Object moving thru a fluid medium

Gonzo is quite correct in his comments about cavitation in water having nothing to do with dissolved oxygen.

 

Cambridge Dictionary :
boil verb (HEAT LIQUID)
to reach, or cause something to reach, the temperature at which a liquid starts to turn into a gas.

Accordingly, if the water "boils" during the phenomenon of cavitation will be, without any doubt, because the temperature of the water increases enormously. I think this is not so.
Can there be some concept that escapes you, Gonzo? Do you have anything to say about the vapor pressure of dissolved gas in water?

 

At sea level, one atmosphere of pressure, water boils at 212F/100C.
As the pressure is reduced water boils at a lower temperature. Boiling being defined as the point at which the vapor pressure of the liquid and the ambient external pressure are the same. So boiling is a phase change from liquid to vapor.

While many would think of the water bubble that is created when boiling water can only occur at around the 212f/100C temperature, this is not the case

As you lower the pressure significantly and the ambient temperature is such that the liquid will "flash" create a bubble, then you will have in essence "boiled" the liquid.

Cavitation at a propeller, areas of high velocity/ low pressure, these bubbles
can occur. As in the case of a propeller. Without an external heat source as you suggest

Low pressure, accommodating temperature, a bubble forms.

An aside but only because this is a boat design forum. The bubble is produced in a localized area due to the extreme low pressure interaction from the prop blade and a specific location (or locations) of the blade. As the bubble moves away from this area or the blade moves away from the bubble, the bubble will implode as the low pressure conditions disappear. If this implosion occurs on the blade, or hub, where the low pressure requirement is not met, the resulting implosion can take a piece of the metal with it. Ie it knocks off a piece of the metal. As the surface begins to get rough, the rate of material being knocked off the surface increases.
This is a well known process called cavitation corrosion

It has been suggested that the force of the implosions are in the hundreds of thousands pounds per square inch of force on a molecular level.

 

@Barry, surely, as has happened other times, these are different interpretations of the same phenomenon or of some word. Cavitation is produced by the air bubbles dissolved in the water that are discharged from the water because it lowers the vacuum pressure much, never because the temperature of the water increases and it boils.
Distilled water boils at 100 ° C at sea level and boils at a lower temperature as pressure decreases, increasing the height. But the pressure at the depth of the propeller, when it is at a standstill, is higher and therefore should boil at over 100 ° C.
I hope I have expressed it so that you may have understood me. Surely because you seem to know well the physical phenomena we are talking about. There are others that confuse bubbles with boiling and that means that nothing is understood of the physics involved in each phenomenon..

 

I wish you would do some reading on cavitation so that you can remove the thought that the bubbles caused by cavitation for a propeller are dissolved air, nitrogen and oxygen, but rather h20 bubbles. This is a proven fact. A cavitation bubble is a water vapor bubble

 

It is possible that you are right, I will think so and, of course, at the time, I will read more about cavitation. I have no objection to saying, if necessary, that I have misinterpreted the phenomenon of cavitation. But let me keep asking the same question, is cavitation due to the boiling water? (Here I ask to go to the definition of the dictionary gives on what is to boil)
Found in Wikipedia :
"The physical process of cavitation inception is similar to boiling. The major difference between the two is the thermodynamic paths that precede the formation of the vapor. Boiling occurs when the local temperature of the liquid reaches the saturation temperature, and further heat is supplied to allow the liquid to sufficiently phase change into a gas. Cavitation inception occurs when the local pressure falls sufficiently far below the saturated vapor pressure, a value given by the tensile strength of the liquid at a certain temperature."

 

Its like I always say, Mr. Efficiency.........."Mystery? Fish and see."

 

If I may intrude upon your discussion regarding cavitation. In fact, all of you have it wrong. Cavitation is caused by Sea Fairies. Sea Fairies live in all water. However, still water is boring. (Unless you're a Cowboys fan.) And Sea Fairies like to move just as fast as they can and preferably in circles and being that Sea Fairies are a generally lazy folk, they prefer to attach themselves to man-made contraptions in order to move at the speed they desire. The faster the propeller moves, the greater the increase in local pressure. The increased local pressure causes the body cavity of the fairy to contract and for air to be expelled out of the waste vent of the fairy. Yes, it is all, in fact, fairy farts.
One of the things I have learned in this discussion is that engineers don't make wild guesses, they make qualified statements. Its been a real pleasure watching you guys argue.

 

@Patrick Hickey, the pleasure is mine to read, in the end, a clear and reasoned explanation of the cavitation. This is one of the good things that this forum has, its members. There are always some that of a stupid subject can give a coherent scientific explanation. Thank you.
By the way, fairies boil or do not boil?

 

I prefer them in a reduction with a little bit of basil and ginger. While its generally not advisable to put a net around your propeller to catch the fairies, sometimes that is the only way. Those darn crafty fairies always seem to get my nets tangled up.

 

The boiling point is a phase change and is directly related to pressure. This is a basic physics concept. TANSL is confusing boiling with effervescence, which is dissolved gas leaving the liquid.

 

@gonzo, since I want to be kind and loving to you, I will advise you not to go that way. No one has spoken of effervescence, we are talking about cavitation and boiling which, although they may be very similar, are not the same thing.
The OP has already explained that cavitation is due to water fairies. What did not you understand?
Boiling point is not a fase change. Boiling point makes a liquid change its fase.
The boiling point essentially depends on the temperature and, to a lesser extent, on the pressure.

 

I would argue that there is more than one kind of fase change going on here. There is the fase of alternate future to consider. Fairies are actually quantum-ly entangled beings and therefore are neither here nor there. What the fairy consumes to create its gaseous emissions does not actually come from this universe but from an entirely different one and we as the occupants of this universe are the recipients of the seed of the fairy. Do we swallow that fairy's seed? It is not for me to question your proclivities in that regard.

 

That is incorrect. Cavitation is a concept that many people don't comprehend, but is basic to marine design. For example, it limits the speed of a propeller and the shape of appendages vs speed. If you refer to dissolved gas, oxygen in your case, then the phenomenon is called effervescence. If you mean the phase change from liquid to gas (boiling) then pressure is one of the parameters it depends on. Pressure does not have a lesser effect than temperature. Below the triple point, solids transform directly to gas; called sublimation.
Typical phase diagram http://ltl.tkk.fi/research/theory/typicalpt.html

 

It is really rude and unproductive to hijack threads with nonsense. There are many forums online for this kind of stupid commentary. Please stay within the limits of what the OP started the thread for.