柴油机喷油泵传动轴防护罩断裂故障分析及优化

为解决某船用柴油机喷油泵传动轴防护罩断裂故障,提升零部件可靠性,运用Hypermesh、Abaqus以及Femfat等仿真软件,对该喷油泵传动轴防护罩断裂故障产生的原因进行仿真分析.结果 显示,防护罩断裂原因为一阶模态小于激振频率的1.2倍,易产生共振.在此基础上提出两种优化方案,对两种方案进行模态、强度及疲劳仿真计算...     

An investigation into the use of a wind shield to reduce the convective heat flux to a nocturnal radiative cooling surface

The effect of a wind shield on the convective heat flux from an ambient air stream blowing over a horizontal surface intended for nocturnal radiative cooling has been studied by computational fluid dynamical calculations and by wind tunnel experiments under conditions appropriate for the climate of Thailand. The test unit was a rectangular plate 312 mm×250 mm, with vertical metal strips for the wind shield having heights up to 100 mm along the edges of the plate. It was found that a wind shield of height 25 mm slightly increased the convective heat transfer due to increased turbulence over the surface, but wind shields of height 50 mm and 100 mm reduced the convection due to a separation of the main airflow from the surface. Radiative cooling was reduced by the wind shields. The net cooling of the surface was best with no wind shield at wind velocities less than about 1 m s^–1, and with the wind shield of height 100 mm at wind velocities greater than about 2 m s^–1.     

Exploration of radiative heat on the Jeffery fluid flow in a microchannel for the impact of suction/injection

The purpose of the present paper is to investigate the flow and heat transfer of thermal radiation on the Jeffery fluid flow within a microchannel for the effects of the superhydrophobic surface (SHS) within suction/injection. The governing differential equations of motion and heat transfer are transformed into nonlinear coupled ordinary differential equations (ODEs) using appropriate similarity transformations. The ODEs are solved along with boundary conditions by adopting Runge–Kutta with shooting technique. Symbolic computational software such as MATLAB, the solver bvp4c syntax examines the behavior of the relevant physical parameters. However, some effective emerging parameters on the flow problem reveal that the microchannel walls within the suction/injection parameter increase the temperature, and the SHS is heated. In contrast, without slip, the opposite behavior is rendered. It is clearly shown that the velocity profile diminishes with increasing the Prandtl number. Furthermore, it is noticed that velocity decreases for increasing values of Hartmann number. Comparison with available results for particular cases is an excellent agreement.     

Tomography based pore-level optimization of radiative transfer in porous media

A non-energy-partitioning Monte Carlo Ray Tracing (MCRT) model is employed to optimize radiative transfer in porous media. The pore level geometry is incrementally modified using 3D equivalents of image manipulation algorithms such as erosion, dilation, opening, and closing. Subsequently, direct, pore-level analysis of radiative transfer is carried out for each modification step to optimize the pore-level geometry for maximum absorptance. Results have been obtained for an opaque, diffusely or specularly reflecting solid phase within a non-participating void phase. Model media studied are: (i) reticulate porous ceramics (RPCs) and (ii) packed beds of CaCO₃ particles. The extinction coefficient and the forward scattering fraction have been determined for the media via a two-flux model of radiative transfer. Optimum porosities for maximizing absorptance at given medium thicknesses are then obtained from the analytical model. For the RPC, the forward scattering fraction varies between 0.38 and 0.57, and the extinction correlation coefficient varies between 9.56 and 7.03. For the packed CaCO₃ particle bed, the forward scattering fraction varies between 0.6 and 0.72, and the extinction coefficient varies between and 2.84 and 2.14.     

Exergy efficiency applied for the performance optimization of a direct injection compression ignition (CI) engine using biofuels

The need to decrease the consumption of materials and energy and to promote the use of renewable resources, such as biofuels, stress the importance of evaluating the performance of engines based on the second law of thermodynamics. This paper suggests the use of exergy analysis (as an environmental assessment tool to account wastes and determine the exergy efficiency) combined with gas emissions analysis to optimize the performance of a compression ignition (CI) engine using biofuels such as cottonseed and palm oils, pure or blended with diesel for different engine loads. The results show that the combination of exergy and gas emissions analyses is a very effective tool for evaluating the optimal loads that can be supplied by CI engines. Taking into account technical constraints of engines, a tradeoff zone of engine loads (60% and 70% of the maximum load) was established between the gas emissions (NO and CO₂) and the exergy efficiency for optimal performance of the CI engine.     

