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.     

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.     

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。     

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.     

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%.     

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.     

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.     

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.     

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.     

Thermal radiative properties of a smooth air-water interface

Thermal radiative properties for an air-water interface were calculated by considering the interface to be smooth and the water to be at uniform temperature. Monochromatic hemispherical and total normal reflectance, monochromatic and total normal transmittance, Planck mean and Rosseland mean absorption coefficients were evaluated. The wavelength interval covered by the calculations was between 0.2 and 200 μ. Other thermal radiative properties, such as emittance and absorptance, were related to the above properties, and a comparison with available results shows favorable agreement. The use of these properties in the area of remote sensing and global energy balance makes the data essential for identifying the most effective region of the spectrum and for explaining some of the naturally occurring processes where radiative transfer plays an important role.     

喷吹塑料对高炉碳排放优化的影响

基于高炉物质、能量守恒及非线性规划理论,考虑高炉喷吹塑料或喷吹煤粉,建立了以高炉碳排放最小为优化目标函数、包含16个优化变量、6个线性等式约束、1个线性不等式约束、1个非线性等式约束、6个非线性不等式约束以及16个变量上下限约束的高炉炼铁过程优化模型;采用序列二次规划法求得优化结果,对比分析了喷吹塑料和喷吹煤粉对高炉碳排放优化的影响,并分析了碳排放最少时,焦比和直接还原度与塑料碳氢比的关系,以及鼓风参数与碳排放最小值和相应焦比的关系。     

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.     

Monte Carlo radiative transfer simulation of a cavity solar reactor for the reduction of cerium oxide

Radiative heat transfer in a solar thermochemical reactor for the thermal reduction of cerium oxide is simulated with the Monte Carlo method. The directional characteristics and the power distribution of the concentrated solar radiation that enters the cavity is obtained by carrying out a Monte Carlo ray tracing of a paraboloidal concentrator. It is considered that the reactor contains a gas/particle suspension directly exposed to concentrated solar radiation. The suspension is treated as a non-isothermal, non-gray, absorbing, emitting, and anisotropically scattering medium. The transport coefficients of the particles are obtained from Mie-scattering theory by using the optical properties of cerium oxide. From the simulations, the aperture radius and the particle concentration were optimized to match the characteristics of the considered concentrator.     

A model for the ignition and extinction of liquid fuel droplets

The model of the ignition and extinction of liquid fuel droplets presented in this paper is an application of stability theory, and specifically of Liapunov's first (indirect) method, which is well developed for lumped parameter autonomous systems. Since the behavior of liquid droplets is usually represented by a distributed nonautonomous system, an important part of the paper deals with the method by which the equations governing droplet combustion are reduced to the form appropriate to this analysis.The model consists of two unsteady autonomous coupled ordinary differential equations in temperature and oxygen mass fraction. Far field assumptions have made it necessary to treat the fuel mass fraction as a parameter. The results include the familiar S curves of temperature versus Damköhler number, as well as a great deal of detailed information about the static and the dynamic stability of the transitions between steady state evaporation and steady state combustion.     

Atomization of liquid droplets in a convective gas stream

New experimental results are reported for the atomization of liquid droplets by a high-speed air stream. A series of experiments are described in which water droplets, ranging in diameter from 1000 to 2700 μ, were introduced into the test section of a shock tube and allowed to interact with the convective flow established by the passage of a propagating shock front. A rotating drum camera system was employed to obtain a collection of streak photographs of the atomization process from which the breakup time, the breakup distance, and the ultimate atomized particle size were determined. The experiments covered a Weber number range given by 0.7 × 10³ ? We ? 85.5 × 10³.     

Photovoltaic-thermal collectors for night radiative cooling of buildings

A new photovoltaic-thermal (PVT) system has been developed to produce electricity and cooling energy. Experimental studies of uncovered PVT collectors were carried out in Stuttgart to validate a simulation model, which calculates the night radiative heat exchange with the sky. Larger PVT frameless modules with 2.8 m² surface area were then implemented in a residential zero energy building and tested under climatic conditions of Madrid. Measured cooling power levels were between 60 and 65 W m⁻², when the PVT collector was used to cool a warm storage tank and 40-45 W m⁻², when the energy was directly used to cool a ceiling. The ratio of cooling energy to electrical energy required for pumping water through the PVT collector at night was excellent with values between 17 and 30. The simulated summer cooling energy production per square meter of PVT collector in the Madrid/Spain climatic conditions is 51 kWh m⁻² a⁻¹. In addition to the thermal cooling gain, 205 kWh m⁻² a⁻¹ of AC electricity is produced under Spanish conditions. A comparative analysis for the hot humid climate of Shanghai gave comparable results with 55 kWh m⁻² a⁻¹ total cooling energy production, mainly usable for heat rejection of a compression chiller and a lower electricity production of 142 kWh m⁻² a⁻¹.