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- Elsevier
- Instituto Politécnico de Bragança
- Universidade Estadual Paulista
- Universidade de Aveiro
- The Royal Society
- Massachusetts Institute of Technology
- Universidade Federal do Rio Grande
- Universidade de Adelaide
- Biblioteca Digitais de Teses e Dissertações da USP
- Biblioteca Digital da Unicamp
- Universidade Cornell
- Instituto de Tecnologia da Califórnia
- American Institute of Physics
- National Advisory Committee for Aeronautics
- Taylor & Francis
- Cambridge University Press
- Latin American applied research
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## ‣ Laminar flow in chevron-type plate heat exchangers: CFD analysis of tortuosity, shape factor and friction factor

Fonte: Elsevier
Publicador: Elsevier

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
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Liquid foodstuffs with high viscosity are usually processed in plate heat exchangers (PHEs) at laminar or low Reynolds numbers, Re, flows. The tortuosity coefficient is used by the manufacturers for the design and optimization of PHE geometries.
Using the finite-element computational fluid dynamics program POLYFLOW®, fully developed laminar flows in double-sine chevron-type PHEs passages are analysed in this work. The corrugation angle and channel aspect ratio of the passages vary in a broad range, PHEs with common area enlargement factors and with high area density being studied.
The tortuosity coefficient and the coefficient K (Kozeny´s coefficient in granular beds) from the friction factor correlations increase with the increase of the channels aspect ratio and the decrease of the chevron angle. The shape factor from the PHEs passages also increases with the decrease of the chevron angle and is weakly influenced by the channel aspect ratio.
In this paper, relations to predict the tortuosity coefficient and shape factor are proposed, the coefficient K being predicted resorting to the tortuosity coefficient and shape factor. The coefficient K compares well with literature data in the region of common chevron angles, channel aspect ratio and area enlargement factor.

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## ‣ Heat transfer to Newtonian and non-Newtonian fluids in cross-corrugated chevron-type plate heat exchangers: numerical approach

Fonte: Instituto Politécnico de Bragança
Publicador: Instituto Politécnico de Bragança

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
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Food fluids are frequently processed in plate heat exchangers (PHEs) and usually behave as non-Newtonian fluids, this behaviour being scarcely considered for PHEs design purposes. Moreover, many food fluids processed in PHEs have a high viscosity and, therefore, data obtained in laminar flow regime is useful to practical applications. The thermal-hydraulic performance of PHEs is strongly dependent on the physical properties of the fluid and on the geometrical properties of the plates namely, on the corrugation angle and on the channel aspect ratio. The mostly widely used PHEs have corrugations of the chevron type with an area enlargement factor defined as the ratio between the effective plate area and projected plate area close to 1.17. In the present work non-isothermal laminar flows of Newtonian and power-law fluids through cross-corrugated chevron-type plate heat exchangers are studied numerically in terms of the geometry of the channels. The plates area enlargement factor was a typical one (1.17), the corrugation angle varied between 30º and 60º and the flow index behaviour, n, between 0.25 and 1. The numerical calculations were performed using the commercial finite element software package POLYFLOW®. The equations solved were the conservation of mass...

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## ‣ Escoamento laminar de fluidos não-Newtonianos em permutadores de calor.

Fonte: Instituto Politecnico de Bragança
Publicador: Instituto Politecnico de Bragança

Tipo: Dissertação de Mestrado

Português

Relevância na Pesquisa
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#Fluxo laminar#Fluidos não-Newtonianos#Permutadores de calor de placas#Factores de fricção de Fanning#Laminar flow#Non-Newtonian fluids#Plate heat exchangers#Fanning friction factors

