SHENG Ganghao, ZHANG Haibin, ZHAO Zhongchuang, LIU Xinshi

2017, 34 (2): 160-165. DOI: 10.7523/j.issn.2095-6134.2017.02.006

Abstract ( 319 ) PDF (KB) ( 2 )

Experimental investigation was carried out on the atomization of the gas-liquid annular flow jet in crossflow. Results show that the liquid film of the annular flow jet realizes steady atomization in crossflow macroscopically. The dimensionless trajectory correlation of the annular flow jet in crossflow is presented based on the captured atomization images. The transient breakup and atomization of the annular flow jet in crossflow was investigated by using high-speed photography techniques. It is found that the transient breakup and atomization processes of annular flow jet are periodic and discontinuous. The mechanisms of the film breakup and atomization were discussed and the influences of different parameters on them were obtained. Results also indicate that the atomization pattern may vary with conditions. Increase in superficial gas velocity improves the atomization effects.

Experimental study on heat transfer characteristics of aqueous NaCl solution in static flash evaporation

WANG Chaoyang, ZHANG Dan, YANG Qingzhong, WANG Yu, YAN Junjie

2017, 34 (2): 166-171. DOI: 10.7523/j.issn.2095-6134.2017.02.007

Abstract ( 253 ) PDF (KB) ( 3 )

Experimental studies on heat transfer characteristics of aqueous NaCl solution in static flash evaporation were carried out, with the mass fraction of aqueous NaCl solution varying between 0 and 0.26, initial height of water film varying between 0.1 to 0.4 m, and superheat varying from 1.5 to 40℃. Results showed that at different stages of flash evaporation the effects of superheat on instantaneous heat transfer coefficient were different. At the early stage, instantaneous heat transfer coefficient decreased with the superheat. At the beginning of the late stage, instantaneous heat transfer coefficient increased with the superheat. At the end of flash evaporation instantaneous heat transfer coefficient was nearly irrelevant to superheat. Results showed that the maximum instantaneous heat transfer coefficient value decreased with the increases of the initial height and initial concentration of water film. A fitting formula for instantaneous heat transfer coefficient of NaCl solution was proposed, and it was in good agreement with experimental results in the experimental range. The boiling states were significantly affected by the transient heat transfer coefficient in static flash evaporation.

Numerical simulation of temperature effect on particle forces in electrostatic precipitators

BI Wenjian, LI Yan, LUO Kun, FAN Jianren

2017, 34 (2): 172-178. DOI: 10.7523/j.issn.2095-6134.2017.02.008

Abstract ( 457 ) PDF (KB) ( 2 )

A computational fluid dynamics (CFD) model is proposed to describe the wire-plate electrostatic precipitator (ESP) in high temperature condition. In this model, the complex interactions among the electric field, temperature field, fluid dynamics, and the particulate flow are taken into account. The finite volume method is used to solve the electric field and the Euler-Lagrange model is used to describe particle-laden flows. The influences of high temperature on particle characteristics in ESP are investigated in the current simulation. Numerical results show that Coulomb force decreases while the Saffman lift force, Brownian force, and drag force increase with the temperature. Besides, the increasing rate of drag force is faster than that of Coulomb force, which may cause the reduced efficiencies at high temperature.

Application of air quality response surface model (RSM) in Hangzhou

DAI Zhixiang, HU Shiwei, LUO Kun, GAO Xiang, FAN Jianren, CEN Kefa

2017, 34 (2): 179-185. DOI: 10.7523/j.issn.2095-6134.2017.02.009

Abstract ( 340 ) PDF (KB) ( 3 )

Based on the CMAQ simulation results, we summarize the function relationships between various pollutant emission control factors and the concentrations of pollutants to establish air quality response surface model (RSM). The cross validation and external validation are used to evaluate the model reliability. In the study of the PM_2.5 response of different pollutants and the future emission control scenarios (Ⅰ and Ⅱ) in Hangzhou, we find that NO_X, SO₂, NH₃, and VOC have obvious nonlinear response characteristics to PM_2.5 emissions and that the effect of scenario Ⅱ is stronger than that of scenario Ⅰ and the effect in summer is stronger than in winter.

