Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
lehpron
Topic Author
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

Does Hot Water Rise Like Air?

Thu Nov 29, 2007 1:12 am

If I had a column of water with a heat source at the base, will the warmer water rise and allow the lesser warmer water recirculate without a pump, or will the water near the heat source simply get hot?
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
ArmitageShanks
Posts: 3780
Joined: Tue Dec 30, 2003 5:30 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 1:21 am

It will work just like air, just maybe a bit slower.

http://en.wikipedia.org/wiki/Convection
 
User avatar
Zkpilot
Posts: 4591
Joined: Wed Mar 08, 2006 8:21 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 1:28 am

hot water rises.. Happens in the ocean all the time.
64 types. 45 countries. 24 airlines.
 
Queso
Posts: 3109
Joined: Sat Jul 08, 2006 12:28 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 1:29 am

Easy enough to prove. Get an aquarium filled with normal tap water, fill a coke bottle with hot water that has food coloring in it, submerge it in the aquarium and open the lid.

Not exactly Mythbusters material, but you'll get your answer.
 
ronglimeng
Posts: 562
Joined: Fri Oct 20, 2006 7:12 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 1:52 am

So hot water rises.... then cold water falls.

Would someone like to explain why lakes and rivers don't freeze from their bottoms up to the surface? I think it happens the other way around.
 
Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 2:03 am



Quoting Ronglimeng (Reply 4):
Would someone like to explain why lakes and rivers don't freeze from their bottoms up to the surface? I think it happens the other way around

It's not so much a top to bottom, it's more like outside-inside. That's why sometimes you'll get ice cubes in the freezer that haven't been in there long enough with bubbles of water in between the ice.
 
NeilYYZ
Posts: 2443
Joined: Mon Jan 23, 2006 12:55 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 2:09 am



Quoting Ronglimeng (Reply 4):
Would someone like to explain why lakes and rivers don't freeze from their bottoms up to the surface? I think it happens the other way around.

I would think that is because it needs to be below 0 centigrade for water to freeze, and what makes the water freeze is the cold outside air, which hits the water at the surface.

For the water to freeze from the bottom up wouldn't the temperature of the ground at the bottom of the body of water have to be colder than the outside air?
It may be too early to drink scotch... But it is NEVER too early to think about it...
 
ArmitageShanks
Posts: 3780
Joined: Tue Dec 30, 2003 5:30 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 2:20 am



Quoting NeilYYZ (Reply 6):
I would think that is because it needs to be below 0 centigrade for water to freeze, and what makes the water freeze is the cold outside air, which hits the water at the surface

Also, doesnt water pressure have to do with it as wee? Even though its below freezing at the bottom of the ocean its still liquid.
 
Queso
Posts: 3109
Joined: Sat Jul 08, 2006 12:28 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 2:33 am



Quoting ArmitageShanks (Reply 7):
Also, doesnt water pressure have to do with it as wee?

Wee is at body temperature when it is released but it cannot be used to judge whether or not hot liquid rises because it has a different specific gravity than water. You could measure some cold wee and then put warm wee in it to see if it rises, but water would probably be easier to work with.
 
AverageUser
Posts: 1824
Joined: Tue Oct 23, 2007 6:21 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 2:58 am



Quoting Ronglimeng (Reply 4):
Would someone like to explain why lakes and rivers don't freeze from their bottoms up to the surface? I think it happens the other way around.

When water cools down to 4 C it has reached its maximun density and sinks to the bottom, thereafter the natural convection is limited to the layers closer to the surface only, the top of which which may then freeze as ice when the temperature drops further. A cover of ice will then act as thermal insulation to the water, but will also self-limit its own growth because of this capability.
 
PlymSpotter
Posts: 10826
Joined: Thu Jun 17, 2004 7:32 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:00 am



Quoting Lehpron (Thread starter):
If I had a column of water with a heat source at the base

I'm about 99.9% sure that you already have one of these. It's called a kettle.  Smile
...love is just a camouflage for what resembles rage again...
 
Toast
Posts: 1249
Joined: Thu Aug 30, 2007 4:04 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:09 am



Quoting Queso (Reply 8):
Quoting ArmitageShanks (Reply 7):
Also, doesnt water pressure have to do with it as wee?

Wee is at body temperature when it is released but it cannot be used to judge whether or not hot liquid rises because it has a different specific gravity than water. You could measure some cold wee and then put warm wee in it to see if it rises, but water would probably be easier to work with.

 rotfl  rotfl  rotfl  rotfl  rotfl 

Good one Mr. Cheese!  bigthumbsup 
Shit Piss Fuck Cunt Cocksucker Motherfucker Tits
 
vikkyvik
Posts: 12621
Joined: Thu Jul 31, 2003 1:58 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:19 am



Quoting ArmitageShanks (Reply 7):
Also, doesnt water pressure have to do with it as wee? Even though its below freezing at the bottom of the ocean its still liquid.

