OPTIMIZED DESIGN OF A NEW GASOLINE DIRECT SWIRL INJECTOR

The internal flow characteristics of a gasoline direct injector (GDI) have been studied to improve fuel economy and reduce exhaust emissions. Computational fluid dynamics (CFD) is used to examine the internal flow of the GDI with the purpose of designing the optimum geometry of the injector. The design parameters include orifice length, cone angle, swirl angle, orifice diameter, and needle lift. Numerical results show that optimum sizes of the orifice length, cone angle, swirl angle, orifice diameter, and needle lift are 0.8 mm, 140°, 120°, 0.8 mm, and 70 m, respectively. The size of the lift does not affect the formation of the air core significantly near the tip of the needle compared with the ball-type needle. The vena contracta phenomenon near the orifice inlet can be released by smoothing the edge.     

风力机叶片外形设计及三维实体建模研究

基于贝茨理论,结合具体工程实际,对某中型风力机叶片进行外形设计.并在此基础上提出了风力机叶片的三维建模方法,即利用点的坐标变换理论来计算叶片各断面翼型的空间实际坐标,然后运用UG强大的三维曲面建模功能来建立叶片复杂曲面.该文提出的方法减少了风力机叶片等复杂曲面的建模工作量;叶片实体模型的建立也为叶片的气动性能计算和结构设计与分析奠定了基础.     

DESIGN AND PERFORMANCE OF AN ORIGINAL FRENCH SOLAR HEATING SYSTEM: DIRECT SOLAR FLOOR HEATING

Direct Solar Floor Heating ( DSFH) is an original solar heating system made of a set of water circulation pipes embedded in a concrete floor which is directly connected to the solar collectors without heat exchanger or any other storage. The concrete slab is thick enough to be used as storage. Performance of many installations in France have been measured and give satisfaction. Furthermore, a simplified sizing method has been proposed. We set forth simulations with EMGP2, in order to improve both of these results and to optimize the economic and technical performances of the system. An optimum size which the method did not anticipate is indeed found if we correctly took into account the function of the floor in the system. Two points have to be supervised: comfort and regulation for which some preliminary informations are given. A methodology is proposed in order to analyse bare results from measured data.     

BEM SHAPE OPTIMIZATION TECHNIQUE APPLIED TO CRYOSURGICAL PROBE TIP DESIGN

This paper describes an iterative numerical optimization procedure for generating the cryosurgical probe tip geometry to produce the desired lethal temperature envelope for steady-state axisymmetric systems. The Kirchhoff transformation is used to include the nonlinear effect of variable thermal conductivity at cryogenic temperatures. The boundary-element method (BEM) is used to solve the governing differential equation at each step in the iteration. The shape optimization procedure involves sequential searches of radial vectors to determine the optimum location for each node at each step in the iteration. Experimental data are obtained for three probe tip geometries, and the experimental data compare favorably with the results of the numerical solution.     

百吨级生物质合成气合成二甲醚中试系统设计及运行分析

该系统以农业废弃物玉米芯经富氧气化制备的低H_2/CO合成气为气源,采用固定床一步法合成二甲醚工艺,高效生产DME产品.运行结果表明,在空速为650h~(-1)和1200h~(-1)时,CO单程转化率分别为82.00%和73.55%.DME选择性分别为73.95%和69.73%,DME时空产率分别为124.28kg/(m~3·h)和203.80kg,(m~3·h).生物质合成气的深度脱氧和脱焦油是保证合成系统稳定运行的关键.合成尾气H_2/CO较高,经脱CO_2后循环利用可大大提高DME的产率.     

APPLICATION OF THE GROWTH-STRAIN METHOD FOR SHAPE OPTIMIZATION OF FLOW SYSTEMS

In this study, the growth-strain method was used for shape optimization of flow systems. It optimizes a shape by making a distributed parameter such as dissipation energy uniform in a flow system. In order to overcome the instability that occurred in the numerical analysis by the growth-strain method, the equation of bulk strain has been modified. And the distributed parameters were variously established in this study. By comparing the optimized shapes with the known optimal shapes for two flow systems, it is confirmed that the modified growth-strain method is very efficient and practical in shape optimization of flow systems.     

