Carbon dioxide bubble dynamics and wall heat transfer in flash chambers: Nucleation departure and cold bubble effects

This study uses the lattice Boltzmann method to explore bubble dynamics and phase-change heat transfer of carbon dioxide during reduced pressure flash evaporation near overheated wall surfaces. The findings show that the bubble advancing rate decreases linearly with increasing superheat and contact angle. Similarly, the detachment diameter decreases linearly as superheat increases. The relationship between detachment diameter and contact angle is strongly influenced by wall wettability: hydrophilic surfaces exhibit a negative linear correlation, while hydrophobic surfaces show a positive linear correlation. A correction term based on the Ca number is introduced to enhance bubble rising velocity predictions. Heat transfer analysis reveals that wall wettability significantly impacts heat flux, with hydrophobic surfaces boosting heat transfer by up to three times. Mechanistically, cold nuclei induced by low-pressure conditions are crucial for improved flash evaporation heat transfer, particularly on hydrophobic surfaces.