Heat Transfer Enhancement of Backward-Facing Step Flow by Using Nano-Encapsulated Phase Change Material Slurry

Abstract

Laminar forced convection of nano-encapsulated phase change material (NEPCM) slurry over a 2D horizontal backward-facing step is numerically investigated using a finite volume method based on a collocated grid. The slurry consists of water as base fluid and n-octadecane NEPCM particles with an average diameter of 100 nm. Uniform heat flux boundary condition is imposed to the downstream wall while the step and upstream walls are subjected to adiabatic boundary condition. The effects of Reynolds number ranging from 20 to 80, volume fractions of nanoparticles ranging from 0% to 30%, as well as heat flux ranging from 500 to 2,500 W/m2 are studied. In order to understand the physics of flow and heat transfer of slurry over the backward-facing step, the streamlines and isotherms of the flow were studied. An enhancement in heat transfer coefficient up to 67% using slurry as working fluid compared with pure water can be observed. However, because of the higher viscosity of mixture compared with pure water, the slurry can cause a higher pressure drop in the system. Furthermore, as wall heat flux and Reynolds number increase, the heat transfer coefficient of the bottom wall increases until a critical heat flux is reached and heat transfer performance becomes independent of heat flux.