二, cavitation phenomenon.
Water and steam can be mutual transformation, and temperature and pressure was the cause of them. If the temperature remains constant, gradually reduce the liquid on the surface of the absolute pressure, when pressure is reduced to a certain value, the water will also vaporize, the pressure value is called water under the condition of the temperature of the vaporization pressure. If in the process of flow, the pressure of a local area is equal to or lower than the water temperature corresponding to the evaporation pressure, water will vaporize in the area.
After vaporization occurs, large quantities of steam and escape of gas dissolved in the water, forming many small bubbles steam and gas mixture, when the bubble with water flowing from low pressure area high, bubble around under the action of high pressure, fracture and condensation, quickly at the instant of the bubble burst, produce local hole, high pressure water flow at high speeds the originally was the space occupied by the bubble, to form a strong collision and high frequency oscillation, if this phenomenon continues, runner material surface on the water hammer pressure under the action of repeated, fatigue damage to formation, from the beginning of honeycomb pitting to severe empty, finally even the material erosion wear.
This due to evaporation have bubbles, the bubbles into the high burst, causing fluid surrounding the high frequency collisions and cause material damage to the whole process is called cavitation. |
