Detailed investigation of flow and thermal field in micro/nano nozzles using Simplified Bernoulli Trial (SBT) collision scheme in DSMC

Flow regimes through micro/nano nozzles experience the continuum behavior as well as the rarefied condition. The occurrence of broad rarefaction regimes due to unique geometry/flow conditions makes the particle-based simulation of micro/nano nozzles computationally expensive. Therefore, the primary aim of the present study is to implement the Simplified Bernoulli trials (SBT) collision algorithm in place of the conventional “No-Time-Counter” scheme in the direct simulation Monte Carlo (DSMC) method, thus reducing the required particle number. We show that the SBT scheme employed on the proper number of grid cells could reduce the computational costs and memory of micro/nano nozzle flow simulations. We also investigated the physical behavior of gas flows in micro/nano nozzles. We report the bimodal behavior of the velocity, temperature and Mach number at the throat at lower Knudsen numbers and the occurrence of Mach < 1 in the throat. We also considered back pressure effects on the flow field and the impact of gas species on the micro/nano nozzle performance. We identified an efficiency reduction due to rarefaction and improvements of the micro/nano nozzle performance due to increasing of the throat dimension. Performance reduction at the nanoscale is also discussed.