Natural Convection Heat Transfer Characteristics Of Nanofluid In A Two-Dimensional Square Cavity And A Three-Dimensional Cubic Enclosure With Brownian Motion Efffect

Nanofluid, a suspension liquid formed by the metal or nonmetal nanoparticles and base fluid, has been made a remarkable progress in theory and engineering field. The fundamental research of nanofluid’s flow and heat transfer model has got very good develpoment and extensive attention. In recent years, steady natural convection of nanofluid in a square cavity has also been conducted in-depth research by many scholars. But if considering the influence of the Brownian motion on nanofluid’s flow and heat transfer, there are many problems worthy to be discussed. This article adopts the theory of numerical simulation methods, with the heat transfer coefficient in combination with the Brownian motion of nanofluid’s calculation model, studied the steady and unsteady natural convection of nanofluid, tried to analyze and research the heat transfer effect under different Ra number and different volume fraction of nanofluid.(1) For a square cavity where the temperature on one side of the wall changes periodical with time, the opposing sidewall maintained at a relatively low temperature, we analysis the unsteady natural convection heat transfer characteristics in a two-dimensional square cavity filled with CuO-water nanofluid. The influence of pertinent parameters such as Ra number, volume fraction of nanoparticals under the effect of Brownian motion on the transient natural convetion heat transfer characteristics is studied. The temperature on hot wall changes periodical with time has great influence on square enclosure. The secondary vortex of main stream appears and disappears periodically with the change of temperature. Geometric average Nusselt number on the hot and cold wall presents sinusoidal variation with the same time period of temperature change. Simulation results show that with the increasing of Ra number and nanopartical volume fraction, making the increase of natural convection of nanofluid.(2) In a square cavity where the temperature on one side of the wall maintained at a relatively high temperature, the opposing sidewall maintained at a relatively low temperature, we analysis the steady natural convection heat transfer characteristics in a two-dimensional square cavity filled with CuO-water nanofluid. Studied the influence of different Ra number, volume fraction of nanoparticales of the steady natural convetion heat transfer under the effect of Brownian motion. Simulation results proved that with the increasing of Ra number, the fluid buoyancy lift increases, making the increase of natural convection of nanofluids. And with the increase of volume fraction, the cavity of nanofluid’s natural convection is enhanced significantly. The two order’s magnitude’s increasing enhances the capability of nanofluid’s natural convection heat transfer apparently.(3) In a three-dimensional enclosure filled with Al2O3-water nanofluid where the temperature of the vertical sidewall is kept as a constant high temperature, the opposing sidewall is cooled at a relatively low temperature, we analysis the characteristics of nanofluid’s steady natural convection in closed cube, and mainly focused on the influence of flow fluid of natural convection heat transfer with different Ra number and volume fraction. Under the Brownian motion thermal conductivity model, the three-dimensional enclosure is similar with the two-dimensional in the flow heat transfer case. And the greater the Ra numbers and the nanoparticle fraction of nanofluid, the stronger the intensity of natural convection. Specially it is not obvious under lower Rayleigh number effect, and under high Ra number, the natural convection heat transfer in the enclosure is stronger.