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Numerical simulation of magnetohydrodynamic natural convection heat transfer in a rhombic enclosure of inclination angle 45 ∘ containing copper-water nanofluid has been presented in this paper. The top and bottom walls of the enclosure are subjected to non-uniform heating while left wall being subjected to lower temperature and right wall being maintained adiabatic. The finite element strategy (COMSOL Multiphysics) is used to solve the governing equations. The numerical simulations are done for the parametric values: 10 4 ≤ Rayleigh number ≤ 10 6 ; 0 ≤ Hartmann number ≤ 100; 0 ≤ volume fraction of nanofluid ≤ 0.05. The phase deviation angle (top wall) is varied in the range from 0 to π with amplitude of non linear heating being maintained constant. The motivation of this research goes with the fact that the associated transport phenomenon conveys the implication of designing an optimal thermal system analogous to the theme of non-uniform heating, with the phase angle being a crucial design parameter. The numerical results depict to the fact, that the rate of heat transfer follows non-monotonic trends and is considerably influenced by interplay of the phase shift angle, Rayleigh number and Hartmann number. The results showed that at Rayleigh number ≥ 10 5 , the heat transfer rate gets inhibited by enhancing the magnetic field intensity. The impact of different types of nano particles is illustrated by comparing the results with the results of three different nanofluids, silver– water, titanium dioxide–water and diamond–water nanofluids. [ABSTRACT FROM AUTHOR]

In this paper, we present a numerical investigation of natural convection heat transfer and entropy generation for a rhombic enclosure with inclination angle, ϕ = 30°, filled with a porous medium. The left and right surface walls of the enclosure are confined to cold temperature bath while we impart non-uniform, varying temperature distribution with unequal phase angles along the top and bottom wall. The flow inside the enclosure is steady, two-dimensional, incompressible and laminar, and the working fluid is air (Pr = 0.71). Numerical experiments have been performed using finite element method-based software COMSOL Multiphysics 5a for Darcy number and Rayleigh number in the extent of 10−4–10−2 and 103–106, respectively, in addition to phase deviation angles varying in the range from 0 to π. The amplitude parameter associated with the temperature delineation of the bottom and top walls is kept constant. The realizations from the numerical investigation are exhibited by streamlines and isotherms, local and average heat transfer Nusselt number along with the local distribution of heat transfer and fluid friction irreversibilities. The rate of heat transfer demonstrates non-monotonic trends and can be considerably influenced by the interplay of the phase shift angle, Rayleigh number and Darcy number. Upon increasing the value of phase shift angle from 0 to π, average Nusselt number initially decreases and thereafter shows an increase in its value. As the Darcy number increases, average Nusselt number for the bottom wall increases, while for the top wall it strongly depends on phase shift angle. In terms of entropy generation, it is found that the significant contributor to irreversibility is induced by heat transfer and the location of maximum entropy varies with the change in phase angle. More specifically, minimum entropy generation for any value of Rayleigh number and Darcy number is obtained for a phase shift angle of π/4 and maximum for 3π/4. The concomitant transport characteristics bear significance from the context of design of thermal systems pertaining to the theme of non-uniform heating with the phase angle being a crucial design parameter. [ABSTRACT FROM AUTHOR]

A numerical study of fluid flow and heat transfer, applying natural convection is carried out in a porous corrugated rhombic enclosure. A uniform heating source is applied from the bottom boundary wall while the inclined side walls are maintained to a constant cold temperature and the top corrugated wall is retained at insulated condition inside the enclosure. The heat transfer and flow features are presented for a wide spectrum of Rayleigh numbers (Ra), 104 ≤ Ra ≤ 106 , and Darcy numbers (Da), 10-3 ≤ Da ≤ 10-2 . The number of undulations (n) for the top and bottom walls have been varied from 1 to 13 keeping the amplitude of undulation fixed. It is revealed that the characteristics of heat transfer are conceivably modulated by changing the parameter of the undulation number on the enclosure walls, specifically at the bottom and top. The influencing control of n in altering the heat transfer rate is felt maximum on the left wall and minimum for the right wall, and there is a strong interplay between Ra and Da together with n on dictating the heat transfer characteristics. The critical value, where heat transfer rate is observed as maximum is at n = 11 and thereafter the values decrease. [ABSTRACT FROM AUTHOR]

