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Old 17-06-2009, 15:36   #16
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They are from a book I am writing about marine refrigeration. It is still a work in progress. I would love to have comments on it.
My plan was to find a way to distribute it for free and this seems to be the place. I would like to attach it but it is 3.4mb in PDF format. If anyon wants a copy of it I will find a way to make it available.
How refrigeration works is not very well understood by the cruising community. What the design parameters are for an energy efficient system is less so.
A system that a person handy with tools that can be easily and inexpensively built and repaired using over the counter parts obtained in Latin America is what I set out to do.
An article in Cruising World, March 2006, The Log of Ithaka, by Douglas Bernon describes the designing of and building one of the earlier systems I built while in the San Blass. Made a lot of mistakes but we had a lot of fun. Going for parts was even more fun.
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Old 17-06-2009, 16:01   #17
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I'd love a copy of your book. I won't have time to rebuild my fridge till I hit the Caribbean later on this year and the advice would be invaluable.
Thanks
Marno
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Old 17-06-2009, 23:11   #18
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Cold Holdover Plates, Problems of Design and Use of

As the eutectic melts the eutectics freezing point is rising. The eutectic point is not a precise point such as 32 F for ice. It is a range. Less cooling occurs and the box temperature rises.

mesquakkee
How does your statement jive with Glacier Bay’s explanation ?
Eutectic Solution
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Old 18-06-2009, 00:40   #19
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Mesquaukee, Please sign me up for a copy of your book.
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Old 18-06-2009, 01:03   #20
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Opps, need a rewrite. The defination of an Eutectic has been mangled.
Both Glacier Bay and I have erred.
Water has never been and will never be an eutectic. Quoting Glacier Bay "Distilled water completely freezes and thaws at 32 degrees F, therefore water is a "eutectic solution" ".
By definition an eutectic is composed of 2 pure substances. The eutectic point is the point where the temperature stays constant during freezing or thawing just as Glacier Bay states. It is also the lowest possible temperature at which any combination of the two substances will freeze. It is a very precise blend of the 2 materials, any deviation from it and it will not be an eutectic.
It is possible to have 3 materials exhibiting a constant freezing point, I believe Portland cement is an example of this.
True eutectic solutions that have an eutectic point that would be useful to us boaters are extremely rare, that is why they are proprietory and generally expensive.
It is common, as I have, to refer to mixtures of water with various salts as an eutectic solution if most of it melts over a relatively narrow temperature range. Once again like an eutectic a very precise amount of a salt will give a solution which is "almost" an eutectic.
Most commercial cold plate systems use these types of solutions
The example of propylene glycol (plumbing antifreeze) and water that Glacier Bay uses is a very very bad example of what is commonly called an eutectic. No one in their right mind would consider using this mixture, it is entirely useless. I have no doubt though a cruiser somewhere has and is using it.

Good to see someone is paying attention. Thanks.

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Old 18-06-2009, 03:10   #21
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I was so embarrassed for misusing the technical term Eutectic that I missed a vital point.

If you plan on using an engine driven compressor or running a generator periodically you are not concerned with energy efficiency so you need not read further.

If you are running your compressor off of batteries do not use a cold holdover plate system. You will use significantly more Ahr/day, approximately 50-100% or more. This is discussed at length in my book along with the supporting engineering data.
You need a temperature differential to move heat, this translates into a pressure differential (pressure is temperature).
In a cold h/o plate system you require a,
1. Temp diff between the refrigerant and freezing point of the cold h/o plate (press diff)
2. Temp diff between the cold h/o plate and the far side of the box. (press diff)
The sum of these 2 temperature differences is significantly higher than that of an evaporator plate that fits your box. This means that a cold h/o plate system needs to be run at a much lower pressure then an evaporator that is built (a do it yourself project) to fit your box.
Lower pressure means less cooling capacity (BTU/hr) and lower mass through put( lbs/hr) of the compressor, they both conspire together to yield much longer run times. The amperage draw is a little less but does not even begin to offset the reduction in capacity.
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Old 18-06-2009, 03:44   #22
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Cold Holdover Plates (Tanks)

And lets not forget about the space they take up and the weight.
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