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Old 30-11-2015, 02:57   #16
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Re: Metal plates as thermal mass in freezer?

Rum and water solutions achieve a delicious slushly like state of a eutectic solution.
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Old 30-11-2015, 04:34   #17
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Re: Metal plates as thermal mass in freezer?

The heat of fusion for water is 144 but/lb so in melting a pound of water it will absorb 144 btu. The specific heat of aluminium is 0.225 btu/lb/degree F. For water the specific heat is 1 btu/lb/degree F. So melting 1 lb of water absorbs 144 times the heat that raising the temperature of water one degree F requires and 640 times more heat than that required to raise 1 lb of aluminium one degree F. Freezing water or water based fluids will provide the longest temperature holdover.
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Old 30-11-2015, 05:05   #18
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Re: Metal plates as thermal mass in freezer?

Again, if using only water in a freezer, it will be going through a phase change continually and not provide any energy savings overall (may actually increase energy use). An eutectic (is that better newhaul?) will absorb heat without going through a phase change and will help in this regard.

You will get much better bang for the buck by adding the same volume of insulation to the inside bottom and sides of your box than adding stuff attempting to provide thermal absorption.

Mark
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Old 30-11-2015, 06:37   #19
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Re: Metal plates as thermal mass in freezer?

Quote:
Originally Posted by colemj View Post
Again, if using only water in a freezer, it will be going through a phase change continually and not provide any energy savings overall (may actually increase energy use). An eutectic (is that better newhaul?) will absorb heat without going through a phase change and will help in this regard.

You will get much better bang for the buck by adding the same volume of insulation to the inside bottom and sides of your box than adding stuff attempting to provide thermal absorption.

Mark
What he said...Our freezer on a lagoon 410 is so deep that the wife couldn't reach stuff on the bottom. I started out using gallon jugs of water to raise the bottom, but after talking to refrigeration gurus, substituted the water for Styrofoam insulation. The insulation we used was 1 inch thick sheets cut to fit. We brought the bottom up 1 foot. The result was the freezer running much less often and I was able to drop down a number on the thermostat. This is a Frigoboat system....The rational was it takes energy to keep that water frozen...
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Old 30-11-2015, 07:42   #20
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Re: Metal plates as thermal mass in freezer?

Quote:
Originally Posted by colemj View Post
Again, if using only water in a freezer, it will be going through a phase change continually and not provide any energy savings overall (may actually increase energy use). An eutectic (is that better newhaul?) will absorb heat without going through a phase change and will help in this regard.

You will get much better bang for the buck by adding the same volume of insulation to the inside bottom and sides of your box than adding stuff attempting to provide thermal absorption.

Mark
My frozen water bottles don't go through a phase change continually, they stay frozen all the time
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Old 30-11-2015, 07:48   #21
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Re: Metal plates as thermal mass in freezer?

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Originally Posted by Sid at SailAway View Post
What he said...Our freezer on a lagoon 410 is so deep that the wife couldn't reach stuff on the bottom. I started out using gallon jugs of water to raise the bottom, but after talking to refrigeration gurus, substituted the water for Styrofoam insulation. The insulation we used was 1 inch thick sheets cut to fit. We brought the bottom up 1 foot. The result was the freezer running much less often and I was able to drop down a number on the thermostat. This is a Frigoboat system....The rational was it takes energy to keep that water frozen...
Hmm, you've got me thinking!

I follow the rational that blocks of styrofoam would be more energy efficient. I guess I'll have to weigh that up against the availability of cold packs for the esky when needed and the emergency reserve water.

Decisions, decisions!
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Old 30-11-2015, 07:56   #22
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Re: Metal plates as thermal mass in freezer?

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Originally Posted by StuM View Post
My frozen water bottles don't go through a phase change continually, they stay frozen all the time

They do stay frozen all the time, but they don't stay frozen by themselves. It takes energy to keep them frozen. The Styrofoam adds some insulation value but also reduces the amount of space. I'm no expert by any means, I just know this works for us...YMMV
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Old 30-11-2015, 08:01   #23
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Re: Metal plates as thermal mass in freezer?

Keep asking what is the point/goal and then what is the best way to get there.

