Experimental investigation of aerosol deposition on slot-and joint-type leaks

This paper deals with the quantification of the sealing effectiveness of slot- and joint-type leaks by aerosol deposits. A sticky aerosol (MMD ˜ 4.9 µm; GSD ˜ 2.7) was injected into a duct and blown out through machined slot- and joint-type leaks located on the duct wall. For both leak-types, the crack exit was a rectangular opening of 1.7 x 50 mm. The pressure across the leaks was kept constant during the plugging process, while the airflow rate through the openings was continuously monitored. The deposition patterns were recorded and the average deposition efficiencies were obtained through the measurement of the particle mass collected in the crack. Instantaneous sealing rates were obtained from the leakage airflow time series. The Normalized Sealing Rate (NSR) introduced in this paper allows one to compare the instantaneous sealing efficiencies as the leaks are subjected to various boundary conditions. For our specific leak geometries and boundary conditions, the three key results of these experiments are that: a) inertial impaction near the entry point is the major cause of the decline of the leakage flow rate for either type leak; b) the pressure variations in the 100-400 Pa range do not have a significant effect the average deposition efficiency; c) the average deposition efficiency of the slot- and joint-type leaks used are in the range of 25% and 85%, respectively. We also observed that there exists a critical joint-leak size below which the NSR decreases significantly.