چكيده به لاتين
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: flow boiling, bubble dynamic, departure and lift-off diameter, horizontal straight
channel, U-shaped channel
