Copyright © 2012 by ASME 1 Proceedings of the ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels ICNMM2012 July 8-12, 2012, Rio Grande, Puerto Rico ICNMM2012-73160 EXTENSION OF THE DSMC METHOD TO NEAR CONTINUUM MICRO/NANO FLOWS USING SMALL NUMBER OF PARTICLE PER CELLS Ali Amiri-Jaghargh Email: amirij@gmail.com Ehsan Roohi Email: e.roohi@ferdowsi.um.ac.ir Hamid Niazmand Email: hniazmand@yahoo.com Department of Mechanical Engineering, Faculty of Engineering. Ferdowsi University of Mashhad, Mashhad, Iran. P.O.BOX: 91775-1111 Stefan Kanchev Stefanov Email: stefanov@imbm.bas.bg Institute of Mechanics, Bulgarian Academy of Science. Acad. G. Bontchev str., 1113, Sofia, Bulgaria. ABSTRACT In this study, it is suggested that the standard collision scheme in the direct simulation Monte Carlo (DSMC) is replaced by the simplified Bernoulli-trials (SBT) algorithm on staggered gird, recently proposed by Stefanov [1], to reduce the computational resource requirements of the DSMC method in solving low speed/low Knudsen rarefied micro/nano flows. The main advantage of the SBT algorithm is that it allows more accurate calculations using much smaller number of particles per cell, i.e., < N > ≈ 1. Compared to the original development of SBT [1], we now extends the use of SBT algorithm to the near continuum rarefied flows, i.e., Kn = 0.005, where a large number of particles per cell should be employed if we utilize the standard NTC scheme. Nonlinear flux-corrected transport algorithm (FCT) is also employed as a filter to extract the smooth solution from the noisy DSMC calculation of low- speed/low-Knudsen number DSMC calculations. Our results show that combination of SBT/staggered grid and FTC filtering not only provides accurate smooth solutions but also reduces the computational time compared to original SBT/staggered grid. INTRODUCTION Heat transfer and fluid flow in Micro/Nano-electro- mechanical systems, MEMS/NEMS, is widely gained importance due to the rapid growth of miniaturization of practical engineering and biomedical devices such as heat exchangers and chemical reactors. It is well established that the fluid behavior in MEMS/NEMS is different from the macroscopic counterpart [2]. However, due to their small dimensions, it is hard to study these behaviors experimentally. Actually, the behavior of gas gradually deviate from thermodynamic equilibrium as the device length scale approaches the mean free path of the gas. Therefore, the numerical modeling of such devises is also problematic because the traditional Navier-Stocks (NS) equations, consistent with near-equilibrium state, refuse to follow the realistic flow features. Knudsen number (Kn), defined as the ratio of gas mean free pass to the characteristic length scale of the flow, is a good measure to characterize the departure from equilibrium. Based on Knudsen number, the flow may appear in four different regimes [3]: continuum, slip flow, transition and free molecular regimes. For the Kn< 0.001, i.e., continuum regime, the NS equation with traditional no-slip boundary condition can be utilized to describe the flow behavior. In slip flow regime, 0.001<Kn<0.1, the NS equation deviate from experimental results and should be accompanied with velocity slip and temperature jump boundary conditions. In the transition regime, 0.1<Kn<10, the core flow gradually departs from the equilibrium and the NS equations are no longer valid. Finally, flow is considered as free molecular as it exceeds the limit of Kn> 10. Many investigations have proved the accuracy of the slip boundary conditions in slip flow regime [4]. Some