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1.
Phoresis, a classic example of particle transport driven by thermodynamic gradients, is enjoying a resurgent research interest motivated both by technological developments and by its relevance to the motility of chemically active particles. Here we succinctly review, using the case of chemophoresis (also called diffusiophoresis), the general framework of phoresis and self-phoresis formulated as a Stokes-flow problem for a liquid solution (solvent and solute) maintained out of thermodynamic equilibrium by solute gradients. Within the constraints of local equilibrium, we discuss the simplest extension of the theory in order to account for correlations in the fluid. We show that this leads to a shift from the paradigm based on the ideal case, in that self-phoresis can no longer be represented as phoresis in a self-generated composition gradient. Our review concludes with a concise overview of a few directions which we think hold the potential to reveal a rich behavior in future investigations.  相似文献   
2.
级间加气是乙烯工业节能增产的重要手段,特别是百万吨乙烯压缩机加气量高达8倍于上游通流流量,对下游叶轮气动匹配及整机性能影响巨大。目前关于压缩机加气特性及与通流相互影响的研究鲜有报道。本文基于计算流体动力学方法,建立了通流部件与径向加气室内部流动的耦合模型,并以百万吨乙烯压缩机为研究对象,通过分析上一级通流特性、通流-加气侧流耦合特性、通流为射流的加气侧流特性,研究通流与侧流相互作用机理。结果表明:通流性能曲线的流动计算结果与压缩机选型程序结果吻合较好;侧流流量远高于通流流量时,通流为射流的加气侧流模型可替代复杂耗时的通流-侧流耦合模型。研究工作为压缩机级间加气的设计优化提供了快速准确的流动计算模型。  相似文献   
3.
The nanofluid and porous medium together are able to fulfill the requirement of high cooling rate in many engineering problems. So, here the impact of various shapes of nanoparticles on unsteady stagnation-point flow of Cu-H2O nanofluid on a flat surface in a porous medium is examined. Moreover, the thermal radiation and viscous dissipation effects are considered. The problem governing partial differential equations are converted into self-similar coupled ordinary differential equations and those are numerically solved by the shooting method. The computed results can reveal many vital findings of practical importance. Firstly, dual solutions exist for decelerating unsteady flow and for accelerating unsteady and steady flows, the solution is unique. The presence of nanoparticles affects the existence of dual solution in decelerating unsteady flow only when the medium of the flow is a porous medium. But different shapes of nanoparticles are not disturbing the dual solution existence range, though it has a considerable impact on thermal conductivity of the mixture. Different shapes of nanoparticles act differently to enhance the heat transfer characteristics of the base fluid, i.e., the water here. On the other hand, the existence range of dual solutions becomes wider for a larger permeability parameter related to the porous medium. Regarding the cooling rate of the heated surface, it rises with the permeability parameter, shape factor (related to various shapes of Cu-nanoparticles), and radiation parameter. The surface drag force becomes stronger with the permeability parameter. Also, with growing values of nanoparticle volume fraction, the boundary layer thickness (BLT) increases and the thermal BLT becomes thicker with larger values of shape factor. For decelerating unsteady flow, the nanofluid velocity rises with permeability parameter in the case of upper branch solution and an opposite trend for the lower branch is witnessed. The thermal BLT is thicker with radiation parameter. Due to the existence of dual solutions, a linear stability analysis is made and it is concluded that the upper branch and unique solutions are stable solutions.  相似文献   
4.
Electrochemical hydrogen storage in porous carbon materials is emerging as a cost-effective hydrogen storage and transport technology with competitive power and energy densities. The merits of electrochemical hydrogen storage using porous conductive carbon-based electrodes are reviewed. The employment of acidic electrolytes in such storage systems is compared with alkaline electrolytes. The recent innovations of a proton battery for smaller-scale electricity storage, and a proton flow reactor system for larger (grid)-scale storage and bulk export of hydrogen produced from renewable energy, are briefly described. It is argued that such systems, along with variants proposed by others, all of which rely on electrochemical hydrogen storage in porous carbons, can contribute to the search for energy storage technologies essential for the transition to a zero-emission global economy.  相似文献   
5.
黄孝龙  李宁  翁春生  康杨 《中国物理 B》2022,31(1):14703-014703
Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution.This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution,to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity.Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform.With simulated optical measurement using H2O feature at 7185.6 cm-1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model,this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2×10-3.This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz,and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry.This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations,which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube.  相似文献   
6.
