Cavitating flow

The onset of cavitation for a globe valve occurs with the onset of choking, as was noted in Section 7.5.2. Hence it will be predicted when W = Wchokr-Cavitation in a rotary valve occurs before choking, when the throat pressure equals the vapour pressure at valve inlet temperature, and equation (7.11) applies. This is of precisely the same form as equation (7.19), but with K replaced by and set to unity. This similarity of form enables us to repeat the development set out in Section 8.3 to determine the flow at choking. Thus we reach the following equation for cavitating flow, IV,., ... 

With V = Va e, use equation (8.17) to calculate the choking flow, (8.19) to calculate the cavitating flow and (8.18) to calculate the actual flow through line and valve. Figure 8.5 shows the result. 

Figure 8.5 Actual flow, compared with choking flow and cavitating flow.

Hydraulic reliability is reflected in the pump s ability to maintain steady discharge pressures and corresponding flow rates in the range of outputs desired. Relatively high flow rates and impeller speeds are conducive to the production of a cavitating flow. Such conditions become critical and hydraulic-flow deterioration occurs when the inlet pressure becomes inadequate for vapor suppression. A criterion for establishing the vulnerability of the pump to incipient cavitation is the well-known dimensionless parameter called suction specific speed. 

A. Lichtarowicz, R. K. Duggins, and E. Markland, Discharge coefficients for incompressible non-cavitating flow through long orifices, Journal of mechanical Engineering Science, 7(2), 210-219, 1965. 

Recent developments in microelectrome-chanical systems (MEMS) have enabled the integration and fabrication of numerous micro components such as pumps, valves, and nozzles into complex high-speed microfluidic machines. These systems possess geometrical dimensions in the range 1-1,000 pm, which are 10-10 -10-10" times less than conventimial machines, and operate at liquid flow speeds up to 300 m/s. It has been confirmed that microfluidic systems, like their large-scale counterparts, are susceptible to the deleterious effects of cavitation when appropriate hydrodynamic conditions develop. Cavitation damage in micro-orifices has been reported by Mishra and Peles [2], Small pits on the silicon surface have been detected after only 7-8 h of operation under cavitating flow. 

Agostino, L. Brennen, C.E. Acosta A.J. Linearised dynamics of two dimensional bubble and cavitating flows over slender surfaces. 

A very useful parameter for quantifying cavitating flows of various intensities is the cavitation number, [Pg.198]

Mishra C, Peles Y (2005) How visualization of cavitating flows through a rectangular slot micro-oilice ingrained in a microchannel. Phys Huid 17(11) 113602-113616... 

With the exception of cavitation, flow-induced corrosion problems are generally termed erosion-corrosion, encompassing flow enhanced dissolution and impingement attack. The fluid can be aqueous or gaseous, single or multiphase [23]. There are several mechanisms described by the conjoint action of flow and corrosion that result in flow-accelerated corrosion (FAC) [24 25] ... 

Senocak I. Computational Methodology jbr the Simulation of Turbulent Cavitating Flows. Gainesville, FL University of Florida, 2002. 

Isentropic turbulent flow [29] and microturbulences in cavitational flow [37-40] ... 

Sensors of this kind were applied at FZR to an air-water flow test loop in a vertical pipeline (inner diameter D = 51.2mm) as well as to a cavitating flow behind a fast acting valve. The high resolution of the sensor allowed to obtain bubble size distributions and to study the evolution of the flow structure along the pipe [7]. The maximum time resolution available to perform these experiments was 1200 measurements per second. Recently, the measuring rate was increased to 10 000 frames per second with sensors of 16 x 16 measuring points. In the result it is possible to visualise and quantify individual bubbles or droplets at a much higher flow velocity, than before. 

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