Experimental Study on Pressure Drop and Heat Transfer Characteristics of Wet Air with Ash Particles across Circular Finned Tube Bundles

In this paper, in order to provide guidance on the design and operation of waste heat recovery heat exchangers for the dryer exhaust of lignite pre-drying, pressure drop and heat transfer characteristics of wet air with ash particles across circular finned tube bundles were experimentally studied under different conditions. The experimental water vapor mass fraction ranged from 5% to 15%, ash particle concentration ranged from 0 to 12.8 g/m³ and mainstream flow velocity ranged from 1.73 m/s to 3.46 m/s, respectively. The pressure drop coefficient generally increases and Nusselt number decreases with time due to the gradual ash deposition. The pressure drop coefficient is sensitive to ash particle concentration, while Nusselt number is sensitive to water vapor mass fraction. Especially, Nusselt number for the ash particle concentration of 1.5 − 5.4 g/m³ is a bit larger than that for the wet air without ash particles. Based on the experimental data, a normalized empirical formula was proposed to calculate the heat transfer characteristics of wet air with ash particles across circular finned tube bundles, and the deviation between experimental data and predicted results is −16.5% to +27.0% for more than 90% of the data.