淋水填料式空气直接蒸发冷却实验的理论基础

为了推广淋水填料式空气直接蒸发冷却这一空调新技术,本文从理论上探讨了填料层热质传递规律,并解决了实验过程中应测量哪些量,实验结果如何整理与表达,如何合理设计实验台等一系列问题.     

在Li_2O-P_2O_5二元系统玻璃中引入BaO对玻璃结构的影响

用径向分布函数(RDF)法、喇曼光谱和红外光谱研究了在Li_2OP_2O_5系统玻璃中引入Ba~(2 )离子取代Li~ 离子对玻璃结构的影响。测试表明,含钡锂磷酸盐玻璃的主要结构为以[P0_4]为单元的链状网络结构。RDF曲线可以提供关于Ba~(2 )离子分布的重要信息。RDF曲线上的4.00—4.15A和7.15—7.45A特征峰位表示Ba-Ba近邻距离。键角ф_(o-p-o)和力常数F_(m-o)的错综变化,在喇曼光谱上表现为玻璃主要结构(如[PO_4]链)特征峰的波数和强度发生微小的变化。玻璃中B~(2 )离子的存在使连接非桥氧的方向键有所加强,将影响磷酸盐链之间离子键的强度,从而导致玻璃的一些物理性质的变化。     

Flame temperatures and species concentrations in non-stoichiometric oxycoal flames

The oxyfuel technology offers the possibility for CO₂ sequestration from coal fired power plants. One drawback is the need for a high external flue gas recirculation to avoid inadmissible high flame temperatures. The concept of controlled staging with non-stoichiometric burners (CSNB) allows a significant reduction of the commonly proposed flue gas recirculation rate while fulfilling all requirements on temperature limitations. The concept aims at a more efficient oxyfuel process with a higher degree of freedom for heat-flux adjustments suitable for a new generation of oxyfuel boilers. The steam generator size could be reduced and in this way a more cost effective steam generator concept is possible. Additionally the energy demand for the flue gas recirculation is lowered.This paper presents the experimental investigations of non-stoichiometric oxycoal flames. Temperature and gas profiles were taken to analyze the combustion behavior of coal with high oxygen concentrations in the oxidizer under oxygen deficiency and accordingly oxygen excess. In addition an optical flame monitoring system allowed a comparison of ignition, flame shape and stability. In the test rig lignite was burned under different stoichiometries ranging from 0.5 to 2.5 and different oxygen concentrations in the oxidant ranging from 30 to 40 vol.%. The thermal input of the burner was 70 kW at a total thermal input of 140 kW and a dry flue gas recirculation was used. The results were compared to a conventional air-blown combustion and showed that similar temperature ranges can be reached even with oxygen concentrations in the oxidizer as high as 40 vol.%.     

Design and analysis of stiffened composite panels including post-buckling and collapse

The European aircraft industry demands reduced development and operating costs, by 20% and 50% in the short and long term, respectively. Contributions to this aim are provided by the completed project POSICOSS (5th FP) and the running follow-up project COCOMAT (6th FP), both supported by the European Commission. As an important contribution to cost reduction a decrease in structural weight can be reached by exploiting considerable reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of post-buckling up to collapse. The POSICOSS team developed fast procedures for the post-buckling analysis of stiffened fibre composite panels, created comprehensive experimental data bases and derived suitable design guidelines. COCOMAT builds up on the POSICOSS results and considers in addition the simulation of collapse by taking degradation into account. The results comprise an extended experimental data base, degradation models, and improved certification and design tools as well as extended design guidelines.One major task of POSICOSS and COCOMAT is the development of improved analysis tools that are validated by experiments performed within the framework of the projects. Because the new tools must comprise a wide range of various aspects a considerable number of different structures had to be tested. These structures were designed under different objectives (e.g. large post-buckling region). For the design process, the consortiums applied state-of-the-art simulation tools and brought in their own design experience. This paper deals with the design process as performed within both projects and with the applied analysis procedures. It is focused on the DLR experience in the design and analysis of stringer-stiffened CFRP panels gained within the scope of these two projects.     

