Please wait a minute...
[an error occurred while processing this directive]
Table of Content
28 March 2014, Volume 22 Issue 3
    Effects of Shape and Quantity of Helical Baffle on the Shell-side Heat Transfer and Flow Performance of Heat Exchangers
    DU Wenjing, WANG Hongfu, CHENG Lin
    2014, 22(3):  243-251.  doi:10.1016/S1004-9541(14)60041-0
    Abstract ( 5083 )   PDF (885KB) ( 160 )  
    References | Related Articles | Metrics
    Shape and quantity of helical baffles have great impact on the shell-side performance of helical baffled heat exchangers (HBHE). In this work, three physical models of HBHE with baffles of different shape (trisection, quadrant and sextant sector) were investigated. Numerical simulations were performed on HBHE at three helix angles (10°, 25° and 40°) by the software ANSYS CFX. Analyses of numerical results indicate that the sextant HBHE shows relatively better fluid flow performance because the leakage flow in the triangle area is evidently reduced and the fluid streamline appears much closer to an ideal spiral flow, while the trisection and quadrant HBHE show more scattered and disordered streamline distributions. The convective heat transfer coefficient and pressure drop in three types of HBHE were presented. Further investigations on the shell side performance with different helical baffles were implemented by the field synergy theory. Both theoretical and numerical analyses gave support on the relations between helical baffle shape and shell-side performance. This paper may provide useful reference for the selection of baffle shape and quantity in HBHE.
    Numerical Modeling and Analysis of Gas Entrainment for the Ventilated Cavity in Vertical Pipe
    XIANG Min, JIANG Zhenyu, ZHANG Weihua, TU Jiyuan
    2014, 22(3):  252-260.  doi:10.1016/S1004-9541(14)60033-1
    Abstract ( 4163 )   PDF (373KB) ( 43 )  
    References | Related Articles | Metrics
    A semi-empirical gas entrainment model was proposed for the ventilated cavity in vertical pipe, based on which, a complete numerical scheme was established by coupling with the Eulerian-Eulerian two-fluid model to predict the multiscale flow field created by ventilated cavity. Model predictions were validated against experimental measurements on void fraction and bubble size distributions. Simulations were carried out to explore the effect of ventilation rate and inlet turbulence intensity on the macroscale cavity shape and the bubbly flow downstream of the ventilated cavity. As the ventilation rate increasing, a reverse trend was observed for the void fraction and bubble size distributions. It is concluded that the average void fraction in the pipe flow region is determined by the volumetric ratio between liquid and gas. However, the bubble size evolution is dominated by the breakage effect induced by turbulence in the vortex region. Furthermore, simulations were conducted to analyze geometric scale effect based upon Froude similitude. The results imply that the velocity distributions were properly scaled. Slight scale effect was seen for the void fraction caused by faster dispersion of bubbles in the larger size model. The comparatively greater bubble size was predicted in the smaller model, implying significant scale effects in terms of turbulence and surface tension effect. It reveals that empirical correlations valid in wide range are required for the extrapolation from small-size laboratory models.
    A Contraction-expansion Helical Mixer in the Laminar Regime
    LIANG Dong, ZHANG Shufen
    2014, 22(3):  261-266.  doi:10.1016/S1004-9541(14)60035-5
    Abstract ( 4018 )   PDF (357KB) ( 75 )  
    References | Related Articles | Metrics
    A contraction-expansion helical mixer which combines several features, viz. helical pipes for induction of secondary flows and sudden expansion and contraction array for expansion vortices, has been designed to enhance flow mixing. A fast competitive-consecutive diazo coupling reaction is used to test the mixing efficiency of contraction-expansion helical mixer. Furthermore, an image processing technique is applied for data visualization and monitoring the extent of mixing. The mixing performance is found to be superior in comparison to the regular helical mixer in the range of Reynolds number from 170 to 1540. Moreover, the mixing time of contraction-expansion helical mixer was found to be reduced by more than 25% compared to the regular helical pipe. Finally, a simple correlation is proposed for predicting the mixing time.