Este trabalho teve como objectivo estudar numericamente o escoamento laminar de fluidos Newtonianos
e não-Newtonianos em canais de permutadores de calor de placas do tipo chevron com ângulo de
corrugação igual a zero (canais do tipo sinusoidal).
Em particular, foram estudados os factores de fricção de Fanning para o fluxo laminar completamente
desenvolvido de fluidos Newtonianos e de fluidos não-Newtonianos (descritos pela lei de potência) em
canais do tipo sinusoidal, sendo os factores de fricção de Fannning, f, descritos pela relação 1 Reg f K −
= ,
em que Reg representa o número de Reynolds generalizado.
Para fluidos Newtonianos o coeficiente K da relação acima referida foi relacionado com o rácio de
aspecto dos diferentes canais sinusoidais. Uma vez que o coeficiente K depende do factor de forma, K0, e
do coeficiente de tortuosidade, t, através de 2
0
K = K t , K0 e t foram também relacionados com o rácio de
aspecto dos diferentes canais.
Foram ainda estabelecidas curvas de fricção únicas para fluidos Newtonianos e não-Newtonianos, através
da implementação de um número de Reynolds generalizado adequado, nos canais referidos.
As relações propostas são simples e úteis para cálculos de engenharia. In this work it were numerically studied the fully developed laminar flows of Newtonian and non-
Newtonian fluids in the channels from chevron type plate heat exchangers with corrugation angle equal to
zero (sinusoidal channels).
In particular...

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## ‣ Simulations of incompressible fluid flows by a least squares finite element method

Fonte: Universidade Estadual Paulista
Publicador: Universidade Estadual Paulista

Tipo: Artigo de Revista Científica
Formato: 274-282

Português

Relevância na Pesquisa
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#Fluid flows#Large eddy simulation#Least-squares finite element#Navier-Stokes equations#Computer simulation#Finite element method#Flow of fluids#Heat flux#Laminar flow#Navier Stokes equations#Partial differential equations

In this work simulations of incompressible fluid flows have been done by a Least Squares Finite Element Method (LSFEM) using velocity-pressure-vorticity and velocity-pressure-stress formulations, named u-p-ω) and u-p-τ formulations respectively. These formulations are preferred because the resulting equations are partial differential equations of first order, which is convenient for implementation by LSFEM. The main purposes of this work are the numerical computation of laminar, transitional and turbulent fluid flows through the application of large eddy simulation (LES) methodology using the LSFEM. The Navier-Stokes equations in u-p-ω and u-p-τ formulations are filtered and the eddy viscosity model of Smagorinsky is used for modeling the sub-grid-scale stresses. Some benchmark problems are solved for validate the numerical code and the preliminary results are presented and compared with available results from the literature. Copyright © 2005 by ABCM.

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## ‣ Materiais de mudança de fase para aquecimento em escoamentos laminares; Phase change materials on heating of laminar flows

Fonte: Universidade de Aveiro
Publicador: Universidade de Aveiro

Tipo: Dissertação de Mestrado

Português

Relevância na Pesquisa
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#Engenharia mecânica#Mudança de fase#Transmissão de calor#Escoamento laminar#Material mudança de fase#PCM#Escoamento laminar

O presente trabalho de dissertação tem como objetivo a caracterização de um sistema de armazenamento de energia térmica latente por meio de um PCM e para aquecimento de fluídos em escoamentos de baixo número de Reynolds usando a metodologia de Taguchi aplicada à otimização do ciclo de ensaios. Foi possível através da realização de um número mínimo de ensaios a otimização das condições de saída. Para tal, criou-se um protótipo de sistema de aquecimento de energia latente e comprovou-se através de testes experimentais a possibilidade de aquecimentos de fluídos.
De facto, foi usada uma bancada experimental propositadamente construída para o efeito. Este conjunto de equipamentos proporcionou registar os parâmetros relevantes nomeadamente a temperatura do fluído à passagem pelo sistema e a temperatura do PCM durante o teste. A otimização determinada. Assim como outros autores já o comprovaram, os resultados obtidos demonstram que o aquecimento de fluídos de baixo número de Reynolds é possível em sistemas de aquecimento por energia latente com recurso a PCM. Finalmente concluiu-se que a configuração física deste sistema terá que ser posta a prova com outras configurações e com sistemas dotados de maior capacidade de armazenamento contribuindo para um aumento do aproveitamento do calor fornecido e obtenção de temperaturas de saída desejadas.; This dissertation is intended to characterize a latent heat thermal energy storage system by use of a PCM for heating fluids of low Reynolds number applying the Taguchi methods for test cycle optimization. Thus...

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## ‣ Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors

Fonte: The Royal Society
Publicador: The Royal Society

Tipo: Artigo de Revista Científica

Publicado em 06/04/2013
Português

Relevância na Pesquisa
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Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows...