Adding Insulation (R-Value) is your best improvement bang for the buck with an existing Refrigeration system. A few sheets of Polyisocyanurate (RMax from Home Depot for $20) can save you mucho power amigo.

A good rule of thumb is that when you double the Rvalue of a box...you halve the power use.
Try that with a few bottles of water or rum....but Rum is more fun....
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Old 30-11-2015, 10:39   #24
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Re: Metal plates as thermal mass in freezer?

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Originally Posted by Reefmagnet View Post
Put in appropriate sized bottles of water. They'll do the same job and also provide cool refreshing drinks as needed.
+1 vote for water. I freeze a few 4 litre jugs at home, as well as a bunch of 500ml bottles. I have never regretted having a little extra ice cold water aboard. Really works great.

Also, as much insulation as possible, especially the lid.
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Old 30-11-2015, 12:28   #25
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Re: Metal plates as thermal mass in freezer?

Never mind grammar. You might want to check spelling.
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Old 30-11-2015, 13:14   #26
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Re: Metal plates as thermal mass in freezer?

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" The next thing you know we will be arguing about what is and isn't a "true eutectic solution".

No, we would never do that here, would we?


What nobody likes the "Beer flywheel"
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Old 30-11-2015, 14:01   #27
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Re: Metal plates as thermal mass in freezer?

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Mark eutectic is not a solution but the word that identifies the point at which phase change happens from frozen solid to a liquid state which with a 23% salt/water solution happens at approximately -6 f a much better solution to use would be ethylene glycol in a 40% solution would be best with a freeze temperature of approximately -10f or even a 30% solution with a 7f freeze point.
I will not intervene in the Grammar wars here, but I used to work with phase change materials, so.....
We mix all sorts of "stuff" to create the phase change at the temp we desire. Often based on the refrigeration we are using, or the effect we need. Not all of these eutectic fluids are equal in terms of user friendliness and some are hygroscopic. Be careful what you use around food.
I will identify that Ethylene Glycol is toxic, causes liver damage etc etc. I know it breaks down relatively quickly, but becomes acidic as it oxidises, strips paint and so forth.
For use in proximity to foods, we use Propylene Glycol.
It is more expensive, but then most food grade products are.
It is safe to use around food, so if your container leaks, then it does not cause an issue.
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Old 30-11-2015, 15:11   #28
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Re: Metal plates as thermal mass in freezer?

Quote:
Originally Posted by Djarraluda View Post
I will not intervene in the Grammar wars here, but I used to work with phase change materials, so.....
We mix all sorts of "stuff" to create the phase change at the temp we desire. Often based on the refrigeration we are using, or the effect we need. Not all of these eutectic fluids are equal in terms of user friendliness and some are hygroscopic. Be careful what you use around food.
I will identify that Ethylene Glycol is toxic, causes liver damage etc etc. I know it breaks down relatively quickly, but becomes acidic as it oxidises, strips paint and so forth.
For use in proximity to foods, we use Propylene Glycol.
It is more expensive, but then most food grade products are.
It is safe to use around food, so if your container leaks, then it does not cause an issue.
You are'correct'my fingers and brain were not awake and I was still waiting on my coffee I meant to say Propylene Glycol.
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Old 30-11-2015, 16:42   #29
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Re: Metal plates as thermal mass in freezer?

It seems that the consensus is:
1) More isolation? Yes.
2) Liquid that freezes/melts just above the target temperature range? Yes.
3) Metal? Not as good as liquid.

I note that OP has used salt water, and it has frozen. That solution might already be close to ideal. Does anyone know how the characteristics of salt + water differ from propylene glycol + water, Arctic Tundra (whatever that is), or alcohol + water?
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Old 30-11-2015, 17:18   #30
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Re: Metal plates as thermal mass in freezer?

Actually IMO the main reason to use propylene glycol vs salt water is what the solution does to the container metal doesn't like salt if you are using your own non Metallic containers I see no reason not to use saltwater in the correct solution for the desired phase change point. It would definitely be cheaper than glycol. Lastly in my experience alcohol doesn't like to freeze it tends to try to separate itself from the water in solution. YMMV
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