Mar 2008, Volume 2 Issue 1
    

  • Select all
  • Heat transfer coefficient of wheel rim of large capacity steam turbines
    SHI Jinyuan, DENG Zhicheng, YANG Yu, JUN Ganwen
    2008, 2(1): 20-24. https://doi.org/10.1007/s11708-008-0015-4
    Download PDF
    A way of calculating the overall equivalent heat transfer coefficient of wheel rims of large capacity steam turbines is presented. The method and formula to calculate the mean forced convection heat-transfer coefficient of the surface of the blade and for the bottom wall of the blade passage, are introduced. The heat transmission from the blade to the rim was simplified by analogy to heat transmission in the fins. A fin heat transfer model was then used to calculate the equivalent heat transfer coefficient of the blade passage. The overall equivalent heat transfer coefficient of the wheel rim was then calculated using a cylindrical surface model. A practical calculation example was presented. The proposed method helps determine the heat transfer boundary conditions in finite element analyses of temperature and thermal stress fields of steam turbine rotors.
  • Dynamic behavior of superheated steam and ways of control
    LI Xu
    2008, 2(1): 25-30. https://doi.org/10.1007/s11708-008-0014-5
    Download PDF
    A simple way of calculating the dynamic behavior of a superheater is presented. A comparison of the measured data with the calculated result verifies the accuracy of this simple method. It is the first time that a phase compensation for real roots, i.e., the twin lead/lag loop which is facile for engineering applications, is used in superheated steam temperature control. Numerous simulation results show that both the response time lapse and maximal dynamic deviation are greatly reduced. Moreover, a formula to calculate the setting parameters is presented, together with a practical example of its engineering application in superheated steam temperature control with single-stage attemperation in a power plant boiler. This method can remarkably improve the control performance of superheated steam temperature and makes it possible for one stage attemperation to be sufficient for the superheater of power plant boilers, thus simplifying the superheater system and reducing investment. Because the control performance is remarkably raised, the set values of the steam temperature control system can be raised above rated values and also the operational economy, without impairing the operation safety.
  • Cavitation in semi-open centrifugal impellers for a miniature pump
    LUO Xianwu, LIU Shuhong, ZHANG Yao, XU Hongyuan
    2008, 2(1): 31-35. https://doi.org/10.1007/s11708-008-0011-8
    Download PDF
    Cavitation in miniature pumps was investigated experimentally for two semi-open centrifugal impellers. Although both impellers had the same blade cross-section, one impeller had a two-dimensional blade, while the other had a leaned blade. The flows were also analyzed using a numerical model of the three-dimensional turbulent flow in the pumps near the peak efficiency point using the k-? turbulence model and the VOF cavitation model. The average cavitation performance of each impeller was satisfactorily predicted by the numerical simulations. The results show that the miniature pumps have similar cavitation performances as an ordinary-size pump, with the cavitation performance of the semi-open impeller reduced by increased axial tip clearances. Also, both the hydraulic and cavitation performance of the semi-open impeller were improved by the leaned blade. The results also show that uniform flow upstream of the impeller inlet will improve the cavitation performance of a miniature pump.
  • Available energy analysis of new tandem double-capillary tube refrigeration system for refrigerator-freezers
    HE Maogang, ZHANG Ying, SONG Xinzhou, ZHANG Jiantao
    2008, 2(1): 36-42. https://doi.org/10.1007/s11708-008-0013-6
    Download PDF
    A new tandem double-capillary tube refrigeration system for refrigerator-freezers is proposed. A capillary tube was added between the two evaporators in the fresh and frozen food storage chests to raise the evaporation temperature of the refrigerating chamber, and reduce the heat exchange temperature difference and the available energy loss. Peng-Robinson (P-R) equation of state was adopted to calculate the thermodynamic properties of the refrigerants, and the available energy analysis of the vapor compression refrigeration cycle was programmed to calculate the thermodynamic performances of the new and the conventional refrigeration cycle of the refrigerator-freezer. The calculation results show that the available energy efficiency of the conventional refrigeration cycle of the refrigerator-freezer is 21.20% and 20.57%, respectively when the refrigerant is R12 and R134a, while that of the double-capillary tube refrigeration cycle of the refrigerator-freezer is 23.97% and 23.44%, respectively. By comparison, the available energy efficiency of the new refrigeration system increases by 13.07% and 13.95%, respectively.
