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flow resistance and its prediction methods in compound channels

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Acta Mechanica Sinica 2007年第1期23卷 23-31页

作者： Kejun Yang Shuyou Cao Xingnian Liu State Key Laboratory of Hydraulics and Mountain River Engineering Sichuan University Chengdu 610065 China

A series of experiments was carried out in a large symmetric compound channel composed of a rough main channel and rough floodplains to investigate the resistance characteristics of inbank and overbank flows. The effective Manning, Darcy-Weisbach, Chezy coefficients and the relative Nikuradse roughness height were analyzed. Many different representative methods for predicting the composite roughness were systematically summarized. Besides the measured data, a vast number of laboratory data and field data for compound channels were collected and used to check the validity of these methods for different subsection divisions including the vertical, horizontal, diagonal and bisectional divisions. The computation showed that these methods resulted in big errors in assessing the composite roughness in compound channels, and the reasons were analyzed in detail. The error magnitude is related to the subsection divisions.

关键词： flow resistance Compound channels Bed roughness Inbank and overbank flows Subsection division

flow resistance AND HEAT TRANSFER CHARACTERISTICS OF A NEW-TYPE PLATE HEAT EXCHANGER

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Journal of Hydrodynamics 2008年第4期20卷 524-529页

作者： LUAN Zhi-jian ZHANG Guan-min TIAN Mao-cheng FAN Ming-xiu School of Energy and Power Engineering Shandong University Jinan 250061 China

A new-type corrugation Plate Heat Exchanger （PHE） was designed. Results from both numerical simulations and experiments showed that the flow resistance of the working fluid in this new corrugation PHE, compared with the traditional chevron-type one, was decreased by more than 50%, and corresponding heat transfer performance was decreased by about 25%. The flow field of the working fluid in the corrugation PHE was transformed and hence performance difference in both flow resistance and heat transfer was generated. Such a novel plate, consisting of longitudinal and transverse corrugations, can effectively avoid the problem of flow path blockage, which will help to extend the application of PHEs to the situation with unclean working fluids.

关键词： plate heat exchanger flow resistance heat transfer numerical simulation blockage

flow resistance of gravel bed channels

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International Journal of Sediment Research 2014年第1期29卷 126-132页

作者： Wen C.WANG David R.DAWDY Multech Engineering Consultants

Existing resistance formulas produce a wide range of friction-factor estimates for gravel bed *** purpose of this paper is to develop a reliable resistance formula in terms of the Darcy-Weisbach friction factor/ Published data were screened and used to establish the *** existing formulas have considered that/is a function of relative roughness D84/R only,where R is the hydraulic radius and D84is the particle size referred to the intermediate diameter that equals or exceeds that of 84 percent of bed *** this paper,/is considered as a function of Froude number in addition to the relative roughness./for D84/R>1 displays a different trend than that for D84/R***/formula for D84/R<1 has been established.

关键词： flow resistance Darcy-Weisbach friction factor Relative roughness Relative submergence Gravel bed channels Open channels

flow resistance adjustments of channel and bars in the middle reaches of the Yangtze River in response to the operation of the Three Gorges Dam

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Journal of Geographical Sciences 2022年第10期32卷 2013-2035页

作者： HU Yong DENG Jinyun LI Yitian LIU Congcong HE Zican State Key Laboratory of Water Resources and Hydropower Engineering Science Wuhan UniversityWuhan 430072China CCCC Second Harbour Engineering Co Ltd Wuhan 430040China

