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Old 22-07-2020, 15:21   #16
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Re: Compressor replacement

A question about glycol mixture in holding plates. The current set up from prior system was a 5:1 water to glycol mixture in the fridge and 4:1 in the freezer. Even when my fridge was set to low, stuff froze in there. Anything near the plate froze solid and it was extremely difficult to keep stuff like lettuce from freezing almost anywhere. In the freezer, I could not get the temp in there below 23 F an it tended to hover around 28F- too warm. The expansion valves on the system were not adjustable, so I was stuck. Now I am putting in adjustable expansion valves. We are considering a 10% glycol solution for the fridge and more like a 30% solution for the freezer. Same holding plates. And we will be adding additional insulation to the exterior of the box.

Sounds reasonable? It would be nice not to have so much frozen stuff in my fridge. But, I also read that glycol solutions can result in ranges from 10-20 degrees F above their freezing point. I realize it is all a compromise.

I appreciate the feedback.
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Old 22-07-2020, 18:53   #17
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Re: Compressor replacement

The simple facts are:
The expansion valve determines refrigerant flow efficiency. Adjusting these valves is only done to maintain super heat exchange inside evaporator

The thermostat controls Eutectic plate ability to freeze solution by stopping compressor generally 10 degrees colder than eutectic plates freeze point. Running compressor below the freeze point is necessary to freeze solution solid.

Polypropylene glycol is sold in various strengths -35 degrees freeze point to -50 degrees best to test the product mixture you plan to use in a plastic bottle with a pencil thermometer inside. When frozen below eutectic point temperature will very quickly rise to eutectic point then rise much slower, unlike water that maintains its freeze point temperature
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Old 23-07-2020, 04:36   #18
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Re: Compressor replacement

Thank you. All of this stuff is slowly sinking in. I am a numbers person and keep looking for a formulaic approach. In discussions with the friend who is creating the system for me, I understand that it is also an art, and apparently one eventually gets the system balanced properly between the glycol mixture and the adjustments on the TXV. Plus we are planning on inserting more insulation on the outside of the box. Simply shooting for a fridge that doesn't freeze so much stuff, a freezer that will keep ice cream solid and a system that doesn't make so much noise that my crew insists on turning it off so they can sleep!
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Old 23-07-2020, 04:45   #19
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Re: Compressor replacement

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Originally Posted by Coolerking View Post
Ill bet you had a Cu-Ni condenser.
Here's a photo of the old condenser pipe. I have tried to find it on the web, but cannot. It doesn't look like CuNi, but I really don't know. I would think that with nickel in there, the metal would look more silvery.
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Old 23-07-2020, 07:54   #20
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Re: Compressor replacement

That is a CU-NI condenser.
The solution in the plates and its specific gravity are tied to the temperature you are trying to achieve in the box.
Buy one of these.
https://www.amazon.com/Antifreeze-Re...dDbGljaz10cnVl
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Old 23-07-2020, 08:19   #21
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Re: Compressor replacement

Would be handy to have, but I just looked for it on-line and cannot get it to Spain for at least a month or more. We have been double checking glycol solutions by freezing samples and testing temps as it melts.
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Old 23-07-2020, 12:46   #22
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Re: Compressor replacement

There is a very important part of building a cold plate that should be pointed out, make sure you have absolutely zero air in the plate, and the walls should be compressed slightly before sealing it up.
I'll post a picture of what happens when you have air in it in a few.
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Old 23-07-2020, 13:30   #23
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Re: Compressor replacement

Why no air, what do you do about expansion?
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Old 23-07-2020, 13:43   #24
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Re: Compressor replacement

A refrigerator professional once told me that he always leaves about 10% gap in the top of a holding plate for expansion.
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Old 23-07-2020, 16:59   #25
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Re: Compressor replacement

