Periodic flow boiling in a non-uniformly heated microchannel heat sink

• The effect of heat flux distribution on flow boiling instability was evaluated.
• Most of non-uniform heating conditions showed instability.
• The instability is correlated with flow pattern transition.
• We relieved the instability by controlling the heat flux along the flow direction.
• We predicted the instability using the transition criteria and flow pattern map.

Hydrodynamic and thermal characteristics of flow boiling in a non-uniformly heated microchannel were studied. Experiments were performed with a single microchannel and a series of microheaters to study the microscale boiling of water under axially non-uniform heat input conditions. A simultaneous real time visualization of the flow pattern was performed with the measurement of experimental parameters. Tests were performed over a mass flux of 309.8 kg/m2 s, and heat flux of 200–600 kW/m2. Test results showed different fluctuations of heated wall temperature, pressure drop, and mass flux with variations of the heat input along the flow direction. The unique periodic flow boiling in a single microchannel was observed at all heat flux conditions except for the increasing heat input distribution case which is the nearly uniform effective heat input distribution condition. The instability is correlated with flow pattern transition. For the nearly uniform effective heating condition, no fluctuation of the wall temperature, pressure drop, or mass flux was observed. We can relieve the instability by increasing total heat input along the flow direction and predict the instability using the transition criteria and flow pattern map.