Self-oscillation mechanism of necking on extension of polymers

A new phenomenon in necking of some polymers, including poly(ethylene terephthalate) (PETP) was detected. It was found that extension of PETP films under certain conditions results in periodic stress oscillations and a periodic change in appearance of the sample. The conditions at which self-oscillations appear have been determined, and the principal regularities of this regime of deformation are described. The following factors are critical for the appearance of self-oscillation: speed of straining and compliance of the sample. The self-oscillation of stress and formation of the periodic transverse bands is attributed to heat dissipation during necking corresponding to local temperature jumps and periodic strong variation of elasticity modulus due to poor heat conductivity of the polymer. Changing the external conditions of heat transfer influences the possibility and development of the effect. The phenomenon is common for various crystallizing polymers, being dependent on physical properties of the polymer and conditions of deformation.     

Effect of surface on the thermodynamic properties of polar liquids and liquid crystals trapped in a porous medium

The heat capacity of some polar liquids (2,6-lutidine, aniline and nitrobenzene) and liquid crystals (nitrophenyldodecyloxybenzoate and dodecylcyanobiphenyl) trapped in glass and nickel porous matrices have been measured by using a high-resolution adiabatic calorimeter. A decrease in the molar heat capacity of substances trapped in porous media compared with the bulk molar heat capacity was observed. A new phenomenon caused by the effect of the glass surface on the confined fluid was revealed. This phenomenon was manifested as an unusual behaviour of the heat capacity versus temperature curve (a ‘crevasse’ in a curve). In addition, we observed the nematic phase of dodecylcyanobiphenyl liquid crystal induced by the variable curvature of the glass matrix surface.     

Full Analysis of Internal Adsorbate Redistribution in Regenerative Adsorption Cycles

Adsorption cycles with heat regeneration are a promising CFC-free alternative to compression cycles, for refrigeration or heat pumping purposes. However, the process is complex and therefore requires efficient analysis tools to understand correctly. These tools are now developed and used here for studying the phenomenon of internal adsorbate redistribution. This phenomenon takes place during the periods when the adsorber is pressurised, or depressurised, under globally isosteric conditions. It can be easily thought that internal adsorbate redistribution reduces the cycle performance. In order to avoid this reduction, the adsorbate redistribution can be reduced by implementing separate vapour compartments inside the adsorbers, which also requires the installation of additive check valves between the adsorber, condenser and evaporator.The present study shows that, in fact, this phenomenon does not affect performance. In addition, thanks to the different analysis tools, a physical explanation of this result, based on first and second laws of thermodynamics is developed. This result is then valid for any heat regenerative cycle using an adsorption pair.     

DSC-TG studies of coal structure modification by the inert gas helium

The influence of the inert gases helium and argon on the thermal properties of coal have been studied using DSC and TG. The coals studied were high-volatile bituminous coal and anthracite. It has been stated that the heat capacity of coal is strongly influenced by helium. This phenomenon is especially distinct for high-volatile bituminous coal. The authors attempt to explain this phenomenon.     

氨基酸与蛋白质体系热容研究

氨基酸与蛋白质都是生命现象和分子生物学研究的最基本和最重要的研究对象.利用热力学方法,特别是从热容的角度出发对其研究,对深入了解蛋白质的折叠与伸展、变性机理、稳定性及生命体的新陈代谢等问题均具有一定的意义.近年来,研究者们对蛋白质或氨基酸体系的热容研究做了大量工作,取得了很大进展,本文对此进行了概述。     

THERMODYNAMIC PROPERTIES OF THE DISSOLUTION OF FATTY ACID SALTS IN WATER*

The enthalpy, entropy and heat capacity change of the dissolution of calcium and barium laurates, myristates and palmitates were determined by reaction calorimetry and by solubility at different temperatures. Heat capacity change, due to water restructuring or "iceberg" formation, was found to increase with the chain length. Linearity was observed up to 12 C-atoms in the chain, while the dissolution of chains with 16 C-atoms was accompanied by a significantly higher increase in the heat capacity than it would be expected. This phenomenon was explained on the basis of synergistic effect, i.e. by mutual promotion in the water restructuring.     

