Laminar forced convection heat transfer in curved rectangular channels
TL;DR: In this article, the authors present flow and heat transfer results obtained by a point successive over-relaxation method for steady fully developed laminar flow in curved rectangular channels under the thermal boundary conditions of axially uniform wall heat flux and peripherally uniform wall temperature.
About: This article is published in International Journal of Heat and Mass Transfer.The article was published on 1970-03-01. It has received 137 citations till now. The article focuses on the topics: Dean number & Heat transfer coefficient.
Citations
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TL;DR: In this paper, a literature review on heat transfer and flow characteristics of single-phase and two-phase flow in curved tubes is presented, where three main categories of curved tubes; helically coiled tubes, spirally coiling tubes, and other coiled tube, are described.
Abstract: The performance of heat exchangers can be improved to perform a certain heat-transfer duty by heat transfer enhancement techniques. In general, these techniques can be divided into two groups: active and passive techniques. The active techniques require external forces, e.g. electric field, acoustic or surface vibration, etc. The passive techniques require fluid additives or special surface geometries. Curved tubes have been used as one of the passive heat transfer enhancement techniques and are the most widely used tubes in several heat transfer applications. This article provides a literature review on heat transfer and flow characteristics of single-phase and two-phase flow in curved tubes. Three main categories of curved tubes; helically coiled tubes, spirally coiled tubes, and other coiled tubes, are described. A review of published relevant correlations of single-phase heat transfer coefficients and single-phase, two-phase friction factors are presented.
441 citations
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TL;DR: The theoretical developments that have made the field of inertial focusing what it is today are described and the key applications that will make inertialocusing a mainstream technology in the future are presented.
Abstract: When Segre and Silberberg in 1961 witnessed particles in a laminar pipe flow congregating at an annulus in the pipe, scientists were perplexed and spent decades learning why such behavior occurred, finally understanding that it was caused by previously unknown forces on particles in an inertial flow. The advent of microfluidics opened a new realm of possibilities for inertial focusing in the processing of biological fluids and cellular suspensions and created a field that is now rapidly expanding. Over the past five years, inertial focusing has enabled high-throughput, simple, and precise manipulation of bodily fluids for a myriad of applications in point-of-care and clinical diagnostics. This review describes the theoretical developments that have made the field of inertial focusing what it is today and presents the key applications that will make inertial focusing a mainstream technology in the future.
429 citations
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TL;DR: In this paper, a new type of micromixer is proposed that relies on the transition of the secondary flow pattern from two to four vortices, and the corresponding helical flows are analyzed for various Reynolds numbers ranging from 1 to 900.
Abstract: Helical flows are investigated in structured microchannels with regard to micromixing by means of computational fluid dynamics (CFD). In the case of bas-relief structured channels the numerical results are found to be in good agreement with experimental findings. The magnitude of the transverse flow is computed for various Reynolds numbers and for different geometries including channels with bas-relief structures on two opposite walls. Transverse flows in structured microchannels are compared to secondary flow patterns in curved square channels. The corresponding helical flows are analyzed for Dean numbers ranging from 1 to 900. Special attention is paid to the occurrence of additional vortices close to the center of the outer channel wall. Based on the results a new type of micromixer is proposed that relies on the transition of the secondary flow pattern from two to four vortices. © 2004 American Institute of Chemical Engineers AIChE J, 50: 771–778, 2004
189 citations
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TL;DR: This work is the first to experimentally and numerically investigate Dean flows in microchannels for Re > 100, and show presence of secondary Dean vortices beyond a critical Dean number, and offers new insights into secondary flow instabilities for low-aspect ratio, spiral microch channels.
Abstract: A wide range of microfluidic cell-sorting devices has emerged in recent years, based on both passive and active methods of separation. Curvilinear channel geometries are often used in these systems due to presence of secondary flows, which can provide high throughput and sorting efficiency. Most of these devices are designed on the assumption of two counter rotating Dean vortices present in the curved rectangular channels and existing in the state of steady rotation and amplitude. In this work, we investigate these secondary flows in low aspect ratio spiral rectangular microchannels and define their development with respect to the channel aspect ratio and Dean number. This work is the first to experimentally and numerically investigate Dean flows in microchannels for Re > 100, and show presence of secondary Dean vortices beyond a critical Dean number. We further demonstrate the impact of these multiple vortices on particle and cell focusing. Ultimately, this work offers new insights into secondary flow instabilities for low-aspect ratio, spiral microchannels, with improved flow models for design of more precise and efficient microfluidic devices for applications such as cell sorting and micromixing.
176 citations
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TL;DR: In this paper, the main velocity redistribution in steady flow through curved conduits of shallow rectangular cross-section is considered and its mechanism is analyzed using a mathematical model of steady incompressible laminar flow in coiled rectangular pipes.
Abstract: The main velocity redistribution in steady flow through curved conduits of shallow rectangular cross-section is considered. Its mechanism is analysed using a mathematical model of steady incompressible laminar flow in coiled rectangular pipes. The transverse transport of main-flow momentum by the secondary circulation is shown to be the principal cause of this velocity redistribution. The importance of the side-wall regions, even in shallow channels, is assessed and the neglect of the influence of the side walls in the commonly applied simplified models of flow through shallow curved channels is shown to be strongly limiting in case of long bends with a rectangular cross-section.
127 citations
References
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TL;DR: In this paper, it is assumed that the actual secondary motion is replaced by a uniform stream; conditions in the central part of the section mainly determines the motion and the appropriate velocity of the stream can be determined from the relation that has been found experimentally between the rate of flow in a curved pipe and the pressure gradient.
Abstract: In the stream-line motion of fluid in a curved pipe the primary motion along the line of the pipe is accompanied by a secondary motion in the plane of the cross-section. The secondary motion decreases the rate of flow produced by a given pressure gradient and causes an outward movement of the region where the primary motion is greatest. It is difficult to deduce these consequences from the exact equations of motion, but it is easy to do so if it is assumed that the actual secondary motion is replaced by a uniform stream; conditions in the central part of the section mainly determines the motion and here the secondary motion is approximately a uniform stream. The appropriate velocity of the stream can be determined from the relation that has been found experimentally between the rate of flow in a curved pipe and the pressure gradient.
714 citations
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TL;DR: In this paper, the effect of curvature on flow resistance and heat transfer in a laminar flow in a curved pipe has been investigated under the condition of uniform heat flux at large Dean numbers and Prandtl numbers.
317 citations
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TL;DR: In this paper, friction and heat transfer results for the laminar flow of oil and the turbulent flow of water in tube coils having ratios of coil to tube diameter of 17 and 104, for Reynolds numbers from 12 to 65 000.
305 citations
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TL;DR: In this article, the steady laminar motion of a fluid in an enclosed cavity is described, the motion being generated by a temperature gradient normal to the direction of the body force.
212 citations
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TL;DR: In this article, a study of the natural convection of a fluid contained in a long horizontal enclosure of rectangular cross section with one vertical wall heated and the other cooled is made, and the governing vorticity and energy transport equations are solved by an implicit alternating direction finite-difference method.
Abstract: A study is made of the natural convection of a fluid contained in a long horizontal enclosure of rectangular cross section with one vertical wall heated and the other cooled. Two-dimensional motion is assumed. The governing vorticity and energy transport equations are solved by an implicit alternating direction finite-difference method. Transient and steady state isothermals and streamlines are obtained for Grashof numbers up to 100,000 and for height-to-width ratios of 1, 2, and 3.
200 citations