A heuristic method for simultaneous tower and pattern-free field optimization on solar power systems

A heuristic method for optimizing a solar power tower system is proposed, in which both heliostat field (heliostat locations and number) and the tower (tower height and receiver size) are simultaneously considered.Maximizing the thermal energy collected per unit cost leads to a difficult optimization problem due to its characteristics: it has a nonconvex black-box objective function with computationally expensive evaluation and nonconvex constraints.The proposed method sequentially optimizes the field layout for a given tower configuration and then, the tower design is optimized for the previously obtained field layout. A greedy-based heuristic algorithm is presented to address the heliostat location problem. This algorithm follows a pattern-free method. The only constraints to be considered are the field region and the nonconvex constraints (which allow heliostats to not collide).The absence of a geometrical pattern to design the field and the simultaneous optimization of the field and the tower designs make this approach different from the existing ones. Our method is compared against other proposals in the literature of heliostat field optimization.     

A study on ceiling jet characteristics in an inclined tunnel

The characteristics of a ceiling jet of an inclined tunnel in a fire will be studied and reported in this paper. Scale modeling experiments on a ceiling jet in a model tunnel of length 3.0 m, width 0.8 m and height 1.0 m inclined at different angles of 0°, 10°, 20° and 30° were carried out. Numerical studies by large eddy simulation were then performed. Both experimental observation and numerical simulation indicated that the characteristics of the temperature and velocity fields near the upper tunnel are different from those obtained using the empirical equations reported in the literature. Another set of empirical equations for gas temperature and flow velocity along the tunnel were fitted by experimental data. These derived empirical equations are useful for estimating the temperature and flow velocity patterns for the ceiling jet in an inclined tunnel with an angle within the range 0–30°.     

天然气水合物颗粒间液桥力的理论研究

天然气水合物聚集堵塞管道是安全输气的一大威胁,而天然气水合物颗粒间的液桥力是决定天然气水合物颗粒聚集与否的主导力。为此,对天然气水合物颗粒间的液桥力进行了相关理论研究,明确了液桥力为静态液桥力和动态黏性力之和,进而分析了接触角、半填充角、颗粒表面间距、颗粒粒径对天然气水合物颗粒间液桥力的影响。结果表明：接触角、半填充角、颗粒表面间距的增加以及天然气水合物颗粒粒径减小都可以有效降低甚至消除天然气水合物颗粒间的液桥力;通过添加表面活性剂增大接触角、添加防聚剂控制天然气水合物颗粒粒径以及增大体系中的水含量来增大半填充角都是降低颗粒间液桥力、防止颗粒聚集的有效手段。同时,还研究了液桥力与液桥破裂能、液桥体积的关系,结论表明：在颗粒表面间距大于液桥临界破裂距离的1/10时,液桥力随液桥体积增大而增大,而液桥破裂能与液桥体积无关。     

Effects of desiccation on mechanical behaviour of concrete

The objective of this work is experimental characterisation and numerical modelling of coupled behaviours between drying shrinkage and plastic damage in concrete. In the first part, we present an original experimental study on an ordinary concrete in order to determine material damage induced by drying shrinkage. Uniaxial compression tests are performed on samples dried for different periods. It is shown that material damage can be caused by drying process. Mechanical behaviour becomes more brittle with higher damage kinetics when concrete is dried. In the second part, a constitutive model is proposed in order to describe coupled hydro-mechanical behaviour of partially saturated concrete. This model takes into account induced damage, mechanical and capillary plastic deformations. Numerical simulations of experimental tests are presented, and show a qualitatively good agreement with experimental data. The results are relevant with respect to the importance of drying process in the durability study of concrete structures.     

Thermal and chemical reaction performance analyses of steam methane reforming in porous media solar thermochemical reactor

In order to investigate the thermochemical reaction performance of steam methane reforming (SMR), the steady heat and mass transfer model coupled with thermochemical reaction kinetics is developed for the volumetric porous media solar thermochemical reactor. The local non-thermal equilibrium (LNTE) model with modified P1 approximation is adopted to investigate the temperature distributions of the solid phase and fluid phase. For the solid phase energy equation, the irradiative heat transfer coupled with chemical reaction kinetics is programmed via User Defined Functions (UDFs). The concentrated solar irradiation is not only considered as the boundary condition at the reactor front surface, but also as the irradiative heat source in the whole volume of reactor. The parametric studies are conducted to investigate the thermal and hydrogen production performances as a function of operational parameters. The numerical results indicate that SMR reaction has big effects on temperature distribution. The generated H₂ mole fraction decreases sharply with the increasing of fluid inlet velocity, porosity and mean cell size. The generated H₂ mole fraction increases significantly with the increasing of incident solar irradiance.     