    Hydrodynamics and Mass Transfer of Oily Micro-emulsions in An External Loop Airlift Reactor
    Mona Ebrahimi Fakhari, Mostafa Keshavarz Moraveji, Reza Davarnejad
    2014, 22(3):  267-273.  doi:10.1016/S1004-9541(14)60050-1
    Abstract ( 3521 )   PDF (245KB) ( 37 )  
    References | Related Articles | Metrics
    This study reports an experimental investigation on hydrodynamics and mass transfer characteristics in a 15.6×10-3 m3 external loop airlift reactor for oil-in-water micro-emulsions with oil to water volume ratio (φ) ranging from 3% to 7% (by volume). For comparative purposes, experiments were also carried out with water. Increase in φ of micro-emulsion systems results in an increment in the gas holdup and a decrease in the volumetric gas-liquid oxygen transfer coefficient and liquid circulation velocity, attributed to the escalation in the viscosity of micro-emulsions. The gas holdup and volumetric mass transfer coefficient for micro-emulsion systems are significantly higher than that of water system. Two correlations are developed to predict the gas holdup and oxygen transfer coefficient.
    Determination of Transport Properties of Dilute Binary Mixtures Containing Carbon Dioxide through Isotropic Pair Potential Energies
    Delara Mohammad-Aghaie, Mohammad Mehdi Papari, Amjad Reza Ebrahimi
    2014, 22(3):  274-286.  doi:10.1016/S1004-9541(14)60018-5
    Abstract ( 3350 )   PDF (323KB) ( 32 )  
    References | Related Articles | Metrics
    The present work is concerned with extracting information about intermolecular potential energies of binary mixtures of CO2 with C2H6, C3H8, n-C4H10 and iso-C4H10, by the usage of the inversion method, and then predicting the dilute gas transport properties of the mixtures. Using the inverted pair potential energies, the Chapman-Enskog version of the kinetic theory was applied to calculate transport properties, except thermal conductivity of mixtures. The calculation of thermal conductivity through the methods of Schreiber et al. and Uribe et al. was discussed. Calculations were performed over a wide temperature range and equimolar composition. Rather accurate correlations for the viscosity coefficients of the mixtures in the temperature range were reproduced from the present unlike intermolecular potential energies. Our estimated accuracies for the viscosity are within ?2%. Acceptable agreement between the predicted values of the viscosity and thermal conductivity with the literature values demonstrates the predictive power of the inversion scheme. In the case of thermal conductivity our results are in favor of the preference of Uribe et al.'s method over Schreiber et al.'s scheme.
    Simulation of Reactive Distillation Process for Monosilane Production via Redistribution of Trichlorosilane
    Sun Shuaishuai, Huang Guoqiang
    2014, 22(3):  287-293.  doi:10.1016/S1004-9541(14)60045-8
    Abstract ( 4424 )   PDF (260KB) ( 137 )  
    References | Related Articles | Metrics
    The reactive distillation process for producing high purity monosilane via trichlorosilane redistribution reaction was simulated. Rigorous RadFrac block was employed in Aspen Plus simulation package. Accurate results could be given when the chemical kinetics was taken into account in the equilibrium stage model. A single column process was used for the verification of previous studies. The results showed that 99.9% purity monosilane could be achieved in the reactive distillation. A pumparound block was employed to reduce the condenser duty with inexpensive coolant. The effects of operating pressure, feed stage location, liquid holdup per stage and pumparound location were also investigated. The energy consumption was limited, but the refrigerant temperature was too low, which is the fatal disadvantage. Therefore, a double columns process was developed to increase the condenser temperature. The simulation results demonstrated that a reasonable temperature could be achieved by varying the recycle stream location.
