Enhancement of forced convection heat transfer in mini and micro channels by liquid-liquid phase separation of lower critical solution temperature systems

A comprehensive experimental study has been conducted to explore the possibility of enhancing the single-phase convective heat transfer at the mini and micro scales by temperature-induced phase separation of partially miscible liquid-liquid systems with a Lower Critical Solution Temperature (LCST). The performance of two LCST coolants has been examined: triethylamine+water (LCST at 18 ^oC) and Lutidine+water (LCST at 34 ^oC). It is shown that phase separation enhances heat transfer rates from a heated surface at a constant heat flux. Average heat transfer coefficients of up to 2.5 times the corresponding single-phase mixture flow were obtained, with no apparent pressure drop increase. The results show no significant effect of downscaling the channel size on the extent of heat transfer augmentation. The heat transfer enhancement is attributed to the lateral convection of the separating domains, which is driven by the so-called Korteweg capillary forces, and the enlarged apparent specific heat due to the endothermic phase separation. The findings are substantiated by numerical solution of a micro-scale diffuse-interface model for simulating the non-isothermal phase separation process.