基于数值模拟的机车柴油机喷油嘴的结构优化

为了改进16V280ZJ型柴油机的性能,对其喷油嘴内的流场进行三维数值模拟,得到了在不同压力条件下详细的流场结构。通过流场分析可知,随着喷射压力的提高,流场湍流强度增大,湍流引起的能量损失增加,流量系数降低。并应用CAD／CAM／CFD集成的方法对喷油嘴结构进行优化,找到了喷油嘴内存在的不合理部位,将喷油嘴结构改为球形针阀后,在同等喷射压力下能够大幅度提高喷油流量。     

Generalized radiative transfer equation for porous medium upscaling: Application to the radiative Fourier law

Many porous media cannot be homogenized as Beerian semi-transparent media. Effective extinction, absorption and scattering coefficients can indeed have no physical meaning for small or intermediate optical thicknesses. A generalized radiative transfer equation (GRTE), directly based on the extinction cumulative distribution function, the absorption and scattering cumulative probabilities and the scattering phase function is established for this optical thickness range. It can be solved by a statistical Monte Carlo approach. For a phase of a porous medium that is optically thick at local scale, the GRTE degenerates into a classical Beerian RTE. In these conditions, a radiative conductivity tensor is directly obtained, by a perturbation method, and expressed with the radiative coefficients of this RTE and temperature. As illustrations, exhaustive radiative conductivity results are given for a set of overlapping transparent spheres within an opaque phase and for opaque rod bundles.     

Pareto optimization of a combined cycle power system as a decision support tool for trading off investment vs. operating costs

The monetary optimization of thermodynamic processes may be approached by inherently thermodynamic frameworks like exergo-economic analysis, or a rigid direct cost evaluation is applied. This paper, treating the optimization of a combined cycle power plant, follows the second path. Operation and investment costs are usually treated as a combined value by means of an annualization factor. Due to the rather far-stretching time horizon of turbine energy conversion systems, differing behaviour of those contributions with time, and varying subjective weighting and assumptions of future developments, this conventional subsumption is not necessarily a sensible one to identify the best solution for a given decision situation. It is therefore favorable to address both costing goals independently and identify the pareto set of the problem prior to a final decision on which parametrization of the system should be chosen. A numerical pareto optimization technique based on an evolutionary base strategy is discussed that addresses this type of problem in an efficient and easy to adapt manner.     

Determination of the anisotropic radiative properties of a porous material by radiative distribution function identification (RDFI)

The anisotropic extinction and absorption coefficients of a high porosity material with a semi-transparent solid phase are directly obtained from identification of the statistical cumulated distribution function of extinction distances in the material, linked to that of the chords, and the corresponding function in the equivalent semi transparent medium. The bidirectional phase function is then determined without any hypothesis. The model only requires the knowledge of the material morphology, given by a X-ray tomography and the phases local radiative properties.     

Evaluation of the radiative properties of a dispersed particulate medium for construction material applications

Recent studies have suggested that the heat buildup of construction materials may be significantly reduced, without affecting the material color, by the incorporation of scattering particles.The scattering particles were found to alter the near infrared diffuse reflectance of the material, depending on their refractive index, volume percent, and particle size combination. In addition, a theoretical model was developed and correlated well with the experimentally measured values, accurately predicted increases in diffuse reflectance and drops in temperature. Thus, the model may be effectively used to design dark colored polymeric materials with reduced heat buildup properties.     

高速牵引车冲坡特性影响因子研究

为了研究高速牵引车的冲坡特性,结合驾驶员的操作规律以及智能驾驶的发展要求,分别就初始车速、坡度、坡道长度等各项影响因子对高速牵引车冲坡特性的影响展开分析研究。结果显示,初始车速、坡度和坡道长度对冲坡都有影响,其中,车速和坡度对动力性和经济性的影响较大。     

Optical design of a high radiative flux solar furnace for Mexico

In the present work, the optical design of a new high radiative flux solar furnace is described. Several optical configurations for the concentrator of the system have been considered. Ray tracing simulations were carried out in order to determine the concentrated radiative flux distributions in the focal zone of the system, for comparing the different proposals. The best configuration was chosen in terms of maximum peak concentration, but also in terms of economical and other practical considerations. It consists of an arrangement of 409 first surface spherical facets with hexagonal shape, mounted on a spherical frame. The individual orientation of the facets is corrected in order to compensate for aberrations. The design considers an intercepted power of 30 kW and a target peak concentration above 10,000 suns. The effect of optical errors was also considered in the simulations.     

New aspects of the diffusion approximation for radiative transfer

The diffusion approximation is generalized to arbitrary locally isotropic participating media. It proves to be an approximate special solution of the full equation of radiative transfer accounting for absorption, scattering, and emission. This special solution must be completed with a solution of the radiative transfer equation without emission term in order to match the boundary conditions for the radiative field. Applied to combined heat and radiative transfer this scheme offers distinct computational advantages and broad applicability. Following these ideas a simple and robust method for one-dimensional radiation–conduction computations is constructed and verified.     

