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Air to Ice Displacement

12/21/2014 4:32 AM

How many cubic feet of airs required to lift a 500 lb block of ice out of salty water? For instance cutting a 4' X 4' block of ice five feet thick, and putting an airbag under it to lift it out of the hole? Thanks

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#1

Re: Air to ice displacement

12/21/2014 5:08 AM

You might want to look at the math for a 4x4x5 block of ice. Not quite 500 lbs. From there you can calculate the required lifting device.

Ice weighs about 92% of what a cubic foot of water weights

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#21
In reply to #1

Re: Air to ice displacement

12/21/2014 10:28 PM

Damn the decimal point.

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#2

Re: Air to ice displacement

12/21/2014 5:08 AM

This sounds like to much a homework question that the OP needs to do the research on their own

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#3

Re: Air to ice displacement

12/21/2014 6:01 AM

Ahmm.. Use Work= Pressure x Displaced Volume and PV=RT equaiton, Potential Energy of Ice should be equal the Work done by air. Use your imagination from then on, then you will certainly learn. Payts!

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#4

Re: Air to ice displacement

12/21/2014 8:16 AM

your calculations are wrong to begin with. a cubic foot of ice is usually around 60 lbs, your 500# is too low

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#5

Re: Air to ice displacement

12/21/2014 8:58 AM

There are some that claim that Archimedes was all wet. Of course he was. He was sitting in his bathtub when he came up with his principal. To lift your block of Ice your air bag will need to displace a volume of salt water weighing as much as or greater than the block of ice ( and of course + the weight of the bag)

Whatever floats your boat.

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#6

Re: Air to ice displacement

12/21/2014 9:12 AM
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#7

Re: Air to ice displacement

12/21/2014 10:01 AM

Your first assignment is to calculate the weight of a block of salty ice that is 4x4x5 feet.

Show your work in detail. And give the answer in pounds. For bonus credit show the weight of the same block of ice on the moon.

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#17
In reply to #7

Re: Air to ice displacement

12/21/2014 4:55 PM

Is there that much ice on the moon?

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#18
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Re: Air to ice displacement

12/21/2014 4:58 PM

SHHhhhhhhhhhhhhhhhhhhhhh.

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#8

Re: Air to ice displacement

12/21/2014 10:42 AM

Salty water - I presume seawater? - is denser than pure water, with a density ranging from 1.020 to 1.029 grams per cu. centimeter.

Ice is less dense than pure water, at 0.9340 grams per cu. centimeter.

Whilst the block is in the water, it will displace a volume of seawater equal to its weight.

For a given volume of ice, find its weight from volume and density, and then calculate the volume of seawater equal in weight to the block of ice.

The depth to which the ice block sits in that volume of seawater will be the height the block has to be lifted to just clear the water. That height will vary depending on the density of seawater.

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#9
In reply to #8

Re: Air to ice displacement

12/21/2014 11:19 AM

Could you convert grams per cc to pounds per cu.ft. for the OP?

Is airs more, or less, dense than plain air?

We haven't even begun to consider the gas laws vs temperature, which I assume will be quite low.

Imperial ice or metric ice?

This problem is getting more complex as we go forward.

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#10
In reply to #9

Re: Air to ice displacement

12/21/2014 11:22 AM

A really snooty person could surely put on enough airs to lift this ice block. About 3psia will do the trick.

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#16
In reply to #10

Re: Air to ice displacement

12/21/2014 2:55 PM

They're certainly not in short supply here.

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#14
In reply to #9

Re: Air to ice displacement

12/21/2014 12:35 PM

It's an interesting problem, actually (at least I think so). It would have made a good Challenge Question.

4'x4'x5' ice block in seawater
.
Volume of ice block in cu. cm:
Vice = (4' x 12"/foot x 2.54 cm/inch) x ( same ) x (5' x 12"/foot x 2.54 cm/inch)
Vice = (4' x 30.48 cm/ft) x ( same ) x (5' x 30.48 cm/ft)
Vice = 121.92 cm x 121.92 cm x 152.4 cm
Vice = 2265347.727 cm3
.
Area of ice-block 'footprint', in sq. cm:
Aice = (4' x 30.48 cm/ft) x ( same )
Aice = 14864.486 cm2
.
Density of ice:
dice = 0.9340 g/cm3
.
Density of seawater:
min: dsea(min) = 1.020 g/cm3
max: dsea(max) = 1.029 g/cm3
.

