Numerical Study On The Optimization Of Blade Parameters Of Rotational Surpercavitating Evaporator

As the depletion of the fresh water resources on earth, desalination will be a key method to produce freshwater in the future. The thermal methods of desalination are limited by the scale formation and heat transfer coefficient, which leads to a large system scale and great difficulties in construction and maintenance. There is a vaporization process on the vapor-liquid interface of supercavity, which is similar to the boiling process on the wall but with a larger heat transfer coefficient. Introduction of this supercavitation technology to desalination can overcome the limit of heat transfer coefficient in thermal methods. So the use of rotational supercavitating evaporator(RSCE) makes it possible to diminish the scale of desalination system greatly. Because of its highly efficient vapor-liquid phase transition mode, the RSCE also has a bright prospect in sewage treatment field.In this paper, a numerical investigation of supercavitation is achieved with the computational fluid dynamics software FLUENT. Firstly, the comparison between planar cavitator and axisymmetric cavitator is presented and the differences of supercavitation formed by these two kinds of cavitators are obtained.Secondly, the supercavitation formed by isosceles triangle and curve-shape planar cavitators are investigated by two-dimensional numerical simulations. The differences between the supercavitation formed by each cavitator are discussed and fitting functions of supercavity size and drag for each cavitator are obtained.Then, based on the fitting functions of two-dimensional planar cavitators, the blades of RSCE are designed to simulate the supercavitation formed in RSCE. The characteristics of supercavitation formed by the blade with different rotational speeds are acquired. The divergence between the designed size and the size of supercavity formed by the blade in simulation is presented and the causes are discussed. The influences of steam extraction on the formation of supercavitation are discussed and it is found that high working temperature can promote the steam extraction. An estimation model for the resistance moment is developed and the estimation error is less than 2%.Finally, a modified design method is presented, by which a new blade is designed. The thermodynamic performances of the newly designed RSCE are investigated. The influences of steam extraction on the temperature distribution and the change of temperature within the supercavity are analyzed, respectively. The preliminary thermodynamic characteristics of the RSCE are obtained.