检索结果-内蒙古大学图书馆

Experimental Investigation of Heat Storage and Heat Transfer Rates during Melting of Nano-Enhanced Phase Change Materials (NePCM) in a Differentially-Heated rectangular Cavity

引用

Journal of Thermal Science 2020年第2期29卷 503-511页

作者： LI Zirui HU Nan TU Jing FAN Liwu Institute of Thermal Science and Power Systems School of Energy EngineeringZhejiang UniversityHangzhou 310027China State Key Laboratory of Clean Energy Utilization Zhejiang UniversityHangzhou 310027China

In this work, an experimental study of melting heat transfer of nano-enhanced phase change materials(NePCM) in a differentially-heated rectangular cavity was performed. Two height-to-width aspect ratios of the cavity, i.e., 0.9 and 1.5, were investigated. The model Ne PCM samples were prepared by dispersing graphene nanoplatelets(GNP) into 1-tetradecanol, having a nominal melting point of 37℃, at loadings up to 3 wt.%. The viscosity was found to have a more than 10-fold increase at the highest loading of GNP. During the melting experiments, the wall superheat at the heating boundary was set to be 10℃ or 30℃. It was shown that with increasing the loading of GNP, both the heat storage and heat transfer rates during melting decelerate to some extent, at all geometrical and thermal configurations. This suggested that the use of NePCM in such cavity may not be able to enhance the heat storage rate due to the dramatic growth in viscosity, which deteriorates significantly natural convective heat transfer during melting to overweigh the enhanced heat conduction by only a decent increase in thermal conductivity. This also suggested that the numerically predicted melting accelerations and heat transfer enhancements, as a result of the increased thermal conductivity, in the literature are likely overestimated because the negative effects due to viscosity growth are underestimated.

关键词： aspect ratio graphene nanoplatelets latent heat storage melting heat transfer phase change material rectangular cavity

来源：评论

学校读者我要写书评

暂无评论

LIQUID BACKMIXING AND CIRCULATION IN rectangular DOWNCOMER

引用

Chinese Journal of Chemical Engineering 1997年第4期5卷 89-93页

作者：俞晓梅田军 Department of Chemical Engineering Zhejiang University of Technology

1 INTRODUCTIONDowncomers,employed in tray columns,are widely used nowadays in industrialseparation *** function as channels for the liquid phase to fall fluentlyfrom one tray onto its neighbouring places for the held-up bubble to separate fromthe liquid *** is well known that liquid flow patterns and mixing characteristicsin downcomers are closely related to the initial liquid distribution on the tray,andhence to tray *** a long period of time,little attention has been paid

关键词： rectangular downcomer backmixing circulation square deviation

来源：评论

学校读者我要写书评

暂无评论

Aspect ratio effects on turbulent and transitional flow in rectangular microchannels as measured with microPIV

引用

JOURNAL OF FLUIDS ENGINEERING-TRANSACTIONS OF THE ASME 2006年第2期128卷 305-315页

作者： Li, H Olsen, MG Iowa State Univ Dept Mech Engn Ames IA 50011 USA

Microscopic particle image velocimetry (microPIV) was used to measure velocities in rectangular microchannels with aspect ratios ranging from 0.97 to 5.69 for 200 /u(max) and /u(max) fluctuations at the channel center... 详细信息

Microscopic particle image velocimetry (microPIV) was used to measure velocities in rectangular microchannels with aspect ratios ranging from 0.97 to 5.69 for 200 < Re < 3267. Mean velocity profiles, velocity fluctuations, and Reynolds stresses were determined from the microPlV data. Transition to turbulence was observed at Re = 1765-2315 for the five aspect ratios studied, agreeing very well with both recent microscale experiments and macroscale duct flow and indicating no evidence of early. transition for any of the aspect ratios studied. The onset of fully turbulent flow was observed at Re=2600-3200. For the fully turbulent flow, the < u >/u(max) and < v'>/u(max) fluctuations at the channel centerline were 6% and 3%-3.5% and generally agreed well with macroscale results. As aspect ratio increased, the < u >/u(max) and < u'>/u(max) profiles became flatter, with nearly uniform values extending for some distance front the centerline of the channel. This region of uniform < u >/u(max) and < u'> u(max) became larger with increasing aspect ratio. The Reynolds shear stress for fully turbulent flow also displayed a strong dependence on aspect ratio. For the W/H=0.97 microchannel, < u' v'>/u(max)(2) steadily increased in value moving from the centerline to the wall, but for the higher steadil 2 aspect ratio microchannels, < u' v'>/u(max)(2) remained close to zero in the center region of the microchannel before increasing in value at locations close to the wall, and this region of near zero < u' v'> u(max)(2) became larger with increasing aspect ratio. This behavior in the max Reynolds shear stress is due to the region of uniform velocity and, hence, small mean shear near the channel centerline of the high aspect ratio microchannels.

