Showing papers on "Combined forced and natural convection published in 2016"

The shape effects of nanoparticles suspended in HFE-7100 over wedge with entropy generation and mixed convection

Abstract: The flow of mixed convection nanofluid over wedge under the effects of porous medium is investigated. The HFE-7100 Engineered Fluid having Nimonic 80a metal nanoparticles of spherical and non-spherical shapes with different sizes is used. The particle shape effects on Bejan number and entropy generation are taken into account. The system of partial differential equations is first written in terms of ordinary differential equations using adequate similarity transformations and then solved analytically. Analytical solutions of the resulting equations are obtained for the velocity and temperature profiles. Simultaneous effects of porous medium, particle volume friction, mixed convection parameter, and angle of wedge in the presence of different shapes nanoparticles are demonstrated graphically. Effects of particle concentrations, sizes on wall stress, heat transfer coefficient of Skin friction, and Nusselt are discussed in the form of tables.

Aggregation effects on water base Al2O3—nanofluid over permeable wedge in mixed convection

Abstract: Two-dimensional heat transfer flow of a nanofluid in the neighborhood of a stagnation point flow in the presence of mixed convection is investigated. The mathematical model consists of continuity and the momentum equations, while a new model is proposed to see the effects aggregations on water base Al2O3 nanofluid over permeable wedge. The variable wall temperature is taken into account. The Mathematica package based on homotopy analysis method is used to solve this problem. Several aspects of the aggregation parameters on velocity and temperature profiles of nanofluid are investigated and shown graphically with respect to the physical parameters involved in it. The tabular results are demonstrated for heat transfer rate and skin friction coefficient. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd.

Self-aggregation of convection in long channel geometry

Abstract: Cloud cover and relative humidity in the Tropics are strongly influenced by organized atmospheric convection, which occurs across a range of spatial and temporal scales. One mode of organization that is found in idealized numerical modelling simulations is self-aggregation, a spontaneous transition from randomly distributed convection to organized convection despite homogeneous boundary conditions. We explore the influence of domain geometry on the mechanisms, growth rates and length-scales of self-aggregation of tropical convection. We simulate radiative–convective equilibrium with the System for Atmospheric Modeling (SAM), in a non-rotating, highly elongated three-dimensional (3D) channel domain of length >104 km, with interactive radiation and surface fluxes and fixed sea-surface temperature varying from 280–310 K. Convection self-aggregates into multiple moist and dry bands across this full range of temperatures. As convection aggregates, we find a decrease in upper tropospheric cloud fraction but an increase in lower tropospheric cloud fraction; this sensitivity of clouds to aggregation agrees with observations in the upper troposphere but not in the lower troposphere. An advantage of the channel geometry is that a separation distance between convectively active regions can be defined; we present a theory for this distance based on boundary layer. We find that surface fluxes and radiative heating act as positive feedback mechanisms, favouring self-aggregation, but advection of moist static energy acts as a negative feedback, opposing self-aggregation, for nearly all temperatures and times. Early in the process of self-aggregation, surface fluxes are a positive feedback at all temperatures, shortwave radiation is a strong positive feedback at low surface temperatures but weakens at higher temperatures and longwave radiation is a negative feedback at low temperatures but becomes a positive feedback for temperatures greater than 295–300 K. Clouds contribute strongly to the radiative feedback, especially at low temperatures.

A survey on experimental and numerical studies of convection heat transfer of nanofluids inside closed conduits

Abstract: Application of nanofluids in heat transfer enhancement is prospective. They are solid/liquid suspensions of higher thermal conductivity and viscosity compared to common working fluids. A number of ...

Dual stratified mixed convection flow of Eyring-Powell fluid over an inclined stretching cylinder with heat generation/absorption effect

Abstract: Present work is made to study the effects of double stratified medium on the mixed convection boundary layer flow of Eyring-Powell fluid induced by an inclined stretching cylinder. Flow analysis is conceded in the presence of heat generation/absorption. Temperature and concentration are supposed to be higher than ambient fluid across the surface of cylinder. The arising flow conducting system of partial differential equations is primarily transformed into coupled non-linear ordinary differential equations with the aid of suitable transformations. Numerical solutions of resulting intricate non-linear boundary value problem are computed successfully by utilizing fifth order Runge-Kutta algorithm with shooting technique. The effect logs of physical flow controlling parameters on velocity, temperature and concentration profiles are examined graphically. Further, numerical findings are obtained for two distinct cases namely, zero (plate) and non-zero (cylinder) values of curvature parameter and the behaviour are presented through graphs for skin-friction coefficient, Nusselt number and Sherwood number. The current analysis is validated by developing comparison with previously published work, which sets a benchmark of quality of numerical approach.

MHD mixed convection of localized heat source/sink in a nanofluid-filled lid-driven square cavity with partial slip

Abstract: Magneto-hydrodynamic mixed convection in a lid-driven square cavity filled with Cu–water nanofluid is investigated in this paper. Partial slip effect is considered along the lid driven horizontal walls. A segment of the left wall is considered as a heat source, meanwhile a heat sink is placed on the right wall of cavity. The remainder cavity walls are thermally insulated. A control finite volume method is adopted as a numerical appliance of the present study. The study is achieved by controlling the effect of a set of pertinent parameters, these are; the size and position of the heat source/sink (B = 0.2–0.8, D = 0.3–0.7, respectively), the Hartman number (Ha = 0–100), Richardson number (Ri = 0.001–10), nanoparticle volume fraction ( ϕ = 0.0 − 0.1 ) , partial slip parameter ( S = 1 − ∞ ) , and the lid-direction of the horizontal walls (λ = ±1) where the positive sign means lid-driven to the right while the negative sign means lid-driven to the left. The results show that the shortest length of the heat source/sink localized midway of the vertical walls give the maximum convective heat transfer, and the best direction of the horizontal walls is that when they are both lid-driven to the left. For very strong applied magnetic field, the lid-direction becomes inactive.