چكيده به لاتين
Abstract:
Abstract
Study of flow boiling in curved channels contains lots of complexity due to the existence of phenomena such as secondary flow, torsion of flow and radial pressure gradient. In this study dynamic behavior of bubbles is studied and compared using analytical and experimental methods in sub-cooled flow boiling, inside two horizontal straight and vertical U-shaped channels. In the first method, physics governing bubble dynamics and applied forces to bubbles are described based on previous studies. Moreover, in this part, models and correlations are developed in order to anticipate diameter and departure and lift-off time of bubbles, in both horizontal straight and U-shaped channels. Afterwards, required experiments were conducted using high-speed imaging in order to validate physical models and developed correlations. During conducting the experiments, effects of flow conditions such as volumetric flow rate, sub-cooled temperature of inlet flow and effect of wall heat flux on dynamic behavior of bubbles were studied. Experimental results showed a good consistency with results of physical models and developed correlations. Furthermore, some of experimental correlations and models represented in literature were employed in order to anticipate diameter and departure and lift-off time of bubbles in both straight and U-shaped channels. Comparison of results showed that presented results in the literature anticipates existing experimental results with Major error percentage that could be due to different reasons such as difference in flow conditions, wall heat flux, fluid, geometrical condition of channels and inexistence of radial pressure gradient term effects and path curvature (for curved channels data) in presented relations; these reasons are estimated to be the cause of major errors in the comparison of results.
Keywords: Sub-cooled flow boiling, dynamic behavior of bubbles, departure and lift-off diameter, horizontal straight channel, U-shaped channel