Stability analysis of multi-electrode excitation strategies for 3D ECT

MAO Mingxu, YE Jiamin, WANG Haigang, ZHANG Jiaolong

2017, 34 (2): 186-190. DOI: 10.7523/j.issn.2095-6134.2017.02.010

Abstract ( 271 ) PDF (KB) ( 2 )

Generally, single-electrode excitation strategy is used for a 3D ECT (electrical capacitance tomography). In this study, the stability of multi-electrode excitation strategies is investigated by using a three-plane ECT sensor for the 3D image reconstruction. Three excitation strategies, including the single-electrode excitation, dual-electrode excitation in the same plane, and dual-electrode excitation in different planes, are considered for comparison. Landweber iteration algorithm is used for image reconstruction. The effect of excitation strategy on image quality and stability is investigated by using the noise-free and noisy data in terms of correlation coefficient. Based on the simulation results, the stability of the three excitation strategies is evaluated.

Bubble dynamic analysis and hydroxyl radical production calculation at bubble collapse in turbulence flow

TAO Yuequn, CAI Jun, LIU Bin, HUAI Xiulan

2017, 34 (2): 191-197. DOI: 10.7523/j.issn.2095-6134.2017.02.011

Abstract ( 241 ) PDF (KB) ( 8 )

Based on Gilmore bubble dynamic equation, a model, which takes the viscosity, surface tension, compressibility, water molecular diffusion, and heat conduction into consideration, is built to describe bubble dynamic behavior in the turbulent orifice flow. The mathematical model is solved by using the fourth Runge-Kutta approach, and the cavitation bubble growth, collapse, and rebound process are described. With the temperature, pressure, and number of water molecules obtained by using the mathematical model as the input parameters, the productions of hydroxyl radicals with high oxidation under different conditions are calculated and the effecting parameters are analyzed.

Lattice-Boltzmann simulation of the effect of particle-fluid density ratio on instability of two-phase flow

LIU Guodong, YIN Xiaolong, WANG Shuai, LU Huilin, ZHANG Yanan

2017, 34 (2): 198-203. DOI: 10.7523/j.issn.2095-6134.2017.02.012

Abstract ( 260 ) PDF (KB) ( 2 )

A lattice-Boltzmann method is used to simulate the hydrodynamic property of particles in a periodic domain. An Archimedes number of 1 432 is used for the system corresponding to the terminal Reynolds number of 30. Simulations are carried out when the average solid volume fraction is 25[WTB4]%[WTBZ], and the density ratio ranges from 2 to 1 000 (from liquid-particle density ratio to gas-particle density ratio). Investigation of the effect of density ratio on stability of the fluid-particle flow system is carried out. The collision among particles is consideved to be elastic. The variations regulations of mean particle velocity, variance, skewness and kurtosis are obtained and analyzed. By combining with the structure factor analysis, the relationships between particle velocity properties and dynamic clusters are determined at different density ratios when the stable-unstable transition occurs, and the density ratio range is also determined.

Predictions of compositional mixing degree in two-component aggregation

ZHAO Hanqing, XU Zuwei, ZHAO Haibo

2017, 34 (2): 204-209. DOI: 10.7523/j.issn.2095-6134.2017.02.013

Abstract ( 303 ) PDF (KB) ( 2 )

Multi-component particle aggregation is one of the main physical mechanisms in the process of particle growth. For two-component aggregation, the compositional mixing degree χ is an important criterion and the key to determination of compositional distribution. Now the dynamic evolution of χ before the attainment of a steady-state value is beyond numerical modeling and theoretical research. In this work, the fast differentially-weighted Monte Carlo method for population balance modeling was used to predict the dependence of time-varied χ on initial feeding conditions through hundreds of systematically varied simulations. It is found that χ is subject to exponential decay in the free molecular regime and the continuum regime. By using the explored exponential formulas for the dynamic mixing degree, it is possible to achieve an optimum control over the compositional distributions during two-component aggregation processes through selecting the initial feeding parameters.

