Investigation of Heat Transfer Improvement of Nanofluid Flows Utilizing Alumina Nanoparticles in Large Annulus Region of Cylinders Using CFD Simulation

Enhancing heat transfer for cooling applications is of high interest since it can provide higher cooling performance of several systems such as large heat exchangers for waste heat removal. For example, the thermal behavior of flows in annuli is an important research area for industrial applications. The heat loss performance by suspending alumina (Al2O3) nanoparticles into the base fluid of air was investigated in lots of previous works. In the present study, CFD simulation is used to study the heat loss behavior of natural convective laminar nanofluid flows (Al2O3/air) inside relatively larger geometries of annuli. The main dimensionless numbers considered in this investigation are the numbers of Knudsen (Kn), Rayleigh (Ra) or modified one (Ram), Aspect Ratio of the annulus geometry/size (AR), and the content (φ) of the suspended solid nano materials (alumina powder). Specific ranges of these physical parameters (Kn, Ra, Ram, and φ) are considered in this work over two selected sizes of annulus gap spacing (AR of 1 and 2). A finite volume code, considering the buoyancies due to density variations using Boussinesq approximation, is simulated to obtain solutions of heat transfer coupled equations.