Abstract

Experimental investigations of the flow and the associated heat transfer were conducted in two-dimensional microchannels in order to test possible size effects on the laws of hydrodynamics and heat transfer and to infer optimal conditions of use from the measurements. The test section was designed to modify easily the channel height e between 1 mm and 0.1 mm. Measurements of the overall friction factor and local Nusselt numbers show that the classical laws of hydrodynamics and heat transfer are verified for e > 0.4 mm. For lower values of e, a significant decrease of the Nusselt number is observed, whereas the Poiseuille number continues to have the conventional value of laminar developed flow. The transition to turbulence is not affected by the channel size. For fixed pressure drop across the channel, a maximum of heat transfer rate density is found for a particular value of e. The corresponding dimensionless optimal spacing and heat transfer rate density are in very good agreement with the predictions of Bejan and Sciubba (1992). This paper is the first time that the optimal spacing between parallel plates is determined experimentally.

Highlights

  • The development of microscale systems has grown rapidly during last decades, making possible many applications

  • Scaling laws pertaining to the hydrodynamics and heat transfer in microchannels are not clearly established, many studies have been devoted to this subject in recent years

  • Published experimental results question the applicability of classical laws when the characteristic dimensions of the channel are of the order of several hundred to one μm

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Summary

Introduction

The development of microscale systems has grown rapidly during last decades, making possible many applications. From these computations it was found that the measurements in sections "2" and "3" are not affected by conductive effects and may be used to determine the heat transfer coefficient in the channel (for more details, see Gao et al, 2002a).

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