Direct information about fluids under supercritical water conditions is unfeasible due to the engineering restrictions at high pressure and high temperature. Numerical investigations based on computational fluid dynamics (CFD) calculations are widely used in order to get extensive information on the fluid behavior, particularly to help the design of a new reactor. This paper presents the numerical investigations performed on an original supercritical water device, especially in the level of the reactor. CFD calculations allow to design and optimize the present reactor described in this study. Currently, this process produces some nanometric oxide powders in continuous way with a production rate of 10-15g h(-1). Examples of synthesized nanomaterials are presented in order to prove the process efficiency. Crystalline ZrO(2) and TiO(2) were produced from a metallic salt and an organometallic as precursors, respectively. XRD and HRTEM analyses show nanosized particles with an uniform size distribution (<= 7nm) and a high crystallinity.