On the Phenomenal Mechanisms and Prediction Methods of Flow Boiling Heat Transfer in Microchannels

Abstract

-This keynote paper presents a comprehensive analysis of phenomenal mechanisms and the available correlations and models of flow boiling heat transfer in micro-channels. First, studies on flow boiling heat transfer behaviours and mechanisms in microchannels are presented. Then, the available correlations and models of flow boiling heat transfer in micro-channels are reviewed and analysed. Comparisons of 12 correlations with a database covering a wide range of test parameters and 8 fluids are presented. It shows that all correlations poorly agree to the database. Furthermore, comparisons of the mechanistic flow boiling heat transfer models based on flow patterns including the Thome at al. three-zone heat transfer model for evaporation in microchannel and the flow pattern based model combining the Thome et al. three zone heat transfer models with the Cioncolini-Thome annular flow model for both macro-and microchannel to the database are presented. It shows that the flow pattern based model combining the three zone model with the annular flow model gives better prediction than the three zone heat transfer model alone. The flow pattern based heat transfer model favourably agrees with the experimental database. According to the comparison and analysis, suggestions have been given for improving the prediction methods in the future. Furthermore, flow patterned based phenomenological models and their applications to micro channels are discussed. According to this comprehensive review and analysis of the current research on the flow boiling heat transfer mechanisms and prediction methods in micro-channels, the future research needs have been identified and recommended. In general, systematic and accurate experimental data of flow boiling heat transfer in micro-channels are still needed although a large amount of work has been done over the past decades. The channel size effect on the flow boiling behaviours should be systematically investigated. Heat transfer mechanisms in micro-channels should be further understood and related to the corresponding flow patterns. Furthermore, effort should be made to develop and improve generalised mechanistic prediction methods and theoretical models for flow boiling heat transfer in micro-channels according to the physical phenomena/mechanisms and the corresponding flow structures. The effects of the channel size and a wide range of test conditions and fluid types should be considered in developing new prediction methods.