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## ‣ Development of a flow-condition-based interpolation 9-node element for incompressible flows

Fonte: Massachusetts Institute of Technology
Publicador: Massachusetts Institute of Technology

Tipo: Tese de Doutorado
Formato: 167 leaves; 6575290 bytes; 6584738 bytes; application/pdf; application/pdf

Português

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The Navier-Stokes equations are widely used for the analysis of incompressible laminar flows. If the Reynolds number is increased to certain values, oscillations appear in the finite element solution of the Navier-Stokes equations. In order to solve for high Reynolds number flows and avoid the oscillations, one technique is to use the flow condition-based interpolation scheme (FCBI), which is a hybrid of the finite element and the finite volume methods and introduces some upwinding into the laminar Navier-Stokes equations by using the exact solution of the advection-diffusion equation in the trial functions in the advection term. The previous works on the FCBI procedure include the development of a 4-node element and a 9-node element consisting of four 4-node sub-elements. In this thesis, the stability, the accuracy and the rate of convergence of the already published FCBI schemes is studied. In addition, a new FCBI 9-node element is proposed that obtains more accurate solutions than the earlier proposed FCBI elements. The new 9-node element does not obtain the solution as accurate as the Galerkin 9-node elements but the solution is stable for much higher Reynolds numbers (than the Galerkin 9-node elements), and accurate enough to be used to find the structural responses in fluid flow structural interaction problems. The Cubic-Interpolated Pseudo-particle (CIP) scheme is a very stable finite difference technique that can solve generalized hyperbolic equations with 3rd order accuracy in space.; (cont.) In this thesis...

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## ‣ Finite element analysis of laminar and turbulent flows using LES and subgrid-scale models

Fonte: Universidade Federal do Rio Grande
Publicador: Universidade Federal do Rio Grande

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
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Numerical simulations of laminar and turbulent flows in a lid driven cavity and over a backward-facing step are presented in this work. The main objectives of this research are to know more about the structure of turbulent flows, to identify their three-dimensional characteristic and to study physical effects due to heat transfer. The filtered Navier–Stokes equations are used to simulate large scales, however they are supplemented by subgrid-scale (SGS) models to simulate the energy transfer from large scales toward subgridscales,
where this energy will be dissipated by molecular viscosity. Two SGS models are applied: the classical Smagorinsky s model and the Dynamic model for large eddy simulation (LES). Both models are implemented in a three-dimensional finite element code using linear tetrahedral elements. Qualitative and quantitative aspects of two and three-dimensional flows in a lid-driven cavity and over a backward-facing step, using LES, are analyzed comparing numerical and experimental results obtained by other authors.

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## ‣ Prediction and delay of 2D-laminar boundary layer separation near leading edges.

Fonte: Universidade de Adelaide
Publicador: Universidade de Adelaide

Tipo: Tese de Doutorado
Formato: 954058 bytes; 102636 bytes; application/pdf; application/pdf

Publicado em //2002
Português

Relevância na Pesquisa
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Boundary-layer flows near leading edges of generally
curved obstacles have been studied for a long time.
Apart from having many practical applications, the
theory and approaches prevailing in this area
stimulate development of a variety of computational tools
and form a ground for testing them.
The specific aim of this work is to study two-dimensional
laminar boundary layer flows near the leading edges of airfoils
and other elongated bodies, and to explore geometries for which
boundary layer separation can be avoided. This class of problems
is relevant to optimal design of wings, aircraft and projectile
noses, laminar flow control methods and adaptive wing technology.
One of the findings of this work suggests that local modifications
to parabolic wing noses can yield up to 11% increase in the
unseparated angle of attack. Another result obtained here is the
set of shortest possible generalised elliptic noses of long symmetric
bodies which allow unseparated flow.
Methods adopted in this work are based on the combined use of numerically
solved Prandtl equations written in Gortler variables, and inviscid
solutions obtained semi-analytically by the conformal mapping method.
The resulting technique being reliable, fast and computationally inexpensive...