为了研究局部凸起对边界层转捩的影响,采用转捩SST模型分别对亚临界、临界和超临界状态下带突起的圆柱绕流问题进行了数值模拟,分析了不同Reynolds数下带突起的圆柱绕流问题的近壁面流动特征以及表面时均压力与摩擦力系数的分布和凸起对圆柱表面流动分离以及转捩的影响,对比了有无凸起两侧圆柱表面时均压力、摩擦力系数的不同. 结果表明:当来流Reynolds数处于临界区时,气流在圆柱上表面凸起处形成了3个反向旋转的漩涡,之后随着θ的增大,发生了流动分离和流动转捩现象;对于不同Reynolds数下的来流,圆柱上表面的凸起可以使气流发生转捩的位置提前;圆柱上表面的凸起使流速增大、压强降低,从而导致圆柱产生升力,随着来流Reynolds数的增大,其升力逐渐变大.   相似文献   
7.
Modern convection-based supports differ substantially in pore size, porosity, and microstructure topology. Due to such variability, it is challenging to evaluate the contribution of a particular microstructure topology on flow resistance. We demonstrated that the flow resistance parameter (ϕ $\phi $) introduced decades ago can be used as a criterion to evaluate the effect of microstructure topology on a pressure drop when the pore size is used as a characteristic support dimension. Furthermore, the ϕ $\phi $ value of simple cubic packing was calculated over the entire range of open porosity and compared to the ϕ $\phi $ values determined for pressure drop models derived for particular convection-based supports and experimental values of various convection-based supports from the literature. It was shown that different convection-based supports become clustered into distinct groups when plotted according to their ϕ $\phi $ and open porosity values, allowing their discrimination.  相似文献   
8.
项目投资与融资匹配程度,不仅关系到项目资金成本的大小,还体现对项目利率风险的对冲。基于债券久期的概念内涵,提出了项目久期与融资结构久期的概念及计算方法。以具体项目的投融资为案例进行研究,对案例公司已拟定的针对独立项目的债券融资方案进行投融资久期匹配、各期现金流匹配评价,并从市场利率曲线中发现融资成本优化空间,从投融资久期差及各期投融资现金流量差中找到优化融资的方案。以此提出结论:项目久期与融资结构久期的匹配是降低项目利率风险的重要手段;应综合融资结构久期与项目久期、现金流大小选择融资结构。  相似文献   
9.
Zhong-Yu Li 《中国物理 B》2022,31(4):40502-040502
Accurate prediction of road traffic flow is a significant part in the intelligent transportation systems. Accurate prediction can alleviate traffic congestion, and reduce environmental pollution. For the management department, it can make effective use of road resources. For individuals, it can help people plan their own travel paths, avoid congestion, and save time. Owing to complex factors on the road, such as damage to the detector and disturbances from environment, the measured traffic volume can contain noise. Reducing the influence of noise on traffic flow prediction is a piece of very important work. Therefore, in this paper we propose a combination algorithm of denoising and BILSTM to effectively improve the performance of traffic flow prediction. At the same time, three denoising algorithms are compared to find the best combination mode. In this paper, the wavelet (WL) denoising scheme, the empirical mode decomposition (EMD) denoising scheme, and the ensemble empirical mode decomposition (EEMD) denoising scheme are all introduced to suppress outliers in traffic flow data. In addition, we combine the denoising schemes with bidirectional long short-term memory (BILSTM) network to predict the traffic flow. The data in this paper are cited from performance measurement system (PeMS). We choose three kinds of road data (mainline, off ramp, on ramp) to predict traffic flow. The results for mainline show that data denoising can improve prediction accuracy. Moreover, prediction accuracy of BILSTM+EEMD scheme is the highest in the three methods (BILSTM+WL, BILSTM+EMD, BILSTM+EEMD). The results for off ramp and on ramp show the same performance as the results for mainline. It is indicated that this model is suitable for different road sections and long-term prediction.  相似文献   
10.
The authors consider the short time existence for Ricci-Bourguignon flow on manifolds with boundary. If the initial metric has constant mean curvature and satisfies some compatibility conditions, they show the short time existence of the Ricci-Bourguignon flow with constant mean curvature on the boundary.  相似文献   
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