Development of a test facility for the study of cold gas dynamic spraying: Rig Characterisation.

摘要

In this dissertation a facility for the study of Shock Wave Induced Cold Gas Sprayingud(SWICGS) is investigated. The objective of the study was to design, construct and test audshock tube rig that will be used to accelerate gas jets to velocities required for deposition inudSWICGS applications. The testing of the rig involved using helium and air as gas drivers,udand testing for different diaphragm configurations on the rig for best performance.udTo understand the problem better a literature review on several aspects surrounding theudfield of SWICGS was conducted. This involved aspects such as particle critical velocity,uddeposition efficiency, shock wave production and several other topics. Based on theudcompiled literature, three conceptual rig designs were generated. Concept B was selected toudbe developed further into detailed design. The main contributing factors in the decisionudmaking with regards to the rig design were the safety of the design, the provision ofudundisturbed flow in the tube and ease of manufacture.udThe final rig has a shock tube with an internal diameter of 5mm. The pressure reservoir ofudthe rig is 0.377 litres, and the total length of the rig is 2 meters, with a safety factor of atudleast 10 for all components. The rig makes use of solenoid valves to work as diaphragms;udthe valves have an opening time of 100ms and a closing time of 100ms. The opening andudclosing of the valves is controlled by a programmed Moeller controller.udSignificantly high jet velocities were obtained at room temperatures using the designed rig,udwith air as the gas driver jet velocities of up to 516.35 m/s were achieved and with heliumudas the gas driver jet velocities of up to 876.92 m/s were achieved within the tested range ofud10 to 50 bars reservoir pressure. These high velocities can be achieved at a wave generationudfrequency of 5 Hz. The rig can generate high velocity jets even at higher frequencies of upudto 20 Hz. The single valve arrangement showed to be generally performing better than theuddouble valve arrangement within the tested range and conditions.