Weight of ice block:

Wice = Vice * dice

Wice = 2265347.727 cm3 * 0.9240 g/cm3
Wice = 2115834.777 g
.
Volume of seawater(@1.020 g/cm3) with this weight
Vmax = Wice / dsea(min)
Vmax = 2115834.777 g / 1.020 g/cm3
Vmax = 2074347.821 cm3
.
Volume of 1 cu. foot in cm3
Vcf = (30.48 cm/foot)3
Vcf = 28316.85 cm3/ft3
.
Volume of seawater(@1.020 g/cm3) in ft3
Vmax-cf = Vmax / Vcf
Vmax-cf = 2074347.821 cm3 / 28316.85 cm3/ft3
Vmax-cf = 73.25 cu. feet **
.
Height of 'block' of seawater(@1.020 g/cm3) having same (4' x 4') footprint:
Hmax = Vmax / Aice
Hmax = 2074347.821 cm3 / 14864.486 cm2
Hmax = 139.551 cm
.
Height ice block must be lifted to just clear seawater(@1.020 g/cm3), in feet:
Hmax-cf = 139.551 cm / 30.48 cm/ft
Hmax-cf = 4.578 feet ***
.
-----
Volume of seawater(@1.029 g/cm3) with this weight
Vmin = Wice / dsea(max)
Vmin = 2115834.777 g / 1.029 g/cm3

Vmin = 2056204.837 cm3

.
Volume of seawater(@1.029 g/cm3) in ft3
Vmin-cf = Vmin / Vcf
Vmin-cf = 2056204.837 cm3 / 28316.85 cm3/ft3
Vmin-cf = 72.61 cu. feet **
.
Height of 'block' of seawater(@1.029 g/cm3) having same (4' x 4') footprint:
Hmin = Vmin / Aice
Hmin = 2056204.837 cm3 / 14864.486 cm2
Hmin = 138.330 cm
.
Height ice block must be lifted to just clear seawater(@1.029 g/cm3), in feet:
Hmin-cf = 139.551 cm / 30.48 cm/ft
Hmin-cf = 4.538 feet ***

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#15
In reply to #14

Re: Air to ice displacement

12/21/2014 1:04 PM

Note that I ignored the weight given and used the dimensions instead because the dimensions are more important than the given weight which is incorrect. A block of ice having the dimensions 4' x 4' x 5' wouldn't weigh 500 pounds; it would weigh 4664.617 pounds - about two and a third tons.

If the given weight is more imporant, then you'll have to scale the dimensions appropriately.

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#22
In reply to #15

Re: Air to ice displacement

12/21/2014 10:36 PM

If you take the question literally, you are asked to give the volume of air. Therefore the weight of the ice is irrelevant. And he doesn't say how high to lift it so you cannot answer the question.

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#45
In reply to #14

Re: Air to ice displacement

12/22/2014 4:38 PM

This challenge is in the bering sea so the salt content is slightly higher, and the temperature is most likely going to be below zero when the time comes, your equations are very helpful. thank you

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#48
In reply to #45

Re: Air to ice displacement

12/22/2014 5:01 PM

OK, golddiver.

So far you've made a number of elementary blunders that lead me to believe you just have a homework problem.

Many brilliant minds here have given you much knowledge about the actual weight of that much ice and how to get it out of the hole.

Aside from mentioning the Bearing Sea, you've not done anything to establish any credibility.

Just read about the "monkey heater".

I withdraw all the questions posed here, except these"

Why would you want to saw a hole in the Bearing Sea? (Waiting for the answer to be to dive for gold)

What will keep the "hot" water from freezing almost instantly?

Where will the water go that somehow doesn't freeze?

How will you keep the hole from closing back up with fresh ice? Quickly?

Regards,

A Warm Land Lubber

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#52
In reply to #48

Re: Air to ice displacement

12/22/2014 5:12 PM

There is actually a sea of Bearings? Where is that? I need to make a lazy-susan for my test photocurrent battery.

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#59
In reply to #48

Re: Air to ice displacement

12/23/2014 6:45 PM

we draw the water for the monkey heater from the sea water, and haven't had a problem with the hole closing up before its cut through takes about 30 minutes to cut and the ambient warm water from the tubing keeps it free, if we left it for a few hours it would start to freeze back together, I brought this question here because ive seen great answers,from great minds in the past, figured I might as well do it right the first time, instead of make four or five bags till it worked. Its our challenge at hand not a homework question, really appreciate everyones input in this thank you all

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#60
In reply to #59

Re: Air to ice displacement

12/23/2014 7:02 PM

Let me know if you want advice from the Antarctic divers.