典型生物质剪切破碎生成颗粒的形状特征

借助光学显微镜和Image J图像处理软件,运用统计方法和分形理论对芦苇、稻秆、豆秸及松木4种生物质经剪切破碎后的颗粒的形状特征进行研究.结果发现:随着粒径的减小,生物质颗粒的长宽比及不同生物质颗粒长宽比之间的差异均变小.芦苇、稻秆、豆秸及松木4种生物质颗粒粒度为0.180～0.425mm时,平均长宽比分别为9.82、9.00、7.01和3.01,差异较大;粒度为0.096～0.125mm时,平均长宽比较接近,分别为2.42、2.70、2.59和2.49.4种生物质颗粒具有分形特性,在所研究的粒径范围内,分形维数处于0.8 ～0.9之间,且4种颗粒的分形维数随颗粒粒径的减小表现出减小趋势,但是松木颗粒的变化相对较小.     

SHAPE DESIGN FOR HEAT CONDUCTION PROBLEMS USING CURVILINEAR GRID GENERATION,CONJUGATE GRADIENT,AND REDISTRIBUTION METHODS

This study is concerned with the application of an approach combining the curvilinear grid generation and conjugate gradient (CG) methods for shape design of heat conduction problems. Shape design for a conductive medium that contains a heating object and features an isothermal outer surface is investigated. Several practical cases with multiply-connected domains associated with various imbedded heating objects and thermal boundary conditions are studied to demonstrate the performance of the approach. Optimal shape profiles that meet different heat transfer requirements are obtained. Meanwhile, a redistribution method is proposed to numerically regularize the ill-ordered grids, which are commonly found during the iterative optimization process. By using the redistribution method, the locations of the nodal points at the outer surface may be adjusted automatically once the ill-ordered grid patterns are detected, so that the convergence of the optimization process can be facilitated.     

AN APPROACH COMBINING BODY-FITTED GRID GENERATION AND CONJUGATE GRADIENT METHODS FOR SHAPE DESIGN IN HEAT CONDUCTION PROBLEMS

The present study is focused on the development of a computational method for shape design of heat conduction problems by using a combination of the body-fitted grid-generation scheme and the conjugate gradient optimization method. The body-fitted coordinate transformation technique is used to generate a curvilinear grid for each iteration automatically, by sensing the change of the shape of the solution domain during the optimization process. The conjugate gradient method is incorporated with direct sensitivity analysis for seeking the optimal shape which minimizes the objective function. The temperature distribution in the solution domain is solved by means of the finite volume method. A practical problem is used for demonstration, and the results show that the proposed method provides a simple and efficient approach for determining the shape profile.     

CONDUCTION SHAPE FACTORS OF LONG POLYGONAL FIBERS IN A MATRIX

The shape factors for steady state, two-dimensional heat transfer across long polygonal fibers in a matrix are computed by a numerical conformal transformation procedure. The coordinate transformation functions in the complex plane and the heat conduction shape factors are expressed in a closed form, but the final results require numerical integration. The semi-analytic approach is a general solution, in the sense that it encompasses many specific geometries such as concentric square regions and concentric hexagonal regions.     

STATIC SHAPE CONTROL OF FORCE-INDUCED INFINITESIMAL DEFORMATIONS SUPERIMPOSED ON LARGE DEFORMATIONS OF THERMOELASTIC BODIES

The present paper is concerned with the geometrically nonlinear static theory of anisotropic thermoelastic solids and structures. We consider infinitesimal incremental deformations superimposed on a given state of possibly large strain, the latter being called the intermediate state. Our goal is to derive a distribution of incremental thermal actuation stresses, which, when applied to the intermediate state together with a given set of incremental body forces and surface tractions, give zero incremental displacements everywhere in the body under consideration. This problem belongs to the field of static shape control, a notion originally introduced by Haftka and Adelman, who developed a procedure for determining temperatures in control elements to minimize the infinitesimal distortion of a large space antenna from its original shape. The present paper is concerned with the extension of shape control to infinitesimal force-induced static distortions from a large pre-deformation. Referring to the intermediate configuration as the reference configuration, we show that, in order to compensate the incremental force-induced deformations everywhere within the body, the incremental thermal actuation stress tensor must be equal to any statically admissible incremental first-order Piola–Kirchhoff stress tensor, a relation that is derived under the assumption that the intermediate state is infinitesimally superstable. We also discuss under which conditions it is possible to work with an isotropic thermal actuation stress. Finally, we present a formulation for shape control of infinitesimal deflections superimposed on a state of possibly large deflections of a slender beam.     

