Nonisothermal flow of a polymeric liquid under a pulsating pressure gradient

A study has been made of the effects of pressure-gradient pulsations on the nonisothermal flow of a nonlinear liquid with memory in an annular channel.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 3, pp. 361–368, September, 1986.     

Novel flow analysis of regenerator under oscillating flow with pulsating pressure

A new model for the oscillating flow combined with pulsating pressure in cryocooler regenerators is developed to overcome inaccuracy of the conventional flow model based on steady flow friction factor. The new model is based on two non-dimensional parameters and one-dimensional governing equations. One of the parameters is the oscillating flow friction factor represented by the amplitudes of the pressure drop and the flow rate. The idea of the other important parameter originates from a volume averaged continuity equation, which includes the characteristic of randomly oriented matrix geometry. This parameter is named as Breathing factor, which implies that the regenerator breathes against the main oscillating flow. Empirical correlations of the parameters are obtained for screen regenerators. It is revealed that the phase angles of the pressure drop and the mass flow rate in regenerators are well predicted by introduction of the Breathing factor.     

Fatigue crack growth in thick-walled cylinders under pulsating internal pressure

The stress intensity factor is derived for both single and multiple longitudinal, elliptical cracks in the wall of a pressurized thick cylinder of given geometry. For this purpose, it is found necessary to combine known solutions to the stress intensity factor for a straight longitudinal crack with the effects of a curved crack front and multiple cracking. The analysis is appraised from a number of fatigue tests reported for % Ni-Cr-Mo cylinders with diameter ratios of between 2 and 3 under repeated and fluctuating pressure cycles. When cylinders with poorly finished bores are assumed to be initially flawed, it is found that their fatigue lives under high ranges of pressure may be predicted reliably for the single crack propagation failures observed. This analysis employs published WOL or SEN fatigue crack growth data for the alloy. The enhancement in fatigue life that results from an improved surface finish has enabled that proportion of life expended during the initiation phase to be determined. It is further shown that the observed effect of mean stress and surface finish on the fatigue limit may be quantified with a change to the threshold of stress intensity for crack growth. A number of tests were conducted with two-step changes to the amplitude of the pressure cycle. In this instance, nonlinear, stress dependent, cumulative damage rules are shown to offer no advantage over Miner's rule in the prediction of fatigue life.     

Measurement of cryogenic regenerator characteristics under oscillating flow and pulsating pressure

This paper describes an experimental apparatus developed to investigate detailed thermal and hydrodynamic characteristics of a regenerator at cryogenic temperature under oscillating flow and pulsating pressure conditions. Cold-end of the regenerator is maintained at approximately 85 K for G-M cryocooler type and 100 K for Stirling cryocooler type operations by means of two cryogenic heat exchangers. At both ends of the regenerator, fine hot wire probes are installed to measure the fast oscillating gas temperature and mass flow rate. The gas temperature sensors installed very close to the ends of the regenerator matrix assure precise gas temperature measurement in the regenerator. In this study, thermal and hydrodynamic behaviors of the well-defined wire-screen regenerator are fully characterized. First, pressure drop characteristics are discussed for different frequencies under room temperature. Second, ineffectiveness of the regenerator is obtained for different cold-end temperatures.     

Buckling of polymer pipes under internal pressure

In this work, the buckling phenomenon of slender pressurized pipes under concentrically applied indirect axial force is experimentally and theoretically investigated. The axial force is applied via a frictionless piston. The deformation trend of a polyvinylchloride pipe sample under this compressive axial force is monitored by means of a number of strain gauges. The strain readings are processed by a computer equipped with strain processing software. The buckling modes as well as the buckling load of the system are thus experimentally determined. To describe the stability behaviour of the pipe analytically, several theoretical models are employed and the buckling phenomenon in such a pressurized pipe is analytically ascertained. Numerical values for the critical buckling loads are also obtained. The experimental and theoretical buckling studies are correlated. Through these correlations, the buckling of pressurized pipes under indirect axial pressure is substantiated and an appropriate theoretical model to describe the phenomenon is established.     

