Flashing is a vaporizing process similar to cavitation.Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion.
Flashing is a vaporizing process similar to cavitation. However, flashing differs from cavitation in that the vapor phase persists and continues downstream because the downstream pressure remains at or below... To avoid dangerous and costly problems in their process systems industrial valve users should understand the basics of the ways in which cavitation and flashing affect control valves. Cavitation. If the speed through the valve is high enough, the pressure in the liquid may drop to a level where the fluid may start bubble or flash. The pressure recovers sufficiently and the bubbles collapse upon themselves. Cavitation may be noisy but is usually of low intensity and low frequency. This situation is extremely destructive and may wear out the trim and body parts of the valve in short time. 1  The Cavitation Number An introduction to and a definition of the Cavitation Number Flashing could be anticipated by hardened material trim therefore to overcome flashing, the selected control valve shall have hardened material trim. However, hardened material trim is not sufficient to handle cavitation.  Non-inertial cavitation is the process in which small bubbles in a liquid are forced to oscillate in the presence of an acoustic field, when the intensity of the acoustic field is insufficient to cause total bubble collapse. In man-made objects, it can occur in control valves, pumps, propellers and impellers. Non-inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. This chapter discusses the fundamentals of cavitation and the related phenomenon of flashing as they apply to control valves. Methods for evaluating cavitation in valves are discussed, including how to test valves and establish cavitation coefficients. To avoid dangerous and costly problems in their process systems industrial valve users should understand the basics of the ways in which cavitation and flashing affect Although with flashing noise and vibration are usually much less than with severe cavitation, flashing can generate excessive vibration associated with high-velocity flow. Reducing velocity and using erosion-resistant materials are effective design strategies that minimize the damage from flashing. To avoid dangerous and costly problems in their process systems industrial valve users should understand the basics of the ways in which cavitation and flashing affect control valves. Extent of the pressure losses in pipes and elbows between the valve and, for example, a vessel at constant pressure, influences valve outlet pressure and, hence, flow status. Either flashing or cavitation can exist when the operating point is near the sharp transition from cavitation to flashing at xF = 1. In case of flashing or two-phase flow, it is imperative that a sufficiently large nominal valve size be selected to limit average flow velocity on the downstream side of the valve, thus minimising the problems described in the section on cavitation and flashing. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Inertial cavitation occurs in nature in the strikes of mantis shrimps and pistol shrimps, as well as in the vascular tissues of plants. In man-made objects, it can occur in control valves, pumps, propellers and impellers. Non-inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion. This results in surface fatigue of the metal causing a type of wear also called cavitation. In man-made objects, it can occur in control valves, pumps, propellers and impellers. Non-inertial cavitation is the process in which a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Flashing is a vaporizing process similar to cavitation. However, flashing differs from cavitation in that the vapor phase persists and continues downstream because the downstream pressure remains at or below the vapor pressure of the liquid. To avoid dangerous and costly problems in their process systems industrial valve users should understand the basics of the ways in which cavitation and flashing affect control valves.
http://www.globalspec.com/reference/13612/179909/Chapter-7-Cavitation-and-Flashing http://www.engineeringtoolbox.com/control-valves-cavitation-d_490.html http://instrumentationportal.com/2011/job-seeker/interview-question/instrument-engineer/flashing-and-cavitation-related-question/ https://en.wikipedia.org/wiki/Cavitation http://www.globalspec.com/reference/13612/179909/Chapter-7-Cavitation-and-Flashing http://www.globalspec.com/reference/13612/179909/Chapter-7-Cavitation-and-Flashing http://www.instrumentation.co.za/article.aspx?pklarticleid=2819 https://en.wikipedia.org/wiki/Cavitation https://en.wikipedia.org/wiki/Cavitation http://www.globalspec.com/reference/13612/179909/Chapter-7-Cavitation-and-Flashing
what is cavitation and flashing