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Journal of Thermal Science 2020年第4期29卷 972-981页

作者： WANG Zhipeng CHENG Shuhao ZHUO Yuqun Key Laboratory for Thermal Science and Power Engineering of the Ministry of Education Department of Energy and Power EngineeringTsinghua UniversityBeijing 100084China Beijing Engineering Research Center for Ecological Restoration and Carbon Fixation of Saline–alkaline and Desert Land Tsinghua UniversityBeijing 100084China China Institute of Atomic Energy Beijing 102413China

The flow and heat transfer characteristics of Maxwell fluid in a pipe under pulsating pressure gradient were studied. The governing equations were made dimensionless. The Rubin boundary condition was adopted. The flow field was solved theoretically and the temperature field was obtained using finite volume method. A general model suitable for various fluctuating characteristics and physical parameters was established. The deborah number(De) was used to characterize the fluidity of the fluid. The influence of De on flow and temperature fields was evaluated. The Nusselt number and start-up process of Maxwell fluid were studied. Results showed that the influence of De on flow field was greater than that on temperature field. The effect of De on Nusselt number was irregular and related to the oscillation parameters. The over-shooting amplitude and oscillation time of axis center velocity in start-up flow grow larger with De.

关键词： Maxwell fluid pulsating flow Hagen-Poiseuille law deborah number start-up flow

A dynamic rheological model for thin-film lubrication

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Chinese Physics B 2013年第1期22卷 426-433页

作者：张向军黄颖郭岩宝田煜孟永钢 State Key Laboratory of Tribology Tsinghua University

In this study, the effects of the non-Newtonian rheological properties of the lubricant in a thin-film lubrication regime between smooth surfaces were investigated. The thin-film lubrication regime typically appears in Stribeck curves with a clearly observable minimum coefficient of friction （COF） and a low-COF region, which is desired for its lower energy dissipation. A dynamic rheology of the lubricant from the hydrodynamic lubrication regime to the thin-film lubrication regime was proposed based on the convected Maxwell constitutive equation. This rheology model includes the increased relaxation time and the yield stress of the confined lubricant thin film, as well as their dependences on the lubricant film thickness. The deborah number （De number） was adopted to describe the liquid-solid transition of the confined lubricant thin film under shearing. Then a series of Stribeck curves were calculated based on Tichy＇s extended lubrication equations with a perturbation of the De number. The results show that the minimum COF points in the Stribeck curve correspond to a critical De number of 1.0, indicating a liquid-to-solid transition of the confined lubricant film. Furthermore, the two proposed parameters in the dynamic rheological model, namely negative slipping length b （indicating the lubricant interracial effect） and the characteristic relaxation time λ0, were found to determine the minimum COF and the width of the low-COF region, both of which were required to optimize the shape of the Stribeck curve. The developed dynamic theological model interprets the correlation between the rheological and interfacial properties of lubricant and its lubrication behavior in the thin-film regime.

关键词： rheology viscoelasticity deborah number thin-film lubrication

Time Periodic Electroosmotic Flow of The Generalized Maxwell Fluids in a Semicircular Microchannel

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Communications in Theoretical Physics 2013年第5期59卷 615-622页

作者：包丽平菅永军长龙苏洁张海燕刘全生 School of Mathematical Science Inner Mongolia University School of Mathematics and Statistics Inner Mongolia University of Finance and Economics College of Mathematical Science Baotou Teacher's College

Analytical solutions are presented using method of separation of variables for the time periodic electroosmotic flow (EOF) of linear viscoelastic fluids in semicircular microchannel. The linear viscoelastic fluids used here are described by the general Maxwell model. The solution involves analytically solving the linearized Poisson-Boltzmann (P -B) equation, together with the Cauchy momentum equation and the general Maxwell constitutive equation. By numerical computations, the influences of electric oscillating Reynolds number Re and deborah number De on velocity amplitude are presented. For small Re, results show that the larger velocity amplitude is confined to the region near the charged wall when De is small. With the increase of the deborah number De, the velocity far away the charged wall becomes larger for large deborah number De. However, for larger Re, the oscillating characteristic of the velocity amplitude occurs and becomes significant with the increase of De, especially for larger deborah number.

关键词： time periodic EOF generalized Maxwell fluids semi-circular micro-channel oscillating Reynolds number deborah number

CHARACTERISTIC DIMENSIONLESS numberS IN MULTI—SCALE AND RATE—DEPENDENT PROCESSES

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China Particuology 2003年第1期1卷 7-12页

作者： YilongBai MengfenXia HaiyingWang FuiiuKe Authortowhomcorrespondenceshouldbeaddressed. StateKeyLaboratoryofNon-LinearMechanics InstituteofMechanicsChineseAcademyofSciencesBeiiing100080P.R.China

Multi-scale modeling of materials properties and chemical processes has drawn great attention from sci-ence and engineering. For these multi-scale and rate-dependent processes, how to characterize their trans-scale for-mulation is a key point. Three questions should be addressed:How do multi-sizes affect the problems?How are length scales coupled with time scales?How to identify emergence of new structure in process and its effect?For this sake, the macroscopic equations of mechanics and the kinetic equations of the microstructural transforma-tions should form a unified set that be solved *** a case study of coupling length and time scales, the trans-scale formulation of wave-induced damage evolution due to mesoscopic nucleation and growth is discussed. In this problem, the trans-scaling could be reduced to two inde-pendent dimensionless numbers: the imposed deborah number De=(ac)/(LV) and the intrinsic deborah num-ber D = (nNc5)/V* ,where a. L, c, V and nN are wave speed, sample size, microcrack size, the rate of micro-crack grovvth and the rate of microcrack nucleation density, respectively. Clearly, the dimensionless number De=(ac)l(LV) includes length and time scales on both meso- and macro- Ievels and governs the progressive process. Whereas, the intrinsic deborah number D' indicates the characteristic transition of microdamage to macroscopic rup-ture since D is related to the criterion of damage localization, which is a precursor of macroscopic rupture. This case study may highlight the scaling in multi-scale and rate-dependent ***, more generally, we compare some historical examples to see how trans-scale formulations were achieved and what are stili open now. The comparison of various mechanisms governing the enhancement of meso-size effects re-minds us of the importance of analyzing multi-scale and rate-dependent processes case by *** multi-scale and rate-dependent processes with chemical reactions and diffusions, there seems to

关键词： multi-scale rate-dependent deborah number