Maximum heat transfer reduction in a horizontal porous annular cavity induced by the attachment of symmetric radial baffles to the hot inner cylinder

Abstract

A numerical model is developed to study the natural convection in a horizontal porous annulus with a heated inner cylinder and a colder outer cylinder. Sequential pairs of radial baffles are attached to the inner cylinder and arranged symmetrically relative to the vertical plane of symmetry. A numerical procedure based on the finite volume method is adopted to solve the system of coupled 2D Darcy–Brinkman–Boussinesq and energy equations. Numerical results show that the insertion of medium-sized baffles modifies the unicellular flow to a co-rotating multicellular flow and induces maximal heat transfer reduction when the baffles are located at appropriate angles measured from the bottom of the inner cylinder. The optimal conditions for maximal heat transfer reduction are determined as a function of the number, size and position of the pairs of baffles for the betterment of thermal insulation of a horizontal pipe. The best improvement for thermal insulation efficiency is obtained with a successive insertion of three pairs of baffles, wherein the maximal reduction of heat transfer can reach 12% as compared to the bare case without baffles. Subsequent insertion of four pairs of baffles generates Rayleigh–Bénard thermal instabilities in the upper part of the porous annulus, which is unfavorable for purposes of thermal insulation.