Alternating Condensation Flow Patterns in Microchannels

A simultaneous visualization and measurement experiment was carried out to investigate condensation flow patterns of steam flowing through an array of parallel microchannels with a hydraulic diameter of 82.8 μm and a length of 30mm in a <100> silicon wafer. These microchannels were covered with a thin transparent pyrex glass from the top that enabled the visualization of flow patterns in the test section. The degassed and deionized water steam flowing in the microchannels was cooled by cooling water of 8°C at the bottom of the wafer. Experiments were performed for different inlet pressures while the outlet pressure was maintained at a value of 10⁵Pa (the atmospheric pressure). When the inlet pressure was decreased to the value of 1.45×10⁵Pa and the corresponding mass flux was decreased to 23.6g/cm²s, a succession of droplet/injection/slug-bubble flow was observed in the microchannels. Under this condition, the upstream, midstream, and downstream of the microchannels were occupied by the droplet flow, injection flow, and slug-bubble flow, respectively. This concurring droplet/injection/slug-bubble flow appeared periodically in the microchannels that caused large fluctuations of wall temperatures and fluid temperatures with respect to time. The droplet/injection/slug-bubble flow pattern in microchannels has never been reported in the literature.