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## ‣ Um esquema \"upwind\" para leis de conservação e sua aplicação na simulação de escoamentos incompressíveis 2D e 3D laminares e turbulentos com superfícies livres; The \"upwind\" scheme to the conservation laws and their application in simulation of 2D and 3D incompressible laminar and turbulent flows with free surfaces

Fonte: Biblioteca Digitais de Teses e Dissertações da USP
Publicador: Biblioteca Digitais de Teses e Dissertações da USP

Tipo: Tese de Doutorado
Formato: application/pdf

Publicado em 26/02/2009
Português

Relevância na Pesquisa
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#Averaged Navier-Stokes equations#Conservation laws#Equações de Navier-Stokes#Equações médias de Reynolds#Escoamentos com superfícies livres#Esquema "upwind" de alta resolução#Finite difference method#Free surface flows#High-resolution upwind scheme#Método de diferenças finitas#Modelagem 'capa'- ' epsilon' da turbulência

Apesar de as EDPS que modelam leis de conservação e problemas em dinâmica dos fluídos serem bem estabelecidas, suas soluções numéricas continuam ainda desafiadoras. Em particular, há dois desafios associados à computação e ao entendimento desses problemas: um deles é a formação de descontinuidades (choques) e o outro é o fenômeno turbulência. Ambos os desafios podem ser atribuídos ao tratamento dos termos advectivos não lineares nessas equações de transporte. Dentro deste canário, esta tese apresenta o estudo do desenvolvimento de um novo esquema \"upwind\" de alta resolução e sua associação com modelagem da turbulência. O desempenho do esquema é investigado nas soluções da equação de advecção 1D com dados iniciais descontínuos e de problemas de Riemann 1D para as equações de Burgers, Euler e águas rasas. Além disso, são apresentados resultados numéricos de escoamentos incompressíveis 2D e 3D no regime laminar a altos números de Reynolds. O novo esquema é então associado à modelagem \'capa\' - \'epsilon\' da turbulência para a simulação numérica de escoamentos incompressíveis turbulentos 2D e 3D com superfícies livres móveis. Aplicação, verificação e validação dos métodos numéricos são também fornecidas; Althought the PDEs that model conservation laws and fluid dynamics problems are well established...

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## ‣ Escoamentos em sistemas anulares : o mapas de velocidades; Flows in annuli systems: velocity maps

Fonte: Biblioteca Digital da Unicamp
Publicador: Biblioteca Digital da Unicamp

Tipo: Tese de Doutorado
Formato: application/pdf

Publicado em 12/11/1994
Português

Relevância na Pesquisa
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O presente trabalho é um estudo sobre os escoamentos anulares, onde se destacam os mapas de velocidades para os sistema excêntricos. Estes mapas foram obtidos através de: (i) algoritmos que foram desenvolvidos utilizando as soluções de Snyder 8c Goldstein (1965) para o regime laminar e (ii) da técnica da inversa:o geométrica como apresentada por Ozgen & Tosun (1987) para os escoamentos laminares e turbulentos. Esta técnica transforma um sistema anular excêntrico em um sistema concêntrico, permitindo estender os poucos pontos disponíveis, experimentais ou de soluções analíticas, para abranger praticamente toda a área da secção transversal do escoamento. Foram utilizados como base de referência turbulento os resultados experimentais de Jonsson & Sparow (1966) . Dez sistemas anulares excêntricos foram selecionados. Cinco para cada regime de escoamento ... Observação: O resumo, na íntegra, poderá ser visualizado no texto completo da tese digital; This work deals with annular flows in concentric and eccentric systems. For the latter, we highlight velocity maps. These maps were obtained from: (i) algorithms created by us, based on the SNYDER & GOLDSTEIN (1965) solutions for the laminar flow case and (ii) the geometric inversion technique as presented by OZGEN & TOSUN (1987) for laminar and turbulent flows. The Latter transforms an eccentric annulus system into a concentric system allowing thereafter to probe the complete flow area through a few available points which can be obtained either experimentally or via analytic solutions. We took JONSSON & SPARROW (1966)'s experimental data for velocities as starting point for our calculations for the turbulent case. Ten eccentric annuli systems were selected...

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## ‣ Polymer transport by laminar flows

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 18/02/2002
Português

Relevância na Pesquisa
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Polymer transport is investigated for two paradigmatic laminar flows having
open and closed streamlines, respectively. For both types of flows we find
transport depletion owing to the action of the polymers elastic degree of
freedom. For flows with closed streamlines the leading mechanism for the
observed transport reduction is the (dynamical) formation of barriers. For
flows with open streamlines the reduction of transport is induced by the
renormalization of the bare diffusion coefficient. Results have been obtained
by means of Lagrangian simulations.; Comment: 4 pages, 4 figures

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## ‣ Large scale flows in transitional plane Couette flow: a key ingredient of the spot growth mechanism

