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Experimental Study of Drop Deformation and Breakup in Simple Shear flows

Chinese Journal of Chemical engineering 2007年第1期15卷 1-5页

作者：林长志郭烈锦 State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University

The experimental results of the deformation and breakup of a single drop immersed in a Newtonian liq-uid and subjected to a constant shear rate which generated by counter rotating Couette apparatus were presented in this paper. From experimental observations, the breakup occurred by three mechanisms, namely, necking, end pinching, and capillary instability. Quantitative results for the deformation and breakup of drop are presented. The maximum diameter and Sauter mean diameter of daughter drops and capillary thread radius are linearly related to the inverse shear rate and independent of the initial drop size, the dimensionless wavelength which is the wave-length divided by the thread width at breakup is independent of the shear rate and initial drop size, and the deforma-tion of threads follows a pseudo-affine deformation for Cai/Cac larger than 2.

关键词： drop deformation breakup Couette shear flow

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Estimation of thermodynamic properties of the ternary molten salt system, LiF-NaF-BeF2, by the modified Peng-Robinson equation

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中国高等学校学术文摘·能源与动力工程 2007年第2期1卷 174-180页

作者： ZHANG Dalin QIU Suizheng SU Guanghui JIA Dounan School of Energy and Power Engineering State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

The molten salt reactor (MSR), which is one of the generation IV reactors, can meet the demand of transmutation and breeding. The thermodynamic properties of the molten salt system like LiF-NaF-BeF2 influence the design and construction of the fuel salt and coolant in the MSR for the new generation. In this paper, the equation of state of the ternary system 15%LiF-58%NaF-27%BeF2, over the temperature range from 873.15 to 1 073.15 K at one atmosphere pressure, is described using a modified Peng-Robinson (PR) equation. The densities of the ternary system and its components are estimated by this equation directly, and compared with the experimental data. Based on the equation of state, the other thermodynamic properties such as the enthalpy, entropyand heat capacity at constant pressure are estimated by the residual function method and the fugacity coefficient method respectively. The densities calculated by PR equation are highly in agr eement with the experimental data, and the enthalpy, entropy and heat capacity evaluated by the two different methods are consistent with each other. It can be concluded that the modified PR equation can be applied to evaluate the density of the molten salt system, and it is recommended that it be used as the basis to estimate the enthalpy, entropy and heat capacity of the molten salt system.

关键词： thermodynamic properties molten salt LiF-NaF-BeF2 Peng-Robinson equation

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Numerical analysis on heat transfer enhancement by longitudinal vortex based on field synergy principle

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中国高等学校学术文摘·能源与动力工程 2007年第3期1卷 365-369页

作者： WU Junmei TAO Wenquan State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China School of Environment and Chemical Engineering Xi'an Polytechnic UniversityXi'an 710048China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China

Three-dimensional numerical simulation results are presented for a fin-and-tube heat transfer surface with vortex *** effects of the Reynolds number (from 800 to 2 000) and the attack angle (30° and 45°) of a delta winglet vortex generator are *** numerical results are analyzed on the basis of the field synergy principle to explain the inherent mechanism of heat transfer enhancement by longitudinal *** secondary flow generated by the vortex generators causes the reduction of the intersection angle between the velocity and fluid temperature *** addition,the computational evaluations indicate that the heat transfer enhancement of delta winglet pairs for an aligned tube bank fin-and-tube surface is more significant than that for a staggered tube bank fin-and-tube *** heat transfer enhancement of the delta winglet pairs with an attack angle of 45° is larger than that with an angle of 30°.The delta winglet pair with an attack angle of 45° leads to an increase in pressure drop,while the delta winglet pair with the 30°angle results in a slight *** heat transfer enhancement under identical pumping power condition for the attack angle of 30° is larger than that for the attack angle of 45°either for staggered or for aligned tube bank arrangement.

关键词： longitudinal vortex heat transfer enhancement field synergy principle

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Simulation of microstructure and rheological properties of surfactant solution

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Transactions of Nanjing University of Aeronautics and Astronautics 2007年第3期24卷 232-238页

作者： Xiong, Xianpeng Liu, Weihua Ang, Haisong Gao, Xiufeng Wei, Jinjia College of Aerospace Engineering NUAA 29 Yudao Street Nanjing 210016 China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

The Brownian dynamics (BD) simulation of a dilute surfactant solution is conducted in a steady shear flow. The rodlike micelle is assumed as a rigid rod composed of lined-up beads. A novel intercluster potential model is introduced for describing the interactions between, micelles. In the model, the Lennard-Jones and the soft-sphere potentials are used as inter-bead potentials for end-end and interior-interior beads, respectively. The micelles are combined at their ends to form a network structure at lower shear rates and are disconnected to become more and more parallel to the shear flow direction with increasing shear rate. The change of micellar microstructures with the variation of the shear rate results in shear thinning characteristics of the computed shear viscosities and first normal stress difference coefficients. The effects of surfactant solution concentration on the micellar structures and rheological properties are also investigated. Results show that the shear viscosities and the first normal stress difference coefficients increase with increasing the viscosity of the surfactant solution.

