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Abstract This paper presents analyses of complex flows and heat transfer induced by twin oblique turbulent slot-jets of different directions (divergent, convergent or parallel) impinging a heated wall. A comparison of the heat transfer characteristics between perpendicular and three cases of twin oblique jets (parallel, convergent and divergent). The twin slot jets are located on a confining adiabatic wall at a distance of 8 slot jet width. Convective heat is investigated numerically examining the effect of Reynolds number (Re) and jet inclination angle (α). This problem is relevant to a wide range of practical applications including nuclear engineering devices, manufacturing, material processing, electronic cooling, drying paper or textile, tempering of glass, etc. All computations are performed using two dimensional large eddy simulations (LES) approach with Smagorinsky sub-grid scale (SGS) models. For all directions and inclinations of the jets, the location of the stagnation points is changed and hence, the location and magnitude of the maximum Nusselt number on the heated wall vary. When Reynolds number increases, Nusselt number is improved for all types of inclination. The averaged Nusselt number shows that the perpendicular impingement gives better heat transfer than that of the oblique jets. The poor heat transfer is obtained for the parallel oblique jets. For the same angle, divergent jets give smallest heat transfer than the convergent jets. Graphical abstract Twin-jets flow configuration. (a) Perpendicular (b) Divergent (c) Parallel (d) Convergent. Image 1 Highlights • Four types of flow patterns of impinging twin jet are studied by Large Dissipation Simulation. • Nusselt number is enhanced for all types of inclination for increasing Reynolds number. • Averaged Nusselt number of the perpendicular impingement gives better heat transfer than that of the oblique jets. • The poor heat transfer is obtained for the parallel oblique jets. • For the same angle, divergent jets give smallest heat transfer than the convergent jets. [ABSTRACT FROM AUTHOR]

In this paper Double Multi Relaxation Time Lattice Boltzmann method (DMRT-LBM) is utilized to investigate the particle motion in a modeled room for the first time. The effect of indoor heating system location has been considered on both particle deposition and convective heat transfer so six different positions have been selected for the heating system. Results are shown for two Rayleigh numbers (104 and 105) and different particle sizes (1 μ m and 10 μ m). To study the particle motion, after the flow reaches steady state, 50 000 particles are randomly injected to the room and the number of deposited particles on the walls has been reported for 100 s. Considering the present results, when the heating system is in the middle of the wall, the maximum heat transfer rate is seen for both Rayleigh numbers. Also, the number of deposited 1 μ m particles on the walls for all locations of the heating system is zero for R a = 104, so the number of suspended particles is the maximum. For both Rayleigh numbers and 10 μ m particles, the number of deposited particles is maximum when the heating system is fixed on the top of the wall. It is also concluded that when the heating system is located on the top of the wall, the number of suspended 1 μ m particles for R a = 105 reaches its maximum value. [ABSTRACT FROM AUTHOR]

The main concern in this paper is to analyze the heat, mass and motile microorganisms transfer rate in the magnetohydrodynamic (MHD) convective flow of tangent hyperbolic material. Analysis is studied in presence of both nanoparticles past an exponential surface. Nanofluid containing gyrotactic microorganisms in addition to nanoparticles is considered. Analysis is carried out in presence of an inclined magnetic field. In fact the idea here is to use the microorganisms just to stabilize the suspended nanoparticles due to bioconvection generated by the combined effects of buoyancy forces and magnetic field. Brownian motion, thermophoretic and Newtonian heating are also studied. The resulting systems of nonlinear systems have been solved by homotopic procedure. The velocity, temperature, nanoparticle concentration and density of motile microorganisms are examined graphically. The skin friction coefficient, local Nusselt, Sherwood and motile microorganism numbers are numerically discussed for the active involved parameters. It is observed that velocity profile is decreased by both magnetic parameter and angle of inclination. It is also noted that the temperature profile increases for larger Nb but it decreases for nanoparticle concentration. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyzes the combined effects of buoyancy force, convective heating, Brownian motion, thermophoresis and magnetic field on stagnation point flow and heat transfer due to nanofluid flow towards a stretching sheet. The governing nonlinear partial differential equations are transformed into a system of coupled nonlinear ordinary differential equations using similarity transformations and then tackled numerically using the Runge–Kutta fourth order method with shooting technique. Numerical results are obtained for dimensionless velocity, temperature, nanoparticle volume fraction, as well as the skin friction, local Nusselt and Sherwood numbers. The results indicate that dual solutions exist for shrinking case. The effects of various controlling parameters on these quantities are investigated. It is found that both the skin friction coefficient and the local Sherwood number decrease while the local Nusselt number increases with increasing intensity of buoyancy force. [Copyright &y& Elsevier]

Abstract: In this paper, we numerically optimize the triggering time of several discrete heaters attached to a channel in forced convection. The flow is assumed laminar and fully developed and the strength of each dissipating heat source is determined by a sinusoidal function of time having a phase lag () and a frequency (ω). The objective of this work summarizes to numerically determine an optimal set of activation phase lag and position for each heater, such that minimal thermal resistance is achieved for the system. The calculations were performed using a finite volume numerical code. The temperature history in any point of the channel was decomposed as a combination of steady-state and two harmonic components leading to a linear system of differential equations. The optimization procedure relied on a genetic algorithm, which was coupled to the numerical code implemented. The optimized results show that the activation phase lag and position of each heater can significantly decrease the overall thermal resistance. The designs optimized with respect to phase lags are relatively insensitive to frequency. The numerical results were found to qualitatively agree with the scale analysis proposed. [ABSTRACT FROM AUTHOR]