努森压缩制冷系统的设计及性能分析

分别以氨、水、R290和R600a为工质设计了努森压缩制冷系统。系统结构尺寸受工质的分子直径和宏观物性影响,其中依靠微尺度热流逸效应工作的努森压缩机设计成由两个功能组组成并采用多级串联形式。根据努森压缩制冷系统的微观与宏观工作机制和系统构建方式建立了性能分析模型。努森压缩制冷系统的运行特性类似于压缩机转速可调的常规蒸气压缩制冷系统,其COP随室内温度升高(或环境温度降低)而增大、制冷量随室内温度升高(或环境温度降低)而减小。综合考虑系统结构、性能、成本等因素,水为工质的努森压缩制冷系统明显优于其它3种工质系统。若按一次能源效率计算,努森压缩制冷的COP与常规蒸气压缩制冷的相差不大,加之其具有可直接利用太阳能和余(废)热资源、且没有运动部件等优点,努森压缩制冷是一种具有发展前景和竞争力的新型制冷方式。     

Characterization of extensional rheological filament stretching with a dual‐mode Giesekus model

A new, simple, formulation that describes capillary thinning as predicted by a two‐mode Giesekus model is derived, and its application in analyzing data from extensional rheometry (capillary thinning) experiments is discussed. An algorithm is presented that can be used to fit the expressions obtained from the Giesekus model to extensional rheometry data. Examples of data fitting are given for an idealized data set, for measurements obtained for aqueous solutions of 6 wt % 900,000 molecular weight polyethylene oxide, and for biological fluids obtained from pitchers of Nepenthes Rafflesiana. Good fits to the data were obtained, with coefficients of determination in excess of 0.98. For each data set, it was possible to calculate values of extensional viscosity and relaxation time for each of the two modes, allowing quantitative comparison of different fluids or of the same fluid as it ages. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2188–2199, 2016     

重卡驾驶室半主动悬置控制方法

为了抑制在路面激励下某型重卡驾驶室的振动加速度响应,研究基于磁流变阻尼器驾驶室半主动悬置系统的控制方法。建立了重卡驾驶室半主动悬置集中质量动力学模型,分别采用比例积分微分(proportion integration differentiation,简称PID)控制理论和模糊最优控制理论设计控制器,并利用磁流变阻尼器动力特性实验数据对模糊最优控制器的参数进行优化。以驾驶室质心垂直、侧倾及俯仰3个方向加速度为控制目标,利用ADAMS/Simulink联合仿真方法,对比分析PID控制和模糊最优两种控制策略与被动状态下重卡驾驶室悬置振动控制效果。针对实际重卡进行不同速度路面激励下的振动控制实验。仿真和实验结果表明,采用PID和模糊最优控制方法均能有效抑制重卡驾驶室半主动悬置的振动加速度响应,其中模糊最优控制效果总体优于PID控制。     

Synthesis and Evaluation of Bis-quaternary-Based Surfactants as Additives for Water-Based Mud

Two series of cationic gemini surfactants, alkanediyl-α,ω-bis[N,N-dimethyl alkyl (octyl or dodecyl)ammonium] dibromide (R-s-R; s = 6, 10, 12 and R = 8 and 12) were prepared and evaluated as additives for water-based mud. The chemical structures of the prepared surfactants were confirmed using FTIR and mass spectroscopy. Surface activity of these compounds has been studied and their surface properties including surface tension, emulsification power, critical micelle concentration, effectiveness, maximum surface excess and minimum surface area were determined. The results showed that the prepared compounds have significant surface activity, especially those of longer hydrophobic chain length. The prepared cationic gemini surfactants were evaluated as viscosifiers and filter loss additives for water-based mud formulated from local Na-montmorillonite clay. XRD analysis was carried out to the Na-montmorillonite clay to determine the interaction of the surfactants with inter layers of the clay structure. Rheological properties, gel strength, thixotropy, filtration properties and the effect of temperature on rheological properties of the water-based mud were studied. The results indicated that the gemini surfactants have a positive effect on the rheological and filtration properties of the Na-montmorillonite clay according to American Petroleum Institute specifications.     

Ideality analysis and general laws of bubble swarm microflow for large-scale gas-liquid microreaction processes

The flow ideality of bubbly microflow remains unclear even though it is vital for the design of microreactors, especially the ideality of bubble swarm microflow for large-scale gas-liquid microreaction processes. This work is the first time to report the ideality analysis of the microbubble swarm in a relatively large microchannel. The bubble swarm microflow has undergone two conditions: quasi-homogeneous plug flow and liquid phase/gas-liquid quasi-homogeneous phase two-phase laminar flow. Both the deviations of void fraction and bubble velocity from the ideal plug flow can divide into two parts, and the two transition points simultaneously happen at the velocity ratio of 1.25. There exists a critical capillary number to maintain the quasi-homogeneous plug flow, which could be regarded as the general laws for the design of gas-liquid microreactors. Finally, a novel model is developed to predict the bubble velocity. This work could be very helpful for the large-scale gas-liquid microreactors design.     

