Any refrigeration experts out there?

No, assuming the working fluid when through a phase change, it will melt at a constant temperature. The OP indicated -40 degree refrigeration requirement for his cold plates. These store "cold" in the form of a latent heat phase change of the working fluid internal to the plate. It will only increase in temperature once all the working fluid has melted. And only then as a function of the many materials specific heats, and weights, and heat source being added. ignator

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ignator
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And just like ice banking for commercial air conditioning to save money using 'off-peak' power to make ice overnight and the ice melt cools the building during the day, that brine phase change cold plate will work fairly well if you need a continuous low rate of cooling but can only supply refrigeration in high-rate bursts because of a restricted power supply - which you would see on a very small vessel like a sailboat, or a small cabin off the power grid.

You'll get solar cell input during the day (but not much), and wind energy when the wind blows fast enough to turn the turbine - and not so fast it trips off the safety and stops. But you only get real high horsepower refrigeration work done when you start a generator set or a propulsion engine, or stoke a boiler and use steam generation, or...

And because of often restricted fuel supplies or the need to manually monitor the prime mover (stoke the boiler) you can't do that

24/7, so you 'bank the cold'. Or you put in a Servel / Dometic ammonia absorption refrigerator and let a small gas flame supply the slow and steady energy input.

But a larger yacht or commercial vessel doing a 5-day run doesn't have nearly the power restrictions as a 18' sailboat trying to do 30 days between ports. You have to be power efficient, but either the main engines or an auxiliary generator set are running most of the time. In that use, IMNSHO the brine plate is going to be FAR more trouble than it's worth.

When you have to fix it yourself with only the supplies and materials on hand, there is one rule: KISS. Keep It Simple, Stupid!

A properly sized 12/24V to 120VAC inverter system (example go look up the "Heart Inverter" perfected in RV use) and a large battery bank can provide seamless switchover between onboard and shore power sources - and a few hours of overnight silence if needed. The inverter can even auto-start the generator when large loads come on or the batteries discharge, then shut it down again when the load drops and the batteries are full.

And if the "Magical" inverter system craps out or the battery string goes flat or open, you thought ahead and built in a bypass. Just throw that big switch and go straight from the generator to the breakers.

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Reply to
Bruce L. Bergman

My point was that R. J. Kinch said "Brines or other fluid mediums cannot work as well, because their temperatures rise as they absorb heat" And my response was that, the melting point of the brine or glycol will result in a constant temperature until all of it is melted.

I've been on sail boats with cold plates, and running the diesel for 2 hours plus twice a day is a PITA. Not to mention that you end up with a solid block or frozen mass that you have to wait to defrost to gain access too, or too damn warm. My last sail had a 12 volt refrigerator, at 5 amps, using battery most of the time and we only ran the diesel long enough to get the amp meter charge down to full enough. The only problem was the Moorings rental either hot wired across the thermostat, or the contacts were welded closed. We cycled the breaker when ever the frost built up a few millimeters. Evidence that this was a problem was two repairs to the evaporator plate where some previous renters used a knife to "defrost". This was the first time sailing that ice would remain frozen as the previous sails, the cold plate either froze everything or the ice melted away. I agree that electric refrigeration is much better. Also Moorings had air conditioning installed in their latest boats, but only ran on shore power, but when your loading provisions, the crew don't get so damn cranky. ignator

Reply to
ignator

Listen: fluid mediums. They're not changing phase.

Ice directly against a cold plate works better than an ice/water bath. The liquid water is merely adding thermal resistance to the heat transfer, not sinking heat itself.

Reply to
Richard J Kinch

My understanding of the construction of the cold plate with phase change storage media is refrigerant tube ways, conducting the heat from the to metal (aluminum) with phase change storage media in the same plate, as all the same structure, there is no air gap. This plate is install in an insulated "ice chest" that has the door on top to limit the cold air flowing out like a standard refrigerator. Yup the plate is surrounded by air, and any thing in contact with it, like a bag of ice. The idea is this plate has a long off cycle between recharging (re-freezing the phase change energy storage media) via the mechanical refrigerant system. Like a refrigerator, you don't want some foods to be in direct contact with the evaporator, unless you like frozen salads. You don't want everything in the ice chest to be in good thermal contact with this cold plate evaporator. ignator

Reply to
ignator

The real problem with this whole thing is this -40 bit. Assuming sea water gives you an equivalent condensing temperature of, say 70 F, which may be very optimistic, then you need a temperature differential of 110 F. While single-stage systems can be built to do this, thay are insanely inefficient. A good home air conditionr can achieve an EER of 10:1 or better. You would be lucky to get an equivalent efficiency of 0.1:1, meaning you will expend many HP to get a TINY amount of cooling.

You would do far better to pull the Peltier coolers out of 4 or

6 in-car coolers and add a couple deep-cycle batteries to power them between recharges. You could also get a battery protector from the solar outfits to shut off the coolers when the batteries run low. My guess is this system would be several times lighter, maybe more efficient by a factor of 10 or so, and less expensive as well as less space-consuming! With multiple Peltier coolers, it would also be redundant, and the salt mist makes anything on a boat less reliable, so that has to be a big advantage.

Jon

Reply to
Jon Elson

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