What is the difference between flashing and cavitation?

The former is liquid turning into gas； The latter is liquid turning into gas, and then back into liquid.

Flash evaporation is a phenomenon in which, as a liquid flows through a valve body and the static pressure drops to the saturation vapor pressure, part of the liquid vaporizes, resulting in a mixture of gas and liquid. Cavitation is a phenomenon in which, again as the liquid flows through a valve body and the static pressure drops to the saturation vapor pressure, part of the liquid vaporizes to form bubbles, which then revert back to liquid. Erosion caused by cavitation is the damage inflicted on materials as a result of this process.

When a liquid flows through a control valve, the flow velocity at the throttle opening increases sharply. According to the law of conservation of energy, an increase in velocity necessarily leads to a decrease in pressure. If the pressure drops below the saturated vapor pressure Pv of the liquid at that temperature, the liquid will vaporize, releasing gas and resulting in a two-phase flow of liquid and gas; this phenomenon is known as flashing. After throttling, the velocity decreases while the pressure rises; once the pressure exceeds the Pv value, further vaporization ceases, and the bubbles in the liquid revert to liquid form. In fluid dynamics, it can be shown that the pressure inside the bubble approaches infinity at this point; this forces the bubble to burst, generating a powerful pressure shock wave. This phenomenon is known as cavitation. Cavitation is the erosion of valve cores, valve seats, and similar components caused by cavation effects.

Here are a few of my thoughts for your reference: Common points: both involve a pressure reduction process; Differences: Flash evaporation: from liquid to vapor; Cavitation: a mixture of vapor and liquid

Vaporization occurs when saturated water under high pressure is introduced into a container at lower pressure; the sudden drop in pressure causes this saturated water to turn into both saturated steam and saturated water at the pressure of the container. Flash evaporation is mainly used in the recovery of boiler drainage in thermal power plants and in geothermal power generation. Characteristics of evaporation: ① Evaporation can occur at any temperature; ② Evaporation takes place only on the surface of the liquid. Regardless of the temperature, a liquid will always evaporate. At a certain temperature, when the pressure is reduced to the vaporization pressure at that temperature, bubbles form in the liquid. This phenomenon of bubble formation is called cavitation. The bubbles formed during cavitation shrink in size as they flow to higher pressure areas, eventually bursting. For steam valves and condensate valves, the primary considerations should be cavitation and flashing phenomena.

Some sources state that when the pressure difference is less than 2.5 MPa, it is not necessary to take measures to prevent cavitation. Is this claim valid?

Upstairs, please indicate the source of the information.

This issue deserves careful discussion; small details can determine success or failure. I’ll also learn about it*