Maximum heat transfer rate density in two-dimensional minichannels and microchannels

摘要

The objective of the present article is to compare previous experimental data of Gao et al. [20] to the predictions of Bejan and Sciubba's analysis [7] on the optimal spacing for maximum heat transfer from a package of parallel plates. 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. The experimental data were processed by using the dimensionless parameters of Bejan and Sciubba's analysis [7]. 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. This article reports the first time that the optimal spacing between parallel plates is determined experimentally.