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#62
In reply to #59

Re: Air to ice displacement

12/23/2014 7:57 PM

Well good luck.

Have you considered how you are going to keep the bag under the block when the block is almost out of the water?

Your bag could "squirt" out from under the block, letting the block fall back into the water.

Will you be able to make another dive hole to allow you to work under the ice to secure the bag/block?

Also assume you will drill some holes and secure some lines to the top to help pull the block over and away?

Send us a picture of the gold.

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#66
In reply to #62

Re: Air to ice displacement

12/23/2014 11:26 PM

if we get the block half way to three quarters out we can pull it with out,

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#67
In reply to #66

Re: Air to ice displacement

12/23/2014 11:41 PM

Don't mess around lifting blocks of ice. Do it the way the professionals do.

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#68
In reply to #67

Re: Air to ice displacement

12/24/2014 12:00 AM

hows that?

how would that be? I'm open to any suggestions on a more efficient way to get them out.

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#69
In reply to #68

Re: Air to ice displacement

12/24/2014 12:20 AM

As it happens the experts I spoke of are at our house tonight as it is Christmas eve here. They will explain the methods they use but maybe not until tomorrow. But I can tell you that they do sometimes lift blocks of ice. It all depends on whether the ice is thick enough to carry a hiab truck and thin enough to chainsaw. If it is helicopter accessible only other methods are used but take longer. Watch this space.

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#70
In reply to #69

Re: Air to ice displacement

12/24/2014 3:14 AM

Hi. I been making holes in ice for some decades now and diving through them. We have used a number of techniques and it all depends on the machinery that you have available and the thickness of the ice.

1. If your ice is only around 3 ft thick or less, then you can use a chain saw. The trick then is not to try to lift the ice out, but to push it under. Cut the block so that the sides are strait, or slightly inclined towards the surface, and use a long-handled chisel to get the ice block oscillating up and down. Then, with perfect timing, get a couple of guys to put all of their weight onto the block and push it down and away under the ice. This sounds more difficult than it is. With 3 ft of ice then there it can pay to cut you block into 4 quarters and push them under one at a time.

2. Thicker ice can be lifted out. This season in Antarctica we used an over-snow vehicle fitted with a hydraulic arm to make a 1 x 1 m hole in 2 m thick sea ice. First drill a hole (we use a Jiffy ice drill, 5 inch) through the ice and lower a chain with a horizontal bar attached to it. Tie a length of rope to one end of the cross bar and lower the bar using this, then pull up on the chain to set the bar across the hole. Then cut the sides of the dive hole. We use a hot water method. A commercial steam cleaner is modified so that it cycles hot glycol through a heat exchanger. The heat exchanger (a milk cooler - this is New Zealand after all) has seawater pumped through the other side, which is sucked up from the Jiffy drill hole, and exits via a copper pipe in the form of an inverted "T". The hot sea water is pumped down the long leg of the T, then exits though a series of holes drilled in the top bar of the T, which is 1 m long. It takes about 20 minutes to melt through 2 m of ice. When all 4 sides are cut lift the block, which weighs 2 tonnes, out with the hydraulic arm.

3. If you have a steam cleaner but no hydraulic arm, the an alternative is to make a copper coil that you can use to melt the ice. The principle is to re-engineer the steam cleaner to cycle hot glycol through this copper coil. Drill a pilot Jiffy Drill hole, then put the coil into the hole and circulate the hot glycol through the coil. This is slow, but certain. This year we made a hole in 4.5 m of lake ice using this method, in around 48 h.

4. We have also lifted blocks of ice out using a chain hoist. For this we first mounted an "A" frame on two sleds and fixed the chain hoist to the top of the frame. We then cut the block, using a chain saw, then set two climbers' ice screws into the top of the cut block (the block must taper outwards). These were then linked to the chain hoist and we could easily lift the ice block. Then slide the sleds away from the hole!

5. I have never heard of anybody using a lift bag, and I cannot really see it as a practical method. Some organisations have augers that fit onto power take off on the back of a large tractor, and others use explosives. The latter is generally a desperate last resort as clearing the broken ice from the hole is anything but easy.

6. Once you have made the hole, you can expect 1-2 inches of ice to form overnight (depending on where you are). Take a heavy, long handled chisel to break this ice ad a heavy duty landing net to get the ice out of the hole.