Believe so, yes. If I remember correctly, you can find super-cooled water at high water pressures (water that is below 0 C, but is still liquid).
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
Klaus
Posts: 21642
Joined: Wed Jul 11, 2001 7:41 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:21 am



Quoting Ronglimeng (Reply 4):
Would someone like to explain why lakes and rivers don't freeze from their bottoms up to the surface? I think it happens the other way around.

Frozen water is less dense than liquid water ("ice swims"). If it was th other way around, the oceans would be a solid block of ice down to the ground with possibly a thin layer of liquid water on top.
 
Toast
Posts: 1249
Joined: Thu Aug 30, 2007 4:04 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:24 am



Quoting Klaus (Reply 13):



Quoting PlymSpotter (Reply 10):



Quoting Toast (Reply 11):

Guys, we're in Europe and it's 4:20 in the morning. It's nice to know I'm not the only insomniac here, but I think going to bed is preferable to discussing physics. Good night!  zzz 
Shit Piss Fuck Cunt Cocksucker Motherfucker Tits
 
PlymSpotter
Posts: 10826
Joined: Thu Jun 17, 2004 7:32 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:29 am



Quoting Toast (Reply 14):
Guys, we're in Europe and it's 4:20 in the morning. It's nice to know I'm not the only insomniac here, but I think going to bed is preferable to discussing physics. Good night!

3:30 actually, I'm in the UK  Wink But yes, with lectures commencing in six and a half hours, its time to hit the hay as well!
...love is just a camouflage for what resembles rage again...
 
Klaus
Posts: 21642
Joined: Wed Jul 11, 2001 7:41 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:29 am



Quoting Toast (Reply 14):
Guys, we're in Europe and it's 4:20 in the morning. It's nice to know I'm not the only insomniac here, but I think going to bed is preferable to discussing physics. Good night!

Okay, now we know what a "cyber-nanny" really is.

Stay crispy!
 
PPVRA
Posts: 8603
Joined: Fri Nov 12, 2004 7:48 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:37 am

Yup, it's how these work:
"If goods do not cross borders, soldiers will" - Frederic Bastiat
 
CastleIsland
Posts: 3212
Joined: Fri Mar 10, 2006 1:40 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:39 am



Quoting Klaus (Reply 13):
Quoting Ronglimeng (Reply 4):
Would someone like to explain why lakes and rivers don't freeze from their bottoms up to the surface? I think it happens the other way around.

Frozen water is less dense than liquid water ("ice swims"). If it was th other way around, the oceans would be a solid block of ice down to the ground with possibly a thin layer of liquid water on top.

Actually, it's entirely possible that if it were the other way around, the water body might never freeze. Here's why: Since the surface of the water body is closest to the cold air, ice would sink and then melt on its way down, since the heat capacity of water is so high, much of a water body remains well above freezing even when it's well below freezing air temperature. Thus, the only way to get the water body to freeze would be an extremely rapid cold snap that would inundate the water body floor with ice that could cool the lower strata of the water body to near freezing before the ice melts.

This is particularly true of oceans, which have a significantly depressed freezing point due to high salinity.
"People don't do what they believe in, they just do what's most convenient, then they repent." - Dylan
 
L-188
Posts: 29881
Joined: Wed Jul 07, 1999 11:27 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 3:54 am



Quoting Lehpron (Thread starter):
If I had a column of water with a heat source at the base, will the warmer water rise and allow the lesser warmer water recirculate without a pump, or will the water near the heat source simply get hot?

Yup, many of the laws that govern air movements are equally applicable to liquids.

Quoting NeilYYZ (Reply 6):
I would think that is because it needs to be below 0 centigrade for water to freeze, and what makes the water freeze is the cold outside air, which hits the water at the surface.

For the water to freeze from the bottom up wouldn't the temperature of the ground at the bottom of the body of water have to be colder than the outside air?

The ice forms at the surface because it is less dense then the water under it. It is less dense because unlike everything else in the known universe it expands as it freezes. This traps oxygen and also make ice a halfway decent insulator.

Actually you can credit this little property for permiting life to exist on this planet, because the water stays fluid under the ice.

Quoting ArmitageShanks (Reply 7):
Also, doesnt water pressure have to do with it as wee? Even though its below freezing at the bottom of the ocean its still liquid.

Yup, the same Volume/Pressure/Temperture law that covers everything from airfoils to steam engines.
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.
 