秸秆直燃发电的生命周期评价

应用生命周期评价(LCA)方法,以秸秆直燃发电项目为研究对象,对秸秆的种植、运输、粉碎干燥和燃烧发电等4个过程进行了清单分析,并分别计算出4个过程的能耗及其对环境的影响.结果表明,每燃烧100kg秸秆发电,对环境的总影响负荷水稻秸为247.36毫人当量,小麦秸为268.74毫人当量,玉米秸为267.33毫人当量.秸秆直燃发电对环境影响主要为烟尘和灰尘,对局部地区的影响占据首位.以水稻秸秆为例,100kg水稻秸秆在直燃发电过程中整个系统共从环境吸收CO2167.60kg,向环境释放CO2164.24kg,由此看到,秸秆直燃发电项目在减少温室气体排放上能起积极作用.     

DIRECT NUMERICAL SIMULATION OF LAYER MERGING IN A SALT-STRATIFIED SYSTEM

Time-dependent double-diffusive convection was studied numerically to clarify the mechanism of layer merging in a salt-stratified system. Using the Chebyshev collocation method, a typical example of stably stratified salt fluid subject to a lateral temperature difference in a rectangular enclosure (Ar = 1.25) is considered for realistic values of parameters (Ra_T = 2.7 X 10⁷, N_i = 0.882, Pr = 7.15, and Sc = 685). Two cases that differ by the initial salt concentration profile, i.e., linear and steplike profiles, are examined. Although globally, in both cases, the layer merging process is characterized by the mass transfer across the interface separating two convection layers, the two instances are quite different with respect to the interface structure. For the linear profile, vertical motion due to salt fingers is dominant, whereas for the steplike profile horizontal motion due to strong shear flows prevails. In particular, in the latter case, unlike for the linear profile case, traveling plumes perpendicular to shear flows that lead to the time variations in temperature and concentration are periodically generated within the interface. Predictions obtained with the simulations are in good agreement with experimental data.     

PERFORMANCE OF A HEAT PUMP USING DIRECT EXPANSION SOLAR COLLECTORS

Theoretical and experimental studies were made on the thermal performance of a heat pump that used a bare flat-plate collector as the evaporator. The analysis used empirical equations to express the electric power consumption of the compressor and coefficient of performance (COP), as functions of temperature of evaporation at the evaporator and that of the heat transfer medium (water) at the inlet of the condenser. The experimental heat pump had a compressor with a rated capacity of 350 W and collectors with the total area of 3.24 m². Around noon in winter the evaporator temperature was found to be about 17°C higher than the ambient air temperature of 8°C, and a COP of about 5.3 was obtained when the water temperature at the condenser inlet was 40°C. These measured evaporation temperatures and COPs were in good agreement with those predicted by the analysis. According to the analysis, the total area of the collectors in the experiment was appropriate for the heat pump system. Also, the 1-mm thickness of the collector's copper plate used in the experiment could be 0.5 mm with little reduction of COP. The pitch of the tube soldered to the copper plate for the refrigerant flow was 100 mm in the experiment, but the COP would only be reduced by about 4% if the pitch were changed to 190 mm.     

DYNAMIC SHAPE CONTROL OF SOLIDS AND STRUCTURES BY THERMAL EXPANSION STRAINS

The present article is concerned with the dynamic shape control of solids and structures by means of thermal expansion strains or, equivalently, by means of thermal expansion stresses. We study transient disturbances produced by imposed forces, and we wish to identify a transient temperature distribution that, when superimposed, leads to zero total displacements of the body. The derivation is based on the theorem of work expended and on Graffi's theorem. Using the anisotropic constitutive equations of linear thermoelasticity, we arrive at a dynamic extension of the principle of virtual forces and at a dynamic extension of Maysel's formula of thermoelasticity. Comparing these two convolution statements, it is found that, in order to make the total displacement zero everywhere in the body, the thermal expansion stress in the thermal problem should be the quasi-static stress minus the thermal expansion stress in the force problem. Any quasi-static stress due to a thermal loading may be added to the thermal expansion stress without changing the validity of this theorem. The practical application of this result is facilitated when the production of heat due to deformation may be neglected and when the applied forces are separable in space and time. The validity of the analytical solution is checked, by means of finite element computations.     

