A confined jet mixer and a counter current mixer for the continuous hydrothermal flow synthesis of TiO2 nano-materials under supercritical water conditions have been investigated using computational fluid dynamics (CF). The fluid flow and heat transfer behaviour, including velocity and temperature profiles in both reactor configurations, are studied using the CED tool ANSYS Fluent,. The tracer concentration profiles are also simulated via solving species equations from which the mixing behaviour in the reactors is examined. A combined CM and population balance model is used to predict the size distribution. The predicted temperature distributions for both reactors vvere found to be in good agreement vvith experimentally measured data. Detailed comparison of the hydrodynamic and thermal behaviours, and particle size distributions between the two reactors helped in the identification of key factors that affect the reactor performance, and also provided suggestions for reactor design optimisation and scale-up. (c) 2014 Elsevier Ltd. All rights reserved.