Freeze desalination is a promising nonconventional method with the advantage of low energy consumption, enduring less corrosion, and operating at a higher brine concentration and normal pressure. Experimental study of salinity gradient in the frozen ice is still lacking, and limited literature addresses the time and energy cost of the system. Here, bottom-up directional freezing experiments are conducted to obtain salinity gradient of the frozen brine under different freezing temperature and salinity conditions. These experiments reveal the developed salinity gradient reaching over 60% reduction in an axisymmetric tray. The obtained salinity distribution is used to determine the localized brine properties and its freezing temperature according to the phase equilibria of the NaCl solution. Results obtained demonstrate there is an optimal freezing condition that enables the high salinity diffusion front to migrate/travel and leave the lowest possible salinity level behind. Relying on the obtained salinity gradient, the first principle heat and mass conservation validated model is then developed to evaluate the freezing time and energy usage. Results suggest that salinity gradient vs crystallinity is a nonlinear behavior while respectively the energy consumption increases linearly with the increase and decrease of initial fluid and sub-cooling temperature. These analyses provide the engineer with an evaluation tool that estimates the freezing time and energy consumption for a successive freeze desalination system.