It is a lot of work, but worth it!

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#73
In reply to #70

Re: Air to ice displacement

12/24/2014 11:54 AM

Sounds good to me.

Merry Christmas.

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#75
In reply to #70

Re: Air to ice displacement

12/24/2014 2:56 PM

I am confused. Are we trying to cut a hole in the ice or are we trying to extract the ice out of the hole? It would seem to lead me in at least two different directions.

I thought the original question was how to remove the 4' x 4' x 5' block of ice from the 4' x 4' x 5' hole. As usual, once we decide the question the answer is fairly simple.

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#76
In reply to #75

Re: Air to ice displacement

12/24/2014 3:38 PM

Nothing is ever simple.

Remove. OP knows how to cut, and has some expert advice too.

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#71
In reply to #68

Re: Air to ice displacement

12/24/2014 3:16 AM

See 70

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#79
In reply to #68

Re: Air to ice displacement

12/25/2014 10:16 PM

Audiver, did you read #70 ?

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#81
In reply to #79

Re: Air to ice displacement

12/26/2014 3:03 AM

yes I did and it was also very helpful , I want to master this part of the project and get it down to under an hour to make our holes, we also put a 2"piece of ridged polyiso insulation over our holes when were done if we cant get to them right away and it keeps them from freezing up completely it just freezes around the edges when it gets in the negatives. merry x mas and happy new year to all.

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#74
In reply to #66

Re: Air to ice displacement

12/24/2014 2:13 PM

You wouldn't happen to be Vernon would you?

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#82
In reply to #74

Re: Air to ice displacement

12/26/2014 3:10 AM

no sir but I do know vern attkins and he hired us to cut quite a few of his holes last season because we have a pretty good method, hoping to kick it up a notch this season

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#83
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Re: Air to ice displacement

12/26/2014 11:25 AM

Happy New years! And stay warm!!

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#84
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Re: Air to ice displacement

12/30/2014 10:14 AM

I just one more idea to add to Oraka's comments:

If you insist on using the lift bag, why not just use it to raise the block in steps? Takes less bag size, and can still use the central hole. For each step raised 12-18", chain saw the raised portion (relatively fast), and slide off to the side, then as the weight is lifted off, the block will rise a bit further each step. At the end, you will be able to finish with a complete lift off, and a couple sledge hammer blows could finish this off? Just thinking aloud, let all of us know what you went with, and how well it worked?

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#85
In reply to #84

Re: Air to ice displacement

12/30/2014 11:53 AM

interesting, our main objective is the quickest way to remove it, ill give this a try if i cant get the bag to lift it high enough this is a good alternative to lightening it up. thank you. ill send pictures of our progress, it just rained in nome this morning! another strange winter, if you look online you can see the nome camera set up off front street fun to watch during ididarod .

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#86
In reply to #85

Re: Air to ice displacement

12/30/2014 12:27 PM

Here in Lubbock it started as freezing mist, but now we are having sleet (I like to call it raining ball bearings! The inexperienced drivers here are sort of fun to watch, just not to be in traffic with.

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#87
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Re: Air to ice displacement

12/30/2014 2:58 PM

Good answer.

I got a pic from one of my Lubbock cousins. Of what? An inch of snow.

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#88
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Re: Air to ice displacement

01/02/2015 11:13 AM

It ended up about an inch or two, but today we are forecast for more than a few inches of snow by this time tomorrow (or by tamale as some of us say). Did you have black-eyed peas and ham yesterday? I made some black-eyed peas with other vegetables and cayenne and curry, it was delicious.

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#53
In reply to #45

Re: Air to ice displacement

12/22/2014 5:18 PM

Please also make sure you phrase your question with consistency between volume and weight (or other units) in the future. B-

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#35
In reply to #9

Re: Air to ice displacement

12/22/2014 2:22 PM

I think someone should consider that the seawater will not freeze to "salty" ice, but simply ice, as this is a means of purifying water. Besides I already gave my answer: use a bag at least as large as the ice block, then get the big tongs on it and lift it the rest of the way out. Otherwise you need a bigger bag to lift the block high enough to clear the surface ice and allow it to slide off.

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#37
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Re: Air to ice displacement

12/22/2014 2:39 PM

Wiki says:

Seawater is denser than both fresh water and pure water (density 1.0 g/ml @ 4 °C (39 °F)) because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F).