A lubricated stagnation point flow of nanofluid with heat and mass transfer phenomenon: Significance to hydraulic systems

The improved thermal association of heat transfer is considerably observed due to interaction of nanoparticles in recent days. The lubrication phenomenon with heat and mass transfer effects plays a key role in the hydraulic systems. In current research, the thermal impact of nanofluid over a lubricated stretching surfaces near a stagnation point analytical has been studied. A thin layer of lubricating fluid with a variable thickness provides lubrication. The inspection of thermophoresis and Brownian motion phenomenon is illustrated via Boungrino model. The analytical finding of refurbished boundary layer ordinary differential equations is obtained by a reliable and proficient technique namely variational iteration method (VIM). The Lagrange Multiplier is a potent tool in proposed technique to reduce the computational work. In addition, a numerical comparison is presented to show the effectiveness of this study. The range of flow parameters is based on theoretical flow assumptions. Physical inspection of involved parameters on velocities, temperatures, concentrations, and other quantities of interest when lubrication is presented. The current results present applications in polymer process, manufacturing systems, heat transfer and hydraulic systems.     

聚醚氨酯薄膜表面性质的反相色谱法研究

本文报道了用反相色谱法研究多嵌段聚醚氨酯与几种低分子化合物的相互作用,测定了表征相互作用的热力学参数。结果表明,由ESCA证明表面软段富集的聚醚氨酯的反相色谱行为主要决定于富集层与探针分子的相互作用;苯及几种烷烃和聚醚氨酯的偏摩尔混合热和它的溶度参数与软段组分的溶度参数差值有关。     

Pt-Au合金团簇热力学性质分子动力学模拟研究

采用分子动力学方法和原子嵌入法模型势模拟了Pt原子和Au原子合金纳米团簇的熔化过程,研究了这些金属原子纳米团簇熔点与团簇组分的关系,发现不同组分纳米团簇的熔点不是单调变化的,同时均出现了负热容现象.通过对各种团簇溶化前后结构的比较研究,分析了导致这种现象的原因.     

Application of a Direct Cooling Method in the Cationic Polymerization of Isobutylene

Inspired by the Leidenfrost phenomenon, a direct-cooled, general-purpose, low-temperature reactor has been developed and its applicability for polymerization was demonstrated. The Leidenfrost reactor is efficiently cooled by introducing relatively inexpensive liquid N₂, (LN₂), directly into the bulk of polymerization charges; the rapid evaporation of the coolant chills the system. The gaseous N₂, generated provides an inert gas blanket that protects moisture- and/or air sensitive charges. The installation of expensive cooling jackets or coils is superfluous and stirring is optional. The virtually complete recovery of cooling energy is possible. In the Leidenfrost reactor, the LN₂, heat sink is virtually in contact with the heat source so that the path of heat transfer is practically nil.     

Heat transfer intensification in microchannel by induced-charge electrokinetic phenomenon: a numerical study

Journal of Thermal Analysis and Calorimetry - In this numerical investigation, the induced-charge electrokinetic phenomenon is used to intensify the convective heat transfer rate in the...     

In-depth analysis of the mathematical model of polyester thermosets curing

In many areas of chemical engineering applications we have to deal with thermosetting polymer structures. One of the major processing techniques for producing such structures is the curing process. This process may be accompanied by undesirable thermal spiking phenomena during which the released energy may be trapped inside the structure. In order to predict the onset of this phenomenon models that couple reaction kinetics and heat transfer are required. The numerical model was constructed by taking into account the heat transferred by conduction through the resin, as well as the kinetics of heat generated by the cure reaction. The contributions to the rise in temperature from heat conduction and chemical reactions are different in different parts of the composite, which can be explained by the temperature–time, or conversion-time histories. The temperatures were measured in the center of a cylindrically shaped mold. Initiator concentration varied from 0.5% to 2.0% of mass fraction throughout the experiments, which governed the reaction kinetics. Introduction of the carbon base filler reduced the amount of heat generated in the composite, and as a result lowered the temperatures of the resin. The analysis of parameter sensitivity and model simulation was performed with data obtained. A good agreement was observed between experimental data and the mathematical model of the curing process in the mold.     

The impact of monocity and hybridity of nanostructures on the thermal performance of Maxwellian thin-film flow with memory and Darcy–Forchheirmer effects

Journal of Thermal Analysis and Calorimetry - This article considers viscoelastic effects on the enhancement of transportation of heat in thin-film flow when the relaxation time phenomenon is...     

