![]() Water cavitating jet technology was firstly used to clean surfaces. A flow cavitation chamber was used by to test concrete and different rock samples subjected to short-duration cavitation. An alternative test for erosion evaluation uses water cavitating jet technology to achieve short test time. A chamber was used by to test concrete samples subjected to short-duration cavitation. In the hydrodynamic cavitation, pressure variations are produced using the geometry of the system, while in the acoustic cavitation pressure variations are effected using sound waves.Ĭoncrete resistance to cavitation damage was investigated by using a Venturi device. Various techniques can be used to induce cavitation, such as, ultrasonic methods, hydrodynamic methods, and high-speed/high-pressure homogenization. Moreover, two alternatives uses for cavitating jets are presented: 1) the inactivation of Escherichia coli, and, 2) the decomposition of persistent compounds in water.Įvaluation of the concrete erosion resistance in hydraulic structures is essential to guarantee adequate operation, and tests should be performed under the same operation conditions. In this chapter the authors discuss the use of high velocity cavitating jets to determine the erosion in high performance concretes for hydraulic structures. It was suggested by defining a methodology to appropriately test the materials, when submitted to cavitation, to be used in hydraulic structures. Evaluation of the concrete resistance erosion in hydraulic structures is essential to guarantee adequate operation. Īn additional complexity is observed in hydraulic structures due to the simultaneous effect of cavitation and high impact of the flow. For example, the substitution of a great area of eroded concrete was required in the case of Porto Colombia hydropower spillway and dissipation basin in the Grande River, Brazil. Therefore, the material properties have to be improved to provide adequate resistance, either during the construction phase or substitution phase. Nevertheless, the operation and maintenance of these structures, which include the spillways and tunnels under high velocity flows, are a great issue. Therefore, as energy demands are continuously increasing, new hydropower plants (dams and appurtenances) are being constructed. ![]() Particularly of interest, in developing countries, hydropower will continue to play a significant role in supplying energy. Therefore, the material properties of the surface have to be improved to provide adequate resistance either during the construction phase or when the substitution of the eroded concrete is required. In hydraulic structures, as the high velocity flow passes over the many irregularities that exist in the concrete surface, cavitation can commence and consequently, damages may occur. The severity of the damage may be related to both intensity of cavitation and exposure time. įlow conditions leading to the onset of cavitation are generally conservative in predicting damage. The collapse of the cavities formed by the cavitating jet generates high-pressure waves, estimated to be approximately 69.00 MPa and high-speed microjets (above 100 m/s), all of which have a significant amount of destructive power. The velocity of this microjet is high and the shockwave produces high pressure responsible for the cavitation damage of a surface. If a boundary is close to where the bubble imploded, it will deform into a microjet. If the bubble collapses, then shock waves form with celerity equal to the speed of sound in water. The process takes place until the bubble diameter becomes microscopic. Īs the pressure is increased, the bubble diameter decreases from the original size reaching a minimum size. Pressure distribution in a submerged body. Then, the cavitation index (σ) is the theoretical value of the negative pressure coefficient, Equation 2: If we consider that cavitation will occur when the normal stresses at a point in the liquid are reduced to zero, then the bubble pressure will assume the value of the vapour pressure, p v. ![]() This pressure will be the bubble pressure. If surface tension is ignored, the pressure p min will be the pressure inside the cavity. This can be accomplished by raising the relative velocity v o for a fixed value of the pressure p o or lowering p o with v o remaining constant. If pressure p reaches a minimum, p=p min (see Figure 1), the pressure coefficient will be minimum, and a set of conditions can be created so that p min drops to a value where cavitation can begin. Where ρ is the density of the liquid v o and p o are the velocity and pressure of an undisturbed liquid, respectively, and (p-p o) is the pressure differential due to dynamic effects of fluid motion.
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