Highlights • MHD natural convection inside a rhombic enclosure filled with nanofluid is studied. • Effect of Rayleigh number, Hartmann number and inclination angles of the enclosure are examined. • The presence of the magnetic field is more perceptible in dictating Nu at higher Ra. • Operating zone of Ra depicting the negative efficacy of nanofluid is presented. • Entropy generation decreases with increase in both Ha and inclination angle. Abstract The present work analyses magnetohydrodynamic natural convection heat transfer and entropy generation in rhombic enclosures filled with Cu-water nanofluids. Numerical simulations were executed for varying Rayleigh number (Ra) in the range 103–106, Hartmann number (Ha) in the range 0–100 and inclination angles of the enclosure (30°, 45° and 60°) considering three different volume fractions of the nanofluid (1%, 3% and 5%). The results indicate that at low Ra , the heat transfer rate remains invariant with the variation in Ha. At high Ra (≥105), the presence of the magnetic field is more perceptible implying that the reduction in heat transfer rate with the increase in magnetic field intensity is far more significant. The heat transfer rate enhances with the increase in inclination angle for all Ha for Ra =103 and 104. However, at high Ra (=105 and 106) the trend becomes contrasting due to the interplay of buoyancy and Lorentz forces. There exists an operating range of Ha in the convection regime wherein the efficacy of the nanofluid in augmenting the heat transfer rate is negated when compared to the corresponding performance of the base fluid. The concomitant thermal identity resulting due to the combined interactions of Hartmann number and volume fraction of the nanofluid have been presented. The entropy generation rate decreases with the increase in Ha for all values of Ra and inclination angles of the enclosure. [ABSTRACT FROM AUTHOR]

The present article numerically investigates the effects of natural convection of Cu-water nanofluid in a two-dimensional rectotrapezoidal enclosure used in application of absorber plate fin. The inclination angle of rectotrapezoidal enclosure, region φ is chosen as 60°. The left and right vertical walls of the enclosure are maintained at a local cold temperature Tc (heat sink) while the bottom wall is kept at a high temperature of Th, respectively. The top wall of the enclosure is adiabatic. After non-dimensionalising the necessary governing controlling equations, the finite element strategy is adopted for solving the same. We present here the results in form of stream line contour, isotherm contours, local and average heat transfer rate (...) adopting a specific gamut of Rayleigh numbers i.e 10³≤Ra≤106. The solid volume fraction range of Cu-water nanoparticles adopted for the present study is (0 ≤ φ ≤ 0.1). The Prandtl number of the numerical simulation is maintained at 6.2. From the results it is observed that the higher stream line intensity is reported at a higher Rayleigh number for higher values of φ and also it is found that with an increase of solid volume fraction φ, of copper water nanoparticles, average heat transfer rate (...) enhancement occurs. Accordingly, heat transfer enhancement greater than 20% as observed for higher Ra =106, whereas 30% heat transfer enhancements are reported using Cu-water nanofluid with Ra=10³. [ABSTRACT FROM AUTHOR]

In this work, we study numerically the natural convection heat transfer and entropy generation characteristics inside a two-dimensional porous quadrantal enclosure heated nonuniformly from the bottom wall. The effect of Darcy number is significant in dictating the Nusselt number only for higher values of Rayleigh number and the variation is more profound for larger values of Darcy number. The variation of entropy generation rate is significant with the Darcy number only for higher values of Rayleigh number. The entropy generation due to heat transfer is the significant contributor of irreversibility at low values of Darcy number, while for larger values of Darcy number and Rayleigh number entropy generation due to fluid friction becomes dominant. [ABSTRACT FROM AUTHOR]