"DSK" wrote in message
...

But what makes the water boil? Increased temps due to friction? Tiny
devil-spirits waving their pitchforks?


Lower pressure.



.... Higher RPM gives higher tangentail blade speeds and greater pressure
differential between the faces of the prop.

Somewhat right, tip speed above a certain linear velocity will cause
cavitation no matter the dP,

Then it would be the void (low pressure) behind the propeller. There is
still cavitation due to drag, which would occur with a spinning disc.


You could also mention the dread voodoo curse "viscous shear" which means
that somebody is trying to force those lazy water molecules to move faster
than they are willing



Fluid flow does a lot of things counter-intuitive to people familiar with
normal physics. One of my favorite engineering profs used to say that
fluid molecules are like basketballs smeared with syrup, which helps
intuit the behavior.

DSK

"Gilligan" wrote in message . ..
|
| "DSK" wrote in message
| ...
|
| But what makes the water boil? Increased temps due to friction? Tiny
| devil-spirits waving their pitchforks?
|
|
| Lower pressure.

Hee hee! Lower pressure never makes any liquid boil. It makes it vaporize.
Boil is a subjective term. It only refers to that temperature at atmospheric
pressure at which a liquid vaporizes. Some engineer you are Mr. Gilligan!

Paladin

--
Posted via a free Usenet account from http://www.teranews.com

http://en.wikipedia.org/wiki/Boiling



Boiling is the rapid vaporization of a liquid, which typically occurs when a
liquid is heated to a temperature such that its vapor pressure is above that
of the surroundings, such as air pressure. Thus, a liquid may also boil when
the pressure of the surrounding atmosphere is sufficiently reduced, such as
the use of a vacuum pump or at high altitudes. Boiling occurs in three
characteristic stages, which are nucleate, transition and film boiling.
These stages generally take place from low to high surface temperatures,
respectively.

Nucleate boiling is characterized by the incipience and growth of bubbles on
a heated surface, which rise from discrete points on a surface, whose
temperature is only slightly above the liquid’s saturation temperature. In
general, the number of nucleation sites are increased by an increasing
surface temperature. An irregular surface of the boiling vessel (i.e.
increased surface roughness) can create additional nucleation sites, while
an exceptionally smooth surface (such as glass) lends itself to
superheating.

When the surface temperature reaches a maximum value, the critical
superheat, vapor begins to form faster than liquid can reach the surface.
Thus, the heated surface suddenly becomes covered with a vapor layer.
Because of the vapor layer’s lower thermal conductivity, this vapor layer
insulates the surface. This condition of a vapor film insulating the surface
from the liquid characterizes film boiling.

Transition boiling may be defined as the unstable boiling, which occurs at
surface temperatures between the maximum attainable in nucleate and the
minimum attainable in film boiling.

"Gilligan" wrote in message . ..
| http://en.wikipedia.org/wiki/Boiling
|
|
|
| Boiling is the rapid vaporization of a liquid, which typically occurs when a
| liquid is heated to a temperature such that its vapor pressure is above that
| of the surroundings, such as air pressure. Thus, a liquid may also boil when
| the pressure of the surrounding atmosphere is sufficiently reduced, such as
| the use of a vacuum pump or at high altitudes. Boiling occurs in three
| characteristic stages, which are nucleate, transition and film boiling.
| These stages generally take place from low to high surface temperatures,
| respectively.
|
| Nucleate boiling is characterized by the incipience and growth of bubbles on
| a heated surface, which rise from discrete points on a surface, whose
| temperature is only slightly above the liquid’s saturation temperature. In
| general, the number of nucleation sites are increased by an increasing
| surface temperature. An irregular surface of the boiling vessel (i.e.
| increased surface roughness) can create additional nucleation sites, while
| an exceptionally smooth surface (such as glass) lends itself to
| superheating.
|
| When the surface temperature reaches a maximum value, the critical
| superheat, vapor begins to form faster than liquid can reach the surface.
| Thus, the heated surface suddenly becomes covered with a vapor layer.
| Because of the vapor layer’s lower thermal conductivity, this vapor layer
| insulates the surface. This condition of a vapor film insulating the surface
| from the liquid characterizes film boiling.
|
| Transition boiling may be defined as the unstable boiling, which occurs at
| surface temperatures between the maximum attainable in nucleate and the
| minimum attainable in film boiling.
|
|

Good info but mostly obfuscation to keeping from saying. "Oops, I
was wrong.

The facts of the matter that the verb boil means to heat to a temperature
at which a liquid vaporizes. I'm saying there is not enough heating going
on in a cavitating prop to vaporize water. Thus to say it boils is to speak
in error.