Numerical study of pressure drop and diffusional collection efficiency of rectangular fibers in filtration

HUANG Haokai, ZHAO Haibo

2017, 34 (2): 210-217. DOI: 10.7523/j.issn.2095-6134.2017.02.014

Abstract ( 210 ) PDF (KB) ( 2 )

In this work, we use a lattice Boltzmann-cellular automaton (LB-CA) probabilistic model to simulate the particle filtration processes of rectangular fibers. The pressure drop and collection efficiency for the diffusion dominant regime are investigated. By normalizing the pressure drop and collection efficiency of rectangular fibers with those of the circular fiber calculated by using the existing classical expressions, the corresponding ratios are oftained. Then the Levenberg-Marquardt algorithm is used to obtain the fitting expressions of the ratios. The proposed fitting expressions are used to calculate the pressure drops and diffusional collection efficiencies of rectangular fibers under different operation conditions. The results show that the pressure drop of rectangular fibers is dependent on the orientation angle and the aspect ratio and that the diffusional collection efficiency is proportional to the aspect ratio but almost independent of the orientation angle.

Influence of rotating velocity on particle mixing characteristics in a three-dimensional tumbler

ZHANG Ziwei, GE Liang, GUI Nan, LI Zhenlin, YANG Yang

2017, 34 (2): 218-225. DOI: 10.7523/j.issn.2095-6134.2017.02.015

Abstract ( 218 ) PDF (KB) ( 2 )

The mixing processes of carbon spherical particles in 3-D tumbler at five typical rotating speeds are simulated by using the open source software OpenFOAM utilizing soft sphere model of discrete element method. The evolution of particle mixing is investigated, and the structural characteristics of particle mixing in different regimes are illustrated. Moreover, with the help of the information entropy and a series of new mixing indexes, which are the difference value functions, we quantitatively analyze the influence of rotating velocity on particle mixing characteristics.

Experimental study on pipeline wax deposition of oil and gas two-phase intermittent flow

GAO Ge, WU Haihao, QUAN Qing, GONG Jing, WANG Wei

2017, 34 (2): 226-231. DOI: 10.7523/j.issn.2095-6134.2017.02.016

Abstract ( 255 ) PDF (KB) ( 3 )

This work studies the effects of oil and gas superficial velocities and temperature on wax deposition thickness and carbon number distribution for intermittent flow of waxy mineral white oil and high-pressure air. The results are shown as follows: the wax deposit around the whole pipe, and the shape changes with the oil and gas superficial velocities. The equivalent deposit thickness decreases with increase of gas velocity, while with increase of oil velocity the deposit thickness increases first and then decreases. Equivalent deposit thickness increases first and then decreases with increase of oil temperature, while decreases with increase of wall temperature at a constant oil temperature. Increases of oil and gas velocities lead to increase of deposition hardness, which is characterized by variation of carbon number.

Experimental study on heat transfer and interfacial distribution of air-water slug flow in cooling process

WANG Xin, DONG Chuanshuai, ZHANG Xiaoling, YUE Xiaoqing, HE Limin

2017, 34 (2): 232-236. DOI: 10.7523/j.issn.2095-6134.2017.02.017

Abstract ( 236 ) PDF (KB) ( 2 )

An experimental rig was constructed for study of non-boiling cooling heat transfer of gas-liquid flow in subsea pipeline in oil and gas industry. The hydrodynamic and heat transfer characteristics of slug flow with 4℃ coolant in the annular pipe were measured by using sensors such as thermocouples,thermopiles,parallel conducting probes, etc. The convective heat transfer coefficients and flow parameters were obtained and a clear temperature difference was measured between the top and the bottom of the pipe. The effects of interfacial distribution of liquid slug and elongated bubble on the heat transfer coefficient were analyzed. The experimental results showed that the convective heat transfer coefficient was slightly affected by superficial gas velocity. The convective heat transfer between the fluid and the lower wall was significantly stronger than that between the fluid and the upper wall.

Capacitance-conductance sensor for water holdup measurement in oil-water two-phase flow

WU Hao, TAN Chao, DONG Feng

2017, 34 (2): 237-243. DOI: 10.7523/j.issn.2095-6134.2017.02.018

Abstract ( 290 ) PDF (KB) ( 8 )

In oil-water two-phase flow measurement, a capacitance-conductance sensor has been designed based on the fact that the capacitance sensor and conductance sensor realize the water holdup measurement in different situations with different sensitive ranges. Electrical switches are used to switch the two measurement methods at high speed in order to make them have the same sensitive fields. The disigned sensor realizes the whole fraction measurement in oil-water two-phase flow with low conductivity water (tap water) and the water holdup measurement error is less than 5[WTB4]%[WTBZ].