THE EARLY DESIGN MODEL FOR PREDICTION OF ENERGY AND COST PERFORMANCE OF BUILDING DESIGN OPTIONS

In order to encourage the use of computer modelling in building environmental analysis, it is necessary to provide a model developed from the designer's point of view. Detailed simulation models require a high degree of expertise and familiarity, further, there is also a need for detailed information not available in the early stages of the design process. Simplified models play an important role in the early stages of a design to achieve an integrated design: firstly, they are easy to use and, secondly, they require information easily available at the start of a design. In the Early Design Model (EDM) the solar gain utilisation factor has been determined as a continuous function of thermal mass. The differences between the annual energy predictions of EDM and SERI-RES ranges from 0.1% to 4.6% for time constants ranging from 378 to 2.52 h. The differences between the two sets of predictions on monthly basis ranges from ?3.6% to ?6.48% (EDM's predictions being larger) during the heating season, and from +2.86% to a maximum of +51% (EDM's predictions being smaller) in the remaining part of the year. In addition to energy predictions, EDM incorporates a facility which gives cost indications.     

中倍聚光太阳电池液浸散热特性的模拟实验

提出了一种将太阳电池液浸到冷却介质中,电池与介质间进行直接接触式换热的冷却方式.设计了小型实验装置,选用二甲基硅油为冷却介质,采用长弧氙灯模拟聚光条件,选择模拟材料制作太阳电池模拟片,进行了模拟实验研究.结果表明:采用液浸冷却方式,能够从模拟片表面带走72.2kW/m~2的热负荷,同时将模拟片的温度冷却到70℃以下;模拟片与介质间的单相对流传热系数能够达到约750W/(m~2·℃);介质温度的改变对模拟片与介质间的对流换热温差和对流传热系数影响较小.     

蒸汽直接冷却槽式太阳集热器的传热流动性能研究

首先在对DSG集热器中水的流型分析的基础上,进行了水在不同状态下对流换热系数计算模型的研究;利用传热热阻原理,分析了DSG集热器热损失的计算方法;考虑到流体流动方向上的温度变化,建立了稳态热传导模型.之后,对集热器的两种不同连接方式(一次通过式和再循环式)的压降进行了分析.最后,分析了太阳能辐射变化时,两种连接方式下集热器场一些主要参数的变化情况,为DSG集热器场的设计及运行提供指导.     

OPTIMUM THERMOELASTIC DESIGN OF LAMINATED PLATES

A thermoelastic optimization procedure is proposed for the design of symmetric. laminated, fiber-reinforced plates. A maximum stiffness criterion is employed, wherein the ply orientations are found by minimizing the complementary strain energy. Approximate solutions for the thermoelastic response are obtained using the Rayleigh-Ritz procedure. Optimization is performed via a quasi-Newton method, with the initial point selected using a random jump routine. Numerical results are presented for simply supported plates subject to a temperature distribution that varies linearly in the thickness direction. Results are given for various composite materials, and the optimum thermoelastic solutions are compared with designs for mechanically loaded laminated plates.     

NUMERICAL SHAPE OPTIMIZATION FOR HIGH PERFORMANCE OF A HEAT SINK WITH PIN-FINS

The design optimization of a 7 × 7 pin-fin heat sink is performed numerically. To achieve higher thermal performance of the heat sink, the thermal resistance at the junction of the chip and the heat sink and the overall pressure drop in the heat sink have to be minimized simultaneously. The fin height (h), fin width (w), and fan-to-heat sink distance (c) are chosen as the design variables, and the pressure drop (ΔP) and thermal resistance (θ _ja ) are adopted as the objective functions. To obtain the optimum design values, we used the finite-volume method for calculating the objective functions, the Broydon-Fletcher-Goldfarb-Shanno method for solving the unconstrained nonlinear optimization problem, and the weighting method for predicting the multiobjective problem. The results show that the optimum design variables for the weighting coefficient of 0.5 are as follows: w = 4.653 mm, h = 59.215 mm, and c = 2.669 mm. The objective functions corresponding to the optimal design are calculated as ΔP = 6.82 Pa and θ _ja  = 0.56 K/W. The Pareto solutions are also presented for various weighting coefficients, and they offer very useful data for designing a pin-fin heat sink.