The fact of the matter is you used the word boil when you should have
corrected DSK and used vaporized instead. It's a pressure thing and
not a temperature thing,

Paladin


--
Posted via a free Usenet account from http://www.teranews.com

"Gilligan" wrote in message . ..
| http://en.wikipedia.org/wiki/Boiling
|
|
|
| Boiling is the rapid vaporization of a liquid, which typically occurs when a
| liquid is heated to a temperature such that its vapor pressure is above that
| of the surroundings, such as air pressure. Thus, a liquid may also boil when
| the pressure of the surrounding atmosphere is sufficiently reduced, such as
| the use of a vacuum pump or at high altitudes. Boiling occurs in three
| characteristic stages, which are nucleate, transition and film boiling.
| These stages generally take place from low to high surface temperatures,
| respectively.
|
| Nucleate boiling is characterized by the incipience and growth of bubbles on
| a heated surface, which rise from discrete points on a surface, whose
| temperature is only slightly above the liquid’s saturation temperature. In
| general, the number of nucleation sites are increased by an increasing
| surface temperature. An irregular surface of the boiling vessel (i.e.
| increased surface roughness) can create additional nucleation sites, while
| an exceptionally smooth surface (such as glass) lends itself to
| superheating.
|
| When the surface temperature reaches a maximum value, the critical
| superheat, vapor begins to form faster than liquid can reach the surface.
| Thus, the heated surface suddenly becomes covered with a vapor layer.
| Because of the vapor layer’s lower thermal conductivity, this vapor layer
| insulates the surface. This condition of a vapor film insulating the surface
| from the liquid characterizes film boiling.
|
| Transition boiling may be defined as the unstable boiling, which occurs at
| surface temperatures between the maximum attainable in nucleate and the
| minimum attainable in film boiling.
|
|

Good info but mostly obfuscation to keeping from saying. "Oops, I
was wrong.

The facts of the matter that the verb boil means to heat to a temperature
at which a liquid vaporizes. I'm saying there is not enough heating going
on in a cavitating prop to vaporize water. Thus to say it boils is to speak
in error.

The fact of the matter is you used the word boil when you should have
corrected DSK and used vaporized instead. It's a pressure thing and
not a temperature thing,

Paladin


--
Posted via a free Usenet account from http://www.teranews.com

http://encarta.msn.com/media_4615415...for_Water.html

"Gilligan" wrote in message . ..
|
| http://encarta.msn.com/media_4615415...for_Water.html
|
|
|

The diagram proves my point. Since there is no significant temperature
change involved with a propeller but there is a significant pressure change
then the water does not vaporize because it boils. Rather it vaporizes because
of the pressure change.

I'm just so brilliant. You can't even manage to misdirect me.

Paladin

--
Posted via a free Usenet account from http://www.teranews.com

"Paladin" noneofyourbusiness.www wrote in message
...

"Gilligan" wrote in message
. ..
|
| http://encarta.msn.com/media_4615415...for_Water.html
|
|
|

The diagram proves my point. Since there is no significant temperature
change involved with a propeller but there is a significant pressure
change
then the water does not vaporize because it boils. Rather it vaporizes
because
of the pressure change.

I'm just so brilliant. You can't even manage to misdirect me.


I can't misdirect you, but I can set you straight.

When water boils, as in your kettle, those "bubbles" are water vapor
suspended in the liquid water.

Cavitation is caused by the propeller slipping on water vapor suspended in
the liquid water.

Would it then be reasonable to say that cavitation is caused by water
boiling?

OR

Cavitation can only happen in your tea kettle?

OK Group,

What happened to the original statement; "Useless propeller" Let's get
back to that! Why is a Two Blade Folding Prop a Useless propeller and a
Four Blade fixed going to work better in rough, choppy sea?




http://community.webtv.net/tassail/ThomPage

"Gilligan" wrote in message
. ..
http://en.wikipedia.org/wiki/Boiling



Boiling is the rapid vaporization of a liquid, which typically occurs when
a liquid is heated to a temperature such that its vapor pressure is above
that of the surroundings, such as air pressure. Thus, a liquid may also
boil when the pressure of the surrounding atmosphere is sufficiently
reduced, such as the use of a vacuum pump or at high altitudes. Boiling
occurs in three characteristic stages, which are nucleate, transition and
film boiling. These stages generally take place from low to high surface
temperatures, respectively.

Nucleate boiling is characterized by the incipience and growth of bubbles
on a heated surface, which rise from discrete points on a surface, whose
temperature is only slightly above the liquid's saturation temperature. In
general, the number of nucleation sites are increased by an increasing
surface temperature. An irregular surface of the boiling vessel (i.e.
increased surface roughness) can create additional nucleation sites, while
an exceptionally smooth surface (such as glass) lends itself to
superheating.

When the surface temperature reaches a maximum value, the critical
superheat, vapor begins to form faster than liquid can reach the surface.
Thus, the heated surface suddenly becomes covered with a vapor layer.
Because of the vapor layer's lower thermal conductivity, this vapor layer
insulates the surface. This condition of a vapor film insulating the
surface from the liquid characterizes film boiling.

Transition boiling may be defined as the unstable boiling, which occurs at
surface temperatures between the maximum attainable in nucleate and the
minimum attainable in film boiling.

The propeller is the thing that makes the boat go, innit?

Max