Fridge holding plate

[DaveAlpine]

What is the liquid make up eutectic fluid within the holding plate? I need to replenish the liquid after a leak and completing repairs. Can I use the liquid from freezer packs or can I make up the solution with anti-freeze?
Thanks
Dave

 

[pvb]

You should use...

You should use a solution of propylene glycol, which I believe is non-toxic, in water. You shouldn't use car antifreeze. The solution strength should be such that it freezes at about -5 deg C (for a fridge). You could probably use the liquid from freezer packs, but this might just be salt in water, in which case there could be an added corrosion risk.

 

[Talbot]

This should be a special refrigerant, and should be no airlocks. If yours is not working due to lack of refridgerant, you need to establish what was in the system, as the new non-cfc ones are not compatible with the older stuff. Get the markings on the plate AND the compressor, and ask penguin or one of the other fridge people.

 

[Anonymous]

Re: You should use...

I want to add a eutectic holding plate for my fridge - do you know where to buy the propylene glycol and any suitable containers - or maybe I would be best to buy a ready-made one?

David

 

[pvb]

It may not be that easy...

Holding plates are basically a sealed vessel containing a liquid which freezes at a lower temperature than 0 deg C. A coil of pipe runs through the liquid in the container, carrying refrigerant. The holding plate is best made from stainless steel so, depending on the tools available to you, this might not be a DIY job.

 

[pvb]

The liquid isn\'t refrigerant...

Refrigerant runs through the coil of pipe inside the holding plate, cooling the eutectic liquid. The liquid itself is relatively simple stuff.

 

[Anonymous]

Re: It may not be that easy...

[ QUOTE ]
A coil of pipe runs through the liquid in the container, carrying refrigerant.

[/ QUOTE ]I haven't come across that sort before. I presume that the eutectic effectively surrounds the evaporator?

Around 30 years ago my father bought one that simply sat on the shelf of a domestic upright freezer and it worked fine - within reason. I have a freezer/fridge that was constructed by the boatbuilder and is cooled with one of the Danfoss compressers with keel condenser and seperate evaporator. At the moment we have it so that the bottom of the box is at around -10C and the top is just on freezing. While there is plenty of cooling power the controls and the layout make it pretty unsatisfactory for the cook. I was wondering whether to put a large eutectic in the bottom section leaving a smallish lower freezer and a large space above cooled mainly by radiation and conduction through the bottom. In which case I would need an odd-shaped holding plate but without any refigerant tubes passing through it. I'd need to be able to source the eutectic material and a suitable container which, as you say, could be made locally out of stainless.

 

[Ships_Cat]

It could be one of a number of fluids, but if you have any of the fluid then it should be easy for someone to identify it. It may be a proprietory true eutectic fluid produced by the refrigeration equipment manufacturer and which will give a longer holdover, or a simple anti freeze such as solutions of propylene glycol, calcium chloride, isopropanol or methylated spirits which are not true eutectics.

I would assume that one could use any of these for complete replacement but may need the expansion valve superheat adjustment altered (however, I am no refrig engineer). We use 40% meths/60% water - if used propylene glycol is, I believe, typically 10% in water.

Anything poisonous (eg car anti freeze which is often, but not always, ethylene glycol) should not be used.

John

 

[Graham_Wright]

Re: It may not be that easy...

Penguin told me that holding plates need to be vertical otherwise any air inside would insulate the eutectic mixture from the fridge contents.

 

[DaveAlpine]

The holding plate is stainless steel and custom made containing coils from a 220v danfos compressor when mains is available and from an engine driven compressor when charging batteries at sea or at anchor. As it is custom made there is a filler plug at the top.
Thanks for the comments made from which I will make up a liquid from what is locally available - the local distilleries produce "pure alcohol" - I have never known quite what to do with it apart from the painless dispatch of Tuna rather than blood all over the cockpit! I'll make up a solution by trial and error with a thermometer that freezes at between -5 to -10 C and see what the results are.
At least this should be non-corrosive and non-toxic!
Thanks to all
Dave

 

[Ships_Cat]

I should have mentioned that we use 40% meths (well that is the % I was told, I did not personally mix it) in a freezer that holds at -18C, so I would assume that for a fridge less alcohol will be needed.

Don't drink too much of it.

John

 

[Anonymous]

I feel a bit nervous about this....we don't seem to have had a definitive answer yet. Some mixtures might result in expansion during freezing/thawing and ruin the metalwork and others might not perform very well. Here is a link to a manufacturer's web page that helps to explain more.....

http://www.glacierbay.com/Eutectic.asp

 

[DaveAlpine]

Thanks,
I was concerned about expansion and possible damage. I was planning to leave about 5cm at the top of the holding plate to account for some expansion.
The graphs on the link leaves me feeling that plain water might be almost effective as dabbling with making up other solutions.
Agree no real answer yet and as I won't be doing anything until next weekend, maybe somebody will come up with a better "solution"!
Dave