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The current study investigates the laminar and two-phase nanofluid flow inside a two-dimensional rectangular microchannel with the ratio of length to height of L/H = 120. This study is simulated by using finite volume method in two-dimensional coordinates. Because most of the miniature equipments are affected by the oscillating heat flux, we try to study the hydrodynamical behavior of flow and heat transfer with oscillating heat flux boundary condition. The present research has been carried out in Reynolds numbers of 150-1000 and Ag nanoparticles volume fractions of 0-4% by applying slip and no-slip boundary conditions. Also, in order to estimate the heat transfer behavior and the computational fluid dynamics, two-phase mixture method is employed. The obtained results are analyzed and presented as the contours of Nusselt number, friction coefficient, pressure drop, thermal resistance and temperature. The results also revealed that, applying slip boundary condition on microchannel walls and the enhancement of fluid velocity, Grashof number and volume fraction of nanoparticles cause the improvement of Nusselt number, reduction of thermal resistance and total entropy generation and the augmentation of pressure drop. According to the obtained results, the presence of oscillating heat flux affects the changes of Nusselt number, significantly. In comparison with the pure water fluid with Reynolds numbers of 1000, 700 and 400, in Grashof number of 1000 with no-slip boundary condition on microchannel walls, the enhancement of average Nusselt number in volume fraction of 4% in the same Reynolds numbers is 45%. Also, in mentioned conditions, the pressure drop increases almost 2.8 times further. [ABSTRACT FROM AUTHOR]

In this paper, the effect of internal serrated fins and eccentricity on natural convection heat transfer between annular spaces with the equivalent circular, square, and triangular cross sections has been studied numerically using control volume method. The annuli's inner and outer walls were maintained at different uniform temperatures of 373 and 327 K, respectively, and Rayleigh number ranges were 105 ≤ Ra ≤ 108. According to the results, although heat transfer coefficient was reduced between the space of fins, fins increased the total heat transfer of both inner and outer walls of annuli. The best heat transfer rate belongs to reverse triangular annulus when fins were mounted on the inner wall. As an example, heat transfer of inner wall of reverse triangular annulus was, respectively, increased about 31 and 10% at Ra = 105 and 108, when serrated fins were mounted on the inner wall. In addition, fin efficiency of inner and outer walls was decreased with the increase in Rayleigh number. Nevertheless, thermal efficiency of reverse triangular annulus was uppermost at all Rayleigh numbers compared to other ones. In addition, eccentric annuli showed better heat transfer rate than concentric ones, in which cases 3.5 and 6.7% thermal improvements have been obtained for 0.6 and 1 mm downward movement of the inner wall at Ra = 108, respectively. [ABSTRACT FROM AUTHOR]