Laminar nanofluid flow in microheat-sinks

In response to the ever increasing demand for smaller and lighter high-performance cooling devices, steady laminar liquid nanofluid flow in microchannels is simulated and analyzed. Considering two types of nanofluids, i.e., copper-oxide nanospheres at low volume concentrations in water or ethylene glycol, the conjugated heat transfer problem for microheat-sinks has been numerically solved. Employing new models for the effective thermal conductivity and dynamic viscosity of nanofluids, the impact of nanoparticle concentrations in these two mixture flows on the microchannel pressure gradients, temperature profiles and Nusselt numbers are computed, in light of aspect ratio, viscous dissipation, and enhanced temperature effects. Based on these results, the following can be recommended for microheat-sink performance improvements: Use of large high-Prandtl number carrier fluids, nanoparticles at high volume concentrations of about 4% with elevated thermal conductivities and dielectric constants very close to that of the carrier fluid, microchannels with high aspect ratios, and treated channel walls to avoid nanoparticle accumulation.     

对微型构造的点滴新认识

本文论述微型结构研究取得的一些新认识，说明小阶地属斜面微型构造，不是正向微型构造；指出在构造平缓，井网密度又很大的油田，一些低幅底微型结构，油井生产受动态因素影响很明显。     

Sensitivity analysis of shock wave Burgers’ equation via a novel algorithm based on scale-3 Haar wavelets

In this paper, a novel technique is being formulated for the numerical solutions of Shock wave Burgers' equations for planar and non-planar geometry. It is well known that Burgers' equation is sensitive to the perturbations in the diffusion term. Thus we use robustness of wavelets generated by dilation and translation of Haar wavelets on third scale to capture the sensitivity information. The present approach is an improved form of the scale-2 Haar wavelet method. The scheme is based on the forward finite difference scheme for time integration, scale-3 Haar wavelets for space integration and the nonlinearity has been tackled via quasilinearzation technique. Through scale-3 Haar wavelet analysis once the wavelet coefficient is calculated then we can compute the solutions at near the perturbation point. The computation cost of the present scheme is negligible. The proposed method is tested on six test problems to check its computational efficiency where the convergence analysis of scale-3 Haar wavelet method is the proof of our computational arguments.     

Gas-liquid dispersions in structured packing with high-viscosity liquids

Gas holdup in bubble columns containing structured packing was determined for varying liquid phase viscosity and different construction materials of the packing. Three columns, containing packing made from smooth nickel plate, perforated nickel plate and plastic sheets, respectively, were tested. The gas holdup in a column with no internals was also measured for comparison purposes. The effect of viscosity on gas holdup was studied by using water, aqueous glycerol and aqueous CMC solutions as the liquid phase; some of the solutions showed non-Newtonian behavior.The experimental results of gas void fraction were correlated in terms of superficial gas velocity and liquid viscosity through a simple homographic expression. The geometric characteristics of the structured packings were found to influence gas holdup, thus yielding slightly different equations for each structured packing. This effect is discussed in detail. Nevertheless, for engineering purposes a single equation representing all the data is also proposed, which permits the prediction of gas holdup in structured packing with sufficient accuracy.     

Enhanced energy storage performance of eco-friendly BNT-based relaxor ferroelectric ceramics via polarization mismatch-reestablishment and viscous polymer process

In this work, we synthesized a novel and eco-friendly relaxor ferroelectric system, i.e., (1?x)(0.8Bi_0.5Na_0.4K_0.1TiO₃-0.2SrTiO₃)-xNaNbO₃ (BS-xNN) ceramics with x = 0.1–0.4 based on a solid state reaction technique. The structural, microstructural, dielectric as well as ferroelectric characteristics of BS-xNN ceramics were comprehensively examined. According to our findings, the Ti–O coupling reduces as the NN content increases, while the Nb–O coupling strengthens, leading in a nano-scale polarization mismatch-reestablishment process that enhances energy storage performance. Because of the reduction in thickness and porosity, the viscous polymer process significantly increases the breakdown strength of ceramic samples. More crucially, at 260 kV/cm, 0.6BS-0.4NN ceramics have an ultrahigh recoverable energy storage density W_rec of 4.44 J/cm³ and a high energy storage efficiency η of 81.8%. Furthermore, thermal stability of energy storage performance is also identified across a wide temperature range of 30 °C from 140 °C at 215 kV/cm. The higher performance of energy storage not only indicates the feasibility of our technique, but also serves as a model for the manufacturing of high-quality dielectric ceramics with a wide range of industrial applications.     

