Review of databases and predictive methods for heat transfer in condensing and boiling mini/micro-channel flows

The importance of flow boiling and condensing mini/micro-channel devices to a large number of modern applications has spurred an unusually large number of research efforts that culminated in many types of predictive tools. These efforts have inadvertently contributed enormous confusion when selecting a suitable predictive method. This study reviews methods for predicting heat transfer in condensing and boiling mini/micro-channel flows. Systematic assessment of predictive accuracy of individual methods requires the development of consolidated mini/micro-channel databases for condensation heat transfer, dryout incipience quality, and saturated boiling heat transfer. These databases cover numerous working fluids and broad ranges of geometrical and flow parameters. It is shown that, despite the success of previous predictive methods for specific fluids and narrow databases, these methods are incapable of providing accurate predictions against entire consolidated databases. The consolidated databases are used to develop ‘universal’ correlations with very broad application range. These include two separate correlations for condensation heat transfer, one for annular flow and the other for slug and bubbly flows. Also developed are correlations for dryout incipience quality and saturated boiling heat transfer; the later is shown to accurately tackle both nucleate boiling dominated and convective boiling dominated regimes up to the location of incipient dryout.