Our company builds hundreds of cold plates a year.
Many of the ones you buy from others are actually built by us.
We fab them in house and fill them ourselves.
We compress the plate to leave the outside surface a little concave, the eutectic is literally flowing out of the fill plug when we screw it in.
When it freezes the first time it returns to it's normal shape.
And there it remains until the user decides to open it up for whatever reason, mainly due to the internet magically making experts out of anyone that can read.
And then it explodes.
And then my phone rings.
And on and on it goes.
Anyhow thought you'd like to know how the pros do it.
I have no knowledge on how to build a plate with air in it.
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Old 23-07-2020, 17:41   #26
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Re: Compressor replacement

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Originally Posted by sailing_gal View Post
A refrigerator professional once told me that he always leaves about 10% gap in the top of a holding plate for expansion.
You are correct 7 to 10 percent air space for expansion is correct on Polypropylene Glycol plates. If this was not correct customers I sold over 300 eutectic plates to would have asked for their money back.
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Old 23-07-2020, 19:10   #27
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Re: Compressor replacement

hmmm, now I AM confused! Is it possible tht one of you is talking about true eutectic solutions and the other is talking about glycol solutions?
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Old 23-07-2020, 19:20   #28
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Re: Compressor replacement

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hmmm, now I AM confused! Is it possible tht one of you is talking about true eutectic solutions and the other is talking about glycol solutions?
I was wondering that myself, but even in salt water, any oxygen is pretty quickly used up with small corrosion and as long as the tank is sealed no further corrosion will occur. Water will have O2 in it anyway.
I know that you can take a 55 gl drum and fill it with water, if itís sealed 20 years later the inside will still show almost no corrosion.
55 gl drums of water were used in some home building years ago as heat sinks
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Old 24-07-2020, 00:03   #29
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Re: Compressor replacement

I suspect both are correct. If you fill the cold plate and then squash it so both sides are concave, you are, essentially, pushing out a bunch of the liquid. So, when whatever is in the cold plate freezes and expands, it has a place to go. You essentially have the liquid and a bit of a vacuum in there. If a novice should then open the valve, they would allow air to enter the space and think that there is not enough liquid in there and introduce additional fluid leaving less than a 7-10% space so the thing expands when freezing and explodes the plate.

However, if a 7-10% space is left in the plate without compressing the plate, you have the space there for the liquid to expand upon freezing.

That's my theory at any rate.....
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Old 24-07-2020, 08:36   #30
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Re: Compressor replacement

Through the years different materials and designs were used in construction of eutectic evaporator plates. Earlier designs were produced by truck refrigeration industries where eutectic holdover plates using 14 gauge carbon material inside and outside welded tanks with salt brine eutectic solution inside. What made them more efficient than today's plates is the evaporator coils inside were attached to the tanks skin lowering box temperature faster than the solution could be frozen. Other methods used to stop dissimilar material corrosion evaporators were steel and other chemicals were added to neutralize the brine corrosion. Finally the expansion air space is tank was evacuated and replaced with nitrogen. Many of these eutectic plates used by Crasby and Grunert and others 30 years ago are still in service in blue water cursing boats. They are generally identified by coating of cold galvanizing paint over plan carbon steel and fill plug is welled in.

Eutectic plates in mobile refrigeration need to avoid problems like: Evaporator coil or tubing need to be spaced no more than 2 inches apart hopefully covering entire solution. No solder or brazed tubing joints inside plate if possible. Evaporator coil must be attached to plate inside or wedged against plate sides to prevent it from act with the dynamic motion of boat when solution partly frozen.

When I compared the Brine and Proprietary secret solution plates against Food grade Propylene glycol my plates needed to be fifteen percent larger to be equal to Brine plate performance. Most every one today uses Glycol in eutectic plates because it is not corrosive.

Glycol water mix does not freeze solid like ice water alone. Glycol water mix frozen resembles soft crystals of a Popsicle. Normall a eutectic plate will not freeze solid completely at the beginning because of the thermostat setting, true performance is a couple of days later.
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