Vortex Generators for Compact Heat Exchangers

Fiebig, M.

doi:10.1615/jenhheattransf.v2.i1-2.60

Cited by 126 publications

(57 citation statements)

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“…To fully utilize the advantages of microchannel cooling technology, such as high energy mitigation capability and low heat resistance and effectively solve the existing two problems encountered by plane microchannels, i.e., high pressure drop and high channel-wise temperature rise, this research project is going to apply vortex generator (VG) technology [2][3][4] in microchannels, i.e., periodically mounting arrays of square cylinders/bars in microchannel to generate self-sustained oscillating flow. Since the ordered laminar oscillating flow requires much less pumping power than turbulent flow to achieve the same heat transfer rate or to get a much higher heat transfer rate at the same pumping power, due to the advantage of ordered laminar self-sustained oscillation over random turbulent fluctuations which yields less viscous dissipation.…”

Section: Research Backgroundmentioning

confidence: 99%

Heat Transfer Enhancement Through Self-Sustained Oscillating Flow in Microchannels

Lin¹

2006

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Section: Research Backgroundmentioning

confidence: 99%

Heat Transfer Enhancement Through Self-Sustained Oscillating Flow in Microchannels

Lin¹

2006

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“…Vortices and their generators incorporate all three enhancement mechanisms. Vortices swirl fluid around their axis of rotation, they induce velocity profiles which are less stable, and their generation implies flow separation and developing viscous layers [2,3]. Even though everybody knows what is meant by a vortex, namely swirling flow, a clear mathematical definition of a vortex is missing, even though vorticity…”

Section: Introductionmentioning

confidence: 99%

“…Self-sustained oscillations associated with vortices have been exploited very little in general, especially for heat transfer purposes. The third mechanism viscous layer interruption and initiation of new developing viscous layers is implied by vortex generation [3]. Vortices are generated by fluid friction and its separation, thus vortex generator (VG) surfaces induce development of a new viscous layers.…”

Section: Introductionmentioning

confidence: 99%

The use of liquid crystal thermography and particle image velocimetry in the exploration of heat transfer measurements

Stąsiek

Stasiek²,

Mikielewicz

et al. 2009

Proceedings of the Sixth International Symposium on Turbulence, Heat and Mass Transfer

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-Generation of vortices enhances heat transfer by swirl, flow destabilization and development of viscous layers. They may increase heat transfer by several hundred percent. Prior to the use of vortices to influence heat transfer it must be known how different vortices are generated and controlled, and how they interact with the base flow and temperature field. To select the most appropriate vortex generators (VG) for a given task it is necessary to know the heat transfer and flow losses associated with the generation of a specific vortex system. The aim of the paper is to asses the state of art and to encourage exploration of heat transfer control by vortices. Flow visualization and heat transfer experiments were conducted using an open low-speed wind tunnel equipped with Liquid Crystals Thermography (LCT) and Particle Image Velocimetry (PIV). In this work we consider five types of transverse vortex generators (TVGs) which where brought to required temperatures by the hot film method. Heat transfer measurements were carried out by LCT.

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“…In certain vortex generation techniques, it is possible to estimate the relatively large penalty due to drag of the vortex generators relative to the benefit attained: a doubling of heat transfer enhancement ratio could incur a quadrupling of the drag penalty ratio (e.g. Fiebig 1995Fiebig , 1996. In addition, considerable surface area, and hence skin friction drag, is incurred in lobed nozzles.…”

Section: Introductionmentioning

confidence: 99%

An extended Reynolds analogy for excited wavy instabilities of developing streamwise vortices with applications to scalar mixing intensification

Liu

2007

Proc. R. Soc. A.

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Studies are presented to elucidate the role of steady streamwise vortex structures, initiated upstream from weak Görtler vortices in the absence of explicit vortex generators, and their excited nonlinear wavy instabilities in the intensification of scalar mixing in a spatially developing mixing region. While steady streamwise vortex flow gives rise to significant mixing enhancement, the excited nonlinear wavy instabilities, which in turn modify the basic three-dimensional streamwise vortices, give rise to further mixing intensification which is quantitatively assessed by a mixedness parameter. Possibility of similarity between the dimensionless streamwise momentum and scalar transport problems leading to an extended Reynolds analogy is sought. This similarity is shown earlier to hold for the steady streamwise vortex flow in the absence of nonlinear wavy instabilities (Liu & Sabry 1991 Proc. R. Soc. A 432, 1-12). In this paper, the momentum conservation equations for the nonlinear wavy or secondary instabilities together with the advected fluctuation scalar problems are examined in detail. The presence of the streamwise fluctuation pressure gradient, which prevents the similarity, is estimated in terms of the fluctuation dynamical pressure and its relative importance to advective transport. It is found from scaling that the fluctuating streamwise pressure gradient, though not completely negligible, is sufficiently unimportant so as to render similarity between fluctuation streamwise velocity and fluctuation temperature and concentration a distinct possibility. The scalar fluctuations are then inferable from the fluctuation streamwise velocity and that the Reynolds stresses of the nonlinear fluctuations and the scalar fluxes are also similar. The nonlinear instabilitymodified mean streamwise momentum and the modified mean heat and mass transport problems are also similar, thus providing a complete 'Reynolds analogy', rendering possible the interpretation of the scalar mixedness for a gaseous medium for which the Prandtl and Schmidt numbers are near unity. It is found that the nonlinearity of the wavy instability, which induces scalar fluxes modifying the mean scalar transport, further intensifies scalar mixedness over a significant streamwise region which is well above that achieved by the steady, unmodified streamwise vortices alone for the numerical example corresponding to the most amplified wavy-sinuous mode.

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Vortex Generators for Compact Heat Exchangers

Cited by 126 publications

References 0 publications

Heat Transfer Enhancement Through Self-Sustained Oscillating Flow in Microchannels

Heat Transfer Enhancement Through Self-Sustained Oscillating Flow in Microchannels

The use of liquid crystal thermography and particle image velocimetry in the exploration of heat transfer measurements

An extended Reynolds analogy for excited wavy instabilities of developing streamwise vortices with applications to scalar mixing intensification

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