The Effects of Effective Thermal Conductivity of Porous Materials Under Vapor Flow in Sudden Enlargement-Contraction Channel on Local Heat Transfer

Abstract

This study aims to obtain the local heat penetration and local heat convection characteristics in a system where a flow of heated vapour cedes thermal energy to a horizontal heat-sink plate. The heat penetrates a bed of porous materials with variations in the thermal conductivity inside a sudden-enlargement-contraction-channel. The two non-dimensional parameters of interest are the local Nusselt and Metais-Eckert numbers. The solid particles used for the porous bed are copper, carbon steel, and ceramics. The study is conducted numerically via the software package Ansys-Fluent to solve the Navier-Stokes equation for the conservation of mass, momentum, and energy to obtain the profiles of local temperature and velocity, both in the porous bed and in the vapour stream. Results of this study show that the overall effective-thermal-conductivity of porous materials filled with vapour mainly affects the local Nusselt number. The local Nusselt number increases with increasing overall effective thermal conductivity of porous materials. The sudden enlargement-contraction of the channel affects the local Metais-Eckert number. This finding is proven by the average Metais-Eckert number's variation along the duct and by its non-proportionality to the overall-effective-thermal-conductivity of each porous material. Together with the local Reynolds number, the local Metais-Eckert number describes the flow regimes that locally occur in the system, namely, transitional-combined-convection, laminar-combined-convection, and laminar-forced-convection. Additionally, based on the local Nusselts number, this study locates the critical point of change from enlargement-affected-zone to contraction-affected-zone at 80 mm along the duct's axis, which means that the switchover-point is not at the centre of the channel.

Keywords

• effective thermal conductivity
• metais-eckert number
• porous materials bed
• sudden enlargement-contraction channel