Sep 2008, Volume 2 Issue 3
    

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  • Simulation of cross-flow-induced vibration of tube bundle by surface vorticity method
    WANG Fenghao, JIANG Gedong, Lin John Zhang
    2008, 2(3): 243-248. https://doi.org/10.1007/s11708-008-0049-7
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    A fluid-structure interaction model based on Surface Vorticity Method (SVM) was used to study flow-induced vibrations of tube bundles in medium space ratio. The flow-induced vibrations of four tubes in a rotated square and a staggered tube bundle in three-row and five-column arrangements were simulated in the high sub-critical Reynolds number (Re) range. The results on fluid forces, tube responses and vorticity maps were presented. The vorticity maps of the four rotated-square tubes changed dramatically when the rigid tubes were replaced by the flexible tubes. From the vorticity maps and vibration responses of the staggered tube bundle of different structural parameters, it was found that with the decrease of tube natural frequency, the maximal vibration response moved from the third row to the first. The results also showed that when more flexible tubes are used, the flow pattern changed drastically and the fluid-structure interaction imposed a dominant impact on the flow.
  • LNG-FPSO: Offshore LNG solution
    GU Yan, JU Yonglin
    2008, 2(3): 249-255. https://doi.org/10.1007/s11708-008-0050-1
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    The floating production, storage and offloading system for liquefied natural gas (LNG-FPSO), is a new conceptual unit and an effective and realistic way for exploitation, recovery, storage, transportation and end-use applications of marginal gas fields and offshore associated-gas resources. However, a real LNG-FPSO unit cannot be built unless some breakthroughs in many key technologies are produced. Many unique characteristics of LNG-FPSO, such as restricted space, platform motion, LNG sloshing in inner storage tank and offloading system, which have not been considered in the onshore projects, are the most rigorous factors to be taken into account during design. In this paper, the overall layout of a typical LNG-FPSO unit is reviewed; the leading liquefaction technologies and processes are compared and discussed. Taking the effects of the vessel motion and limited space into account, the applicability of the main systems and key equipments of storage, offloading and power supply, are analyzed.
  • Numerical investigation on side heat transfer enhancement in 300 kA aluminum reduction cell
    WANG Changhong, ZHU Dongsheng, LEI Junxi, ZHOU Jiemin
    2008, 2(3): 256-260. https://doi.org/10.1007/s11708-008-0051-0
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    Industrial test and numerical simulation were synchronously applied to analyze the side heat transfer process and enhance heat transfer in aluminum reduction cell. The 3D slice finite element model of aluminum reduction cell was developed, with which the sidewall temperature field of the cell was computed by using software ANSYS. The main influencing factors on heat dissipation were analyzed and some effective measures were proposed to enhance sidewall heat transfer. The results show that the shell temperature of the test cell and the common cell is respectively 312°C and 318°C and the ledge thickness is 16 cm and 15 cm when side coefficient of heat transfer between the shell and the surroundings is 70 W/(m2K). With the increase of the side coefficient of heat transfer between the shell and the surroundings, the temperature of the shell decreases but the thickness of the side ledge increases when the electrolytic temperature, the ambient temperature, the coefficient of heat transfer between molten bath and ledge, the eutectic temperature and the thermo-resistance of the side lining are constant.
  • Effects of Fischer-Tropsch diesel fuel on combustion and emissions of direct injection diesel engine
    HUANG Yongcheng, WANG Shangxue, ZHOU Longbao
    2008, 2(3): 261-267. https://doi.org/10.1007/s11708-008-0062-x
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    Effects of Fischer-Tropsch (F-T) diesel fuel on the combustion and emission characteristics of a single-cylinder direct injection diesel engine under different fuel delivery advance angles were investigated. The experimental results show that F-T diesel fuel exhibits shorter ignition delay, lower peak values of premixed burning rate, lower combustion pressure and pressure rise rate, and higher peak value of diffusion burning rate than conventional diesel fuel when the engine remains unmodified. In addition, the unmodified engine with F-T diesel fuel has lower brake specific fuel consumption and higher effective thermal efficiency, and presents lower HC, CO, NOx and smoke emissions than conventional diesel fuel. When fuel delivery advance angle is retarded by 3 crank angle degrees, the combustion duration is obviously shortened; the peak values of premixed burning rate, the combustion pressure and pressure rise rate are further reduced; and the peak value of diffusion burning rate is further increased for F-T diesel fuel operation. Moreover, the retardation of fuel delivery advance angle results in a further significant reduction in NOx emissions with no penalty on specific fuel consumption and with much less penalty on HC, CO and smoke emissions.
