In this section we will investigate pressure driven channel flows, and we will compare our results with some existing micro-flow experiments. In other words for given inlet to exit pressure ratio, the measured mass-flow rate was significantly higher than the predictions of the continuum models. Variation of experimental mass flow rate non-dimesionalized with the corresponding continuum model prediction as a function of inlet to exit pressure ratio along the channels is presented in figure below. The slip flow theory predictons for this flow using the first-order slip boundary conditions is shown by dashed lines. A similar theory that employs second-order slip corrections is shown by solid lines.
Computations made by mu-flow at four different pressure ratios is shown by dots.
It is seen that the numerical results and second-order slip flow theory results match identically. The experimental data shows deviations from the both theories, and scatter of the experimental data makes it difficult to examine particular trends. The approximate analytical models shown by lines are based on balancing the pressure drop with the viscous forces for completely isothermal flows. However in compressible flows inertial terms can be important and assuming constant temperature is not a very good assumption either. Nevertheless such approximations are required in order to obtain analytic solutions to the problem.