An experimental investigation of flow boiling in microchannels

In this Ph.D. thesis, flow boiling in rectangular microchannels is studied experimentally in detail. Values of pressure, temperature, flow rate and heating power are measured and detailed flow visualization tests are conducted using high-speed camera. In this context, different geometrical dimensions, and various values of mass flux and heat flux are examined. The effects of mass flux, vapor quality, channel width to channel depth ratio (AR), hydraulic diameter and heat flux on the two phase heat transfer coefficient and total pressure drop were investigated and, important results were obtained related to physical mechanism. The experimental results obtained for the heat transfer coefficient were evaluated according to the existing correlations and a new correlation was developed. Both the experimental measurements and flow visualization results show that flow boiling in microchannels has unique characteristics and, it differs considerably from macro channel counterparts. Saturated flow boiling in microchannels has quasi-periodical characteristics. The main flow patterns are observed as elongated bubble flow and annular flow. The dominant heat transfer mechanism is shown to be convective boiling. It is disclosed that the aspect ratio and the hydraulic diameter are important parameters affecting the flow and heat transfer characteristics.