    Effect of Temperature on Segregation Coefficients of Impurities in Phosphorus
    LIU Xuefeng, LI Jun, LUO Jianhong, ZHOU Kun, YANG Zhaopeng
    2014, 22(3):  294-298.  doi:10.1016/S1004-9541(14)60044-6
    Abstract ( 3315 )   PDF (282KB) ( 41 )  
    References | Related Articles | Metrics
    The present work is focused on the relationship between effective segregation coefficient keff and temperature of melting zone for purification of phosphorus by zone melting method. Values of keff at four temperatures of melting zone are obtained for zone pass n =1 at travel velocity of molten zone v =5×10-3 m·h-1 and initial impurity concentration C0≤10 μg·g-1. lnkeff is a linear function of 1/T. The keff values of Al, Ca, Cr, Fe, Cd and Sb increase with temperatures while that of Mg is almost constant. The purification is acceptable at lower temperature of melting zone such as 323 K. The variations of enthalpy and entropy between impurities and phosphorus in the liquid and solid phases are also presented.
    A Bi-component Cu Catalyst for the Direct Synthesis of Methylchlorosilane from Silicon and Methyl Chloride
    WANG Chao, WANG Guangrun, WANG Jinfu
    2014, 22(3):  299-304.  doi:10.1016/S1004-9541(14)60034-3
    Abstract ( 3231 )   PDF (378KB) ( 76 )  
    References | Related Articles | Metrics
    A bi-component catalyst comprising CuCl and metallic copper was used in the direct synthesis of methylchlorosilane to study the catalytic synergy between the different copper sources. The catalyst exhibited high activity and high selectivity of dimethyldichlorosilane (M2) in the stirred bed reactor. The effect of the proportion of CuCl used was studied and 10%-30% CuCl gave the best yield of M2. The use of CuCl decreased the induction period of reaction, improved the selectivity in the induction stage, and gave a longer stable stage. These results suggest that bi-component catalyst has advantages in the direct synthesis reaction.
    Superparamagnetic Supported Catalyst H3PW12O40/γ-Fe2O3 for Alkylation of Thiophene with Olefine
    XU Cuixia, YANG Kedi, LIU Zili, QIN Zuzeng, HE Wei, DAI Qianwen, ZHANG Jianjie, ZHANG Fan
    2014, 22(3):  305-311.  doi:10.1016/S1004-9541(14)60053-7
    Abstract ( 4376 )   PDF (394KB) ( 44 )  
    References | Related Articles | Metrics
    The alkylation of sulfur compounds with olefine is considered to be an attractive way to attain high level of sulfur removal by raising the boiling point of sulfur-containing compounds to ease their separation from light fractions by distillation. A series of superparamagnetic supported catalysts, used for alkylation of thiophene with 1-octene, were prepared by loading H3PW12O40 (HPW) onto commercially available nanoparticles γ-Fe2O3 through incipient wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD), Fourier transform infra-red (FT-IR), thermo gravimetric analysis (TG), N2-adsorption and vibrating sample magnetometer (VSM). The physicochemical characterization reveals that γ-Fe2O3 could be accommodated to immobilize and disperse HPW. Moreover, possessing high magnetization of 26.1 A·m2·kg-1 and with mesoporous structure with specific surface area of 35.9 m2·g-1, the 40% (by mass) HPW loading catalyst is considered the proper catalyst for olefinic alkylation of thiophenic sulfur (OATS) and can be separated in an external magnetic field. The catalytic activity was investigated in the alkylation reaction of thiophene with 1-octene, and the conversion of thiophene is up to 46% at 160 ℃ in 3 h. The 40% (by mass) HPW/γ-Fe2O3 catalyst can be reused 6 times without too much loss of activity and keeps its property of superparamagnetism.