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 03/02/2015
Português

Relevância na Pesquisa
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Using Particle Image Velocimetry (PIV) in a new experimental plane Couette
flow, we investigate the dynamics of turbulent patches invading formerly
laminar flows. We evidence experimentally for the first time in this geometry
the existence of large scale flows. These flows appear as soon as laminar and
turbulent domains coexist. Spectral analysis is used to study the dynamical
evolution of these large scales as well as that of the small scales associated
with turbulence. We show that large-scale flows grow before turbulent spots
develop and we point out the crucial role they play in the growth mechanism and
possibly also in the emergence of organised patterns.

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## ‣ Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
38.339678%

Shear flow significantly affects the transport of swimming algae in
suspension. For example, viscous and gravitational torques bias bottom-heavy
cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary
to understand how such biases affect algal dispersion in natural and industrial
flows, especially in view of growing interest in algal photobioreactors.
Motivated by this, we here study the dispersion of gyrotactic algae in laminar
and turbulent channel flows using direct numerical simulation (DNS) and the
analytical swimming dispersion theory of Bees and Croze (2010). Time-resolved
dispersion measures are evaluated as functions of the Peclet and Reynolds
numbers in upwelling and downwelling flows. For laminar flows, DNS results are
compared with theory using competing descriptions of biased swimming cells in
shear flow. Excellent agreement is found for predictions that employ
generalized-Taylor-dispersion. The results highlight peculiarities of
gyrotactic swimmer dispersion relative to passive tracers. In laminar
downwelling flow the cell distribution drifts in excess of the mean flow,
increasing in magnitude with Peclet number. The cell effective axial
diffusivity increases and decreases with Peclet number (for tracers it merely
increases). In turbulent flows...

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## ‣ On the dynamical origin of asymptotic t^2 dispersion of a nondiffusive tracer in incompressible laminar flows

Fonte: Instituto de Tecnologia da Califórnia
Publicador: Instituto de Tecnologia da Califórnia

Tipo: Article; PeerReviewed
Formato: application/pdf

Publicado em /06/1994
Português

Relevância na Pesquisa
47.62015%

Using an elementary application of Birkhoff's ergodic theorem, necessary and sufficient conditions are given for the existence of asymptotically t^2 dispersion of a distribution of nondiffusive passive tracer in a class of incompressible laminar flows. Nonergodicity is shown to be the dynamical mechanism giving rise to this behavior.

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## ‣ Experimental and theoretical scaling laws for transverse diffusive broadening in two-phase laminar flows in microchannels

Fonte: American Institute of Physics
Publicador: American Institute of Physics

Tipo: Article; PeerReviewed
Formato: application/pdf

Publicado em //2000
Português

Relevância na Pesquisa
47.99446%

This letter quantifies both experimentally and theoretically the diffusion of low-molecular-weight species across the interface between two aqueous solutions in pressure-driven laminar flow in microchannels at high Peclet numbers. Confocal fluorescent microscopy was used to visualize a fluorescent product formed by reaction between chemical species carried separately by the two solutions. At steady state, the width of the reaction-diffusion zone at the interface adjacent to the wall of the channel and transverse to the direction of flow scales as the one-third power of both the axial distance down the channel (from the point where the two streams join) and the average velocity of the flow, instead of the more familiar one- half power scaling which was measured in the middle of the channel. A quantitative description of reaction-diffusion processes near the walls of the channel, such as described in this letter, is required for the rational use of laminar flows for performing spatially resolved surface chemistry and biology inside microchannels and for understanding three-dimensional features of mass transport in shearing flows near surfaces.

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## ‣ Investigation of the Stability of the Laminar Boundary Layer in a Compressible Fluid

Fonte: National Advisory Committee for Aeronautics
Publicador: National Advisory Committee for Aeronautics