Natural gas pipeline small leakage feature extraction and recognition based on LMD envelope spectrum entropy and SVM

As it is difficult to identify the scale and aperture of small leaks occurring in a natural gas pipeline, this paper proposes a small leak feature extraction and recognition method based on local mean decomposition (LMD) envelope spectrum entropy and support vector machine (SVM). First, LMD is used to decompose the leakage signals into several FM–AM signals, i.e. into product function (PF) components. Then, based on their kurtosis features, the principal PF components that contain most of the leakage information are selected. Wavelet packet decomposition and energy methods are used to analyze and then reconstruct the principal PF components. The Hilbert transform is applied to these reconstructed principal PF components in order to acquire the envelope spectrum, from which the envelope spectrum entropy is obtained. Finally the normalized envelope spectrum entropy features are input into the SVM as leakage feature vectors in order to enable leak aperture category identification. By analyzing the acquired pipeline leakage signals in field experiments, it shows that this method can effectively identify different leak categories.     

Preparation and corrosion behavior of Ni and Ni–graphene composite coatings

The graphite oxide was synthesized using the Hummers method, and then it was reduced by hydrazine hydrate to obtain graphene. It was characterized with UV (ultra violet), IR (infra red), XRD (X-ray diffraction) spectra and SEM (scanning electron microscope) images. The composite coating of Ni–graphene on mild steel specimens was obtained by the electrodeposition technique. The composite coating was subjected to various electrochemical tests to know its corrosion behavior and compared with pure Ni coating. The EIS (electrochemical impedance spectroscopy) was performed to confirm the corrosion resistance property. The composite film was studied by recording its XRD and SEM. The crystallite size, texture coefficients and hardness of coating was measured.     

Design,simulation and experimental study of a directly-irradiated solar chemical reactor for hydrogen and syngas production from continuous solar-driven wood biomass gasification

The use of concentrated solar energy as the high-temperature heat source for the thermochemical gasification of biomass is a promising prospect for producing CO₂-neutral chemical fuels (syngas). The solar process saves biomass resource because partial combustion of the feedstock is avoided, it increases the energy conversion efficiency because the calorific value of the feedstock is upgraded by the solar power input, and it also reduces the need for downstream gas cleaning and separation because the gas products are not contaminated by combustion by-products. A new concept of solar spouted bed reactor with continuous biomass injection was designed in order to enhance heat transfer in the reactor, to improve the gasification rates and gas yields by providing constant stirring of the particles, and to enable continuous operation. Thermal simulations of the prototype were performed to calculate temperature distributions and validate the reactor design at 1.5 kW scale. The reliable operation of the solar reactor based on this new design was also experimentally demonstrated under real solar irradiation using a parabolic dish concentrator. Wood particles were continuously gasified at temperatures ranging from 1100 °C to 1300 °C using either CO₂ or steam as oxidizing agent. Carbon conversion rates over 94% and gas productions over 70 mmol/g_biomass were achieved. The energy contained in the biomass was upgraded thanks to the solar energy input by a factor of up to 1.21.     

段塞流从单管流入并联分离器的分流实验研究

为了研究油气集输系统中并联分离器出现的气液偏流现象,自主设计并搭建了气液两相流分流实验系统。该实验系统中采用数据采集系统对流量、压力、压降、液位、持液率等多种实验参数进行记录。设计了两种结构的气液分流管路,并在两种管路结构（水平管⁃T型管⁃水平管结构与水平管⁃T型管⁃立管⁃水平管结构）下进行了段塞流分流实验,分别研究了对称管路条件与非对称管路条件下的气液分流特性。实验结果表明,两种管路结构下,当管路条件对称时,在实验流速范围内,段塞流的气液两相等流量分配到两台并联分离器内;对于实验中的两种管路结构,分离器气相出口管路条件的不对称会引起气、液两相的偏流,且液相的偏流程度均小于气相。基于压降计算建立了非对称条件下气液两相流的分流模型,对气液流速对分流特性的影响进行了简单解释。     

四氢呋喃和一氟二氯乙烷水合物颗粒聚结特性

实验研究了四氢呋喃（THF）水合物和一氟二氯乙烷（HCFC-141b）水合物颗粒聚结特性,将实验得到的水合物颗粒聚结粒度分布（PSD）与正态分布、对数正态分布、伽马分布、威布尔分布拟合曲线对比,探讨了初始四氢呋喃溶液和一氟二氯乙烷溶液浓度以及搅拌速度对水合物颗粒聚结的影响,并对四氢呋喃水合物和一氟二氯乙烷水合物颗粒特性进行了对比。结果表明,四氢呋喃水合物和一氟二氯乙烷水合物颗粒聚结粒径符合对数正态分布;初始溶液浓度越低、搅拌速度越大,水合物颗粒聚结粒径越小,可以起到防治水合物颗粒聚结的作用;四氢呋喃水合物颗粒粒径是一氟二氯乙烷水合物颗粒粒径的1.3倍左右,从成浆输送的角度来说,一氟二氯乙烷水合物颗粒更易于在管道中输送。