  • Thermodynamic performance experiment and cooling number calculation of a counter-flow spray humidifier in the HAT cycle
    WANG Yuzhang, LI Yixing, WENG Shilie, WANG Yonghong
    2008, 2(1): 43-47. https://doi.org/10.1007/s11708-008-0005-6
    Download PDF
    An experimental investigation of the thermodynamic performance of a counter-flow spray humidifier was conducted on the basis of theoretical analysis of the heat and mass transfer mechanism inside the humidifier. Critical parameters such as the temperature and relative humidity of air and the temperature of water at the inlet and outlet were measured. The influence of every measured parameter on the thermal performance of the humidifier was obtained under different experimental conditions. The cooling number, whose variation was also obtained, was calculated according to the measured data. The experimental results show that both the temperature and the temperature increment of outlet humid air and the temperature of outlet water increase with an increase of the water-gas ratio, whereas the cooling number decreases. Under all experimental conditions, the outlet humid air reaches or is close to the saturation level. The lower cooling number is favorable for the system, but it has an optimal value for a certain humidifier.
  • Three-dimensional numerical simulation of the basic pulse tube refrigerator
    DING Wenjing, GONG Liang, HE Yaling, TAO Wenquan
    2008, 2(1): 48-53. https://doi.org/10.1007/s11708-008-0008-3
    Download PDF
    A three-dimensional physical and numerical model of the basic pulse tube refrigerator (PTR) was developed. The compressible and oscillating fluid flow and heat transfer phenomenon in the pulse tube were numerically investigated using a self-developed code. Some cross-section average parameter variations such as velocity, temperature and pressure wave during one cycle were revealed. The variations of velocity and temperature distributions in the pulse tube were also analyzed in detail for further understanding of the working process and refrigeration mechanism of PTRs.
  • Experimental study on film combustion formed by spirally fluted horizontal tube
    MEI Ning, ZHANG Bin, ZHAO Jian, ZHANG Ming
    2008, 2(1): 54-58. https://doi.org/10.1007/s11708-008-0023-4
    Download PDF
    Falling fuel film on the spirally fluted surface of a horizontal tube can provide rapid fuel evaporation and homogeneous mixture formation. This fuel film combustion could be applied in a micro-combustion system even without a fuel pump. A test bed was established and experimental comparisons were made between the prototype and a transferred cup atomizer micro-combustor. The theoretical and experimental results show that film combustion has a higher combustion efficiency, a lower pollutant emission and a better working performance.
  • Numerical investigation of the effects of fuel spray type on the interaction of fuel spray and hot porous medium
    ZHAO Zhiguo, XIE Maozhao
    2008, 2(1): 59-65. https://doi.org/10.1007/s11708-008-0022-5
    Download PDF
    The interaction between two types of fuel spray and a hot porous medium is studied numerically by using an improved version of KIVA-3V code. The improved KIVA-3V code is incorporated with an impingement model, a heat transfer model and a linearized instability sheet atomization (LISA) model to model the hollow cone spray. An evaporating fuel spray impingement on a hot plane surface was simulated under conditions of experiments performed by Senda to validate the reasonability of the KIVA-3V code. The numerical results conform well with experimental data for spray radius in the liquid and the vapor phases. Computational results on the interaction of two types of the fuel spray and the hot porous medium show that the fuel spray can be split, which provides conditions for quick evaporation of fuel droplets and mixing of fuel vapor with air. The possibility of fuel droplets from hollow cone spray crossing the porous medium reduces compared with that from solid cone spray, with the same initial kinetic energy of fuel droplets in both injection types.