  • Experimental study and product analysis of lignocellulosic biomass hydrolysis under extremely low acids
    WANG Shurong, LUO Zhongyang, CEN Kefa, ZHUANG Xinshu
    2008, 2(3): 268-272. https://doi.org/10.1007/s11708-008-0046-x
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    Using our self-designed facility for lignocellulosic biomass hydrolysis under extremely low acid, and under the optimal reaction conditions of hemicellulose and cellulose determined by xylan and quantitative filter paper as the model, two-step dilute acid hydrolysis was carried out in detail on pine, fast-growing poplar and maize straw. The corresponding conversion ratio is 41.78%, 57.84% and 53.44% and the total reducing sugar conversion ratio is 39.28%, 42.83% and 23.82% respectively. Simultaneously, sugar component analysis of the products was performed by high performance liquid chromatography (HPLC) and monosaccharide and oligosaccharide content were compared. Finally, poplar hydrolysis residues were analyzed by proximate and ultimate analysis.
  • Impingement of hollow cone spray on hot porous medium
    ZHAO Zhiguo, XIE Maozhao
    2008, 2(3): 273-278. https://doi.org/10.1007/s11708-008-0048-8
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    To have a good understanding of the formation of homogenous mixture in a porous medium engine, the interaction between hollow cone spray and hot porous medium was studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, heat transfer model and linearized instability sheet atomization (LISA) model to simulate the hollow cone spray. The reasonability of the impingement model and heat transfer model was validated. With a simple model to describe the structure of the porous medium, the interaction between hollow cone spray and hot porous medium was simulated under different ambient pressures and spray cone angles. Computational results show that the fuel spray could be divided into smaller ones, which provides conditions for the quick evaporation of fuel droplets and the mixing of fuel vapor with air. Differences in ambient pressure and spray cone angle affect the distribution of droplets in the porous medium.
  • Impact of dimethyl ether on engine seal materials
    WU Ning, ZHANG Wugao, HUANG Zhen
    2008, 2(3): 279-284. https://doi.org/10.1007/s11708-008-0042-1
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    The resistance of many kinds of rubber materials to dimethyl ether (DME) was studied. Both the mass and volume change of rubber materials, which were put in DME and then exposed to the air for different periods of time were measured. The results show that fluorine rubber (FKM), silicone rubber (SIR), and nitrile rubber (NBR) are unsuitable as seal materials for DME engines. Common polyvinylchloride (PVC) dissolved completely in DME, which has almost no impact on vulcanizing nylon material. The constitution of ethylene propylene terpolymer rubber (EPDM) has a major impact on its resistance to DME. A kind of EPDM with good resistance to DME was found, whose reliability was validated by 100 hours of DME engine operation.
  • Ignition delay of dual fuel engine operating with methanol ignited by pilot diesel
    ZOU Hongbo, WANG Lijun, LIU Shenghua, LI Yu
    2008, 2(3): 285-290. https://doi.org/10.1007/s11708-008-0060-z
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    An investigation on the ignition delay of a dual fuel engine operating with methanol ignited by pilot diesel was conducted on a TY1100 direct-injection diesel engine equipped with an electronic controlled methanol low-pressure injection system. The experimental results show that the polytropic index of compression process of the dual fuel engine decreases linearly while the ignition delay increases with the increase in methanol mass fraction. Compared with the conventional diesel engine, the ignition delay increment of the dual fuel engine is about 1.5° at a methanol mass fraction of 62%, an engine speed of 1600 r/min, and full engine load. With the elevation of the intake charge temperature from 20°C to 40°C and then to 60°C, the ignition delay of the dual fuel engine decreases and is more obvious at high temperature. Moreover, with the increase in engine speed, the ignition delay of the dual fuel engine by time scale (ms) decreases clearly under all engine operating conditions. However, the ignition delay of the dual fuel engine increases remarkably by advancing the delivery timing of pilot diesel, especially at light engine loads.
