The heat transfer and flow phenomena during phase separation of partially miscible liquid solvent system were investigated experimentally. The experiments were conducted with a three components system which has an upper critical solution temperature, using critical and off-critical compositions of the solvent mixtures. The convective heat transfer rates were studied for laminar flow in a small diameter horizontal tube and for free convection from its outer surface. It was found that with phase separation the forced convective heat transfer can be augmented by up to 130% compared to heat transfer rates obtained in single phase flow (without phase separation). However, for low quenching rate and depth associated mainly with experiments conducted with critical compositions, deterioration of the heat transfer rates The free convection heat transfer coefficients were found to be augmented up to 100%. was observed, Macro- and micro-flow visualization were also conducted to follow the flow phenomena during the phase separation, and the mechanisms responsible to the heat transfer enhancement are discussed. (C) 2008 Elsevier Ltd. All rights reserved.