Comprehensive review of enhancement techniques and mechanisms for flow boiling in micro/mini-channels

•Summary of various enhancement approaches and formation techniques in micro/mini-channels.•Flow boiling heat transfer, CHF, flow patterns and instability in enhanced micro/mini-channels.•Systematic analysis of the physical mechanisms of flow boiling in enhanced micro/mini-channels.•Discussion composite enhancement techniques and optimization issues of enhanced micro/mini-channels.•Recommendations for future research on flow boiling enhancement in micro/mini-channels. Due to the urgent need for heat dissipation of high heat flux devices in many engineering applications to maintain high performance and stable operation, flow boiling in micro/mini-channel heat sinks is an enabling and promising approach to tackling high heat flux cooling issues in emerging cutting-edge technology. Various enhancement techniques for flow boiling in micro/mini-channels have been investigated in recent years. These mainly include various surface modifications, enhanced channel structures and composite enhancement techniques. These techniques are able to improve flow boiling heat transfer coefficient (HTC), critical heat transfer (CHF) and mitigate two phase flow instabilities. The composite enhancement techniques take the advantage of each individual technique for flow boiling to achieve more efficient heat transfer and stable flow. However, there are challenges to optimizing these techniques and understanding the very complex mechanisms involved in these emerging techniques. This paper presents a comprehensive review of the studies of various enhancement techniques for flow boiling and mechanisms in micro/mini-channels having hydraulic diameter of 0.1–3 mm over the past five years. First, the criteria for distinction of micro/mini-channels and classification of flow boiling enhancement techniques are discussed. Then, studies of flow boiling enhancement techniques using surface modification techniques and enhanced structures are critically reviewed. Next, the effects of surface modification techniques and enhanced structures on flow boiling heat transfer, CHF, two phase flow patterns, two phase flow instability and mechanisms in micro/mini-channels are discussed and analyzed. Other enhancement techniques such as using surfactants to enhance flow boiling is also mentioned. Finally, future research needs have been identified and recommended according to the comprehensive review and deep analysis. Systematic research on the physical mechanisms underlying the composite heat transfe