  • Flow and heat transfer in compact offset strip fin surfaces
    DONG Junqi, CHEN Jiangping, CHEN Zhijiu
    2008, 2(3): 291-297. https://doi.org/10.1007/s11708-008-0061-y
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    Experimental studies of air-side heat transfer and pressure drop characteristics of offset strip fins and flat tube heat exchangers were performed. A series of tests were conducted for 9 heat exchangers with different fin space, fi
  • Optimization for operating modes based on simulation of seasonal underground thermal energy storage
    ZHAO Jun, CHEN Yan, LI Xinguo
    2008, 2(3): 298-301. https://doi.org/10.1007/s11708-008-0053-y
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    A simulation was performed, which concerned the feasibility of seasonal underground thermal energy storage (UTES) in Tianjin, China. The investigated system consisted of 8 boreholes. In summer, residual solar thermal energy was emitted into the soil surrounding the borehole heat exchangers through which the stored energy was extracted in winter with a ground coupled heat pump (GCHP) to provide a proper heating temperature. A simulation study was performed to study the influence of system operation modes on thermal recovery based on the experimental data of a GCHP system, local meteorological conditions and soil properties in Tianjin. The results indicate a thermal recovery ratio of less than 67% and different temperature distributions under three modes. Finally, an operation mode was suggested based on both lower loss and better thermal recovery in the UTES.
  • Vibration analysis of blade-disc coupled structure of compressor
    WANG Chunjie, SONG Shunguang, ZONG Xiao
    2008, 2(3): 302-305. https://doi.org/10.1007/s11708-008-0064-8
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    While a 3D assembly model of blade-disc structure was established, a finite element model for calculating the vibration characteristics during blade-disc coupling was built by taking into consideration the coupling action of contact stress between the blade and the disc. The vibration characteristics of the blade-disc coupling structure was calculated and analyzed using cycle analysis method with the aid of ANSYS software. The modeling experiment shows that this method is feasible for analyzing the rabbet assembly structure.
  • Aerodynamic performance of bowed compressor cascades with different camber angles
    CHEN Shaowen, CHEN Fu, WANG Keli, GU Jun, WANG Zhongqi
    2008, 2(3): 306-312. https://doi.org/10.1007/s11708-008-0056-8
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    The effects of a positively bowed blade on the aerodynamic performance of annular compressor cascades with different camber angles were experimentally investigated. The distributions of the exit total pressure loss and secondary flow vectors of the compressor cascades were analyzed. The static pressure was measured by tapping on the cascade surfaces, and the ink-trace flow visualizations were conducted. The results show that the value of the optimum bowed angle and optimum bowed height decrease because of the increased losses at the mid-span with the increase of the camber angle. The C-shape static pressure distribution along the radial direction exists on the suction surface of the straight cascade with larger camber angles. When bowed blade is applied, the larger bowed angle and larger bowed height will further enhance the accumulation of the low-energy fluid at the mid-span, thus causing the flow behavior to deteriorate. Under 60° camber angle, flow behavior near the end-wall region of some bowed cascades even deteriorates instead of improving because the blockage of the separated flow near the mid-span keeps the low-energy fluid near the end-walls from moving towards the mid-span region. As a result, a rapid augmentation of the total loss can easily take place under a large bowed angle.
  • Numerical simulation of three-dimensional turbulent flow in multistage axial compressor blade row
    JIANG Jian, LIU Bo, WANG Yangang, NAN Xiangyi
    2008, 2(3): 320-325. https://doi.org/10.1007/s11708-008-0041-2
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    Numerical simulation of three-dimensional turbulent flow in a multistage axial compressor blade row is conducted. A high resolution, third-order ENN scheme is adopted to catch the shockwave and simulate the turbulent flow correctly,
  • Reduced kinetic mechanism of -heptane oxidation in modeling polycyclic aromatic hydrocarbon formation in opposed-flow diffusion flames
    ZHONG Beijing, XI Jun
    2008, 2(3): 326-332. https://doi.org/10.1007/s11708-008-0047-9
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    A reduced mechanism, which could couple with the multidimensional computational fluid dynamics code for quantitative description of a reacting flow, was developed for chemical kinetic modeling of polycyclic aromatic hydrocarbon formation in an opposed-flow diffusion flame. The complete kinetic mechanism, which comprises 572 reactions and 108 species, was reduced to a simplified mechanism that includes only 83 reactions and 56 species through sensitivity analysis. The results computed via this reduced mechanism are nearly indistinguishable from those via the detailed mechanism, which demonstrate that the model based on this reduced mechanism can properly describe n-heptane oxidation chemistry and quantitatively predict polycyclic aromatic hydrocarbon (such as benzene, naphthalene, phenanthrene and pyrene) formation in opposed-flow diffusion flames.