Multi-objective optimization of the engine performance and emissions for a hydrogen/gasoline dual-fuel engine equipped with the port water injection system

Hydrogen is one of the most promising options being considered as the fuel of future. However, injection of hydrogen into modern gasoline fueled engines can cause some issues such as power loss. This study, therefore, aims to address this challenge in a simulated hydrogen/gasoline dual-fueled engine by developing a novel and innovative approach without possible side effects such as NOx increment. To achieve this goal, the impacts of water injection and the start of the combustion (SOC) modification in a gasoline/hydrogen duel fueled engine have been rigorously investigated. In current methodology, an engine is simulated using AVL BOOST software and the model is validated against the experimental data. The Latin Hypercube design of experiments method was employed to determine the design points in 3-dimensional space. Due to the existing trade-off between NOx and BMEP, multi-objective optimization using genetic algorithm (GA) was implemented to determine the optimum values of water injection and SOC in various hydrogen energy shares and the effects of optimum design parameters on the main engine performance and emission parameters were investigated. The results showed that the proposed solution could recover the brake mean effective pressure (BMEP) and in some hydrogen energy shares even increase it above the level of single fueled gasoline engine with the added benefit of there being no increase in NOx compared to the original level. Furthermore, other emissions and engine performance parameters are improved including the engine equivalent Brake specific fuel consumption (BSFC) which was shown to increased up to 4.61%.     

About the equivalent radiative temperature for clear skies

The cold sky radiation constitutes a heat sink mainly used for passive cooling systems. The usefulness of this resource is commonly expressed in terms of the equivalent sky temperature T_c, whose accurate determination still remains as an interesting problem. Increasing the number and the diversity of the observations is necessary. An inexpensive pyrradiometer, made for that purpose, is described here. In addition, analysis of five years of observations with the Carpentras pyrradiometer (National Meteorology) lead us to propose a formulation for T_c which points out the influence of the boundary layer.     

Passive downward heat transport: experimental results of a technical unit

A bench scale model for passive downward transport of heat has been built and tested. The heat is transported by evaporation of a fluid in an evaporator at a higher level and condensation at a lower level. The condensate is returned to the evaporator by the periodic operation of a self-actuated float valve without disconnectding the heat delivery to the evaporator. The cost of lifting the liquid back to the evaporator is a temperature difference of a few degrees centigrade between the evaporator and the heat store. The unit works under moderate pressure (a maximum of 9 bar at 85°C). The actual vertical distance between heat source and heat store is about 1 m; a pressure difference equivalent to a vertical distance of 15 m was introduced by two spring-loaded check valves; in these conditions the ΔT between heat source and heat store is about 10°C. This ΔT is comparable to that occurring in the condenser to promote heat transfer to the heat store medium. Most of the components of the 1000 W model are similar to those used in conventional refrigerators or heat pumps. The system can easily be integrated with a solar heat collector working with a 2-phase fluid.     

Experimental and numerical study of downward bubbly flow in a pipe

An experimental and numerical study of the local structure of downward gas–liquid flow in a vertical pipe with 20-mm inner diameter is reported. In the experiment, the electrodiffusion technique was used in combination with electrical conductivity measurements. To examine the effect of gas-phase dispersion on flow characteristics, two different gas–liquid mixers were used capable of producing large-diameter (>1 mm) and small-diameter (<1 mm) gas bubbles at identical rate characteristics of the flow. The unified heterogeneous-medium mechanics approach was used to develop, in the Eulerian two-velocity approximation, a calculation model for downward turbulent liquid/air bubble flows. It is shown that, as the volumetric gas flow rate of the mixture at the inlet to the pipe increases, local maxima of continuous phase velocity and bubble concentration emerge in the near-wall zone of the flow, with liquid turbulence suppressed in the wall zone and enhanced in the core of the flow.     

A study of a polymer-based radiative cooling system

A radiative cooling system consisting of unglazed flat plate radiators, water as heat carrier and a reservoir is presented. The radiators are twin-wall sheets made of a modified PPO (polyphenylenoxid) resin, which are proposed as low cost roof integrated modules. The thermal performance of a system with a radiator aperture area of 5.3 m² and reservoir volume of 280 l has been investigated in experiments for Oslo climate. A parameterisation for the cooling performance of a tilted radiator surface for clear and cloudy atmospheres is proposed and applied to model the experimental results. The impact of the tilt angle, the aperture area and the reservoir volume on the cooling performance has been studied in simulations. The feasibility of a radiative cooling system designed for a single-family house at southern latitudes has been modelled. Except for mid-summer ambient temperature and high relative humidity, the simulations show that the radiative cooling system seems to cover the demand.