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#38
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Re: Air to ice displacement

12/22/2014 3:17 PM

Britannica states:

"As seawater freezes and ice forms, liquid brine and air are trapped within a matrix of pure ice crystals. Solid salt crystals subsequently precipitate in pockets of brine within the ice. The brine volume and chemical composition of the solid salts are temperature-dependent.

Liquid ocean water has an average salinity of 35 parts per thousand. New ice such as nilas has the highest average salinity (12-15 parts per thousand); as ice grows thicker during the course of the winter, the average salinity of the entire ice thickness decreases as brine is lost from the ice. Brine loss occurs by temperature-dependent brine pocket migration, brine expulsion, and, most importantly, by gravity drainage via a network of cells and channels. At the end of winter, Arctic first-year ice has an average salinity of 4-6 parts per thousand. Antarctic first-year ice is more saline, perhaps because ice growth rates are more rapid than in the Arctic, and granular ice traps more brine."

I am pretty sure pack ice or even sea ice is less saline by a large margin than seawater, else why would people be interested in towing icebergs to Dubai?

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#40
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Re: Air to ice displacement

12/22/2014 4:00 PM

FYI James, icebergs come from glaciers which are formed from snow and therefore are not saline.

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#41
In reply to #40

Re: Air to ice displacement

12/22/2014 4:11 PM

OP did not state his slab of ice to be off of an iceberg. I think he is possibly referring to thin to medium thickness sea ice more than one year of age.

Suggestion for getting the air bag under the slab: send either Lyn or Oraka through a smallish drill hole with the bag for postioning, wet suit, and/or SCBA optional (just kidding). Local safety rules may apply, make sure to check with LynDor industries that MSD for sea water is on hand, and all personnel have read and understood.

Real option: use drill holes to establish a network of guidepoles near the slab with one large drill hole closer in for the air bag, and supply hose. Once the inflation of the air bag has begun to displace the slab, guidepoles can be taken out to allow passage of the slab to discard area.

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#42
In reply to #41

Re: Air to ice displacement

12/22/2014 4:13 PM

This is homework.

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#44
In reply to #41

Re: Air to ice displacement

12/22/2014 4:29 PM

No James, the OP did not mention icebergs but you inferred that they originate from salt water, which they do not.

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#47
In reply to #41

Re: Air to ice displacement

12/22/2014 4:57 PM

we have designed a copper tubing system with perfrations through out the loop which we push hot water through with a monkey heater and it cuts the blocks free, were planning on putting the air bag in with one hole augured down the center of the block and inflate it from there. thank you

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#51
In reply to #47

Re: Air to ice displacement

12/22/2014 5:08 PM

In the future, it would be really great if you could supply more information with the initial posting. Having said that:

I do not believe you will have a lot of success with central hole, because with it there you will still struggle to move the slab away from the hole once freed and lifted, as long as the gas bag is in place.

Of course, if it was my wife being used as the gas bag, there would be no slab to remove in the first place, as all ice would melt.

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#50
In reply to #40

Re: Air to ice displacement

12/22/2014 5:05 PM

OK OK. Icebergs come from glaciers and are not particularly salty. Some of the sea ice that is older ice is containing some salt, but not nearly as salty as the seawater, and one could probably melt this and survive on it for a time.

Not the sea ice or the sea water is as salty as some of the comments I have seen on here from time to time. Thanks for pointing out the errors of my insinuations.

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#54
In reply to #50

Re: Air to ice displacement

12/22/2014 5:29 PM

Yes I know what you are saying. In fact, a lot of scientists worry that, if the sea ice surrounding the North Pole melts, the fact that it is nearly fresh water and therefore, being less dense than the sea, it will not sink quickly. This could upset the Atlantic 'conveyor belt' and make much of Western Europe uninhabitable for an era or so.

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#63
In reply to #38

Re: Air to ice displacement

12/23/2014 9:31 PM

Wanna play poker anyone? Seem like you are throwing cards one at a time James

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#65
In reply to #63

Re: Air to ice displacement

12/23/2014 9:50 PM
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#43
In reply to #9

Re: Air to ice displacement

12/22/2014 4:22 PM

i agree sounded like an easy equation at first, but all the comments have been very helpful and the temperature is going to be below zero.

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#11

Re: Air to ice displacement

12/21/2014 11:55 AM

This has to be a homework problem. It reeks of a preposterous scenario.