Numerical simulation of vapor-feed direct methanol fuel cell

XIE Xu, DENG Hao, JIAO Kui

2017, 34 (2): 244-250. DOI: 10.7523/j.issn.2095-6134.2017.02.019

Abstract ( 228 ) PDF (KB) ( 1 )

A two-dimensional, two-phase, and non-isothermal model is developed for a vapor-feed direct methanol fuel cell (DMFC) based on alkaline anion exchange membrane system by using the multi-fluid approach. The model will lead to better understanding of the mass-transfer and electrochemical phenomenon in the cell. In the model, the vapor generated from the liquid methanol in the tank goes through a composite material made of Nafion membrane and hydrophobic porous layer into the cell. In the study, the vapor transport layer (VTL) and micro porous layer (MPL) are taken into account, and two symmetrical exits in the VTL are set for the CO₂ removal. With this model, effects of the CO₂ exit length and the hydrophobic MPL on performance and inner water distribution of DMFC are investigated.

Experimental study of migration of micro particles in porous media

LEI Haiyan, CUI Mingjie, DAI Chuanshan, LI Qi

2017, 34 (2): 251-258. DOI: 10.7523/j.issn.2095-6134.2017.02.020

Abstract ( 330 ) PDF (KB) ( 2 )

In this work, we carried out experimental study on migration of micro particles in porous media, taking physical clogging in sandstone during geothermal reinjection as research background. Underground aquifer was simulated by filling the cylindrical pipe with spherical glass beads. Particle deposition in the porous and at the fluid/porous media interace was respectively analyzed, with the particle size d_p values of 12.96 and 22.81 μm, porous medium particle diameter D_p values of 408.9 and 659.2 μm, and carrier fluid concentrations ranging from 0.3 to 2.0 g/L. The results shows that the amount of particles deposited inside the porous medium is much larger than at the interface of porous medium when d_p=12.96 μm. However, when d_p=22.81 μm, there is little difference between the two depositions as C<0.3 g/L, whereas this difference increases as the concentration of the carrier fluid increases, indicating that more particles deposited at the fluid/porous medium interfaces and the "sieve" effect occurs. The results would be useful in the next numerical simulations.

Study of fine particles impacting a pendant charged droplet

ZUO Ziwen, WANG Junfeng, HUO Yuanping, XU Rongbin

2017, 34 (2): 259-264. DOI: 10.7523/j.issn.2095-6134.2017.02.021

Abstract ( 199 ) PDF (KB) ( 2 )

An in-house designed device is used to investigate the behavior of fine particles impacting the pendant charged droplet by electrostatic attraction. The results show that part of the particles bounce off the droplet surface after physical contact. Nearly half of the particles rebound when their impact angles are smaller than 85°. Due to the loose structures, particle clusters disintegrate when impacting the droplet surface, and most generated daughter particles rebound subsequently. The larger volume of particle cluster enables it to capture more free charge during its motion, which may even offset the initial polarity and result in repulsion by the charged droplet. The reentrainment caused by particle rebound and cluster disintegration or escape significantly reduces the capture efficiency of the charged droplet.

Numerical simulation on the gas-liquid two-phase flow in the direct commissioning process of a hilly pipeline

ZHANG Xinyu, XIE Jing, YU Bo

2017, 34 (2): 265-272. DOI: 10.7523/j.issn.2095-6134.2017.02.022

Abstract ( 219 ) PDF (KB) ( 2 )

Direct commissioning of oil pipeline is a complex gas-liquid two-phase flow process. In the highly hilly area, the complex flow status in the pipeline poses great threat to the safety of pipeline. Numerical approach is adopted in this work to study the gas-liquid two-phase flow in the hilly pipe. Physical models are established and commercial software is utilized to monitor the flow field. Characteristics and influencing factors for varied types of pipes are studied.

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