  • Study of two-phase flow regime identification in horizontal tube bundles under vertical upward cross-flow condition using wavelet transform
    HUANG Xinghua, WANG Li, JIA Feng
    2008, 2(3): 333-338. https://doi.org/10.1007/s11708-008-0043-0
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    A wavelet-transform based approach for flow regime identification in horizontal tube bundles under vertical upward cross-flow condition was presented. Tests on two-phase flow pattern of R134a were conducted under low mass velocity and flow boiling conditions over ranges of mass flux 4–25 kg/m2s, vapor quality 0.02–0.90. Time series of differential pressure fluctuations were measured and analyzed with discrete wavelet transform. Different time-scale characteristics in bubbly flow, churn flow and annular flow were analyzed. The wavelet energy distributions over scales were found to be appropriate for flow regime identification. Based on the wavelet energy distribution over characteristic scales, a criterion of flow regime identification was proposed. The comparison with experiment results show that it is feasible to use the discrete wavelet transform as the tool of flow regime identification in horizontal tube bundles under vertical upward cross-flow condition.
  • Experimental study on heat transfer characteristics of supercritical carbon dioxide in horizontal tube
    LV Jing, FU Meng, QIN Na, DONG Bin
    2008, 2(3): 339-343. https://doi.org/10.1007/s11708-008-0045-y
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    The heat transfer characteristics of supercritical carbon dioxide in a horizontal tube with water in the vertical cross flow form were experimentally investigated. The results indicate that the changes of inlet pressure, mass flow rate, and cooling water flow rate have major effects on heat transfer performance. The variations of Reynolds number and Prandtl number were obtained in counter flow and vertical cross flow. The four conventional correlations for convection heat transfer of supercritical carbon dioxide were verified by the experimental data in this study and the correlation agree with this experimental condition was determined.
  • Shock wave of vapor-liquid two-phase flow
    ZHAO Liangju, GAO Hong, TANG Jingwen, YUAN Yuexiang, WANG Fei
    2008, 2(3): 344-347. https://doi.org/10.1007/s11708-008-0065-7
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    The shock wave of vapor-liquid two-phase flow in a pressure-gain steam injector is studied by building a mathematic model and making calculations. The results show that after the shock, the vapor is nearly completely condensed. The upstream Mach number and the volume ratio of vapor have a great effect on the shock. The pressure and Mach number of two-phase shock conform to the shock of ideal gas. The analysis of available energy shows that the shock is an irreversible process with entropy increase.
  • Optimization of cold end system of steam turbine
    ZHAO Bin, LIU Ling, ZHANG Wenbing
    2008, 2(3): 348-353. https://doi.org/10.1007/s11708-008-0036-z
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    An optimization of the movement characteristic of the cold end system of the steam turbine was conducted from an overall consideration of the condenser and the circulation water pump. An analysis method based on thermodynamics theory
  • Parameter for judging reactivity of coal and coke
    HE Hongzhou, LUO Zhongyang, CEN Kefa
    2008, 2(3): 354-358. https://doi.org/10.1007/s11708-008-0052-z
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    To eliminate the judgment error of char reactivity arising from different carbon content of samples, a new parameter called specific maximum weight loss rate was introduced. It is defined as the quotient of the maximum weight loss rate in non-isothermal thermogravimetric analysis (TGA) experiment to the carbon content of the corresponding sample. The reactivity of different kinds of coal, the reactivity of the same coal type with different lithotype, and the reactivity of the char with different carbon conversion rates were checked by using the specific maximum weight loss rate, and the results were analyzed and compared with those obtained by using other criteria. The results show that the specific maximum weight loss rate can be used as a commonality parameter to evaluate and distinguish the reactivity of different coal and char. The heating rate selected in TGA experiment has no effect on the judgment.
  • Molecular dynamics simulation of diffusivity
    LIU Juanfang, ZENG Danling, LI Qin, GAO Hong
    2008, 2(3): 359-362. https://doi.org/10.1007/s11708-008-0039-9
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    Equilibrium molecular dynamics simulation was performed on water to calculate its diffusivity by adopting different potential models. The results show that the potential models have great influence on the simulated results. In addit