Inhibited radiation transmittance and enhanced thermal stability of silica aerogels under very-high temperature

Silica aerogels are applied extensively in thermal insulation due to their extra-low density and thermal conductivity. However, this can be heavily undermined under high temperature, especially beyond 700–800 °C, due to not only a high transparency for radiation heat transfer, but also an instability caused by nanoparticle collapse. The present study demonstrated a solution to this problem by two steps. Firstly, the size effect of nanoparticles is explored by experimentally preparing unconventional samples composed of large-diameter particles (larger than 20 nm). The prepared sample microstructures and radiative characteristics are investigated by SEM apparatus and FTIR measurements, respectively. Additionally, based on the fractal structures reconstructed using the Diffusion-Limited Colloid Aggregation (DLCA) method, the effects of particle size on thermal stability of silica aerogels are theoretically investigated and the light shielding performance is numerically analyzed by the Generalized Multiparticle Mie-solution (GMM) method. The simulation and experimental results indicate that the enhanced size of nanoparticles can improve the radiative inhibition and thermal stability property under high temperature significantly. However, the ideal above should be refined as it brings an increasing contribution of conduction heat transfer. Thus, a novel structure of core-mantle nanoparticle is proposed to retain the excellent resistance in radiation but avoid an increased thermal conduction. The present work may pave a new direction for developing aerogels under extreme temperature conditions, compared with the widely-used opacifier addition.     

Entropy optimized CNTs based Darcy-Forchheimer nanomaterial flow between two stretchable rotating disks

Here entropy optimized CNTs based flow of viscous liquid is addressed between two stretchable surfaces of disks. Both upper and lower disks stretch and rotate with different rates and angular frequencies. Carbon nanotubes (single and multi-walls) are considered as a nanoparticles and water as continuous phase liquid. Xue model is utilized in the mathematical modeling for the transport of nanoparticles. Energy expression is developed through first law of thermodynamics and discussed in the presence of viscous dissipation. Main attention is given to the modeling of entropy generation subject to CNTs nanoparticles. Total entropy rate is calculated. Average residual error is calculated through implementation of optimal homotopy analysis method. Flow parameters are graphically discussed for both single and multi-walls carbon nanotubes. Furthermore, engineering quantities like skin friction and Nusselt number are numerical calculated and discussed through Tables. From obtained outcomes it is examined that entropy rate boosts up versus larger Brinkman number and nanoparticles volume friction. No such attempt is yet done by the researchers on entropy optimized Darcy-Forchheimer CNTs based nanomaterial flow between two rotating disks. The obtained outcomes are compared with published literature and found good agreement.     

Effect of Friction and Wear on Formation of Polysiloxane Films at Iron Oxide Surface in Viscous Couplings

Friction tests were conducted with silicone fluids containing iron oxide particles to investigate the effects of friction and wear on the formation of a micro-gel in viscous couplings. Polysiloxane films were formed on the surface of iron oxide particles as sliding distance increased. The relative viscosity of the particle dispersion increased as well. Frictional heat had a significant effect on the formation of polysiloxane films which had an abundance of cross-linking and terminal trimethyl structures of polydimethyl siloxane. The iron oxide surface was indicated to participate in the tribo-chemical formation of polysiloxane films. A model anti-wear agent suppressed the increase in relative viscosity with less polysiloxane films formed on the surface of the iron oxide. The metal-to-metal contact between adjacent VC plates most likely generates chemically active iron oxide surfaces with frictional heat and wear, which promotes the formation of the polysiloxane film on the surface, leading to the micro-gel.     

地下水热催化裂化降粘开采稠油新技术研究

针对辽河油田的3种稠油,筛选陋一种合适的水热裂解催化剂（过渡金属盐）,确定了水热裂解的最佳条件,在0．2％该催化剂顾在下,3种稠油样在240℃经水热裂解反应24h后,50℃粘度分别下降89．9％－77．7％,饱和烃和芳香烃含量大幅上升,胶质,沥青质含量下降,烃碳数分布移向低碳数方向,产生大量气体和少量固体,在辽河油田曙光采油3口蒸汽吞吐井进行的地下稠油催化剂水热裂解降粘开采现场试验获得成功,采出的稠油粘度大同度降低。     

Spectral and Haar wavelet collocation method for the solution of heat generation and viscous dissipation in micro-polar nanofluid for MHD stagnation point flow

The aim and significance of paper presents, the semi-numerical investigation of magnetohydrodynamic flow of micropolar nanofluid with stagnation point is carried out under the influence of viscous dissipation and heat generation. The micropolar nanofluids are electrically conducting non-Newtonian fluids. The important applications of these fluids are observed in many research areas viz. bioengineering, biofuels and biomedical sectors etc. The appropriate similarity transformations are used to transform the governing equations into system of coupled nonlinear ordinary differential equations and are solved by using shifted Chebyshev collocation method and Haar wavelet collocation method. The variations in velocity, angular velocity, temperature and concentration profiles under the impact of various physical parameters, characterizing the flow field are discussed and are presented via graphs and tables. Temperature enhancement occurs with increment in each parameter except for Prandtl number. The concentration near the surface decreases with increment in the values of parameters and gradually it increases, except for Prandtl number and Schmidt number. The reverse trend of heat transfer occurs​ near a surface, when the dominance of stream velocity over stretching velocity is observed.     

油层矿物对蒸汽作用下稠油组成与粘度变化的影响

实验考察了辽河田曙光采油厂的两种稠油在有和无油层岩心存在时水热裂解反应产物的差别,裂解反应温度240℃,反应时间24小时,油层岩心岩石矿和粘土矿物组成已知,作为对照,还考察了相同条件下的热裂解反应产物。实验结果表明该油层矿物对低含硫稠油的水热裂解有催化作用,与单纯水热裂解结果相比,有油层矿物参与的水热裂解使两种稠油的饱和烃芳香烃组分含量增加,胶质,沥青质组分含量减少,稠油平均相对分子质量略有下降,沥青质组分的平均相对分子质量有较大幅度下降,气体（H2,C1－C3烷烃,CO2及H2S）生成量增加,两种稠油的粘度（初始值88．5和124．3Pa.s)在水热裂解后分别下降13．4％和10．6％,在油层矿物参与下水热裂解后则分别下降25．6％和23．4％,这一实验研究结果有助于研制高效的稠油水热裂解催化剂。     

甘油聚醚型注汽前预处理剂GYG的研究与应用

本文介绍了甘油聚醚型注汽前预处理剂的组成及机理，室内实验研究和现场应用情况。该剂在锦州采油厂不同稠油区块现场试验12口井，取得了良好效果。