Fragmentation of wood char in a laboratory scale fluidized bed combustor

Casuarina equisetifolia, a hard wood, and a popular energy crop in many tropical countries, was investigated experimentally for its char fragmentation in a laboratory scale atmospheric bubbling fluidized bed combustor. The effect of fuel shape and size on wood char fragmentation was studied. Wood particles of spherical, cylindrical (aspect ratio of 1), and cubical shapes of different sizes ranging from 10 to 25 mm were used in the experiments. Fragmentation of wood char was quantified in terms of various parameters, such as Number of Fragments (NF), Percentage of Fragmentation Events, Frequency of Fragmentation, Timing interval of Fragmentation, Size distribution of char and Fragmentation Index (FI). Also, qualitative observations on the evolution of char in terms of deformation, cracks and surface texture are discussed. It was observed that Casuarinaequisetifolia wood of sizes greater than 15 mm, of all shapes undergoes primary fragmentation during the devolatilization phase. Furthermore, chars fragment at the early stages (1st or 2nd quarter) of the char combustion phase, underscoring the significance of the phenomenon in fluidized bed combustion. For all the shapes of wood considered, there appears to be a cut-off size of the initial wood, below which its char certainly undergoes fragmentation. It was observed that the average char particle size at any instance during its combustion falls in a narrow range of 3.7–6.9 mm, 3–6.6 mm and 3–9.5 mm for spherical, cylindrical and cubical wood particles, respectively. Wood of initially cylindrical shape undergoes extensive fragmentation when compared with spherical and cubical shapes.     

在应力梯度下边缘加劲板的试验和设计

薄钢板结构有3种典型类型:非加劲(无边缘加劲板),加劲(有充足边缘的加劲板)和部分加劲(有部分边缘加劲板)。当被用于冷弯薄壁型钢时,在承受均匀压力和应力梯度下,钢板可能发生弹性屈曲,有6种可能的荷载组合条件。除了应力梯度作用下的部分加劲构件,对所有类型的钢板都进行了试验研究并提出了设计公式。阐述了当部分加劲板的加劲单元尺寸从零到足够产生加劲作用时,在应力梯度作用下部分加劲板的试验情况。研究了单一加劲和复合加劲的边缘加劲类型。利用有效宽度概念,提出了部分加劲构件在应力梯度作用下的设计公式。在此基础上提出了适用于所有构件在任意荷载条件下的有效宽度公式。     

Portfolio optimization using Mixture Design of Experiments: Scheduling trades within electricity markets

Deregulation of the electricity sector has given rise to several approaches to defining optimal portfolios of energy contracts. Financial tools - requiring substantial adjustments - are usually used to determine risk and return. This article presents a novel approach to adjusting the conditional value at risk (CVaR) metric to the mix of contracts on the energy markets; the approach uses Mixture Design of Experiments (MDE). In this kind of experimental strategy, the design factors are treated as proportions in a mixture system considered quite adequate for treating portfolios in general. Instead of using traditional linear programming, the concept of desirability function is here used to combine the multi-response, nonlinear objective functions for mean with the variance of a specific portfolio obtained through MDE. The maximization of the desirability function is implied in the portfolio optimization, generating an efficient recruitment frontier. This approach offers three main contributions: it includes risk aversion in the optimization routine, it assesses interaction between contracts, and it lessens the computational effort required to solve the constrained nonlinear optimization problem. A case study based on the Brazilian energy market is used to illustrate the proposal. The numerical results verify the proposal's adequacy.     

Cooling of oil injected screw compressors by oil atomisation

This paper addresses the effect of oil atomisation in an oil-injected screw compressor. A test rig was built to assess the performance of different types of atomisers. Atomisers varying from fine atomisation to coarse atomisation were tested. Experiments on the test rig show that lowering the oil droplet diameter results in a considerably higher heat transfer. Growing oil flow rate, also gives a better cooling effectiveness. In parallel with the experiments, a thermodynamic model is developed by which the compression process can be calculated for every degree of revolution of the male-rotor. This way the influence of cooling oil temperature, cooling oil mass flow rate and injection point can be analysed. Having a better heat transfer effectiveness does not give a considerable gain in specific work. Lowering oil temperature gives better results, while changing the oil flow rate only gives small gains. Furthermore it is shown that cooling oil coming from the bearings has a negative influence on the performance. This paper shows that trying to reach isothermal compression through oil atomisation is not possible. The importance of the cooling effectiveness in the thermodynamic process is too small to have a significant influence.     

用赫尔槽实验分析PCB电镀铜电解液光泽剂

文章通过实验设计方法,用赫尔槽实验检验了PCB电镀铜溶液中主要成分产生的影响,找出一些看槽片的规律。一方面为初入门技术人员深入了解赫尔槽实验提供了学习的资料,另一方面也为同行展示了一份电镀铜电解液性能特性较详细的第一手数据信息。