Critical review of the definitions of the Bejan number - first law of thermodynamics

摘要

This paper is an extension of our recently published paper (Zimparov et al., 2020 [1]), proving that the unique form of the Bejan number (Be) is derived from the classic fluid mechanics and that the other forms, derived from the first law of thermodynamics (related to the convection heat or mass transfer), are combination of unique Bejan number with Prandtl (Pr) or Schmidt (Sc) numbers respectively. In this study we continue to maintain this idea through presenting many new examples of problems in the field of periodic or time dependent pure laminar duct flows and laminar flows in channels filled with porous medium, with critical review. The evaluation of the friction factor for channel flow or external cross flow over tube bank have also been critically discussed. The discriminated dimensional analysis has been again applied as a tool to reveal the role and physical meaning of the unique Bejan number (Be) as criterion of similarity or dimensionless variable.