The transition flow regime is the most complicated domain for modeling since the transition regime is a varying mixture of different transport mechanisms. Modeling the Navier-Stokes equations with the appropriate second order slip boundary condition at high Knudsen numbers is further explored in this paper. The general models proposed by one of the authors are validated against extensive numerical and experimental data in the literature. It is noteworthy that the geometry and the partial momentum accommodation are taken into account by the models. The present work provides a markedly simple way to compute quantities of engineering interest in microchannels and nanochannels of various cross sections over the full transition flow regime that is estimated to be accurate to 10%, with most data within 5%. As in the transition regime no data exist for most various geometries, this proposed engineering model fills this void. This paper further explores and validates working engineering macro models that can be easily implemented in applications.