  • Multi-objective optimization of a 3D vaneless diffuser based on fuzzy theory
    GAO Chuang, GU Chuangang, WANG Tong, SHU Xinwei
    2008, 2(1): 66-70. https://doi.org/10.1007/s11708-008-0006-5
    Download PDF
    An optimization model based on fuzzy theory was set up and the corresponding Interactive modified simplex (IMS) method was developed to solve it. Both static pressure recovery and total pressure loss were considered in the model. Computational fluid dynamics (CFD) method was applied to solve the Reynolds-Averaged Navier-Stokes equation (RANS) and to find flow field distribution to get the value of the object function. After receiving the new shroud curve, grid movement and redrawing technology were adopted to avoid grid-line crossing and negative cells. The shroud curve was fitted with B-spline. The optimized results concur with the results reported in references.
  • Numerical investigation and analysis of heat transfer enhancement in channel by longitudinal vortex based on field synergy principle
    TAO Wenquan, WU Junmei
    2008, 2(1): 71-78. https://doi.org/10.1007/s11708-008-0001-x
    Download PDF
    3-D numerical simulations were presented for laminar flow and heat transfer characteristics in a rectangular channel with vortex generators. The effects of Reynolds number (from 800 to 3 000), the attack angle of vortex generator (from 15° to 90°) and the shape of vortex generator were examined. The numerical results were analyzed based on the field synergy principle. It is found that the inherent mechanism of the heat transfer enhancement by longitudinal vortex can be explained by the field synergy principle, that is, the second flow generated by vortex generators results in the reduction of the intersection angle between the velocity and fluid temperature gradient. The longitudinal vortex improves the field synergy of the large downstream region of longitudinal vortex generator (LVG) and the region near (LVG); however, transverse vortex only improves the synergy of the region near vortex generator. Thus, longitudinal vortex can enhance the integral heat transfer of the flow field, while transverse vortex can only enhance the local heat transfer. The synergy angle decreases with the increase of Reynolds number for the channel with LVG to differ from the result obtained from the plain channel, and the triangle winglet performs better than the rectanglar one under the same surface area condition.
  • Study of combustion and emission characteristics of turbocharged diesel engine fuelled with dimethylether
    WU Junhua, HUANG Zhen, QIAO Xinqi, LU Jun, ZHANG Junjun, ZHANG Liang
    2008, 2(1): 79-85. https://doi.org/10.1007/s11708-008-0002-9
    Download PDF
    An experimental study of a turbocharged diesel engine operating on dimethyl ether (DME) was conducted. The combustion and emission characteristics of the DME engine were investigated. The results show that the maximum torque and power of DME are greater than those of diesel, particularly at low speeds; the brake specific fuel consumption of DME is lower than that of diesel at low and middle engine speeds, and the injection delay of DME is longer than that of diesel. However, the maximum cylinder pressure, maximum pressure rise rate and combustion noises of the DME engine are lower than those of diesel. The combustion velocity of DME is faster than that of diesel, resulting in a shorter combustion duration of DME. Compared with the diesel engine, NOx emission of the DME engine is reduced by 41.6% on ESC data. In addition, the DME engine is smoke free at any operating condition.
  • Application of micro-genetic algorithm for calibration of kinetic parameters in HCCI engine combustion model
    HUANG Haozhong, SU Wanhua
    2008, 2(1): 86-92. https://doi.org/10.1007/s11708-008-0003-8
    Download PDF
    The micro-genetic algorithm (?GA) as a highly effective optimization method, is applied to calibrate to a newly developed reduced chemical kinetic model (40 species and 62 reactions) for the homogeneous charge compression ignition (HCCI) combustion of n-heptane to improve its autoignition predictions for different engine operating conditions. The seven kinetic parameters of the calibrated model are determined using a combination of the Micro-Genetic Algorithm and the SENKIN program of CHEMKIN chemical kinetics software package. Simulation results show that the autoignition predictions of the calibrated model agree better with those of the detailed chemical kinetic model (544 species and 2 446 reactions) than the original model over the range of equivalence ratios from 0.1–1.3 and temperature from 300–3 000 K. The results of this study have demonstrated that the mGA is an effective tool to facilitate the calibration of a large number of kinetic parameters in a reduced kinetic model.