Since the Three Gorges Dam(TGD)was put into operation,the flood water level at an identical discharge rate has not displayed a decreasing trend along the middle reaches of the Yangtze River(MYR).The flow resistance variations of the channel and bars in response to the operation of the TGD remain poorly understood,despite the importance of understanding these for water disaster mitigation and water environment ***,the impacts of the TGD on the downstream flow resistance of the channel and bars in the MYR were analyzed using systematic surveys of hydrological datasets,cross-sectional profiles,sediment datasets,and remote sensing images,during different *** the actual natural conditions in the MYR,a modified semi-empirical formula,which considered the grain,dune resistance,as well as the topographic features of the riverbed,was proposed to predict the channel ***,the effect of various dam-control flow and sediment elements on the variation in different flow resistance components,and the corresponding relationships among them were *** showed a decline in the comprehensive,channel,and bar resistances as the discharge increased,whereas there was a slight increase when reaching the bank-full ***,the bar resistance occupied 65%,while the channel resistance,in which dune resistance was much larger than grain resistance,contributed 35%to the comprehensive *** addition,while flow resistance rose over time,there was a decline as the distance from the TGD *** conclusion,the increased dune and bar resistances,interpreted by the fluctuated channel longitudinal profile and growing vegetated area on bars,were the dominant factors preventing the flood water level from dropping.

关键词： flow resistance water level channel geomorphology bar Three Gorges Dam Middle Yangtze River

Numerical investigation of pyrolysis effects on heat transfer characteristics and flow resistance of n-decane under supercritical pressure

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Chinese Journal of Aeronautics 2018年第6期31卷 1249-1257页

作者： Zhi TAO Xizhuo HU Jianqin ZHU Hongwei WU National Key Laboratory of Science and Technology on Aero-thermodynamies School of Energy and Power EngineeringBeihang University Beijing 100083 China School of Engineering and Technology University of Hertfordshire Hatfield AL10 9AB United Kingdom

Pyrolysis of hydrocarbon fuel plays an important role in the regenerative cooling process. In this article, a Two-Dimensional（2D） numerical model is proposed to investigate the pyrolysis effects on the heat transfer characteristics and flow resistance of n-decane under supercritical pressure. The one-step global pyrolytic reaction mechanism consisting of 19 species is adopted to simulate the pyrolysis process of n-decane. The thermophysical and transport properties of the fluid mixture are computed and incorporated into the numerical model for simulation. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. In order to better understand the complicated physicochemical process, further investigations on the turbulent flow and heat transfer coupled with pyrolysis in a tube have been performed under various operating conditions. The results indicate that the pyrolysis intensively takes place in the high fluid temperature region. The occurrence of the heat transfer deterioration would lead to increasing n-decane conversion at the beginning of the heated section. It is found that the pyrolysis could improve the heat transfer deterioration and promote the heat transfer enhancement. Meanwhile, pyrolysis gives rise to an abrupt increase of flow resistance. The mechanisms of the physicochemical phenomena are also analyzed in a systematic manner, which would be very helpful in the development of the regenerative cooling technology.

关键词： n-Decane Convective heat transfer flow resistance Pyrolysis Supercritical pressure

Investigation of flow resistance characteristics of endothermic hydrocarbon fuel under supercritical pressures

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Propulsion and Power Research 2013年第2期2卷 119-130页

作者： Chunben Zhang Guoqiang Xu Hongwu Deng Kun Zhu National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics School of Energy and Power EngineeringBeihang UniversityBeijing 100191China xi'an Aerospace Propulsion Institute Xi'an 710100China

The characteristics of flow resistance of a typical hydrocarbon fuel(RP-3)flowthrough adiabatic horizontal miniature tubes at supercritical pressures are experimentallyinvestigated for both laminar and turbulent *** experiments are conducted by using along tube measuring section and a short tube measuring section simultaneously in order toeliminate the effect of local pressure *** these experiments,the temperature of RP-3changes from(295 to 789)K and the reduced pressure(P/Pc,Pc=2.33 MPa)ranges from 1 to2.58,the mass flux is up to 1572.7 kg/(m^(2).s).Test results indicate that frictional pressuredrops for various supercritical pressures at the same mass flux can be considered as equalwith each other when the reduced temperature Tb/Tpc0.95,differenceappears and increases with the increase of Tb/***,the friction factor(f)of thesupercritical fluid for turbulent flow has a critical value at Tb/Tpc=1,the values of f at thispoint for all pressures and mass fluxes are equal with each ***,at the same massflux,there are two comresponding friction factors for the same Re,one is in the region of Tb/Tpc ***, classical conelations of frictionfactor is inapplicable when Tb/Tpc>0.95 at supercritical pressure and a new coelation hasbeen obtained based on the experimental data.

