Mixed convection and thermodynamic irreversibilities in MHD nanofluid stagnation-point flows over a cylinder embedded in porous media

Abstract

The impingement of CuO-water nanofluid flows upon a cylinder subject to a uniform magnetic field with constant surface temperature and embedded in porous media is investigated for the first time in literature. The surface of the cylinder can feature uniform or non-uniform mass transpiration and is hotter than the incoming nanofluid flow. The gravitational effects are taken into account and the three-dimensional governing equations of mixed convection in curved porous media, under magnetohydrodynamic effects, are reduced to those solvable by a finite difference scheme. Through varying a mixed convection parameter, the situations dominated by forced, mixed and free convection are examined systematically. The numerical solutions of these equations reveal the flow velocity and temperature fields as well as the Nusselt number and induced shear stress. These are then used to calculate the rate of entropy generation within the system by viscous and heat transfer irreversibilities. The results show that Nusselt number increases with increasing the concentration of nanoparticles, while it slightly deceases through intensifying the magnetic parameter. Non-uniform transpiration is shown to strongly affect the average rate of heat transfer. Importantly, it is demonstrated that the specific mode of heat convection can majorly influence the intensity of entropy generation and that the irreversibilities are much larger under natural convection compared to those in mixed and forced convection. Calculation of Bejan number shows that this is due to more pronounced relative contribution of viscous irreversibilities when free convection effects dominate the mixed convection process.

Magnetohydrodynamics, Natural Convection, and Entropy Generation of CuO–Water Nanofluid in an I-Shape Enclosure—A Numerical Study

“…Table 3 also shows that the average Nusselt number decreases through increasing Ha. These declines are more obvious at Ra=10 5 and 10 6 , in which convection is the dominant mechanism of heat transfer and, once again, are in keeping with the literature [33][34][35][36]. Fig.…”

“…This notion has been investigated in a series of numerical studies by Sheikholeslami and Ganji and their co-workers, e. g. [33][34][35]. Further, a wide variety of configurations have been analysed by other authors [21,36,37]. In particular, configuration with curved walls [38] and those containing multiphase-phase fluids [38,39] have been extensively analysed.…”

Effects of radiation and magnetic field on mixed convection stagnation-point flow over a cylinder in a porous medium under local thermal non-equilibrium

“…Thermal radiation effect A two-equation model is used here to express the transport of thermal energy in the porous medium. The energy equation for the nanofluid phase is written as [32] u…”

“…[40]. Equations (16), (21), (27) and 30, and the boundary conditions (18)(19)(20), (22)(23)(24), (28)(29) and (31)(32), were numerically solved by employing an implicit, iterative tri-diagonal finite-difference method [41][42][43].…”

“…The hydrodynamics of nanofluids under magnetic effects are already well investigated [32], and therefore they are not further elaborated in here. Nonetheless, to illustrate the flow field, Fig.…”