Partial structure factors of a simulated polymer melt

Fully atomistic molecular dynamic simulations were carried out by using the Insight (Insight II 4.0.0 P version) and the Discover-3 programs from MSI with the polymer consortium force field. The model system used in these simulations was built using the Amorphous Cell module. The polymer system simulated was glassy polyisoprene (PI) as used in previous neutron scattering (NS) measurements. A first molecular dynamics at 363 K was run for 1 ns using the Discover-3 program collecting data every 0.01 ps and a subsequent one (taking the previous output sample as an input for the following dynamics) was run for 2 ns collecting data every 0.5 ps. The results of the second run agreed to those of the first run, indicating that the sample was well equilibrated at this high temperature. Starting from the obtained atomic trajectories we have calculated the partial static structure factors for NS corresponding to different PI samples with different levels of deuteration (PId3, i.e., methyl group deuterated and main chain protonated; PId5, i.e., methyl group protonated and main chain deuterated; PId8, i.e., fully deuterated and PIh8, i.e., fully protonated). The results obtained are compared to the coherent NS cross-sections measured on real samples by means of D7 spectrometer with polarization analysis (ILL, Grenoble). A good agreement is obtained between experimental and simulated data validating the simulated sample. Moreover, the dynamic evolution of these correlations has also been calculated from the simulations. With these time dependent functions, the magnitude measured in a neutron spin echo (NSE) experiment can be constructed. Here we present two examples dealing with the fully deuterated sample PId8 and a partially deuterated sample, PId5, that show how computer simulation constitutes an invaluable tool for interpreting NSE results.     

Investigation on the pressure drop characteristics of cryocooler regenerators under oscillating flow and pulsating pressure conditions

This paper proposes a new oscillating flow model of the pressure drop in oscillating flow through regenerator under pulsating pressure. In this oscillating flow model, pressure drop is represented by the amplitude and the phase angle with respect to the inlet mass flow rate. In order to generalize the oscillating flow model, some non-dimensional parameters, which consist of Reynolds number, Valensi number, gas domain length ratio, oscillating flow friction factor and phase angle of pressure drop, are derived from a capillary tube model of the regenerator. Two correlations in the model are obtained from the experiments for the twill square screen regenerators under various operating frequencies and inlet mass flow rates. It is found that the oscillating flow friction factor is a function of Reynolds number while the phase angle of pressure drop is a function of Valensi number and the gas domain length ratio. Experiment also shows the effect of the mesh weave style on the oscillating flow friction factor and the phase angle. Proposed oscillating flow model can accurately describe the amplitude and the phase angle of the pressure drop through the regenerator.     

Miniature fiber-optic pressure sensor with a polymer diaphragm

The fabrication and experimental investigation of a miniature optical fiber pressure sensor for biomedical and industrial applications are described. The sensor measures only 125 microm in diameter. The essential element is a thin polymer diaphragm that is positioned inside the hollow end of an optical fiber. The cavity at the fiber end is made by a simple and effective micromachining process based on wet etching in diluted HF acid. Thus a Fabry-Perot interferometer is formed between the inner fiber-cavity interface and the diaphragm. The fabrication technique is described in detail. Different sensor prototypes were fabricated upon 125 microm-diameter optical fiber that demonstrated pressure ranges from 0 to 40 and from 0 to 1200 kPa. A resolution of less than 10 Pa was demonstrated in practice. The fabrication technique presented facilitates production of simple and low-cost disposable pressure sensors by use of materials with that ensure the required biocompatibility.     

Dynamic characteristics of pulsating turbulent flow of compressible gas in a channel

A model of turbulent transfer that allows for the effect of flow-rate oscillations on the turbulent stress is used to investigate pulsating turbulent flow of a compressible gas in a narrow channel. An algorithm for solving numerically the system of equations that describes this process by the finite-difference method with the use of an implicit iteration scheme is proposed. The effect of operating parameters on the amplitude-frequency characteristic is considered.     

模板浸润法制备聚合物纳米管阵列

以孔径为200nm的多孔氧化铝膜（AAO）为模板、常规分子量的通用聚合物为原料,采用聚合物溶液或熔体浸润模板纳米孔的物理技术,进行了多种聚合物纳米管的制备研究。结果表明：聚苯乙烯、尼龙66、聚丙烯、ABS、热塑性聚氨酯等多种聚合物纳米管及其纳米管阵列成功制得。运用扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察了纳米管的微观形貌和阵列结构。并探讨了聚合物性质、纳米管制备工艺与纳米管结构的关系,初步探索了多孔模板法制备聚合物纳米管的机理。     

静水压力下高分子材料黏弹性动力学参数测量

提出测量静压下高分子材料黏弹性动力学参数方法。分别制作均匀实心覆盖层及圆柱空腔覆盖层样品,测量实心覆盖层复反射系数计算复纵波波数,测量圆柱空腔覆盖层复反射系数,结合圆柱空腔结构变形,利用圆柱管中轴对称波特征方程计算复剪切波波数,综合复纵波波数与复剪切波波数计算静压下复杨氏模量及复泊松比。对橡胶材料进行声管测试,分析、总结静压对黏弹性动力学参数影响规律。测量某吸声覆盖层静压下反射系数,并与用实测材料参数计算的反射系数进行比较,验证方法的可靠性。