Eutectic plates

[Nookymonsta]

Hi guys, first up let me say I know very little about refrigeration apart from the principles of it

I'm trying to build my own Eutectic plates for a fridge/freezer which has to deal with very high ambient temps (up to 50c)

I've sorted the compressor side (Going to run a Danfoss BD 80F)

My main concern is that I will be in remote locations for extended periods of time so energy efficiency is critical

I've nutted out the construction of the actual plate but my main issue is the solution. I've read another thread on this forum and it seems most of you guys are using Glycol or salt solutions, my issue with those is that they aren't true "Eutectic" solutions and as such don't have as high a thermal capacity and aren't as efficient.

I've only found two companies in Australia who make such systems and both are hideously expensive and both won't sell their solutions (Or reveal if they are even true Eutectic) solutions

Here's hoping you guys can help me out or maybe suggest somebody who'll supply it to me

[Frikkie]

Glycol or salt solutions, my issue with those is that they aren't true "Eutectic" solutions and as such don't have as high a thermal capacity and aren't as efficient.

I might be wrong but think salt solution can be a eutectic if correct in quantities.

[Peter_1]

Why you think a salt solution not eutectic?
I did the tests long ago with salt, 'the special solutions' from Dupont and glycol.
Mine lasted longer solid !!
Now you.

[Nookymonsta]

Classical and temperature-modulated DSC methods used to study aqueous solutions of NaCl in the whole concentration range and the temperature interval of -120°C to 30°C. New interpretation of experimental data based on the state diagram has shown that transitions observed at temperatures below the melting temperature of ice are glass transitions of two amorphous phases in the system—the maximally freeze-concentrated phase (MFCP) and the solution surrounding NaCl crystals. At low temperatures, these solutions pass into the glassy state. Structure of these frozen solutions is inhomogeneous. It includes at least two crystalline phases and two amorphous glasses. This behaviour is characteristic of diluted and semi concentrated solutions. The solutions of composition close to the eutectic one usually freezes directly into glassy solid; during re-heating water crystallises and a liquid phase is separated with a concentration differing from the original concentration of the initial solution.

[HallsEngineer]

Any mixture where the mixture freezes lower that either on its own is a eutectic mixture so keep going. My advice is to freeze water as this is the most efficient refrigerant known to man. The efficiency comes from the latent energy required to change the mixture back to a liquid. My advice to you is to buy dry ice. Cheap and efficient to -80'c.

[Peter_1]

Classical and temperature-modulated DSC methods used to study aqueous solutions of NaCl in the whole concentration range and the temperature interval of -120°C to 30°C. New interpretation of experimental data based on the state diagram has shown that transitions observed at temperatures below the melting temperature of ice are glass transitions of two amorphous phases in the system—the maximally freeze-concentrated phase (MFCP) and the solution surrounding NaCl crystals. At low temperatures, these solutions pass into the glassy state. Structure of these frozen solutions is inhomogeneous. It includes at least two crystalline phases and two amorphous glasses. This behaviour is characteristic of diluted and semi concentrated solutions. The solutions of composition close to the eutectic one usually freezes directly into glassy solid; during re-heating water crystallises and a liquid phase is separated with a concentration differing from the original concentration of the initial solution.

A whole mouthful of bla-bla-bla. And now in understandable English please.
The whole point, does this change anything for your application? This is pure explained on a scientific base. I'm speaking about practical experience of making this plates ourselves since 20 years.

The solutions of composition close to the eutectic one usually freezes directly into glassy solid; during re-heating water crystallises and a liquid phase is separated with a concentration differing from the original concentration of the initial solution.
This is always the case - even when you freeze pure water - unless you should stir continuously while freezing the solution. Are we then speaking of a temperature difference of 0.1K or 10 K and does this matter for a cold storage application?