Bubble dynamics of R-134a boiling in enhanced surfaces having pores on sub-tunnels

Abstract

Structured enhanced surfaces are widely used to promote nucleate boiling heat transfer in refrigeration and process industries. Despite the wide usage of the enhanced surfaces, there appears a significant lack of understanding on the boiling mechanism or predictive models. In this study, bubble dynamic data – bubble departure diameter, bubble generation frequency, nucleation site density – were obtained for R-134a boiling on horizontal surfaces having circular pores. Nine samples included pore diameters from 0.1 mm to 0.3 mm and pore pitches from 0.75 mm to 3.0 mm. Tests were conducted at 4.4 °C and 26.7 °C saturation temperatures. Results showed that bubble departure diameter increased as pore diameter increased, or pore pitch and saturation temperature decreased. Furthermore, nucleation site density increased as heat flux increased or pore pitch decreased. Bubble generation frequency generally increased as pore diameter or pore pitch increased. The existing bubble dynamic models did not adequately predict the present bubble dynamic data, and a new model was developed.