关键词： Surface active agents

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Numerical investigation on the dryout point of annular flow in the upward narrow annuli with bilateral heating

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中国高等学校学术文摘·能源与动力工程 2007年第3期1卷 264-272页

作者： SU Guanghui DUAN Feng QIU Suizheng XIAO Zejun HUANG Yanping State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an 710049China National Key Laboratory of Bubble and Natural Circulation Nuclear Power Insitute of ChinaChengdu 610041China

Based on the fundamental conservation principles-the mass,momentum,and energy conservation equtions of liquid films and the momentum conservation equation of vapor core,a theoretical three-fluid model has been developed to predict the dryout point of upward annular flow in vertical narrow annuli with bilateral *** range of the parameters are:pressure from 0.5 to 5.0 MPa;mass flow Through numerically solving the model,the relationships among the parameters of the critical quality (Xc),critical heat flux (QCHF),mass flow rate,system pressure,and the ratio of heat flux on the inner wall of the outer tube to that on the outer wall of the inner tube (qo/qi) are obtained and *** predicted results accurately match with the experimental *** a fixed qo,Xc will increase with the decreases in the gap size and the tube curvature when the dryout point occurs on the outer wall of the inner ***,for a fixed qi,when the dryout point occurs on the inner wall of the outer tube,the parametric trend is *** the dryout point on the inner and outer walls occurs simultaneously,Xc reaches a peak value,and the ratio of qo/qi at this position changes with the gap size and the tube curvature.

关键词： critical heat flux critical quality annular flow dryout numerical simulation

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An efficient and robust numerical scheme for the SIMPLER algorithm on non-orthogonal curvilinear coordinates: CLEARER

An efficient and robust numerical scheme for the SIMPLER alg...

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作者： Cheng, Y.P. Lee, T.S. Low, H.T. Tao, W.Q. Laboratory of Fluid Mechanics Department of Mechanical Engineering National University of Singapore Singapore Singapore State Key Laboratory of Multiphase Flow in Powering Engineering School of Energy and Power Engineering Xian Shaanxi China Laboratory of Fluid Mechanics Department of Mechanical Engineering National University of Singapore 119260 Singapore Singapore

In this article, an Improved SIMPLER (CLEARER) algorithm is formulated to solve the incompressible fluid flow and heat transfer on the nonstaggered, nonorthogonal curvilinear grid system. By virtue of a modified momentum interpolation method in calculating the interface contravariant velocity in both the predictor step and the corrector step, the coupling between pressure and velocity is fully guaranteed, and the conservation law is also satisfied. A second relaxation factor is introduced in the corrector step, of which the convergent solution is independent. By setting the second relaxation factor less than the underrelaxation factor for the velocity to some extent, both the convergence rate and robustness can be greatly enhanced. Meanwhile, the CLEARER algorithm can also overcome the severe grid nonorthogonality. With the simplified pressure-correction equation, the convergent solution can still be obtained even when the intersection angle among grid lines is as low as 1, which may provide valuable guidance in studying the fluid flow in complex geometries.

关键词： Computational fluid dynamics

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Natural convection heat transfer of water in a horizontal circular gap

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中国高等学校学术文摘·能源与动力工程 2007年第2期1卷 167-173页

作者： SU Guanghui Kenichiro Sugiyama WU Yingwei State Key Laboratory of Multiphase Flow in Power Emgineering Xi'an jiaotong University Xi'an 710049China Faculty of Engineering Hoddaido University North Ward Sapporo 060-8628Japan

An experimental study on the natural convection heat transfer on a horizontal downward facing heated surface in a water gap was carried out under atmospheric pressure conditions. A total of 700 experimental data points were correlated using Rayleigh versus Nusselt number in various forms, based on different independent variables. The effects of different characteristic lengths and film temperatures were discussed. The results show that the buoyancy force acts as a resistance force for natural convecti on beat transfer ona downward facing horizontal heated surface in a confined space. For the estimation of the natural convection heat transfer under the present conditions, empirical correlations in which Nusselt number is expressed as a function of the Rayleigh number, or both Rayleigh and Prandtl numbers, may be used. When it is accurately predicted, the Nusselt number is expressed as a function of the Rayleigh and Prandtl numbers, as well as the gap width-to-heated surface diameter ratio; and uses the temperature difference between the heated surface and the ambient fluid in the definition of Rayleigh number. The characteristic length is the gap size and the film temperature is the average fluid temperature.