    Synthesis of a Novel Solid Acid with both Sulfonic and Carbonyl Acid Groups and Its Catalytic Activities in Acetalization
    CHENG Yuxiao, ZHOU Yuyan, ZHANG Jidong, FEI Xudong, MA Tengzhou, LIANG Xuezheng
    2014, 22(3):  312-317.  doi:10.1016/S1004-9541(14)60048-3
    Abstract ( 3016 )   PDF (346KB) ( 37 )  
    References | Related Articles | Metrics
    The novel solid acid with both sulfonic and carbonyl acid groups has been synthesized from 3-((2-sulfoethoxy) carbonyl)acrylic acid and tetraethyl orthosilicate (TEOS). The catalytic activities were investigated through the acetalization. The results showed that the novel solid acid was very efficient for the reactions with the high yields. The high acidity, high stability and reusability were the key feature of the novel solid acid. Moreover, the sulfonic and carbonyl acid groups could cooperate during the catalytic process, which improved its catalytic activities. The catalyst shows recyclability, and hold great potential for replacement of homogeneous catalysts.
    A Real-time Updated Model Predictive Control Strategy for Batch Processes Based on State Estimation
    YANG Guojun, LI Xiuxi, QIAN Yu
    2014, 22(3):  318-329.  doi:10.1016/S1004-9541(14)60057-4
    Abstract ( 4291 )   PDF (344KB) ( 37 )  
    References | Related Articles | Metrics
    Nonlinear model predictive control (NMPC) is an appealing control technique for improving the performance of batch processes, but its implementation in industry is not always possible due to its heavy on-line computation. To facilitate the implementation of NMPC in batch processes, we propose a real-time updated model predictive control method based on state estimation. The method includes two strategies: a multiple model building strategy and a real-time model updated strategy. The multiple model building strategy is to produce a series of simplified models to reduce the on-line computational complexity of NMPC. The real-time model updated strategy is to update the simplified models to keep the accuracy of the models describing dynamic process behavior. The method is validated with a typical batch reactor. Simulation studies show that the new method is efficient and robust with respect to model mismatch and changes in process parameters.
    Model and Design of Cogeneration System for Different Demands of Desalination Water, Heat and Power Production
    WU Xianli, HU Yangdong, WU Lianying, LI Hong
    2014, 22(3):  330-338.  doi:10.1016/S1004-9541(14)60036-7
    Abstract ( 3317 )   PDF (214KB) ( 75 )  
    References | Related Articles | Metrics
    In order to improve the energy efficiency, reduce the CO2 emission and decrease the cost, a cogeneration system for desalination water, heat and power production was studied in this paper. The superstructure of the cogeneration system consisted of a coal-based thermal power plant (TPP), a multi-stage flash desalination (MSF) module and reverse osmosis desalination (RO) module. For different demands of water, heat and power production, the corresponding optimal production structure was different. After reasonable simplification, the process model of each unit was built. The economical model, including the unit investment, and operation and maintenance cost, was presented. By solving this non-linear programming (NLP) model, whose objective is to minimize the annual cost, an optimal cogeneration system can be obtained. Compared to separate production systems, the optimal system can reduce 16.1%-21.7% of the total annual cost, showing this design method was effective.
    In-situ Observation of the Growth of Fibrous and Dendritic Crystals in Quasi-2-dimensional Poly(ethylene oxide) Ultrathin Films
    ZHOU Yuan, HAN Xia, LIU Honglai, HU Ying
    2014, 22(3):  339-345.  doi:10.1016/S1004-9541(14)60046-X
    Abstract ( 3178 )   PDF (1593KB) ( 86 )  
    References | Related Articles | Metrics
    Crystal growth processes of poly(ethylene oxide) were followed from the original nucleation sites by using atomic force microscopy. Two distinct quasi-2-dimensional crystals about 4 nm thick were obtained from as-spun polymer ultrathin films: fibrous crystals, generated by the shearing field via spin-coating, coexist with conventional dendrites. The growth of the two structures is dominated by diffusion limited aggregation, though the growth rate of the fibrous crystals is around one order of magnitude faster than that of the dendrites. The fibrous crystals are more stable than the dendritic ones.