  • Aerodynamic design by jointly applying S2 flow surface calculation and modern optimization methods on multistage axial turbine
    ZHAO Honglei, WANG Songtao, HAN Wanjin, FENG Guotai
    2008, 2(1): 93-98. https://doi.org/10.1007/s11708-008-0007-4
    Download PDF
    A three-stage axial turbine was redesigned by jointly applying S2 flow surface direct problem calculation methods and multistage local optimization methods. A genetic algorithm and artificial neural network were jointly adopted during optimization. A three-dimensional viscosity Navier–Stokes equation solver was applied for flow computation. H-O-H-topology grid was adopted as computation grid, that is, an H-topology grid was adopted for inlet and outlet segment, whereas an O-topology grid was adopted for stator zone and rotor zone. Through the optimization design, the total efficiency increases 1.1%, thus indicating that the total performance is improved and the design objective is achieved.
  • Thermal-hydraulic performance of novel louvered fin using flat tube cross-flow heat exchanger
    DONG Junqi, CHEN Jiangping, CHEN Zhijiu
    2008, 2(1): 99-106. https://doi.org/10.1007/s11708-008-0010-9
    Download PDF
    Experimental studies were conducted to investigate the air-side heat transfer and pressure drop characteristics of a novel louvered fins and flat tube heat exchangers. A series of tests were conducted for 9 heat exchangers with different fin space and fin length, at a constant tube-side water flow rate of 2.8 m3/h. The air side thermal performance data were analyzed using the effectiveness-NTU method. Results were presented as plot of Colburn j factor and friction factor f against the Reynolds number in the range of 500–6500. The characteristics of the heat transfer and pressure drop of different fin space and fin length were analyzed and compared. In addition, the curves of the heat transfer coefficients vs. pumping power per unit heat transfer area were plotted. Finally, the area optimization factor was used to evaluate the thermal hydraulic performance of the louvered fins with differential geometries. The results showed that the j and f factors increase with the decrease of the fin space and fin length, and the fin space has more obvious effect on the thermal hydraulic characteristics of the novel louvered fins.
  • Probability strength design of steam turbine blade and sensitivity analysis with respect to random parameters based on response surface method
    DUAN Wei
    2008, 2(1): 107-115. https://doi.org/10.1007/s11708-008-0018-1
    Download PDF
    Many stochastic parameters have an effect on the reliability of a steam turbine blade during practical operation. To improve the reliability of blade design, it is necessary to take these stochastic parameters into account. An equal cross-section blade is investigated and a finite element model is built parametrically. Geometrical parameters, material parameters and load parameters of the blade are considered as input random variables while the maximum deflection and maximum equivalent stress are output random variables. Analysis file of the blade is compiled by deterministic finite element method and applied to be loop file to create sample points. A quadratic polynomial with cross terms is chosen to regress these samples by step-forward regression method and employed as a surrogate of numerical solver to drastically reduce the number of solvers call. Then, Monte Carlo method is used to obtain the statistical characteristics and cumulative distribution function of the maximum deflection and maximum equivalent stress of the blade. Probability sensitivity analysis, which combines the slope of the gradient and the width of the scatter range of the random input variables, is applied to evaluate how much the output parameters are influenced by the random input parameters. The scatter plots of structural responses with respect to the random input variables are illustrated to analyze how to change the input random variables to improve the reliability of the blade. The results show that combination of the finite element method, the response surface method and Monte Carlo method is an ideal way for the reliability analysis and probability strength design of the blade.
  • Combustion instability detection using the wavelet detail of pressure fluctuations
    JI Junjie, LUO Yonghao
    2008, 2(1): 116-120. https://doi.org/10.1007/s11708-008-0019-0
    Download PDF
    A combustion instability detection method that uses the wavelet detail of combustion pressure fluctuations is put forward. To confirm this method, combustion pressure fluctuations in a stoker boiler are recorded at stable and unstable combustion with a pressure transducer. Daubechies one-order wavelet is chosen to obtain the wavelet details for comparison. It shows that the wavelet approximation indicates the general pressure change in the furnace, and the wavelet detail magnitude is consistent with the intensity of turbulence and combustion noise. The magnitude of the wavelet detail is nearly constant when the combustion is stable, however, it will fluctuate much when the combustion is unstable.