Klaus
Posts: 21642
Joined: Wed Jul 11, 2001 7:41 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 4:16 am



Quoting CastleIsland (Reply 18):
Actually, it's entirely possible that if it were the other way around, the water body might never freeze. Here's why: Since the surface of the water body is closest to the cold air, ice would sink and then melt on its way down, since the heat capacity of water is so high, much of a water body remains well above freezing even when it's well below freezing air temperature.

But that is exactly just because of the special property water possesses - if ice was heavier than liquid water, the convection would continue to transport heat to the surface and increasingly cold water to the bottom, until the entire water column was frozen (if at least partially the air temperature was cold enough for ice to form).
 
User avatar
nighthawk
Posts: 4890
Joined: Sun Sep 16, 2001 2:33 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 12:00 pm

Ahhh all those chemistry lectures are flooding back. The reason ice floats is due to Hydrogen Bonding. If you take any othe rliquid, (say alcohol) and freeze it, the molecules lose energy, and start to contract together, producing a solid which is much denser than the liquid form, as such the solid of a substance will always sink when placed in its liquid form.

Water is different. Hydrogen has a special property: hydrogen bonding. Two molecules of hydrogen will attract to each other and form a very weak bond. When water is frozen, the molecules lose energy and stop moving, and start to contract. Once energy is lost beyond a certain point, the hydrogen bonding comes into play, and the hydrogen molecules will attract towards each other, and at the same time repelling the oxygen molecules. this causes the density to start to decrease, as the molecules once more spread out. The ice is therefore less dense than the water, and the ice floats.
 
ALexeu
Posts: 1447
Joined: Tue Oct 16, 2007 9:01 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 12:05 pm

Could Bernoulli's princip work in water?

As the air gets faster, the pressure is lower (that's the basic Bernoulli's equation). p+1/2rho*vo^2=const.
 
ronglimeng
Posts: 562
Joined: Fri Oct 20, 2006 7:12 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 4:37 pm



Quoting AverageUser (Reply 9):
When water cools down to 4 C it has reached its maximun density and sinks to the bottom, thereafter the natural convection is limited to the layers closer to the surface only, the top of which which may then freeze as ice when the temperature drops further. A cover of ice will then act as thermal insulation to the water, but will also self-limit its own growth because of this capability.

AverageUser:

I think you get the prize.

Thanks to all.

Ronglimeng
 
D L X
Posts: 12722
Joined: Thu May 27, 1999 3:30 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 4:51 pm



Quoting Queso (Reply 8):
Wee is at body temperature when it is released but it cannot be used to judge whether or not hot liquid rises because it has a different specific gravity than water. You could measure some cold wee and then put warm wee in it to see if it rises, but water would probably be easier to work with.

Gross.

(And I think he meant "well", not "wee")

Quoting AlexEU (Reply 22):
Could Bernoulli's princip work in water?

As the air gets faster, the pressure is lower (that's the basic Bernoulli's equation). p+1/2rho*vo^2=const.

Absolutely! That's how a hydrofoil works (an airfoil for water). You can also experience this with a water hose. Place your index finger and thumb opposed to each other, like you're trying to grasp the water coming out of the hose. If you turn the water up higher, it will feel like it's pulling your finger and thumb together.
 
David L
Posts: 8551
Joined: Tue May 18, 1999 2:26 am

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 6:08 pm



Quoting FLY2HMO (Reply 5):

It might have something to do with it but it's not the main reason.  Smile

Quoting NeilYYZ (Reply 6):

Ditto.  Smile

Quoting L-188 (Reply 19):
The ice forms at the surface because it is less dense then the water under it. It is less dense because unlike everything else in the known universe it expands as it freezes

Bingo! Though it's below 4oC that water (and ice) is less dense.

Quoting Nighthawk (Reply 21):
this causes the density to start to decrease, as the molecules once more spread out. The ice is therefore less dense than the water, and the ice floats.

 thumbsup 

Funny stuff, water.  Smile
 
bagpiper
Posts: 1050
Joined: Mon Nov 13, 2006 11:24 pm

RE: Does Hot Water Rise Like Air?

Thu Nov 29, 2007 6:18 pm



Quoting Queso (Reply 8):
Wee is at body temperature when it is released but it cannot be used to judge whether or not hot liquid rises because it has a different specific gravity than water. You could measure some cold wee and then put warm wee in it to see if it rises, but water would probably be easier to work with.



Quoting D L X (Reply 24):
Gross.

Oh come on dude, where's your sense of humor? Of course he meant "well".


Queso - I laughed long and hard at that  Silly
 
lehpron
Topic Author
Posts: 6846
Joined: Tue Jul 10, 2001 3:42 am

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 12:16 am

Thanks everyone for the replies, I suppose I knew it but then I been having these weird experiences with heating things up in our microwave (stuff gets hot in one corner while the rest of cold), it must have threw me off.

