Two-state boiling patterns in cooling microchannel arrays

Microchannel cooling is commonly used in power electronics. In normal operation, the coolant flowing in microchannels stays liquid. When overload occurs, liquid starts to evaporate, dividing the microchannels into sections of liquid and annular flow. The vapor phase distribution displays distinct two-state behaviour: When vaporization occurs in a channel, the gas bubble (a section of annular flow) rapidly grows and then remains stationary, occupying a significant part of the channel and leading to the flow re-distribution across the manifold. Continuing heat supply initiates boiling in other channels with complicated dynamic patterns occurring in the system. We investigate formation and evolution of the two-phase patterns with the ultimate aim of utilizing the vaporization enthalpy to increase the system cooling capacity.