关键词： Turbulent Flow wall ASPECT RATIO Transition flow microchannels Shear stress rectangular high aspect ratio

来源：评论

学校读者我要写书评

暂无评论

2-PHASE FLOW PATTERNS AND TRANSITIONS IN A SMALL, HORIZONTAL, rectangular CHANNEL

引用

INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 1991年第3期17卷 327-342页

作者： WAMBSGANSS, MW JENDRZEJCZYK, JA FRANCE, DM UNIV ILLINOIS DEPT MECH ENGNCHICAGOIL 60680

Horizontal two-phase flow was studied in a small cross-sectional-area (19.05 x 3.18 mm) rectangular channel with both the short and long sides forming the base, resulting in aspect ratios of 6 and 1/6, respectively. Adiabatic flows of air/water mixtures were tested over a large mass flux range (50-2000 kg/m2s). The full quality range was considered whenever experimentally achievable. Flow patterns were established and both mean and dynamic pressure measurements were used to accurately establish the plug/bubble-to-slug flow transition. This result, together with visual observations and supplemented with photographic data, was used to develop flow pattern maps. A comparison of existing flow pattern maps for circular pipes, capillary tubes and larger rectangular channels led to the conclusion that, while qualitative agreement exists, these maps are not generally applicable to the subject small rectangular channel on the quantitative basis.

关键词： 2-PHASE FLOW HORIZONTAL rectangular FLOW PATTERNS TRANSITIONS

来源：评论

学校读者我要写书评

暂无评论

Modelling of laminar flow in the inlet section of rectangular microchannels

引用

JOURNAL OF MICROMECHANICS AND MICROENGINEERING 2009年第2期19卷 025013 (9p-025013 (9p页

作者： Martinelli, Matteo Viktorov, Vladimir Turin Tech Univ Politecn Turin Turin Italy

This paper is a study of laminar flow in rectangular microchannels. The behaviour of compressible and incompressible fluids in microchannels was simulated using CFD software. Numerical data were compared to experimental measurements to test the validity of CFD models. The velocity profile of flow developing inside the channel is described as a function of the Reynolds number Re, varying from 100 to 2000, and the aspect ratio h/w, ranging from 1 to 0.125. The fundamental importance of the entrance length of microchannels is highlighted. Numerical data were applied to define analytical formulae covering the minimum entrance length for fully developed laminar flow of compressible fluids, viscous stress and incremental pressure drop effect during flow development, and the velocity profiles of flow for compressible and incompressible fluids.

关键词： VELOCITY PROFILING Pressure decline microchannels laminar flow rectangular incompressible fluids Statistical Data compressible entrance length Modeling

来源：评论

学校读者我要写书评

暂无评论

A critical heat flux experiment with water flow at low pressures in thin rectangular channels

引用

NUCLEAR ENGINEERING AND DESIGN 2014年第0期278卷 669-678页

作者： Lu, Donghua Wen, Qinglong Liu, Tong Su, Qianhua China Nucl Power Res Inst CGN Shenzhen 518026 Peoples R China

Experimental investigation was performed on the critical heat flux (CHF) in thin rectangular channels with very wide mass velocity range at low pressures. Different test sections were adopted with the different heated length and heated width. Both the vertical upward flow and downward flow were tested during the experiment. The results prove that the effect of the heated length on the CHF exists in the high mass velocity test but it is not very strong. The CHF rises with shorter heated length. At low mass velocities, the CHF at downward flow is much lower than that at upward flow. Empirical correlations were compared with the experimental data both from present and others' studies. Empirical correlations provided by Katto and Gambill gave out good prediction for the low upflow and the high downflow respectively. The Sudo correlation had wide flow range but it overestimated at low mass velocity and underestimated at high mass velocity. A new CHF correlation for the large flow rate shows good agreement with the present and others' studies. High pressure drop was found in the experiment at high flow rate conditions. It was analyzed and discussed in the paper. (C) 2014 Elsevier B.V. All rights reserved.

关键词： rectangular low pressure detection zone mass velocity Congestive Heart Failure CRITICAL HEAT FLUX Heating mass upflow Flow rates high flow rate Heat flux Water flow

来源：评论

学校读者我要写书评

暂无评论

A new closed-form approximate solution to diffusion with quadratic Fujita's non-linearity: the case of diffusion controlled sorption kinetics relevant to rectangular adsorption isotherms

引用

HEAT AND MASS TRANSFER 2019年第2期55卷 261-279页

作者： Hristov, Jordan Univ Chem Technol & Met Dept Chem Engn 8 Kliment Ohridsky BU-1756 Sofia Bulgaria

A new approximate solution relevant to case of rectangular (Langmuirian) adsorption isotherms has been developed on the basis of the integral-balance method with double integration technique. The solution is based on the model developed by Ruthven for slab and spherical adsorption pellets where the adsorption is controlled by the diffusion in macropores. This model results in a concentration-dependent diffusion coefficient with a quadratic nonlinearity of Fujita's type. The new approximate solution utilizes the concept of finite penetration depth of the diffusant penetration and almost shockwave shape of the concentration profiles. The solution is based on an assumed parabolic profile with unspecified exponent. The solution analysis allowed determining the optimal exponents of the concentration profile as a function of the nonlinearity parameter of the Fujita's concentration relationship. The approximate solutions have been compared to existing results from the literature and especially the data published by Ruthven and Crank, for concentration distributions and fractional uptakes in an adsorbent slab pellet.

