IMECE2009-11579 CONTROLLED FLOW EVAPORATION IN COMPLEX MICROCHANNELS WITH NON- UNIFORM WALL TEMPERATURES

ABSTRACT This paper presents an experimental study of flow evaporation in non-uniform microchannels, demonstrating the ability to provide a stable flow of evaporated fluid for energy conversion and chip cooling applications. Two mechanisms are proposed to stabilize the internal flow evaporation. The first mechanism is to establish a temperature gradient along the channel to separate the room temperature inlet fluid from the steam exit flow. The second mechanism is to change the direction of the surface tension forces acting on the meniscus to fix its position along the channel. To achieve this, shaped channels are formed of contractions and expansions with varied wall angles. The device consists of a silicon wafer with through-etched complex microchannels, that is anodically bonded to a glass wafer on each side. Inlet and exit holes for the fluid are machined in the glass wafers. Water is forced through the chip while it is heated on the exit side of the three layer chip. The qualitative nature of the two-phase flow along the shaped channels is observed through the glass cover wafer, for different flow rates and wall temperatures. The temperature gradient achieved with different thickness of channel walls shows agreement with the modeling results. Also, the benefit of having multiple expansions in the channels was demonstrated. By using these two mechanisms the onset of water evaporation was fixed along the channel. This will lead to the development of adequate two-phase flow micro heat exchangers