Two-phase flow patterns, pressure drop and heat transfer during boiling in minichannel and microchannel flow passages of compact evaporators

The small hydraulic diameters employed during flow boiling in compact evaporator passages are becoming more important as they are employed in diverse applications including electronics cooling and fuel cell evaporators. The high pressure drop characteristics of these passages are particularly important as they alter the flow and heat transfer, especially in parallel multi-channel configuration. The pressure drop oscillations often introduce dryout in some passages while their neighboring passages operate under single-phase mode. This paper presents a comprehensive review of literature on evaporation in small diameter passages along with some results obtained by the author for water evaporating in 1-mm hydraulic diameter multi-channel passages. Critical heat flux is not covered in this paper due to space constraint.