Surface tension of water

[NPloysa]

I manage the boilers and softeners at work (museum) as part of my job. One thing I do is test the water hardness of the softeners and do sulfite (oxygen scavenger) tests on the boiler water. The hot water boilers are closed loop, but the two steam (humidity requirements for art work) are not, therefore I test it.



Anyway, I use a glass beaker, a cylindrical glass flask, cylindical plastic flask for my tests. Anyway, the glass containers always have a bit of surface tension and the plastic one does not have any.



Just wondering why this is? One of those weird observations! Maybe its the fact that water molecules adhere to the glass differently and don't "smooth" out into a flat surface like they do on the plastic. Is glass more porous?



Nick

 

[rbattelle]

Are you talking about the meniscus that forms on the surface of the water? That parabolic arc that forms rather than a straight line?



What's the difference in diameter between the plastic flask and the glass one? Glass has very low porosity (maybe none?) but plastic has very high porosity.



-Ryan

 

[AfterBurner]

Nick,

The property that water has that forms the meniscus (or whatever it's called) is called capillarity. "Capillarity results from a competition between the intermolecular forces within the liquid (cohesive forces) and those between the liquid and the tube walls (adhesive forces)" the H in H2O bonds with the oxygen in the glass (glass-mostly SiO2), so the water climbs as far as it's intermolecular forces (the ones pulling the molecules back together) will let it (when the forces hit equalibrium).

Mercury, due to hits high cohesive forces and low adhesive forces (since it's metallic) actually causes a convex surface.

So, to answer your question, whatever it is that makes up plastic must not bond to the water molecules, or maybe just very slighty.

After extensive research, I have come to the conclusion that a . 5" diameter bullet, fired perpindicular to the surface, at a range of 1000 yards, contains the necessary force to overcome all known surface tensions. :-laf

hope that helps some.

Never thought this chemistry class would actually come in handy

Forrest

 

[NPloysa]

Forrest, thanks! Makes sense. Ryan, the glass and plastic flasks are the same size, about an inch in diameter, 4 inches tall. The other glass beaker is about 3 inches diameter at the base, tapering up to the neck to about an inch.

 

[rbattelle]

Forrest explains it well... better than I would have. I thought maybe if the diameters were significantly different you might not notice the meniscus in the plastic one.



I swear I've seen a meniscus in a plastic graduated cylinder, but maybe I'm imagining things. And why would the hydrogen atoms "bond" with the oxygen in the glass if the glass oxygen is happily satisfied by the silicon and the water hydrogen is happily satisfied by the oxygen to which it is bonded? And what's the nature of the bond... Vanderwaals forces?



-Ryan

 

[The patriot]

What water tests do you do on the boilers?

What type of boilers are they? (type of construction)

What type of softeners do you have?

What type of heating system is used in there?

Sorry for all the questions. I'm bored, havent worked since May.

Eric

 

[AfterBurner]

Forrest explains it well... better than I would have. I thought maybe if the diameters were significantly different you might not notice the meniscus in the plastic one.



I swear I've seen a meniscus in a plastic graduated cylinder, but maybe I'm imagining things. And why would the hydrogen atoms "bond" with the oxygen in the glass if the glass oxygen is happily satisfied by the silicon and the water hydrogen is happily satisfied by the oxygen to which it is bonded? And what's the nature of the bond... Vanderwaals forces?



-Ryan

Water is a polar molecule. "The O nucleous attracts the elections more strongly than the H nucleous, creating an uneven distribution of electrons. " Hence, the reason water has a bent geometry as opposed to a linear shape, as with most 3 atom molecules. The electrons that cruise around each of the O-H bonds spend most of their time around the O (since it has a higher electron affinity than H). So this leaves the O side with a slight negative charge and the H sides with a slightly positive charge (since e's are negative). It's not as powerfull as an ionic charge, since H2O is a covalent compound. it's more like the electrons have just shifted, causing the charges.



Yes, van der Waals forces do play a part, since they limit the strength of the intermolecular forces. because of the limitted strenght, the individual molecules are allowed to "climb" the wall until the gravity pull and the adhesive force equal out.



So i guess to answer your question, neither the H atoms nor the O atom are completley satisfied by their relationship. They tend to look at other atoms and run around on each other, apparently atoms have no concept of adultury. :-laf



This explains why some molecules, that don't have enough bonding forces, will become seperated and surround by H2O molecules. this is called dissassociation, or dissolving.

Somebody please correct me if I'm wrong!

Forrest

 

[AfterBurner]

My posts almost seem to contradict each other in explaining what limits the hieghth of the meniscus, a further explanation:

What limits the height is gravity. however intermolecular forces do play a major part. because of the intermolecular forces, the molecules that are bonding to the wall, must drag other molecules with it. Most of these other molecules aren't bonding to the glass, not supporting their own weight, so that at a certain height, they become so heavy that the lead molecule (the one doing all the work) just can't go overcome gravity to go anyhigher.

IF not for the intermolecular forces (causing surface tension) you would have water molecule running all over your peice of glass. Eventually they would all climb out of your flask! :--)

Forrest

 

[E7mack96]

so, in space the water would creep out of its' container?



that would be cool to see.

 

[rbattelle]

Well, that all makes sense... thanks for the chemistry review, Forrest.



It would be interesting to see liquids "climbing" out of their glasses.



-Ryan

 

[HEMI®Dart]

afterburner,



Is it true that heavy water weighs 20% more than regular water? Is it thicker?

 

[NPloysa]

What water tests do you do on the boilers?

What type of boilers are they? (type of construction)

What type of softeners do you have?

What type of heating system is used in there?

Sorry for all the questions. I'm bored, havent worked since May.

