In the last 25 years a number of Micro Electro Mechanical System (MEMS) have been developed. These MEMS devices not only include the mechanical systems but also the fluids. Knowledge about fluid flows in this scale is not as mature as the mechanical properties of the MEMS . As their dimensions are between 1 mm and 1 micron , gas flows related with the MEMS devices have higher Knudsen numbers (Kn) similar to high atmosphere flights. If Kn is higher than 0.1, instead of the classical continuum based Euler or Navier-Stokes (N-S) equations, deterministic or stochastic atomistic models should be used. This is due to the departure from local thermodynamic equilibrium with increasing gradient, and linear relation between heat conduction and temperature gradient are lost.