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Proceedings of CHT-17 ICHMT International Symposium on Advances in Computational Heat Transfer
May 28 - June 1, 2017, Napoli, Italy

DOI: 10.1615/ICHMT.2017.CHT-7


ISBN Print: 9781-56700-4618

ISSN: 2578-5486

GAS FLOWS WITH HEAT TRANSFER IN MICRO CHANNELS: CLARIFICATIONS ABOUT THE NUSSELT NUMBER

pages 1277-1291
DOI: 10.1615/ICHMT.2017.CHT-7.1360
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RESUMO

This paper deals with the modelling of weakly rarefied and dilute flows in heated micro channels by the continuum approach, valid for Knudsen numbers smaller than about 0.1. The first order slip and thermal jump model usually used for the forced convection of flows in long micro channels between two infinite plates is discussed. Indeed, in the huge literature related to this subject, it appears that simplified models are often used without justifying them and that recurrent errors propagate from one paper to the other. The erroneous models particularly concern the heat transfer analysis and the energy equation. The compatibility of the pressure work and viscous dissipation in the energy equation with the power of the viscous forces at the walls and the choice of an appropriate Nusselt number are particularly discussed. Our aim is to provide a consistent model for gaseous micro-flows and the linked heat transfer. Then, a dimensional and asymptotic analysis is performed in the context of long micro channels and an analytical solution for the temperature field and the Nusselt number is proposed in the case of a compressible flow in a long micro-channel maintained at a constant wall temperature. This solution is compared with the numerical solution of the full model taking into account the first order slip and thermal jump conditions at the walls, the power of the viscous forces in the wall heat flux, the thermal creep term and the pressure work and viscous dissipation in the bulk. The vanishing values of the Nusselt number measured in the experiments by Demsis et al. (2009, 2010) are explained for the first time.

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