Thrust effectiveness of micronozzle

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute. Thrust of the divergent part of axially symmetric micronozzle is under the study. It’s input to total thrust is considered by means of analysis of relative thrust determined as divergent part’s thrust related to nozzle’s thrust without divergent part when gas issuing into vacuum. An inviscid one-dimensional flow is used as start condition of analysis. For this case, it is shown from conservation laws that divergent part of infinite length has finite relative thrust depending only on sort of issuing gas. Analysis of the influence of shear stress on thrust of divergent part with the use of theory of laminar boundary layer shows that optimal nozzle wall angle at the exit increases and optimal length decreases with decreasing of nozzle’s dimension in comparison with initial inviscid case. This conclusion is approved by results of numerical simulation of flow inside nozzles with throat diameter 10 micrometers and various form of divergent part based on Navier – Stokes equations with both no-slip and slip wall conditions. Detailed analysis of flow shows advantage of micronozzles with wall form far from traditionally used in “large” thrusters. This study is partially supported by the Russian Foundation for Basic Research (Project 11-08-00422-а).