But then when I boil water for pasta, initially before it starts to boil, the bottom will be hotter than the top. Having said that, I always use the hottest water from the tap, reduces boil time.

Quoting PlymSpotter (Reply 10):

When then I guess you 99.9% wrong, I don't have a kettle.  Smile
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
redngold
Posts: 6686
Joined: Wed Mar 22, 2000 12:26 pm

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 12:31 am



Quoting PPVRA (Reply 17):
Yup, it's how these work:

Actually, no. It's the hot wax which is less dense than the water that rises, and then cools and sinks.
Up, up and away!
 
Nancy
Posts: 461
Joined: Sat May 08, 2004 1:54 pm

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 12:33 am

Water has the greatest density at about 4 c. It gets slightly less so as it cools to 0. Don't ask me why.
 
AverageUser
Posts: 1824
Joined: Tue Oct 23, 2007 6:21 pm

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 12:43 am



Quoting Ronglimeng (Reply 23):
AverageUser:

I think you get the prize.

Thank you!  Smile I'll definitely have this one framed on the wall as it's my first one ever!
 
baroque
Posts: 12302
Joined: Thu Apr 27, 2006 2:15 pm

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 6:36 am



Quoting ArmitageShanks (Reply 7):
Also, doesnt water pressure have to do with it as well? Even though its below freezing at the bottom of the ocean its still liquid.

The influence of pressure is complex because water expands as it freezes. Whatever, deep ocean temperatures are very close to the theoretical 4 degrees C. Basically, the whole water mass below about 1 km from the sea surface is within about 0.1 degrees of 4 C. Or that is what the sea bottom temperatures are reported as for deep water oil wells.

Ed to ruin Queso's day.  Big grin  Big grin
 
britjap
Posts: 264
Joined: Tue Aug 01, 2006 12:47 pm

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 7:45 am



Quoting Lehpron (Reply 27):
Quoting PlymSpotter (Reply 10):


When then I guess you 99.9% wrong, I don't have a kettle.

Surely then that would make him 100% wrong!  Smile
 
Klaus
Posts: 21642
Joined: Wed Jul 11, 2001 7:41 am

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 12:41 pm



Quoting Lehpron (Reply 27):
Thanks everyone for the replies, I suppose I knew it but then I been having these weird experiences with heating things up in our microwave (stuff gets hot in one corner while the rest of cold), it must have threw me off.

In solid or very viscous foods (such as a thick sauce) the heat can't spread through convection, so the water content and the radiation exposure would determine how well the components are heated in a microwave oven.

When the liquid content is more fat and oil than water or when the food is relatively dry, the microwaves won't find as much resonance in the food and it can remain relatively cool. And the short exposure time prevents the heat to spread conventionally.

I'm just speaking from theory here - I just don't like to expose my food to intense radar emissions.

Quoting Lehpron (Reply 27):
But then when I boil water for pasta, initially before it starts to boil, the bottom will be hotter than the top.

Yes. And when you're looking closely you can see convection columns emerge. If you put some herbs into the clear water, for instance, the convective motion is easy to observe.

It is also one reason why soups or thinner sauces normally won't burn: Thermal convection has the heated liquid rise from the bottom and the cooler liquid sink down from the top, so a mostly even heat distribution is automatically achieved.

Thicker stews don't allow convection to equalize the energy distribution. That's why those need help by stirring to prevent the substance at the bottom from getting "cooked out" (water evaporating and the solid remaining in place) and burning up.

Quoting Lehpron (Reply 27):
But then when I boil water for pasta, initially before it starts to boil, the bottom will be hotter than the top. Having said that, I always use the hottest water from the tap, reduces boil time.

I generally wouldn't recommend that. House boilers are good enough for a shower, but I wouldn't normally eat anything made with water having gone through them.  yuck 

Exceptions apply, of course, but the warm water pipes (including those in the boiler) are often more corroded than the cold water ones because heat accelerates corrosion. I don't know about your house, but often you can taste the difference (a rusty or otherwise metallic taste, for instance, or a chemical plastic taste, depending on your tubes).
 
AverageUser
Posts: 1824
Joined: Tue Oct 23, 2007 6:21 pm

RE: Does Hot Water Rise Like Air?

Fri Nov 30, 2007 6:23 pm



Quoting Klaus (Reply 33):
Having said that, I always use the hottest water from the tap, reduces boil time.

I generally wouldn't recommend that. House boilers are good enough for a shower, but I wouldn't normally eat anything made with water having gone through them.

And a warmish shower may be a splendid place to catch Legionella pneumophila... link Luckily you don't usually get sick unless you have a weak immunity system.

Who is online

Users browsing this forum: 1337Delta764, Bing [Bot], Ken777, Narfish641, Snuffaluffagus and 36 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos