Microchannel Flow Boiling Heat Transfer, Update on the Latest Experimental and Numerical Contributions
The scope of the present paper is to provide a brief and concise survey of the most recent experimental and computational studies aimed at characterizing local heat transfer in microchannels in flow boiling conditions. The significant developments in the measurement techniques have allowed detailed flow visualizations and 2D temperature fields to be obtained simultaneously, thus improving the understanding of the microscale flow boiling dynamics and thermal behavior. First of all, flow patterns are seen to have a dominant influence on the heat transfer trends, and thus need to be accounted by visualization during experiments and during modeling. A clear distinction between steady, unsteady, well- and maldistributed flows needs to be made to avoid any confusion when presenting and comparing the heat transfer coefficient trends. Moreover, several features peculiar to the microscale, which have to be accounted for to accurately and reliably reduce the raw data to local heat transfer values, are also illustrated. In particular, the calculated values of several terms involved in the heat transfer coefficient determination are influenced by the data reduction procedure, especially the procedure to deduce the local saturation pressures/temperatures, and may lead to conflicting trends and errors approaching 100 % in local heat transfer coefficients. In addition to experiments, two-phase CFD simulations are emerging as a tenable tool to investigate the local heat mechanisms, especially those details not accessible experimentally. It is also shown here that targeted computations can provide valuable insights on the local flow structures and heat transfer mechanisms, which can aid to update mechanistic boiling heat transfer prediction methods.
Keynote Paper TP-003
Record created on 2013-06-20, modified on 2016-08-09