Development of Nusselt number correlation in natural convection over the walls of a blast furnace: A CFD approach

Abstract

Blast furnaces are large and costly devices, and contribute enormous wealth to world economy. A tiny improvement of furnace performance can translate to huge saving not only in cost of operation but also in air pollution. It presents a numerical solution of the continuity, momentum, and energy equations for a fluid domain surrounding the outer cylindrical surface of a vertical cylinder with the specific longitudinal section using ANSYS FLUENT 18. The main parameters of this study are the dimensionless ratio of cylinder length to the maximum diameter varying between 3.24 and 5.4, the Rayleigh number ranging between 104 and 107, and the cylinder surface temperature ([Formula: see text]) varying between 375 K and 600 K, the ambient temperature being taken as 300 K. These parameters have been varied during the simulation to determine their influence on the free convection characteristics. The study clearly shows that the computed Nusselt number increases with increase of Rayleigh number and surface temperature, the increment being minimal for high values of length to the maximum diameter. It is also observed from the simulation that the rate of heat transfer goes down with increase of length to the maximum diameter. The results present local heat transfer and skin friction coefficients over the outer cylindrical surface of the blast furnace of chosen dimensions. The thermal plume and the velocity vector field around the furnace are displayed. An empirical Nusselt number to Rayleigh number relationship has been proposed for the blast furnace of any size within range of Rayleigh numbers covered in this study. This formula derived is correct within ±5%, and is expected to be very useful to field engineers.