Experimental investigation into unstable two phase flow phenomena during flow boiling in multi-microchannels

Experiments of unstable vapor liquid two phase flow phenomena during flow boiling with HFE-7100 in two parallel rectangular multi-microchannels with aspect ratios of 0.2364 and 0.3182 were conducted under a wide range of test conditions: the mass flux from 380 to 3500 kg/m2s, the heat flux from 0 to 1080 kW/m2 and the compressive volumes of 0, 5, 10 and 20 ml, respectively. First, characteristics of flow boiling heat transfer and two-phase pressure drop in the two parallel multi-microchannels are compared with each other. It shows that the maximum dissipated heat flux in the microchannels with the aspect ratio of 0.3182 is 34.4% larger than that in the microchannels with the aspect ratio of 0.2364 while the pressure drop in the microchannels with higher aspect ratio is up to 80% less than that in the microchannels with lower aspect ratio under the test conditions. Then, experimental results of unstable vapor liquid two phase processes in the two parallel multi-microchannels are compared with each other. It shows that the minimum heat flux decreases with decreasing the aspect ratio at the same compressive volumes. Finally, the physical mechanisms of unstable vapor liquid two phase phenomena in the parallel multi-microchannels have been analyzed according to a simplified mathematical model based on the mass and momentum conservation. It is concluded that a wide flat regime in the hydrodynamic curves may decrease the unstable vapor liquid two phase flow phenomena.