关键词： natural convection downward facing heated surface gap size buoyancy force

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Hydrogen production from sludge in supercritical water and its energy evaluation

Hydrogen production from sludge in supercritical water and i...

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5th International Energy Conversion engineering Conference

作者： Qinming, Zhang Shuzhong, Wang Liang, Wang Donghai, Xu Lingling, Lu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China Department of Thermal Engineering Xi'an Jiaotong University AIAA

ISBN: (纸本)1563479028

Gasification of high moisture content biomass in supercritical water has been identified as a promising alternative system for producing renewable hydrogen. Supercritical water partial oxidation is the process by which an oxidant appears during the reaction. The key advantage of this process is the rapid heating of the gasification medium, resulting in less char formation and improved hydrogen yield. Many researchers have studied the supercritical water gasification of model compounds. However, real biomass which is of importance for large production of hydrogen has yet to be thoroughly examined. In this paper, gasification of high moisture content municipal sludge was studied in a continuous reactor employing hydrogen peroxide as an oxygen source. The reaction was tested across temperatures and pressures in the range of 673 to 873 K and 24 to 30 MPa, and across various residence times ranging from 3 to 15 minutes. We found that sludge at low concentrations can be completely gasified with no observable char or tar formation. The improvement of gasification efficiency by partial oxidation was accompanied with a high yield of hydrogen and carbon monoxide. Through this, we evaluated the energy efficiency of sludge gasification. Our thermodynamic calculations show that the energy efficiency reaches 50% when considering hydrogen, carbon monoxide, and methane as the valuable gases in the ideal case. Taking into account the energy recovery from the hot water at 30 MPa and 873 K and assuming the ideal scenario of no external heat loss, the overall energy yield potentially reaches 85%. Our results show that the key mechanism of the gasification process is energy recovery, as the chemical reaction is endothermic and requires high temperatures.

关键词： Hydrogen production

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New revised correlation to predict pressure drop for oil-gas two-phase flow through horizontal pipe

New revised correlation to predict pressure drop for oil-gas...

引用

International Petroleum Technology Conference 2007, IPTC 2007

作者： Liu, Wenhong Guo, Liejin Zhang, Ximin Lin, Kai Yang, Long Feng, Yaorong Tubular Goods Research Center of CNPC Key Laboratory for Mechanical and Environmental Behavior of Tubular Goods China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University China

ISBN: (纸本)9781615673360

An experimental investigation on oil-gas two-phase flow through a straight horizontal plexiglas pipe within 40mm inner diameter was conducted. The superficial velocity ranges of oil and air were 0.05-0.612m/s and 0.024-50.64m/s, respectively. The atmospheric temperature condition was maintained throughout the *** frictional pressure drop multiplier of two-phase flow was expressed using the Lockhart-Martinelli parameter correlation in accordance with typical flow pattern, but the modification factor C in the correlations was defined afresh according to flow conditions. New predict correlations for pressure gradient in accordance with typical flow patterns were proposed and the mechanisms of pressure drop production were analyzed for each flow patterns. The proposed models give a good agreement with the experimental data. Copyright 2007, International Petroleum Technology Conference.

关键词： Two phase flow

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Effects of geometric parameters on steady laminar heal transfer in wavy channels

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Jisuan Wuli/Chinese Journal of Computational Physics 2007年第2期24卷 192-196页

作者： Xie, Gongnan Wang, Qiuwang Zeng, Min Luo, Laiqin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 110049 China

Periodically fully developed convective heat transfer characteristics in a two-dimensional wavy channel are investigated numerically with a constant wall temperature. The calculations are performed with Pr=0.7, Re=20-500 on non-orthogonal non-staggered grids generated by an elliptic equation system. A semi-implicit method for pressure linked equations revised (SIMPLER) algorithm in curvilinear body-fitted coordinates is employed. Effects of Reynolds number and geometric parameters, such as aspect ratio φ and shape ratio γ, on heat transfer and friction factor are studied. It shows that no recirculation region occurs through the whole channel at low Reynolds numbers, small aspect ratio or small shape ratio. With the increase of Reynolds number, aspect ratio or shape ratio, heat transfer is enhanced due to flow recirculation. Corresponding friction factor increases simultaneously.

关键词： Heat convection

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