Theoretical Study On The Hydrocyclone Applied To The Ships' Ballast Water Treatment

Hydrocyclone has a good prospect in the treatment of ballast water due to its unique advantages such as handiness and safety in operation, cost effective and no pollution associated. Therefore, theoretical analysis and research are carried out on the application of hydrocyclone to the treatment of ships' ballast water in the thesis. The main contents are as follows:Based on the vortex theory and the hydrodynamic basic equations, taking account of the viscosity effect, the expressions of the tangential speed distribution and the tangential stress distribution of the fluid in hydrocyclone are analyzed and deduced, the impact on the tangential speed and stress caused by the circumvolving of the outside wall of the hydrocyclone are analyzed qualitatively. The circumvolving of the wall, which increases the tangential speed of the fluid partial in the separator together with the decrease of the tangential stress, will greatly increase the separation efficiency.As for the turbulence model used in the calculation of turbulence fluid field, an index judgment method on the usability of the turbulence model by comprehensively taking account of factors such as the applicability, accuracy, cost effectivity and complexity of the turbulence model, and the calculating method is put forward, and thus a quantitative judgment is provided on the selection of the turbulence model.The finite-analytic-isoparametric-element method as a new calculation method is put forward in the thesis. This method, which not only include all the advantages of finite-analytic method and isoparametric element method, but also overcomes the shortcomings such as the inapplicability of the finite-analytic method when the border regions are complex, the irrelevance between the interpolation function of the isoparametric element method and differential eguation, has a broader applicability under precondition of high accuracy.Using finite-analytic method to automatically draw the grid, which is put forward in this thesis, is not only more simple in use, more exact in accuracy and easier in controlling the density of the coordinates than the exist method of automatically drawing the gridding, but also making the method of drawing grid standard.Applying the non-isotropic viscosity k-s turbulence model, finite-analytic-isoparametric-element method and multiple grid method to the numeric simulation of the one-phase turbulent flow in the hydrocyclone, comparing with the test data in related literatures to verify the validity, the thesis proves that the non-isotropic viscosity k-s turbulence model can be well applied in the numeric simulation of the turbulent flow in the hydrocyclone, accurately reflect the characteristic of the heavy vortex turbulent flow, as well as the accuracy and effectivity of applying the finite-analytic-isoparametric-element method to simulate the anomalistic boundary fluid field. Based on the simulating and analyzing of the turbulent flow in the hydrocyclone, the impact, which is caused by the rotating of the wall, the inlet flux and the flux ratio, on the separation efficiency and pressure drop is discussed.In this thesis, the certain-orbit model for the two-phase flow is revised and a model of particle orbit model applicable to non-isotropic viscosity two-phase turbulent flow is given. At the same time, a new thought of considering the grid unit as control unit, in which the particles could be tracked down and calculated, thus the distribution characteristic of particles in the whole fluid field could be solved. Numeric simulation of the two-phase flow in hydrocyclone is carried out, as well as discussing the impact on the movement of particles and efficiency of separation caused by the flux, specific gravity and diameter of the particle.An elementary principle of designing a hydrocyclone is put forward in this thesis. Also, the selection of size and range of hydrocyclone specific for ship's ballast water is advised: to choose hydrocyclone with a small diameter (within tens mm) , small cone angle (within 3°) , long cone type, overflow pipe being little inserted, and underflow pipe with enough length. A new rotating hydrocyclone is designed for ships' ballast water. Four kinds of technique procedure are designed for the separation of ships' ballast water together with the compare with each other and discussions, 6 types of combination that could choose to use are presented. The type of placement of the hydrocyclone and the arrangement of units are discussed, useful and effective combined systems in series or parallel connection systems are designed, together with some kinds of installation and control technology, that could be achieved for the hydrocyclone groups, being put forward aiming at guarantying the hydrocyclone operating reliably, safely, and high effectively while at the same time it could achieve easy maintenance and auto control.While hydrocyclone is a kind of separating method with high reliability and efficiency, it is not a kind of separating method for all, particular for the ships' ballast water, which is a little difficult to separate at some degree. Although theoretically, 100% efficiency of separation could be achieved after enough levels and stages, the cost is expensive at all. Generally speaking, after several levels and stages, most of the particles (microorganism) in ships' ballast water could be separated, and the rest could be treated with other methods (e.g. ultraviolet.radiation, electrolysis et al.). Therefore, it is feasible, effective, environment allowable, and economic to instantly treat ships' ballast water in ship with hydrocyclone.