Many experimental works appeared in the last decade in the open literature dealing with forced convection through microchannels. The earliest experimental results on single-phase flows in microchannels evidenced that for channels having a hydraulic diameter less than the conventional continuum models can no longer be considered as able to accurately predict pressure drop and convective heat transfer coefficients. This conclusion seemed to be valid for both gas and liquid flows. Sometimes the authors justified this conclusion by invoking new micro-effects, e.g., electrostatic interaction between the fluid and the walls or scaling effects (axial heat conduction, viscous forces, conjugate heat transfer, wall roughness, and so on). In this paper the role of the viscous dissipation in liquids flowing through heated microchannels will be analyzed by using the conventional theory. We will present a correlation between the Brinkman number and the Nusselt number for silicon ⟨100⟩ and ⟨110⟩ microchannels. It will be demonstrated that the fluid is of importance in establishing the exact limit of significance of the viscous dissipation in microchannels; a criterion to analyze the significance of the viscous effects will be presented. The role of the cross-section aspect ratio on the viscous dissipation will be highlighted. The main goal of this work is to demonstrate that the problem of heat transfer enhancement in microdevices cannot be solved by indefinitely reducing the microchannel dimensions because the viscous dissipation effects shall offset the gains of high heat transfer coefficients associated with a reduction in the channel size.
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The Role of the Viscous Dissipation in Heated Microchannels
Gian Luca Morini,
e-mail: gianluca.morini@mail.ing.unibo.it
Gian Luca Morini
DIENCA-Università degli Studi di Bologna, Viale Risorgimento 2
, 40136 Bologna, Italy
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Marco Spiga
Marco Spiga
Dipartimento di Ingegneria Industriale,
Parco Area delle Scienze 181A
, 43100 Parma, Italy
Search for other works by this author on:
Gian Luca Morini
DIENCA-Università degli Studi di Bologna, Viale Risorgimento 2
, 40136 Bologna, Italye-mail: gianluca.morini@mail.ing.unibo.it
Marco Spiga
Dipartimento di Ingegneria Industriale,
Parco Area delle Scienze 181A
, 43100 Parma, ItalyJ. Heat Transfer. Mar 2007, 129(3): 308-318 (11 pages)
Published Online: May 12, 2006
Article history
Received:
November 30, 2005
Revised:
May 12, 2006
Citation
Morini, G. L., and Spiga, M. (May 12, 2006). "The Role of the Viscous Dissipation in Heated Microchannels." ASME. J. Heat Transfer. March 2007; 129(3): 308–318. https://doi.org/10.1115/1.2430725
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