microchannel, leakage, clearance
An important source of thermodynamic and volumetric inefficiency in compressors is the leakage of gas through clearances. For instance, in reciprocating compressors this leakage may occur through the piston-cylinder gap or between the valve and its seat. Due to the fact that for some specific situations the characteristic length of these clearances can be of the same order of magnitude as the gas molecular mean free path, gas rarefaction must be taken into account in the modeling of the fluid flow. Under these conditions, the conventional continuum approach is not appropriate in order to predict the flow and alternative formulations on the basis of the kinetic theory of gases must be sought. Typical examples of non-equilibrium phenomena which cannot be predicted by the classical Navier-Stokes equations are slip, thermal transpiration and temperature jump in the proximities of the solid boundaries containing the fluid. In this work we propose an original compact experimental device that allows the characterization of gas flows in micrometric clearances. Through the aid of this device coefficients, such as the viscous slip coefficient to be introduced in the modified boundary conditions of the Navier-Stokes equations for slightly rarefied, will be obtained. These coefficients are necessary in order to model rarefied gas flows, and they can be as important as the coefficient of viscosity and thermal conductivity. Furthermore, the experimental results obtained will help us to validate a numerical model that predicts gas-leakages in compressors that was developed in-situ.