Combined influence of lateral thermal coupling and inlet restrictors on flow boiling maldistribution in many parallel microchannels

• A lumped two-phase flow model is developed for many parallel heated microchannels. • Linear stability is used to assess the flow stability and maldistribution in the system. • Channel-to-channel thermal conductance is shown to mitigate flow maldistribution. • The effect of thermal conductance on stability reduces with more parallel microchannels. • Inlet restrictors are more effective in suppressing maldistribution with higher thermal conductance. Flow boiling in parallel microchannel heat sinks is attractive for heat dissipation from telecommunications devices, data center server chips, and electrified vehicle power converters and motors. However, there are practical implementation challenges associated with two-phase flow maldistribution through parallel microchannels, which can degrade thermal performance and reliability. Therefore, predicting and understanding the flow distribution mechanics in parallel microchannels based on analysis of the system stability is essential. It has been shown that lateral channel-to-channel thermal coupling has the potential to reduce maldistribution for systems having only two parallel channels. Yet, the effect of thermal coupling on system stability and maldistribution in larger sets of many parallel channels, as would be common in microchannel heat sinks and other components, is unexplored. In the current work, a lumped fluid flow model, which also incorporates the wall thermal capacity effects on the system dynamics, is developed to assess flow distribution with lateral thermal coupling between neighboring parallel microchannels. Linear stability analysis establishes that the effectiveness of lateral thermal coupling in reducing maldistribution weakens with an increasing number of parallel microchannels. And for many parallel microchannels, it is confirmed that lateral thermal coupling alone cannot stabilize the system, and the entire two-phase flow operating region becomes inherently maldistribution-prone, with similar stability to thermally isolated parallel channels. However, with the addition of inlet restrictors to the channels, the impact of lateral thermal coupling becomes significant, regardless of the number of channels. Inlet restrictors are more effective in suppressing maldistribution when there is a higher lateral thermal conductance between neighboring channels. This unintuitive combined influence of lateral thermal coupling and the inlet restrictors in reducing maldistribution is attributed to nonlinear behavior that is explained based on the eigenvalues of the parallel microchannel system.