After one has cut out this section of an ice berg with a six foot long chain saw, how does one get the air bag under the block of ice? What prevents the block of ice from tumbling off of the air bag while lifting? If this block is now a piston of ice in an iceberg sheet, how high does one have to lift the block out of this ice hole for it to fall out of the way? When it falls off of the airbag, the sudden removal of weight on this partially submerged bag may launch the air bag, hosing, and pressurized air tank to a dangerous height.

Ice naturally floats on sea water and as such is easier to move in the water than out of the water. Once this block is calved from the iceberg, push the block closer to the dock or ship that has a crane.

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#12
In reply to #11

Re: Air to ice displacement

12/21/2014 12:01 PM

Gedanken experiments always confer godlike powers to the experimenter. If we can travel alongside photons at the speed of light, we can certainly teleport airbags underneath ice blocks cut exactly to the dimensions given.

I do all my Christmas shopping via the Gedanken Method - I just imagine everyone on my list having received the Ideal Present come Christmas morning and I'm done for the year. What could be easier?

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#19
In reply to #11

Re: Air to ice displacement

12/21/2014 7:07 PM

Not really, I made a martini the other night and I needed that size ice cube. For the lack of a cube I had to drink it warm. Can you dare think of the problem that caused me.

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#57
In reply to #11

Re: Air to ice displacement

12/22/2014 10:47 PM

Yes, homework. But are we reading too much into it or assuming too much in our answers?

OP does not state that this perimeter of the block of ice is contained within another section of ice (cut from ice sheet). It could be floating by itself with the top being nearly level with the water.

The dimensions of the air bag is not limited to the area of the bottom of the ice block. It could be larger, could be two or more stacked on each other (this is the preferred way to lift vehicles in accidents). They could also be constructed in such a way that the outer sections of the bottom or top are thicker than the center. This would presumably provide more lift around the perimeter to lessen the risk of rotating so the top is not the top any more. Air bags come in numerous sizes, configurations, thicknesses, pressure capabilities, with or without eyelets (grommets), etc. Are we limiting ourselves to only the obvious equipment or at least that which we are aware of?

Just asking questions of an apparent genius on the subject. (Pat on your back, but not the lowest back!)

Good Luck, Old Salt

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#13

Re: Air to ice displacement

12/21/2014 12:11 PM

Slice it into sections and sink each section, push it out of the way under the ice.

Or, make ice cubes and lift each one out.

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#49
In reply to #13

Re: Air to ice displacement

12/22/2014 5:03 PM

because we will be diving in the hole, pushing the block under creates a danger of it moving back in the hole blocking our exit out so it has to be removed for safety measures

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#55
In reply to #49

Re: Air to ice displacement

12/22/2014 5:37 PM

If the hole is to dive through, you should have said. My daughter and her partner are scientists and experienced ice divers and dive through 3 meters of ice in Antarctica. The could advise you.

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#20

Re: Air to Ice Displacement

12/21/2014 7:47 PM

One only has to calculate the displacement of the water of the floating cube....replacing this volume with air will bring the bottom of the cube to the surface...

....but then you have to be able to move it....!

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#23
In reply to #20

Re: Air to Ice Displacement

12/21/2014 10:43 PM

SE Did you slice that ice cube out of your pond?

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#24

Re: Air to Ice Displacement

12/22/2014 12:05 AM

The question is very ambiguous. Is the ice in the block fresh water (only water) or is it "salt water"? Salt water would include any concentration of sodium chloride from 0+ up to 26.3% salt in water (the highest liquid concentration possible). The higher the concentration of salt in 4'x4'x5' the heavier the block.

What is the salt concentration of the water that the block is floating in? The higher the concentration, the denser the water and therefore the less air needed to float the block.

Most air needed is with maximum concentration salt/water for the block and fresh water for the water the block is floating in. Opposite is also true.

A submarine in salt water will float higher in a concentrated salt solution than it will in sea water. A submarine will float higher in sea salt water than it will in fresh water.

Good Luck, Old Salt

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#25

Re: Air to Ice Displacement

12/22/2014 12:10 AM

I wonder if the 5' wasn't a 5",

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#26

Re: Air to Ice Displacement

12/22/2014 2:29 AM

Why do you need anything to lift? The block will float on water by itself.

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#29
In reply to #26

Re: Air to Ice Displacement

12/22/2014 9:40 AM

Yap only about 10% approximately using ((s.g salt water-s.g ice)/s.g. salt water)x 100%

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#36
In reply to #26

Re: Air to Ice Displacement

12/22/2014 2:34 PM

Only if you want to lift it out of the water. Or if you are simply trying finish your home work assignment before Friday.

