Experimental And Theroical Studies On Gas Flow In Micro-nozzles

Micro-propulsion system based on MEMS technology has some advantages of low cost, low mass quality, small size, high integrated level. The relative position between the satellites orbits and high precision of the attitude control put forward higher requirement to Micro-propulsion system. Micro-nozzles, as the key subassembly of micro-propulsion system, require high quality and precision of design and processing, work at a complex condition, and are impacted greatly by inner flow status. However, the characteristic size of micro-nozzle is quite small, which results in flow and heat transfer becoming more complicated. Some physical phenomena in microscale flow are needed new recognizing and explanations. It is very meaningful to study the characteristic of gas flow in micro-nozzle.Aiming at micro-nozzles, this paper researched on gas flow characteristics in the nozzles respectively by the theoretical analysis and experimental study and numerical simulation. The flow of ideal gas in polytropic process was theoretical studied in micro-nozzle, and the influences of polytropic exponent were also analyzed. At the same condition, polytropic exponent increases, meaning heat loss from the nozzle increases, will lead to outlet velocity and local acoustic velocity decreasing, but Mach number increasing. Experimental studies were carried out by using particle image velocimetry (PIV) measuring the outlet flow distribution of nozzle. Using smoke as tracer particles, the flow distributions were obtained under different pressure and flow rate. The measured data of outlet velocity distribution along the axis and the numerical simulation results are in good agreement. Commercial CFD software, Fluent, was adopted to simulate the gas flow in mircoscale nozzles with varied temperatures, flow rates and pressures. And the distribution laws of inner velocity, pressure and temperature were analyzed.