Fundamental Principles Laminar Boundary Layer Flow Laminar Duct Flow External Natural Convection Internal Natural Convection Transition to Turbulence Turbulent Boundary Layer Flow Turbulent Duct Flow Free Turbulent Flows Convection with Change of Phase Mass Transfer Convection in Porous Media.

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Convection Heat Transfer

Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

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Microfluidics: Fluid physics at the nanoliter scale

Conceptions for heat transfer correlation of nanofluids

Dipstick and lateral-flow formats have dominated rapid diagnostics over the last three decades. These formats gained popularity in the consumer markets due to their compactness, portability and facile interpretation without external instrumentation. However, lack of quantitation in measurements has challenged the demand of existing assay formats in consumer markets. Recently, paper-based microfluidics has emerged as a multiplexable point-of-care platform which might transcend the capabilities of existing assays in resource-limited settings. However, paper-based microfluidics can enable fluid handling and quantitative analysis for potential applications in healthcare, veterinary medicine, environmental monitoring and food safety. Currently, in its early development stages, paper-based microfluidics is considered a low-cost, lightweight, and disposable technology. The aim of this review is to discuss: (1) fabrication of paper-based microfluidic devices, (2) functionalisation of microfluidic components to increase the capabilities and the performance, (3) introduction of existing detection techniques to the paper platform and (4) exploration of extracting quantitative readouts via handheld devices and camera phones. Additionally, this review includes challenges to scaling up, commercialisation and regulatory issues. The factors which limit paper-based microfluidic devices to become real world products and future directions are also identified.

Paper-based microfluidic point-of-care diagnostic devices

The structural properties of free nanoclusters are reviewed. Special attention is paid to the interplay of energetic, thermodynamic, and kinetic factors in the explanation of cluster structures that are actually observed in experiments. The review starts with a brief summary of the experimental methods for the production of free nanoclusters and then considers theoretical and simulation issues, always discussed in close connection with the experimental results. The energetic properties are treated first, along with methods for modeling elementary constituent interactions and for global optimization on the cluster potential-energy surface. After that, a section on cluster thermodynamics follows. The discussion includes the analysis of solid-solid structural transitions and of melting, with its size dependence. The last section is devoted to the growth kinetics of free nanoclusters and treats the growth of isolated clusters and their coalescence. Several specific systems are analyzed.

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Structural properties of nanoclusters: Energetic, thermodynamic, and kinetic effects

Sir Geoffrey Taylor has recently discussed the dispersion of a solute under the simultaneous action of molecular diffusion and variation of the velocity of the solvent. A new basis for his analysis is presented here which removes the restrictions imposed on some of the parameters at the expense of describing the distribution of solute in terms of its moments in the direction of flow. It is shown that the rate of growth of the variance is proportional to the sum of the molecular diffusion coefficient, D, and the Taylor diffusion coefficient $\kappa $a$^{2}$U$^{2}$/D, where U is the mean velocity and a is a dimension characteristic of the cross-section of the tube. An expression for $\kappa $ is given in the most general case, and it is shown that a finite distribution of solute tends to become normally distributed.

On the Dispersion of a Solute in a Fluid Flowing through a Tube

The method used in an earlier paper (Aris 1956) to discuss the dispersion of a solute in a fluid flowing through a tube is applied here to the case in which the solute can also pass into another fluid phase flowing in an annular region around the first. The apparent diffusion coefficient is the sum of the molecular and Taylor diffusion coefficients in the two phases and a term due to the finite rate of partition between them. It is shown how the Taylor diffusion coefficients depend on the ratio of amounts of solute held in the two phases and how this gives a connexion between the coefficient a 2 U 2 /48 D found by Taylor (1953) for viscous flow in a circular tube and the 11 a 2 U 2 /48 D found by Westhaver (1942) in his analysis of the distillation column. The use of these apparent diffusion coefficients in distillation and partition chromatography is illustrated.

On the Dispersion of a Solute by Diffusion, Convection and Exchange between Phases

The effective dispersion coefficient of a solute in pulsating flow through a circular tube is here found. The case of a viscous flow under a pulsating pressure gradient is treated in detail and it is found that the Taylor diffusion coefficient contains terms proportional to the square of the amplitude of the pressure pulsations. However, the coefficients of these terms tend rapidly to zero, and the effect of pulsation will rarely contribute a fraction of more than 1/128 (the ratio of the amplitude of pressure gradient pulsation to mean pressure gradient) 2 to the total dispersion coefficient. The methods may be applied to diffusion in any periodic flow.

On the dispersion of a solute in pulsating flow through a tube

Bifurcation behavior in homogeneous-heterogeneous combustion: II. Computations for stagnation-point flow☆

Les auteurs montrent comment une cinetique d'ordre deux, caracterisant une reaction ou une partie des composes chimiques est inactive, peut devenir une cinetique d'ordre inferieur a deux lorsque ces composes chimiques deviennent actifs. Ils etudient le cas d'une reaction de craquage catalytique

Rutherford Aris

Papers

On the Dispersion of a Solute in a Fluid Flowing through a Tube

On the Dispersion of a Solute by Diffusion, Convection and Exchange between Phases

On the dispersion of a solute in pulsating flow through a tube

Bifurcation behavior in homogeneous-heterogeneous combustion: II. Computations for stagnation-point flow☆

On apparent second‐order kinetics