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#27

Re: Air to Ice Displacement

12/22/2014 5:38 AM

The volume of air in that part of the bag that is still submerged after the ice is lifted must equal the weight of the ice. 1lb of water occupies 0.016ft³ so 500 lbs is 8ft³. You must add extra volume to account for the thickness of ice i.e how far you want to lift the base of the block above the water surface. Ice weighs 57.2lbs/ft³. The figures will vary slightly because water changes in density as the temperature lowers but they are within 1% of the required volume.

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#28

Re: Air to Ice Displacement

12/22/2014 8:54 AM

If you're planning on diving Prudhoe, cut into smaller slices they'll be easier to pull....how do you propose to get the airbag under it to begin with? Ice tongs, tripod, come along or winch...use the "airs" to keep the hole open......been there, done that.

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#30

Re: Air to Ice Displacement

12/22/2014 9:45 AM

Assuming a perfectly 'square' air bag that completely fits the hole, it will contain 4 x 4 x 5 = 80 cu.ft of air when the ice block is raised to ground level.

The area of the block is 4 x 4 x 144 = 2304 sq.ins.

Requiring a pressure of 500/2304 = 0.217 psig to support the block.

So one answer is 80 cu.ft of air at 0.217 psig.

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#31

Re: Air to Ice Displacement

12/22/2014 10:28 AM

A 500 lb slab of ice 4' x 4' would be 6½" thick not 5'. If all you want to do is create a hole in the ice, rather than recover the block for ice carving, or a very large vodka martini. Take a 25kg weight, tie a rope round the handle so that the weight can be recovered. Cut the 4' x 4' edges. Place the weight in the middle of the block. An ice block of that size is only 45lbs lighter than water so the additional 55lb weight will sink the ice and it can easily be pushed to the side under the solid ice. Pull on the rope and recover the weight.

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#32

Re: Air to Ice Displacement

12/22/2014 11:13 AM

Not to forget the weight of the air itself.

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#58
In reply to #32

Re: Air to Ice Displacement

12/22/2014 10:54 PM

Also the weight of the air bag. Some of the larger ones with thick surfaces can weigh a lot. A 4' x 4' one with thick walls would be heavy. Also the weight of the hoses, connections, and anything else in the water.

Good Luck, Old Salt

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#33

Re: Air to Ice Displacement

12/22/2014 11:55 AM

You are needing to lift a 5000# block of ice out of the hole. Thus, you will need a 4'x4'x5' air bag at a minimum, to get the bottom of the ice block even with the top of the water, or thereabouts. If you make the air bag larger, the tendency will be to push the ice block further up, until clear of the ice around the block. The solid ice pack around the block will not produce any bouyancy by filling the air bag into the void left by the ice block, so a lot depends on the water level (this should normally be within 16% of the top of the ice from the bottom.

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#34

Re: Air to Ice Displacement

12/22/2014 12:57 PM

You might find the raising of the Costa Concordia interesting reading. Not made of ice, but, whatever.

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#39

Re: Air to Ice Displacement

12/22/2014 3:47 PM

"How many cubic feet of airs required to lift a 500 lb block of ice out of salty water? For instance cutting a 4' X 4' block of ice five feet inches thick, and putting an airbag under it to lift it out of the hole? Thanks"

Ok, now I am referring to lifting 5" slab of ice from an ice surface floating on seawater. Strangely enough ice density varies according to measurement technique, position above or below the waterline etc.

A review of sea ice density

Abstract

The density of sea ice is an important property in many applications. However, due to its multi-phase composition of solid ice, solid salts, liquids and gas, the definition and measurement of density is not straightforward. The reported values vary over a wide range from 0.72 Mg m−3 to 0.94 Mg m−3, with an average of approximately 0.91 Mg m−3. The reasons for the spread are partly real, and partly a function of the test technique used for determining the density. Accurate measurements which represent the in situ density of first-year sea ice range from 0.84 to 0.91 Mg m−3 for the ice above the waterline, and 0.90 to 0.94 Mg m−3 for the ice below the waterline.

Copyright © 1996 Published by Elsevier B.V. If someone should be interested in purchasing this book.