Tipo: Report or Paper; PeerReviewed
Formato: application/pdf

Publicado em /09/1946
Português

Relevância na Pesquisa
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In the present report the stability of two-dimensional laminar flows of a gas is investigated by the method of small perturbations. The chief emphasis is placed on the case of the laminar boundary layer.
Part I of the present report deals with the general mathematical theory. The general equations governing one normal mode of the small velocity and temperature disturbances are derived and studied in great detail. It is found that for Reynolds numbers of the order of those encountered in most aerodymnic problems, the temperature disturbances have only a negligible effect on those particular velocity solutions which depend primarily on the viscosity coefficient ("viscous solutions"). Indeed, the latter are actually of the same form in the compressible fluid as in the incompressible fluid, at least to the first
approximation. Because of this fact, the mathematical analysis is greatly simplified. The final equation determining the characteristic values of the stability problem depends on the "inviscid solutions" and the function of Tietjens in a manner very similar to the case of the incompressible fluid. The second viscosity coefficient and the coefficient of heat conductivity do not enter the problem; only the ordinary coefficient of viscosity near the solid surface is involved.
Part II deals wlth the limiting case of infinite Reynolds numbers. The study of energy relations is very much emphasized. It is shown that the disturbance will gain energy from the main flow if the gradient of the product of mean density and mean vorticity near the solid surface has a sign opposite to that near the outer edge of the boundary layer.
A general stability criterion has been obtained in terms of the gradient of the product of density and vorticity...

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## ‣ An Extension of the flow boiling correlation to transition, laminar and deep laminar flows in minichannels and microchannels

Fonte: Taylor & Francis
Publicador: Taylor & Francis

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
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Flow boiling in mini- and microchannels offer very high heat transfer capabilities and find
applications in many emerging technologies, such as electronics cooling and fuel cells. The low flow
rate employed in such geometries, coupled with the small flow channels, often results in a laminar
flow with all flow as liquid. Since the single-phase flow with all liquid is in the laminar range, the
flow boiling correlations developed for conventional tubes with an inner diameter larger than 3 mm
and turbulent flow need to be carefully reviewed. In the present work, flow boiling correlation for
large diameter tubes developed by Kandlikar [1, 2] is modified for flow boiling in minichannels by
using the laminar single-phase heat transfer coefficient for all liquid flow. The correlation is also
extended for flow boiling in microchannels using the nucleate boiling as the dominant part of the
original correlation. The trends in heat transfer coefficient versus quality are compared in the
laminar and deep laminar regions in minichannels and microchannels. Excellent agreement is
obtained between predicted values and experimental data.; RIT community members may access full-text via RIT Libraries licensed databases: http://library.rit.edu/databases/

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## ‣ Patterns of solidification in channel flows with surface cooling

Fonte: Cambridge University Press
Publicador: Cambridge University Press

Tipo: Artigo de Revista Científica

Português

Relevância na Pesquisa
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#Keywords: Channel flow#Heat convection#Laminar flow#Shear flow#Solidification#Flow structures#Surface cooling#Fluid mechanics#fluid mechanics#solidification

Understanding the rates of cooling and solidification in laminar flows down sloping channels is central to predicting the advance of lava flows. The mechanisms involved include thermal convection and a competition between shear strain rate and the rate of formation of solid at the chilled surface of the flow. We report experiments in which polyethylene glycol wax flows in a laminar fashion down an inclined, open channel of rectangular cross-section under cold water. Two distinctly different flow regimes are recognized: 'tube' flow in which solidification of the flow surface creates a stationary roof while melt continues to flow through a relatively well-insulated 'tube' beneath, and a 'mobile crust' regime in which a solid surface crust develops only in the centre of the channel. In the latter regime the crust is carried down the channel, separated from the walls by crust-free shear regions in which cooling produces only dispersed fragments of solid owing to the effects of shearing. This flow structure is quasi-invariant over a large distance downstream. We show that thermal convection takes place in organized rolls that have axes aligned with the shear flow, and conclude that transition between the two flow regimes occurs at a critical value of the combined parameter ν = Ψ(Ra/R0)1/3...

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## ‣ Fully developed laminar convection whit variable thermophysical properties between two heated vertical parallel plates

Fonte: Latin American applied research
Publicador: Latin American applied research

Tipo: Artigo de Revista Científica
Formato: text/html

Publicado em 01/01/2009
Português

Relevância na Pesquisa
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In this work, the influence on the flow and heat transfer of the density, viscosity and thermal conductivity temperature dependence was analyzed. A perturbation analysis was applied to a vertical fully developed laminar stationary flow between two heated parallel flat plates. For small values of the dimensionless numbers associated with the buoyancy, viscosity and thermal conductivity changes effects, the influence of the different properties temperature dependence was obtained. Application examples to water and air flows are also presented.

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