剪切稀化流体中微粒子聚集行为研究

在化工过程、生物工程等领域中,实现颗粒分离至关重要。通过整合微流控技术、高速显微图像采集技术和数字图像处理技术,探究微粒尺寸、通道流量和液相流变特性对微粒聚集的影响规律。结果表明,在剪切稀化流体羧甲基纤维素钠(CMC)水溶液中,随着通道流量和颗粒粒径增大,微颗粒聚集位置逐渐向剪切速率较高的一侧偏移;随着CMC质量分数增加,聚集位置不断向剪切速率较低的一侧偏移。利用求解的幂律型剪切稀化流体速度和剪切速率方程,结合对微颗粒的受力分析,证明稠度系数越大,聚集位置越偏向剪切速率较低处;剪切稀化特性越强,聚集位置越偏向剪切速率较高处,说明在幂律型剪切稀化流体中的黏度变化是微颗粒发生特殊迁移聚集行为的一个重要原因。     

Effect of Temperature and Relative Humidity on Friction and Wear Properties of Silicone-Based Magnetorheological Elastomer

In this study, the effect of varying temperature and humidity on the friction and wear properties of a silicone-based isotropic magnetorheological (MR) elastomer were examined with an applied magnetic field. Specifically, MR elastomer specimens were fabricated, and a temperature- and humidity-adjustable reciprocating friction tester was employed. The results indicated that the friction coefficient decreased across all tests when a magnetic field was applied. The friction coefficient increased when the temperature increased and slightly decreased following an increase in relative humidity. The wear depth results also exhibited an increasing pattern as the temperature increased and a decreasing pattern when the relative humidity increased. The surface state experienced significant changes under varying temperatures and relative humidity conditions with and without a magnetic field.     

Time‐series and extended Karhunen–Loève analysis of turbulent drag reduction in polymer solutions

Direct numerical simulations and statistical analysis techniques are used to study the drag‐reducing effect of polymer additives on turbulent channel flow in minimal domains. Additionally, a new formulation of Karhunen–Loève decomposition for viscoelastic flows is introduced, allowing the dominant features of the polymer stress fields to be characterized. In minimal channels, there are intervals of “active” and “hibernating” turbulence that display very different structural and energetic characteristics; the present work illustrates how the statistics of these intervals evolve over the entire range of drag reduction (DR) levels. The effect of viscoelasticity on minimal channel turbulence is twofold: first, it strongly suppresses the active turbulent dynamics that predominate in Newtonian flow and second, at sufficiently high Weissenberg number it stabilizes the dynamics of hibernating turbulence, allowing it to predominate in the maximum drag reduction regime. In this regime, the stress fluctuations become delocalized from the wall region, encompassing the entire flow domain. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1460–1475, 2014     

Control of the permeability of a porous media using a thermally sensitive polymer

Experiments explore the reduction in permeability of a porous bead pack when a suspension of thermally responsive polymer is injected and the temperature then increased above the thermal activation temperature. The change in permeability is greater with higher polymer concentration, provided that the ionic concentration of the solution is sufficient for floc formation. The time for activation of the blocking effect is within tens of seconds to minutes of when the polymer solution is heated. This is consistent with the timescale for diffusion‐limited aggregation, although the detailed value depends on the geometry and polymer concentration. Dynamical experiments demonstrate that once the porous media is blocked, adding additional polymer has no effect. The mechanism for permeability reduction may be modeled in the context of a pore‐network model, and we build a simple model to illustrate the permeability reduction as a function of the fraction of pores links which are blocked. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1193–1201, 2014     

Oscillatory shear rheology of dilute solutions of flexible polymers interacting with oppositely charged particles

Fluids with both attractions and repulsions among its constituents can exist in multiple states depending on nature of the interactions. An external flow can induce such systems to transition between the different states, such as the globule‐stretch transition for polymers in poor solvents. Brownian dynamics simulations of a dilute solution of polymers and colloids interacting via short‐ranged potentials are presented. For some values of the strength and range of interactions, compact structures of polymers and colloids are formed. An external flow is capable of pulling these globules apart, causing the polymers to stretch at a critical shear rate. In oscillatory shear, the shear rate can cycle between being above and below this critical shear rate leading to interesting dynamics. These dynamics are quantified using the rheological response in large amplitude oscillatory shear. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1365–1371, 2014