If the ice density comes in around average at 910Kg/m3 , then we calculate volume as 4'x4'x5" = 6.667 ft3 or 0.1888 m3 , and the mass of ice is 171.8 Kg (378.7 lb). The density of seawater is approximately 1025 Kg/m3, (depends on salinity and temperature), thus the minimum displacement required to raise the slab of ice its own thickness (5") is 0.1888*1025/910 = 0.2127 m3 (7.51 ft3) air (contained in bag), and since the air bag is expected to be 4' edge, the thickness inflated should be around 0.46'(5.6"). In other words my hypothesis is that the surface of local sea ice is about 0.6" higher than the waterline.

Practically speaking, if one produced an air bag that could inflate to an arbitrary volume, then there is no difficulty at all in lifting out a slab of ice (quickly), and discarding this nearby. The only other engineering requirement would be that the sea ice will be thick enough to support the added weight of the slab removed.

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#56
In reply to #39

Re: Air to Ice Displacement

12/22/2014 6:11 PM

OP's question is: "How many cubic feet of airs required to lift a 500 lb block of ice out of salty water? For instance cutting a 4' X 4' block of ice five feet thick, and putting an airbag under it to lift it out of the hole?"

Not cut and diced to what we think is should be.

These are very poorly stated questions and hopefully they have enough sense not to base their thesis upon these two questions and result findings!

It could be full of airs!

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#46

Re: Air to Ice Displacement

12/22/2014 4:42 PM

The OP is certainly going to get an "A" when he hands in his compilation of this thread.

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#61

Re: Air to Ice Displacement

12/23/2014 7:49 PM

You might not need a bag at all. If you drill a hole in the center of the block and blow air down through it (sealing off the hose), the air can start to lift the block, which then forms a "dome" to trap further air. A regenerative blower would be about the right pressure range for this, better and faster than a compressor.

Another method would be to make a large "toggle bolt" and lift the block out with a hoist.

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#64

Re: Air to Ice Displacement

12/23/2014 9:42 PM

Since so many have already answered this question in a serious manner, I feel free to be absurd.

Melting arctic ice in the Bering Sea with a monkey heater to look for gold sounds like an episode of Tintin than a real engineering problem.

Real or not, it baffles me why anyone should care how much air it should take for this exercise. What if the ice is 10% thicker than you anticipated. Blame CR4 for an error in calculation? Do you need to know the minimum quantity of compressed air needed because you will be limited to carrying a fixed quantity compressed air tanks to the ice flow. Why not bring an air compressor along with this monkey heater to get through the ice? How does the hot water flow of a monkey heater make a square hole in the ice? Wouldn't a saw be easier? How long does it take for the ice block to refreeze in place?

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#80
In reply to #64

Re: Air to Ice Displacement

12/26/2014 2:56 AM

we have a square copper tube with perferations that direct the water down it takes about 30 minutes to go through 4-5 feet, we have used a six foot chain saw, if the temperature is below zero it will start to freeze up in ten minutes or so as soon as we turn the monkey heater off, we have cut them into smaller blocks we've built hoists on skis which requires the block to be cut into two pieces because of the weight, i'm looking for the most practical way to remove the block quickly, this is our fourth season and every year we get more efficient, I thank everyone who put their two bits in its been very helpful my cups half full i'm always looking for a better quicker faster way to accomplish a task that has been a pain in the butt in the past .

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#72

Re: Air to Ice Displacement

12/24/2014 5:03 AM

Wait until Summer, the ice will melt, then use a water pump.

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#77

Re: Air to Ice Displacement

12/25/2014 8:22 PM

I wonder why my previous reply 30 has been marked of 'Off-Topic'.

It is a direct answer to your question, and as good as any other, considering the lack of information you have provided..

Why should posters make dozens of assumptions, and spend valuable time to come up with dozens of possible answers, many of which will be of no practical value to you, because now it appears, after much effort, it is the hole you want, and not the ice block.

So why not cut smaller blocks of ice that can be lifter out and dispersed by human strength - and cut as many as necessary to make the hole big enough for diving.

PS:

An eskimo was fishing through a hole in the ice. A voice from the heavens called out - "You are wasting your time - there are no fish down there - fish somewhere else". The eskimo called back - "Why should I? - how do you know? - are you God". "No" was the reply "I'm the skating rink manager..."

Happy Christmas!

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#78
In reply to #77

Re: Air to Ice Displacement

12/25/2014 9:07 PM

"The area of the block is 4 x 4 x 144 = 2304 sq.ins"

But, the volume of the block is 138,240 cu.in.

I did not mark it OT.

Merry Christmas.

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