Boiling Dynamics and Entropy Generation in Inclined Tubular Systems: Analysis and Optimization

This research explores the characteristics of boiling in inclined pipes, a domain of great importance in engineering. Employing an experimental visualization technique, the boiling dynamics of deionized water are examined at varying inclination angles, paying special attention to the emerging flow patterns. The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0° to 90° range. As the heat flux rises, bubbles form in the liquid. The liquid’s inertia extends the bubble-wall contact time, thereby delaying the onset of bulk bubble flow. Beyond a 90° inclination, however, the patterning behavior is more influenced by the fluid velocity. At low speeds, incomplete pipe filling results in a large liquid plug hindering flow, while high speeds lead to full pipe filling. In general, gravity, inertia, buoyancy forces, and capillary forces are the main influential factors in the considered problem. However, an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern. Finally, an optimal mass flux and inclination angle, able to minimize total entropy generation and improve heat transfer efficiency, are determined by means of an entropy generation analysis.