Reduced-Order Fluidic Model for Flow Instabilities in Two-Phase Microfluidic Heat Exchangers

Two-phase microfluidic heat exchangers have the potential to provide high-heat flux cooling with lower thermal resistance and lower pumping power than single-phase heat exchangers. However, the process of phase change in two-phase heat exchangers can cause flow instabilities that lead to microchannel dryout and device failure [1–3]. Modeling these flow instabilities remains challenging because the key physics are highly coupled and occur over disparate time and length scales. This work introduces a new approach to capture transient thermal and fluidic transport with a reduced-order model consisting of fluidic, thermal, and phase-change submodels. The present study presents a reduced-order, transient, multichannel fluidic circuit submodel for integration into this proposed modeling approach. The fluidic submodel is applicable in flow regimes in which a thin liquid film exists around the bubble. Flow response to boiling is modeled considering bubble overpressure. An adaptive time step approach is used to treat the rapid flow response at short time scales after initial bubble vaporization. Using a seeded bubble technique for testing two-phase flow response, the model predicts a stability threshold at 0.015 W of localized superheating for two 100-micron square channels in parallel with a pump flow rate of 0.15 ml/min. Once integrated with the proposed reduced-order thermal and phase change models, this fluidic circuit model will yield criteria for stable two-phase heat exchanger operation considering factors such as pumping pressure, channel geometry, and applied heat flux that can be compared to experimental observations.