A microscale approach to entropy generation in respiratory flow

Abstract Entropy generation at the microscale within individual airway branches has received limited attention despite the fact that extensive research has been carried out on respiratory thermodynamics. This study presents a second law-based analysis of the human respiratory tract from a microengineering perspective, evaluating entropy generation across the 23 generations of the tracheal tree. Thermodynamic irreversibility due to heat transfer and viscous dissipation are quantified under various respiratory flow regimes. The Bejan number (Be) indicates the relative influence of thermal and fluid friction irreversibilities. Environmental factors such as temperature and humidity are found to affect local entropy generation. The study enhances understanding of internal flow behavior in the lungs and provides a framework for future investigations in respiratory thermodynamics under realistic physiological conditions.