Two-phase flow operational maps for multi-microchannel evaporators

Predicting two-phase flow distribution and stability in systems with many parallel heated channels

“…Flow maldistribution in parallel-channel two-phase heat sinks has been observed experimentally in various studies [8][9][10][11][12][13]. Maldistribution can have several causes: asymmetrical inlet header designs, differences in channel geometry or surface properties, non-uniform heating, and the non-monotonic nature of channel pressure drop as a function of flow rate.…”

“…This limits the heat flux that can be safely dissipated without inducing an extreme temperature rise in the heat source. Several remedies have been proposed to suppress two-phase flow maldistribution and other (parallel-channel) instabilities: inlet restrictions [3,11,16,17], reentrant cavities [18], diverging cross-sections [19], seed bubbles [20], increased system pressure [21], self-sustained high-frequency oscillations [22], and active control of pump and/or valves [23][24][25][26]. However, these measures may not effectively suppress maldistribution specifically, may be infeasible to implement in some applications, or may increase pressure drop.…”

Electronics Thermal Management in Information and Communications Technologies: Challenges and Future Directions

“…Several geometric enhancements have been proposed to suppress instabilities, such as inlet restrictions [101], channel tapering [102] and the use of surface roughness [103]. Recent work at Stanford has focused on vapor/liquid phase separation, i.e., vapor extraction from a microchannel flow using permeable membrane surfaces [104] or heat pipeinspired separation using phase-separator coatings on a porous medium which keeps liquid contained within structure by surface forces, yet allows evaporation at the boundaries.…”

Heat transfer enhancement of self-rewetting aqueous n-butanol solutions boiling in microchannels

“…The main issues revolving around flow boiling in microchannels are the instabilities, which were thoroughly covered by Kandlikar et al [6]. Several researchers implemented inlet restrictors to mitigate vapor backflows during boiling and potential nucleation cavities to lower the temperatures of the onset of nucleate boiling (ONB) [7][8][9][10][11][12][13]. Another challenge in microchannel flow boiling presents the formation of solely annular flow, when the hydraulic diameter is smaller than the detaching bubble diameter [14].…”