Design And Research Of Hydrodynamic Cavitation Equipment

Cavitation is a universal hydrodynamic phenomenon occurred in liquid region where local pressure is lower than the saturated vapor pressure at ambient temperature. If water-surface pressure is smaller than the critical one, under the condition water temperature is constant, the small bubbles in water originally expended rapidly and formed relatively large air bubbles which contain steam or other gas, we call this phenomenon cavitation. Cavitation phenomenon which is an unsteady process comprises of the process of development, expansion, collapse, and rebound of the bubbles. The liquid in the low-pressure region mixing mass cavity formed steam-water two-phase flow, cavity with the cavity flow will collapse following through the lower high-pressure region. Bubble collapse can cause extremely physical condition such as high transient pressure and temperature and luminescence and high-speed jet at local site resulting in mass energy release. The results showed that bubble collapse can produces high transient pressure (above 50MPa) and temperature (about 5200K) at local site, accompanied by forceful impact wave and micro-jet more than 100 m/s. It is a brand-new discipline to enhance some process by the energy of bubbles collapse, it also can providing special environment for some physical or chemical reaction difficult to occur in general cases.The dynamical differential equations in two-phase flow have been conducted, the Rayleigh Equation which is the famous Radial Motion Equation is introduced. Through analyzing the static equilibrium condition of single spherical bubble, the phenomenon of gas nucleus expanded to relatively large air bubbles can be explained qualitatively. On this basis the Harvey Nucleus Theory was analyzed to explain all cavitation phenomenon. Subsequently the Cavitation Number which is the state representation of cavitation and Incipient Cavitation Number which discriminates whether cavitation occurs is introduced, and analyzed the factors influencing cavitation incipient.Based on comprehensive analysis of a vast amount of scientific literatures in this paper, a designed experimental device of hydrodynamic cavitation with orifice as cavitation generator is described in this paper. This paper recorded the experimental data of inlet pressure of orifice, outlet pressure of orifice and pressure-fall of orifice and flow rate in pipeline under different pipeline condition for various orifice of opening ratio and the distribution of holes. Influence of opening ratio and the distribution of holes on inlet pressure of orifice, and pressure-fall of orifice is given. Consequently the Hydraulic Characteristics of orifice can be further researched, in a word, the paper provides the theory reference for improvement and optimization of the experimental device of hydrodynamic cavitation.The experimental results indicate that: the bubbles before orifice vary obviously with increasing flow rate, and they are very sensitive to flow states after orifice, so incipient cavitation is delayed because of the bubbles before orifice. The maximum flow rate increases with opening ratio raising, and under the same opening ratio, the maximum flow rate changes with the distribution of holes. The effect of distribution of holes on the inlet pressure of orifice and the pressure-fall of orifice varies with opening ratio, and the effect changes with different flow rate range.