    Improved Correlations for Prediction of Viscosity of Iranian Crude Oils
    Majid Taghizadeh, Mehdi Eftekhari
    2014, 22(3):  346-354.  doi:10.1016/S1004-9541(14)60017-3
    Abstract ( 4168 )   PDF (323KB) ( 134 )  
    References | Related Articles | Metrics
    Empirical equations for predicting the viscosity of Iranian crude oils above, at and below the bubble-point pressure were developed based on pressure-volume-temperature (PVT) data of 57 bottom hole samples collected from central, southern and offshore oil fields of Iran. Both statistical and graphical techniques were employed to evaluate these equations compared with other empirical correlations. The results show that the developed correlations present better accuracy and performance for predicting the viscosity of Iranian crude oils than those correlations in literature.
    Measurement and Correlation of Vapor-Liquid Equilibrium of the 1,2-Epoxycyclohexane-Cyclohexanone Binary System at 101.3 kPa
    WANG Xunqiu, ZHUANG Xinliang, JIANG Denggao
    2014, 22(3):  355-359.  doi:10.1016/S1004-9541(14)60042-2
    Abstract ( 4004 )   PDF (336KB) ( 37 )  
    References | Related Articles | Metrics
    Many by-products are generated in the process of oxidizing cyclohexene to produce 1,2-epoxycyclohexane by hydrogen peroxide, including cyclohexanol, cyclohexanone, etc. To obtain high-purity 1,2-epoxycyclohexane, the by-products must be removed through rectification. Refining 1,2-epoxycyclohexane through rectification requires vapor-liquid equilibrium (VLE) data of the related system. Therefore, the VLE data of 1,2-epoxycyclohexane- cyclohexanone system were measured at 101.3 kPa using an improved EC-2 VLE still. The thermodynamic consistency of the data was then tested by Herington's method and the rigorous point-to-point method. The results obtained were exemplary. The VLE data were correlated by the Wilson and non-random two-liquid (NRTL) equations, using the error sum squares of the vapor composition as the objective function to obtain the model parameters. The difference between the calculated values and the experimental data is minor, indicating that the VLE data are suitable for engineering design.
    Preparation and Characterization of Sodium Sulfate/Silica Composite as a Shape-stabilized Phase Change Material by Sol-gel Method
    GUO Qiang, WANG Tao
    2014, 22(3):  360-364.  doi:10.1016/S1004-9541(14)60047-1
    Abstract ( 4265 )   PDF (560KB) ( 79 )  
    References | Related Articles | Metrics
    A sodium sulfate (Na2SO4)/silica (SiO2) composite was prepared as a shape-stabilized solid-liquid phase change material by a sol-gel procedure using Na2SiO3 as the silica source. Na2SO4 in the composite acts as a latent heat storage substance for solid-liquid phase change, while SiO2 acts as a support material to provide structural strength and prevent leakage of melted Na2SO4. The microstructure and composition of the prepared composite were characterized by the N2 adsorption, transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The results show that the prepared Na2SO4/SiO2 composite is a nanostructured hybrid of Na2SO4 and SiO2 without new substances produced during the phase change. The macroscopic shape of the Na2SO4/SiO2 composite after the melting and freezing cycles does not change and there is no leakage of Na2SO4. Determined by differential scanning calorimeter (DSC) analysis, the values of phase change latent heat of melting and freezing of the prepared Na2SO4/SiO2 (50%, by mass) composite are 82.3 kJ·kg-1 and 83.7 kJ·kg-1, and temperatures of melting and freezing are 886.0 ℃ and 880.6 ℃, respectively. Furthermore, the Na2SO4/SiO2 composite maintains good thermal energy storage and release ability even after 100 cycles of melting and freezing. The satisfactory thermal storage performance renders this composite a versatile tool for high-temperature thermal energy storage.