A numerical investigation of the wettability effect on minitube flow boiling using the volume of fluid method

Abstract

Flow boiling within minitubes holds immense promise for efficient heat dissipation owing to its substantial latent heat exchange capacity. The performance and efficacy of the pump, crucial beyond just necessitating high heat flux, are closely tied to maintaining a low-pressure drop. Surface treatment stands out as one of the techniques to augment thermal efficiency. While the significance of microscale surface properties, particularly wettability, in influencing flow boiling has been established, only a limited number of studies have explored its impact on pressure drop. This study rigorously investigates the wettability's influence on flow boiling within minitubes using the VOF approach. It reports key parameters within a 200 ms interval, including vapor volume fraction, average heat flux, and pressure drop. Employing a mass flux of 560 kg/m2s along a 10 mm length minitube, the study attains an impressive average heat flux of up to 324,966.9 W/m2 on a hydrophilic surface exhibiting a 5° contact angle. In contrast, a hydrophobic surface boasting a 150° contact angle achieves a significantly reduced total pressure drop (∆p) of 698.4 Pa, effectively preventing tube-clogging. Simultaneously accounting for heat flux and pressure considerations, it is conceivable that selecting a surface featuring a contact angle of 105° could represent an optimal choice for a 30 mm length minitube. The findings highlight that the hydrophilic surface encourages greater liquid presence, enhancing heat exchange efficiency considerably. Conversely, hydrophobic surfaces facilitate vapor layer stabilization, leading to reduced total pressure drop and minimized fluctuations. This work offers comprehensive insights into the fundamental relationship between wettability, flow boiling, and pressure drop, thereby providing valuable guidance for future miniube design strategies in cooling applications. Such insights hold immense potential to revolutionize various industrial and engineering sectors.