Sub-atmospheric pressure effects on bubble dynamics in counter current flow diverging microchannel heat sink

• Bubble dynamics in counter current flow diverging microchannel under the condition of atmospheric and sub-atmospheric pressures. • The bubble growth and shrinking was obviously detected. • Proposed a theoretical model to illustrate channel-to-channel heat transfer effect. • Suitable for electronic cooling system. The heat dissipation of high-power electronics or devices has become an important issue in industry, especially with the emergence of artificial intelligence. We had proposed and developed an innovative channel-to-channel Counter Current Flow Diverging Micro-channels (CFDM) heat sink with ultra-high performance via the channel-to-channel heat transfer effect. Notably, boiling of water has to occur at sub-atmospheric pressures in many applications to reduce the saturation and surface temperatures. The present study focuses on bubble dynamics, which is essential for understanding the boiling heat transfer, at inlet pressures of 40, 65, 80, and 120 kPa in a CFDM heat sink with an area of 8 cm 2 . For all pressure conditions, the bubble growth and shrinkage are investigated at the heat flux of the onset of nucleate boiling in the heat sink. The shrinkage of bubbles demonstrates the chilling effects of neighboring channels through the channel-to-channel counter flow design. Furthermore, the average peak length and the bubble shrinking time generally increase with decreasing pressure due to the increase in density ratio of liquid to vapor. The bubble frequency significantly decreases while the bubble departure length increases with decrease in inlet pressure.