Experimental Measurements of the Thermal Conductivity of Ash Deposits:  Part 2. Effects of Sintering and Deposit Microstructure

Abstract

This paper describes an experimental study that examines the influence of sintering and microstructure on ash deposit thermal conductivity. The measurements are made using a technique developed to make in situ, time-resolved measurements of the effective thermal conductivity of ash deposits formed under conditions that closely replicate those found in the convective pass of a commercial boiler. The technique is designed to minimize the disturbance of the natural deposit microstructure. The initial stages of sintering and densification are accompanied by an increase in deposit thermal conductivity. Subsequent sintering continues to densify the deposit, but has little effect on deposit thermal conductivity. SEM analyses indicate that sintering creates a layered deposit structure with a relatively unsintered innermost layer. We hypothesize that this unsintered layer largely determines the overall deposit thermal conductivity. A theoretical model that treats a deposit as a two-layered material predicts the observed trends in thermal conductivity.