Enhancing heat transfer rates by inducing liquid-liquid phase separation: Applications and modelling

This paper focuses on heat transfer enhancement during spinodal decomposition, and it provides an updated review as well as a discussion of future developments. The analysis is mainly based on the work of two research groups at Tel-Aviv University (Israel) and at University of Brescia (Italy). We review the theory of spinodal decomposition of liquid−liquid binary mixtures and we discuss the diffuse interface (DI) approach. While mass and momentum equations in the DI approach have been developed and discussed in other works, we also look into the energy equation, which has been only recently investigated. Direct visualizations of both static and flowing mixture during decomposition are provided. Visualizations of the decomposition in a quiescent fluid have been previously reported, while flowing conditions have been analyzed only recently. Interestingly enough, the morphology is rather different during flowing conditions, where the decomposition exhibits a nucleationlike morphology and not the typical bicontinuous structure observed during spinodal decomposition of a quiescent fluid. Enhancement of heat transfer performances is shown in channels (sizes of 0.8 and 2 mm) using an upper critical solution temperature (UCST) mixture. Although different conditions are analyzed, the results show a consistent enhancement of the heat transfer. The paper reports also some new experimental work on the heat transfer for a lower critical solution temperature (LCST) mixture that can be actually used in cooling applications. A coarse-grained model that could be potentially used for the sizing of large-scale equipment is discussed in term of a possible future development that needs to be further investigated and validated.