Numerical simulation of bubble growth in different nucleation positions and bubble merging near pin fin under the influence of non-closed droplet structure

• Published in: International communications in heat and mass transfer Vol. 159; p. 108058
• Main Authors: Sang, Keyi, Hua, Junye, Zhang, Shuntao, Liu, Huiyan, Lan, Hai, Niu, Baolian, Xia, Yi
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-12-2024
• Subjects: Bubble; Bubble dynamic characteristics; Microchannel; Non-closed droplet pin-fin; Vapor-liquid two-phase; Vapor-liquid two-phase; Bubble; Microchannel; Non-closed droplet pin-fin; Bubble dynamic characteristics
• ISSN: 0735-1933
• DOI: 10.1016/j.icheatmasstransfer.2024.108058

The microchannel heat transfer technology is a solution to the problem of efficiently dissipating heat in tight spaces. It's commonly used in electronic components, power equipment, and other heating systems. In this manuscript, a numerical simulation has been conducted to study the dynamic characteristics of bubbles in microchannels with non-closed droplet shaped pin fins, with the CFD (Computational Fluid Dynamics) method utilized. The results show that the opening structure design can help reduce the impact of fluid flow and encourage the formation and growth of vaporization cores, which is beneficial for improving the heat transfer performance in microchannels. The conclusions show that during the growth of bubbles, there is little difference in the shape of bubbles at the three different nucleation positions. The bubbles at points A (at the opening of the non-closed droplet micro pin-fin), B (at the sidewall of the non-closed droplet micro pin-fin), and C (at the tail of the non-closed droplet micro pin-fin) first experience slow growth, followed by rapid growth, and finally steady growth. However, the bubble at the opening of non-closed pin fin grows fastest and holds the largest volume. At t = 0.00223 ms, the bubble diameter can reach 0.0183 mm, and after t = 0.0641 ms, the bubble volume on the pin-fin side is the largest. In the study of merging two bubbles, the two bubbles show flat growth. The left bubble (bubble in point I) grows faster and has a larger volume than the right bubble (bubble in point II) because it is closer to the fin wall with higher heat flux density.
Meanwhile, it has been observed that the expansion velocity of the bubble at point I is marginally quicker than that of the bubble at point II. At t = 0.013 ms, the disparity between them reaches its peak at 0.035 mm, subsequently stabilizing at approximately 0.03 mm. Before the merger of two bubbles, there are some vortices around the bubbles. As the merger initiates, the velocity at the junction between the bubbles is minimal and the unidirectional. During the partial merging process, multiple velocity vectors arise at the junction, fostering local circulation patterns. Following the completion of the merge, the velocity vectors at the former junction resume a uniform distribution.
•The mechanism of bubble growth and coalescence in the microrib region is well revealed.•Bubble growth rate and temperature rise are faster at the opening of the pin fin.•The open structure accelerates bubble detachment.•There are some vortices around the bubbles before they merge.