Research On Technology And Equipment For Super-gravity Vacuum/low Pressure Formation Suitable For Seawater Desalination

Desalination technology is an effective way to solve the shortage of fresh water resources.Although the conventional desalination technology is relatively mature,there are many shortcomings.Therefore,the development of new desalination technology has become one of the hot issues in this field.The super-gravity vacuum evaporation seawater desalination technology is a new type of low-temperature low-pressure and low-energy seawater desalination technology.The formation of super-gravity vacuum is the premise and necessary condition for the realization of this technology.Based on the theory of super-gravity vacuum formation,the formation method and equipment design technology of the super-gravity vacuum region were studied in this paper.Three driving modes of super-gravity vacuum evaporation chamber were designed to form the super-gravity vacuum region.The CFD simulation model of the core component rotary cylinder of the super-gravity vacuum evaporation chamber was established.The simulation results were used to select the double-cylinder rotary type as the optimal driving mode.Based on this model,the influences of four key parameters of outlet pressure,outer cylinder radius,rotation speed and evaporation chamber height on the formation process of super-gravity vacuum are obtained.The simulation results are consistent with the theoretical prediction.The error is only about 3%.The volume of the super-gravity vacuum region has a negative correlation with the outlet pressure,and has a positive correlation with the radius of the outer cylinder,the height of the evaporation chamber,and the rotational speed.The resulting influence law can guide the design and operation of the equipment.Based on the selected double-cylinder rotary drive mode,the super-gravity vacuum evaporation chamber is designed.Due to the limitation of laboratory space and manufacturing raw material size,the super-gravity vacuum region can be obtained only when the rotating speed is 360 r/min.When the rotating speed is lower,the super-gravity low-pressure region will be generated,and when the rotating speed is higher,the low-pressure environment will be destroyed.The three-dimensional model of the super-gravity vacuum evaporation chamber was established and introduced into the ANSYS Workbench for modal analysis.The results showed that under the action of rotating prestress and fluid load,the super-gravity vacuum evaporation chamber would resonate when the drum reached the maximum speed of 360r/min.It might affect the formation of the super-gravity vacuum region.The fluid load had little effect on the frequency of the super-gravity vacuum evaporation chamber and might not be considered during design and experimentation.A test platform for super-gravity vacuum evaporation chamber was built,and the formation process of super-gravity vacuum/low pressure environment was tested.During the test,the super-gravity low-pressure region was successfully generated.Lowering the outlet pressure and increasing the rotation speed within a certain range all contributed to the formation of the super-gravity low-pressure environment.The lowest pressure measured in the experiment was close to the theoretical calculation result,and when the rotational speed was 360 r/min,the lowest pressure reached 8.9 kPa,which was in the same order of magnitude as the saturated vapor pressure corresponding to the ambient temperature.In the experiment,the theoretically predicted vacuum area was not obtained.On the one hand,due to the speed slip of the drum and the fluid,the relative speed slip reached a maximum value of 6%when the rotating speed of the drum was 360r/min.On the other hand,the operating frequency of the equipment approached the resonance frequency of the modal analysis,and the excessive vibration occurred,resulting in the rebound after the pressure reaches the minimum.The maximum energy consumption of the super-gravity vacuum evaporation chamber was about 425W,which was very small compared with the total energy consumption of thermal seawater desalination,and had certain energy consumption advantages.The coupling method of super-gravity vacuum/low pressure forming technology and seawater desalination process were studied.The technology of super-gravity low pressure membrane distillation seawater desalination technology was proposed.The overall process flow was designed.The technical feasibility and advantages were analyzed.The energy consumption was predicted.The conceptual design of key components was carried out,which laid a foundation for further study of this technology.