No abstract

Freezing desalination (FD) is attractive and more sustainable option due to the low energy consumption and less maintenance. However, technical challenges such as low freezing rate and process complexity arising from the salt trapping in the produced ice hinder the commercialization of this method. In this work, freezing experiments of water-NaCl solution are carried out to investigate the ice propagation and its salinity distribution to understand the salt trapping phenomena. Results reveals subcooling followed by a homogenous temperature jump occurs in the solution at an early stage of freezing suggesting ice freezing happens to large solution bulk. The Ice-front in brine is also characterized with many sharp and disorderly ice tips and there are many channels filled with liquids inside the formed ice block. This heterogeneous growth of ice promotes salt trapping. The salt distribution in the formed ice reveals that the salinity gradient in that early freezing stage is quite small and it rises dramatically at the last several layers of ice. The salinity in the first 10% frozen ice is only half of initial salinity which suggests a suitable freezing fraction of initial solution in freezing desalination. Finally, the developed first principle model based on the obtained salinity gradient is proved to be reasonably accurate to predict the freezing time with acceptable discrepancies and less computation cost.

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.

Accurate characterization of oilwell cement mechanical properties is a prerequisite for maintaining long-term wellbore integrity. The drawback of the most widely used technique is unable to measure the mechanical property under in situ curing environment. We developed a high pressure and high temperature vessel that can hydrate cement under downhole conditions and directly measure its elastic modulus and Poisson's ratio at any interested time point without cooling or depressurization. The equipment has been validated by using water and a reasonable bulk modulus of 2.37 GPa was captured. Neat Class G cement was hydrated in this equipment for seven days under axial stress of 40 MPa, and an in situ measurement in the elastic range shows elastic modulus of 37.3 GPa and Poisson's ratio of 0.15. After that, the specimen was taken out from the vessel, and setted up in the triaxial compression platform. Under a similar confining pressure condition, elastic modulus was 23.6 GPa and Possion's ratio was 0.26. We also measured the properties of cement with the same batch of the slurry but cured under ambient conditions. The elastic modulus was 1.63 GPa, and Poisson's ratio was 0.085. Therefore, we found that the curing condition is significant to cement mechanical property, and the traditional cooling or depressurization method could provide mechanical properties that were quite different (50% difference) from the in situ measurement.

Nonionic surface active agent AO-1, n-butanol, kerosene and water were mixed in varying proportions to compound micro-emulsion. According to different phase states of each micro-emulsion, some systems with representative were picked up, and then tested the interface properties of oil phase of the systems above. The experimental results show that there is a system with low interfacial tension and steady surface tension.