"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?

"Gilligan" wrote in message . ..
|
| "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.

You've done an inadequate job of it so far...

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

Agreed. But, suspended is a poor word choice. I prefer to call it
water vapor displacing the liquid water.

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

Quaintly envisioned. Highly inadequate. Cavitation is a descriptive term used
to describe the vaporization of the water near the low pressure side of the
propeller blades resulting in over-revving of the engine. The over-revving of
the engine is caused by the prop losing contact with the water.


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

Not in the case of a boat unless it was in a giant pot of boiling water
on the stove.

| OR
|
| Cavitation can only happen in your tea kettle?

Cavitation could very well be caused by operating a prop in boiling
water but the prop doesn't cause the water to boil. The fire under
the tea kettle is doing that job.

Now, who's straightening out whom?

Paladin


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

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

Thom Stewart wrote:

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?


Well, a two-blade folder isn't really useless, it has it's
own uses and unfortunately that means it will not do as good
a job driving the boat under less-optimal conditions. OTOH
it will allow the boat to sail much better.

The problem with most folding props is
1- they are expensive, leading most people to buy the size
smaller than they really need
2- the hubs often develop some play, allowing the blades to
twist unfavorably and lose power

These two things are why they don't work well in reverse and
don't work well in choppy water.

I have a little experience with the Luke three blade
feathering prop, which is expensive but a very practical
alternative.

A good friend of mine had a small keelboat with a big
2-blade folder... the boat was very slow under power. This
was the opposite case of above, the previous owner had gone
for "conspicuous consumption" and outfitted the boat very
expensively but not efficiently. Among other things, the
prop was pitched for much higher RPM. When we were motoring
out to a race one time, we discussed the issue and since
thenengine reached full RPM easily, there was no reason not
to adjust the pitch. After two successive adjustments the
boat went almost 2 knots faster under power. It also motored
quite well in rough water... certainly much better than the
same type boat with an outboard.

Fresh Breezes- Doug King