Isothermal Drying of Pore Networks: Influence of Friction for Different Pore Structures

An existing network model for isothermal drying of capillary porous media is extended to account for viscosity in the liquid phase so that it is no longer restricted to structures with large pores. Modeling challenges and solution methods are presented in detail. The model is compared with a bundle of capillaries model of drying. Finally, simulation results for two-dimensional pore networks with mono-modal and bimodal pore structure are shown and discussed.     

FIVE-SPOT INJECTION/PRODUCTION WELL LOCATION DESIGN BASED ON FRACTURE GEOMETRICAL CHARACTERISTICS IN HEAVY OIL FRACTURED RESERVOIRS DURING MISCIBLE DISPLACEMENT: AN EXPERIMENTAL APPROACH

Mapping fracture characteristics by using seismic acquisition and processing is important not only to identify sweet spots, but also to optimize production, especially for unconventional heavy oil reservoirs. In this experimental work we used five-spot micromodels initially saturated with heavy oil to find the optimum well locations during first-contact miscible displacement. The experiments were performed at a fixed injection rate on fractured micromodels with various patterns. The optimum location for injection/production wells was found in the pattern where fractures make an angle of 45° with the mean flow direction. Moreover, oil recovery was increased with the density, length, level of scattering, and discontinuity of fractures. The analysis of the experimentally measured recovery curve revealed that there are three distinct stages for each displacement. The efficiency of the first stage was found to be dominated by dispersion and diffusion. However, the recovery of the second stage was significantly affected by the fracture orientation. The displacement efficiency of the third stage was controlled by solvent dispersion, which is at maximum for the pattern with higher density, length, scattering, and discontinuity of fractures. Saturation monitoring showed that the fracture geometrical characteristics strongly affected the splitting, spreading, and shielding of the produced fingers and solvent front shape and consequently affected the recovery factor. As a result, five-spot micromodels can be used to investigate the optimum location of injection/production wells during miscible displacements in fractured heavy oil reservoirs.     

Flow-guided sieve-valve tray (FGS-VT) – A novel tray with improved efficiency and hydrodynamics

Flow-guided sieve tray (FGST) has been widely used as column internal for mass and energy transfer between gas and liquid, or liquid and liquid, due to its low pressure drop, high efficiency, and high capacity. But as sieve tray, improving the operation flexibility is the urgent task which has to be resolved. Flow-guided sieve-valve tray (FGS-VT) was designed to overcome the shortcoming of FGST by putting some valves onto the FGST, which do not change the original structure before the valves are open. Comparison of the hydrodynamic and mass transfer performances of FGS-VT, FGST, and Glitsch V1 valve tray was done, using air–water–oxygen system in a 0.6 m diameter plexiglass column, and the mathematical model of dry-plate pressure drop for FGS-VT was established. The results showed that the FGS-VT has higher operation flexibility and tray efficiency than FGST and Glitsch V1 valve tray.     

阻燃PLA共混物的流变性能

利用毛细管流变仪研究了新型无卤阻燃剂对聚乳酸(PLA)流变性能的影响。结果表明:无卤阻燃剂对PLA起到了增塑作用,使PLA熔体的流动性能有所改善。当无卤阻燃剂用量为5%时,熔体非牛顿指数n趋近于1牛,顿性增加;熔体的黏流活化能△E和结构黏度指数△最小。