The aim of this paper is to study the applicability of the theory of micropolar ﬂuids to modelling and calculating ﬂows in microchannels depending on the geometrical dimension of the ﬂow ﬁeld. First, it will be shown that if the characteristic linear dimension of the ﬂow becomes appropriately large, the equations describing the micropolar ﬂuid ﬂow can be transformed into Navier-Stokes equations. Next, Poiseuille ﬂows in a microchannel is studied in detail. In particular, the maximal cross-sectional size of the channel for which the micropolar eﬀects of the ﬂuid ﬂow become important will be established. The experimentally determined values of rheological constants of the ﬂuid have been used in calculations.
This paper presents the analysis of momentum, angular momentum and heat transfer during unsteady natural convection in micropolar nanofluids. Selected nanofluids treated as single phase fluids contain small particles with diameter size 10-38.4 nm. In particular three water-based nanofluids were analyzed. Volume fraction of these solutions was 6%. The first of the analyzed nanofluids contained TiO2nanoparticles, the second one contained Al2O3nanoparticles, and the third one the Cu nanoparticles.