Experimental analysis of micro-sized particles time-wise adhesion: the influence of impact velocity and surface roughness

Micro-sized solid particle adhesion affects several industrial processes and machines. Particle adhesion is responsible for reducing reliability and efficiency. A great example is represented by gas turbines and heat exchangers. These machines collect a huge amount of contaminants during their common operation. These deposits determine operability issues and efficiency losses. In this work, the particle deposition phenomenon and its development over time are studied in-depth through an experimental campaign. A high-speed airflow laden with micro-sized sand particles has impinged onto a flat surface. The particle mass flow, after being carefully dosed by an aerosol generator (contaminant concertation equal to 50 mg/m3), is injected into the main airflow using an aerodynamic eductor. The tests were conducted with different impact velocities ranging from 22 m/s to 48 m/s, and considering different exposure periods. For each test, different roughness levels were tested to define the influence of the surface quality on the particle sticking capability. The deposits amount was evaluated in quantitative and qualitative ways. Weighing measurement was used for extracting quantitative information about particle sticking, while the video and stereomicroscope image analyses were used to gain insight into the morphology of the surface and its modification over the exposure time. The results show a strong dependence of particle sticking on both flow/particle velocity and the roughness of the substrate, characterized by non-linear correlations due to the action of the detachment process.