关键词： Solution Approximate Penetration depth Solutions CRANK diffusion control rectangular diffusion Adsorption isotherms Plate slabs Quadratic nonlinearity

来源：评论

学校读者我要写书评

暂无评论

Dependence of flow characteristics of rectangular cylinders near a wall on the incident velocity

引用

ACTA MECHANICA 2011年第3-4期222卷 273-286页

作者： Maiti, Dilip K. Birla Inst Technol & Sci Dept Math Pilani 333031 Rajasthan India

Numerically simulated results are presented for a family of rectangular cylinders with aspect ratios r (1) (=b/a with height a and width b) ranging from 0.1 to 1.0 (square cylinder) to gain a better insight into the dependency of the aerodynamic characteristics on the operational dimensionless parameters, namely Reynolds number Re and aspect ratio r (1). This work describes the flow from a long cylinder of rectangular cross-section placed parallel to a wall and subjected to a uniform shear flow. The flow is investigated in the laminar Reynolds number range (based on the incident stream at the cylinder upstream face and the height of the cylinder) at cylinder to wall gap height 0.5 times the cylinder height. The governing unsteady Navier-Stokes equations are solved numerically through a finite volume method on a staggered grid system using QUICK scheme for convective terms. The resulting equations are then solved by an implicit, time-marching, pressure correction-based SIMPLE algorithm for Reynolds number up to 1,000. The critical Reynolds numbers at which vortex shedding from the cylinder is started are specified for both the cases: far from the wall and near to the wall. It is reported that the vortex shedding from the rectangular cylinder of lower aspect ratio r (1) (a parts per thousand currency sign 0.25) becomes regular and insensitive to the Reynolds number, while the aerodynamic characteristics of the rectangular cylinders with higher aspect ratio r (1) (a parts per thousand yen 0.5) are strongly dependent on the Reynolds number.

关键词： wall Aerodynamic characteristics ASPECT RATIO Grid systems rectangular flow characteristics vortex shedding DEPENDENCE

来源：评论

学校读者我要写书评

暂无评论

Higher-dimensional chaotic dynamics of a composite laminated piezoelectric rectangular plate

引用

Science China(Physics,Mechanics & Astronomy) 2009年第12期52卷 1989-2000页

作者： ZHANG Wei GAO MeiJuan YAO MingHui YAO ZhiGang College of Mechanical Engineering Beijing University of TechnologyBeijing 100124China

The analysis on the chaotic dynamics of a six-dimensional nonlinear system which represents the averaged equation of a composite laminated piezoelectric rectangular plate is given for the first time. The theory of normal form and the energy-phase method are combined to investigate the higher-dimen-sional chaotic dynamics of the composite laminated piezoelectric rectangular plate. Firstly,the theory of normal form is used to reduce the six-dimensional averaged equation to the simpler normal form. Then,the energy-phase method is extended to analyze the global bifurcations and chaotic dynamics of a six-dimensional nonlinear system. The analysis results indicate that there exist the homoclinic bi-furcation and Shilnikov type multi-pulse chaos for the composite laminated piezoelectric rectangular plate. Finally,numerical simulations are also used to investigate the nonlinear dynamic characteristics of the composite laminated piezoelectric rectangular plate. The results of numerical simulations also demonstrate that there exist the chaotic motions and the multi-pulse jumping orbits of the composite laminated piezoelectric rectangular plate.

关键词： composite laminated piezoelectric rectangular plate normal form energy-phase method numerical simulation jumping orbits chaotic motion

来源：评论

学校读者我要写书评

暂无评论

The Superposition-Galerkin method for free vibration analysis of rectangular plates

引用

JOURNAL OF SOUND AND VIBRATION 1996年第2期194卷 187-198页

作者： Gorman, DJ Ding, W UNIV OTTAWA DEPT MECH ENGN 770 KING EDWARD AVE OTTAWA ON K1N 6N5 CANADA

It is known that exploitation of the traditional superposition method for analyzing plate free vibration problems becomes a very demanding and difficult task when one moves from thin isotropic plate theory to the thick plate Mindlin theory, and to the analysis of laminated plates. Difficulties arise because of the vast families of roots encountered, real and complex, when solving associated differential equations. The presence of hyperbolic functions tends to produce computer over-flow and under-flow and computational difficulties. In this paper, the modified Superposition-Galerkin method is introduced. All of the above problems are eliminated and excellent agreement is encountered when results obtained by both methods are compared. (C) 1996 Academic Press Limited

关键词： free vibrations exploitation rectangular Hyperbolic functions plate theory Galerkin method WWOX gene Real number Superposition technique Vibration analysis thick plates

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：