Eric

Eric, no problem.



We have four boilers, natural gas fired. Two closed-loop hot domestic (with glycol), two steam.



All four are Cleaver-Brooks Flex-Tubes. I am not sure of their capacity but I can find out.



The tests I run on the steam boilers only, are conductivity and sulfite tests. The conductivity reads, in micro-siemens, how much TDS, or total dissolved solids are in the water. I try to keep it at 3000-4000.



Sulfite is an oxygen scavenger and keeps all the oxygen out of the water. This slows rust and scaling. I just test to make sure the pumps are working at correct stroke and pulse.



Softeners are twin alternating. Not exactly sure on the capacity. They are about a foot in diameter and four feet tall each. I test the hardness of their water and also the water in the deaerator tank.



Our heating system is forced air from our 3 air handlers, from the hot water system and heating coils. Steam is injected just upstream of the Air Handler 1's fan. Only the main air handler has steam. The other air handlers have heating and cooling only, one serves the Iwerks theater and the other serves the the main and prep kitchens.



Anything else? I like talking about this stuff!



Thanks Forrest, wonderful explanation!



Nick

 

[The patriot]

I'm familiar with the Cleaver Brooks, but I never heard of a flex tube. Maybe you mean fire tube? I've seen water tube CB's but the fire tube is by far the most common.



We ran conductivity, sequestriant, sulfite, and alkalinity on the boiler.

I hope youre adding the sulfite@ the D. A. tank. That's the best place.

If youre softener dont go hard, and you have no leans in the system (like in a reactor, or a heat exchanger) testing the D. A. for hardness isnt really necessary.

Do you have the heating/cooling system on computer? I've dont some work with Johnson Controls. Neat system.

Do you work with the fire system? The few places I did, I HATED IT!!

I used to call it Satan, everyone knew what I was talking about.



In the place I used to work at, we had one 1500 HP B&W with a combo gas/#6 oil burner. This handled 2 of our waste streams, and provided steam for the reactors, and process equipment.

We also had one 700 HP C. B. It too was a gas/#6 burner.

I was also "responsible" for 20 acres of other crap. It's too late in the night to start to type all that out.

Eric

 

[AfterBurner]

afterburner,



Is it true that heavy water weighs 20% more than regular water? Is it thicker?

This is what I have found:

"Heavy water is chemically the same as regular (light) water, but with the two hydrogen atoms (as in H2O) replaced with deuterium atoms (hence the symbol D2O). Deuterium is an isotope of hydrogen; it has one extra neutron. Thus the deutrium atom consists of one proton and one neutron in the atomic nucleus and one orbiting electron. It is the extra neutron that makes heavy water "heavy", about 10% heavier in fact. "



"Heavy water is essential to the operation of Canada's CANDU nuclear power reactors; used as both a moderator and a heat transfer agent. The function of the moderator is to slow down the emitted neutrons, which increases the fission reaction rate, thus enabling a sustained chain reaction. Ordinary water is also a good moderator, but it absorbs neutrons, which is why light water reactors must use enriched fuel. The use of D2O in CANDUs makes it possible to use non-enriched natural uranium. "

Check this out:

The heavy water for the Sudbury Neutrino Observatory (SNO) is on loan from Atomic Energy of Canada Limited (AECL), and has a value of over $300 million (can)



I didn't know anything about heavy water- this is just some stuff I pulled from resources. Never thought I would research water properties on a weekend! Thanks for enlightening me on heavy water! :-laf

here's a website that was interesting, it can tell you more than i can:

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

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

 

[NPloysa]

Eric,



They are fire tube boilers, Flex Tube (flexible fire tubes compressed to lock into the drums with no mechanical connection) is the model name of the CB boilers. They are small. Our building is only 66,000 square feet, and the boilers are used only for the heating/humidity. The sulfite is injected into the DA tank. And yes, there is a heat exchanger on the hot water but do not test the hardness on the hot water line (closed loop).



The reason I do test the hardness is cause our softeners are prone to going down. One's solenoid valve stuck open but got it fixed.



No, I don't work on the fire system, thank goodness!

 

[The patriot]

They must be a little smaller than I'm used to seeing.

How many HP are they?

Yea, our softeners werent too reliable either. Theyre about 8' tall, and the brine tank is like a 550 gal tank set on it's side.



What I meant by "not needing to test hardness on the D. A. was, you test the M. U. water coming out of the softener, so you dont really need to test the D. A, so long as you dont have any heat exchangers (that could cause hardnedd to enter they system) in the system. However you do have heatexchangers, so that explains why you do.

Ramble mode off. :{

Eric

 

[NPloysa]

They must be a little smaller than I'm used to seeing.

How many HP are they?

Yea, our softeners werent too reliable either. Theyre about 8' tall, and the brine tank is like a 550 gal tank set on it's side.



What I meant by "not needing to test hardness on the D. A. was, you test the M. U. water coming out of the softener, so you dont really need to test the D. A, so long as you dont have any heat exchangers (that could cause hardnedd to enter they system) in the system. However you do have heatexchangers, so that explains why you do.

Ramble mode off. :{

Eric

The hot water boilers are 5 horse, steams are 3. I used to test the deaerator water but now I only test the softeners, because if the softeners are soft, then the DA is also. Also, only the hot water boilers have the heat exchanger on them, and since they are closed loop I do no testing on em.

 

[The patriot]

Yea, theyre on the small side.

Eric

 

[Skydiver]

Been working in water for 24 years 11 months 2 weeks and a day. Never studied surface tention. Surface water treatment plant.

As to weight of the water Hemi-dart was probably meaning specific gravity.

"Come on 25 years"---Can you say retirement!!

Tim