关键词： Supercritical Hydrocarbon fuel flow resistance Friction factor Pressure drop

Influence of regenerator flow resistance on stability of pulse tube cooler

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Journal of Southeast University(English Edition) 2005年第3期21卷 277-281页

作者：蒋彦龙陈国邦南京航空航天大学航空宇航学院南京210016 浙江大学机械与能源工程学院杭州310027

Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current （DC） flow induced by the introduction of a double-inlet in a pulse tube cooler is investigated theoretically. The calculation results show that increasing regenerator flow resistance can lead to a smaller extent of DC ***,a better stability performance of the cooler can be *** this basis,the stability characteristics of the cooler with various regenerator matrix arrangements are studied by *** replacing 30% space of 247 screens of stainless steel mesh at the cold part of the regenerator by lead balls of 0.25 mm diameter,a long-time stable temperature output at 80 K region is achieved. This achievement provides a new way to obtain stable performance for pulse tube coolers at high temperature and is helpful for its application.

关键词： pulse tube cooler flow resistance stability

Investigation of flow resistance in a U-Shaped Channels at Rotating Conditions Based on Similarity Theory

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风机技术 2023年

作者： Ru-quan You Cai-rui Li Hai-wang Li Beihang Univ Natl Key Lab Sci & Technol Aero Engines AerothermAircraft Engine Integrated Syst Safety Beijing Ke

In this paper,the numerical simulation method is used to study the flow resistance law of u-shaped channels under rotating conditions based on similarity *** study compares three geometric models:real model,completely similar model and incompletely similar model for cooling typical U-shaped channels inside turbine rotating *** completely similar model is geometrically 4.8 times magnification of the real model,and the rotation radius ratio of the real model is 5.4 times that of the incomplete similar *** is found that the friction factor of the completely similar model increases with the rotation number,and the difference varies from 6% to 38%.The friction factor of the model after incomplete similarity amplification decreases with the increase of rotation number,and the difference varies from -2% to- 30%.The friction factor of the laboratory imperfectly similar amplification model combined the effects of the above two laws,and the predicted difference was within 12%.This study provides a theoretical basis for subsequent experiments related to flow resistance.

关键词： flow resistance Rotating Channel Similarity Theory Scaled-up Channel

flow-resistance analysis of nano-confined fluids inspired from liquid nano-lubrication:A review

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Chinese Journal of Chemical Engineering 2017年第11期25卷 1552-1562页

作者： Xianzhu Huang Jian Wu Yudan Zhu Yumeng Zhang Xin Feng Xiaohua Lu College of Chemical Engineering State Key Laboratory of Materials-Oriented Chemical EngineeringNanjing Tech UniversityNanjing 210009China Division of Machine Elements Lulea University of Technology

How to reduce flow resistance of nano-confined fluids to achieve a high flux is a new challenge for modern chemical engineering applications, such as membrane separation and nanofluidic devices. Traditional models are inapplicable to explain the significant differences in the flow resistance of different liquid–solid *** the other hand, friction reduction in liquid nano-lubrication has received considerable attention during the past decades. Both fields are exposed to a common scientific issue regarding friction reduction during liquid–solid relative motion at nanoscale. A promising approach to control the flow resistance of nano-confined fluids is to reference the factors affecting liquid nano-lubrication. In this review, two concepts of the friction coefficient derived from fluid flow and tribology were discussed to reveal their intrinsic relations. Recent progress on low or ultra-low friction coefficients in liquid nano-lubrication was summarized based on two situations. Finally, a new strategy was introduced to study the friction coefficient based on analyzing the intermolecular interactions through an atomic force microscope(AFM), which is a cutting-point to build a new model to study flowresistance at nanoscale.

关键词： flow resistance Membrane separation Liquid nano-lubrication Model Intermolecular interactions AFM