The solution of Pennes' bio-heat equation with a convection term and nonlinear specific heat capacity using Adomian decomposition

Journal of Thermal Analysis and Calorimetry - Pennes' bio-heat equation is the most widely used equation to analyze the heat transfer phenomenon associated with hyperthermia and cryoablation...     

Liquid–liquid transition in polymers and glass-forming liquids

It is shown that many simple glass-forming liquids exhibit a phenomenon known in the area of polymer science as the liquid–liquid transition. The phenomenon manifests itself as a third-order transition in the equilibrium liquid-specific heat data around approximately 1.2 T_g and also as a bifurcation of the liquid relaxation into primary and secondry processes. It is stressed that the above phenomenon is due to a smooth changeover of the liquid from one dynamic regime to the other and hence is not due to any real phase transition. It is suggested that a liquid cluster kind of picture for the supercooled liquid regime, is capable of explaining the above phenomenon and is consistent with observation made on polymers and monomeric liquids. © 1993 John Wiley & Sons, Inc.     

Experimental Setup for Studying the Chain Activation of Low-Temperature Boiling Sites in Superheated Liquid Droplets

An experimental setup for the realization of chain activation of the boiling sites in superheated liquid droplets is described. Previously, this phenomenon was observed only in experiments on heat transfer upon the boiling of emulsions containing low-boiling dispersed phases. The data obtained are discussed in terms of a previously proposed model, in which the boiling sites are the flocs that are composed of several colloidal-size particles and adsorb the gas dissolved in the liquid.     

Morphology and strain rate effects on heat generation during the plastic deformation of polyethylene/carbon black nanocomposites

The phenomenon of internal heat generation during the plastic deformation of polyethylene/carbon black nanocomposites at high strain rates was investigated using a high resolution thermal camera. Material morphology, strain rate and carbon black (CB) content were found to be critical factors that affected heat generation during tensile testing, and consequently changed the mechanical behaviour. Two processing methods (M1 and M2) were used to prepare the materials, with CB contents of 0.5, 1 and 3 wt.%. The results showed a significant increase in internal heat generation after yielding, with temperatures exceeding 70 °C for materials processed using M1 and 55 °C for materials processed using M2. The temperature increase was dependent on the processing method, the CB content and the strain rate. The increase in temperature due to plastic heat generation affected the properties of the material, reducing the plastic hardening and reducing the tensile strength at high strain rates. This is of significance when considering the use of these materials in applications involving high strain rates, such as impact protection.     

高温下甲苯在不同去阳离子丝光沸石上的吸附性质和表面反应

用脉冲色谱法测量了不同交换度的NaHM上甲苯的吸附热,並用动态法测量了程序升温脱附和反应。结果表明:吸附量小于5微升/克,交换度小于32％时,主要显示Na⁺中心的吸附性质。其吸附热基本上不随交换度变化。交换度大于32％时,在H⁺中心上的吸附渐趋显著,吸附热也随交换度的增加而渐次下降。 比保留体积随交换度变化的曲线在交换度为32-41％处有极大值。通过吸附熵的计算认为这可能与交换过程中主孔道阳离子空间位阻的下降有关。     

High Pressure Calorimetry. Comparison of two systems (differential vs. single cell). Application to the phase change of water under pressure

In high pressure calorimetry the pressure change is used to obtain the desired phenomenon (i.e. phase change) at constant temperature. Two high pressure calorimeters have been developed to measure the latent heat of fusion of pure water (hexagonal ice-type I) at subzero temperature. Both calorimeters used a constant pressurisation rate produced with a high pressure pump driven by a step motor. The first calorimeter was a single cell calorimeter where mercury acted as the pressurisation fluid, while the second one was differential (two cells) and was pressurised with pentane. Both calorimeters gave high accuracy data of latent heat of fusion of pure water, which were determined taking into account that either the fluid used to pressurise or the pressurisation rate affected the calorimetric signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

有机硅改性聚氨酯的合成与性能

在无溶剂条件下利用二步法合成了一系列氨基硅油改性聚氨酯,采用红外光谱对预聚体进行了表征,同时测试了材料的力学性能、耐热性、表面水接触角及微观形态,结果表明,改性后的聚氨酯具有优良的力学性能、耐热性及表面疏水性,且材料呈微观相分离形态。