(46d) Eddy Impaction as An Ash Deposition Mechanism: An Experimental and Theoretical Investigation

Ash deposition represents a long-standing operational and design research issue. Coal or biomass ash may deposit on a variety of surfaces and grow at a variety of rates. As ash deposits grow, they increase the heat transfer resistance between the deposition surface and the adjacent medium. This increased resistance is due to a decrease in the heat transfer coefficient and emissivity. Eddy impaction is a specific category of ash deposition mechanism, and is defined as a particle impaction rate that has too little momentum to transit average fluid boundary layers around surfaces. The dual focus of this study is to present an analytical eddy impaction ash deposition model and validate obtained results via comparison with experimentally gathered data. The eddy impaction ash deposition model predicts eddy impaction rates as a function of turbulence intensity, boundary layer thickness, and gas velocity. The experimental apparatus utilizes either the blender or flask method to introduce toner particles (5µm diameter) into a gas stream (air, SF6) flowing through a horizontal pipe (Re 2,300-8,000). The toner particles impact onto the pipe wall and the total mass of impacted particles is measured.