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Old 02-08-2009, 18:57   #46
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Yes it does
Thank you very much
Lorenzo
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Old 02-08-2009, 19:48   #47
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Quote:
Originally Posted by chala View Post
Not to often someone tell me that I am right, at least it will please some CF members who do not like shinny things.

Mesquaukee, here are some data taken some years ago during an Australian winter in the tropics, a pleasant day with low humidity 25% min., and ambient average temperature of 26C (78.8F)
Compressor was supplied by shore power 240V nominal 0.8A.
Fans 12V dc current 0.22A * 2, ex Amstrad computer. Switching the fans on will bring the high side down by 8C at start up.

Time ..... box temp. Low side .....High side......High side .......Ambient
C/F............C/F.........C/F........no fans C/F.....with fans C/F......C/F
10.54..... 26.6/79.88............................................. ..........28.5/83.3
11.02..... 1.3/34.4.....................59/138.2.........................28.5/83.3
11.11......-2.0/28.4......................................51/123.8......28.5/83.3
11.14......-3.6/25.52.....................................50/122........29.0/84.2
11.16......-4.4/39.92.....................................49/120.2......29.3/84.74

The base load was and is still made of 5 * .75 = 3.75 l of brine at 5% table salt and of 4 * .85 = 3.4 kg of Ice Bricks of unknown eutectic solution. I think the solution must be only water at 144Btu/lb heat of fusion because the bricks swell. I have not been able to find yet the heat of fusion for the above brine.
The change of state when cooling occurred at around -20C/-4F
.............-19.8/-4.18.........-28.5/-19.3.......49/120.2.......36.1/96.98
.............-21.0/-5.8...........-29.0/84.2........45/113..........30.9/87.62
I hope the above did not confuse you too much.

Same load as above but in summer season (wet) ambient average temperature 31C, (87.8F).
Tuesday Start 9.22 box temp. -4.0C/24.8F
Stop 12.01 -21.5C/ -6.7F run time 2.39

Wed. Start 9.56 box temp. -4.8C/23.36F
Stop 11.56 -18.7C/ -1.66F run time 2.00

Thu. Start 10.16 box temp -1.6C/29.12F
Stop 12.45 -19.1C/-2.38 run time 2.29

Running the freezer for 2 ½ hours a day is sufficient to maintain the box at this temperature range. Spreading the run time over the day keeps the range lower. The budget for cooking and charging the battery on our boat (37 feet) using the inboard 5kW generator, no LPG on board, is 2 hours or 4 liters of diesel. The demand on the battery is only for ½ hour. If using the main engine for motoring, there is no demand on the battery and the box can be brought colder than the minimum –21C/5.8F.
Sorry, above time does not include the making of ice and I have never heard of cocktail being cooled by “ice brick”


Mesquaukee your “Colibri” and Fahrenheit make for long editing.



I will try to explain in another post my understanding of this 50%
For a 5% (weight) solution of table salt (NaCl) and water the freezing point is -3.2 C. The density should be 1.038 grams/ml (I am from Canada no problem with metric, imperial or any other unit).
Are you sure it is a 5% by weight solution? From your data it looks like you need 16 C degrees to drive the freezing of the solution based on the numbers from the gauges.
I would guess the latent heat of fusion of a 5% solution would be 95% 0f 143 BTU/lbs or 136 BTU/lb, here we go with the units again, 75.5 Kcal/Kgm.
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Old 03-08-2009, 07:32   #48
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If you could take a household fridge or freezer and add insulation to it that would help however where do you add it. A lot of fridges and freezers use the exterior skin as the condensor. The other problem is the front opening door, the cold air dumps out when you open it, very bad. Also the gasket, that magnetic thing is very thin and has a considerable length, it leaks heat.
So true.
So Lorenzo you have to find a vertical freezer with an external condenser, take off the condenser and turn it into a chest freezer, make your own condenser you also have to make sure that the evaporator follow gravity. Put as much isolation as possible on the outside and if you are not happy with the result put some inside. You get a good box with a door that fit nicely and because it is a freezer and you would not really like to open the door every five minutes, you can make another insulated door who’s top become a chart table and this freezer may work as well if not better than a more expensive kit.
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Old 03-08-2009, 11:01   #49
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Are you sure it is a 5% by weight solution? From your data it looks like you need 16 C degrees to drive the freezing of the solution based on the numbers from the gauges.
It is on my note, they are fairly old but you are right it is looking like 20% of table salt I also experimented with glycol (-12C/10.4F and other) by the way the load also included the making of 2.25kg/4.96lb of ice.
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Old 03-08-2009, 12:33   #50
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O K lets say I either build or reuse a large horizontal freezer box with really thick insulation and with a tight hatch door and good gaskets and that the inside space is about 10 cu ft and that power supply is not critical, I'm running a 20kw genset with house banks of 4 8d batteries, what do you recommend in the way of a cold plate kit or compressor. Bear in mind I'm neither a plumber or electrician but a mere numb nut carpenter, so a plug and play kit would be great.
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Old 03-08-2009, 19:10   #51
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Where are you planning to use it, what is the air temperature in the space, if water cooled the water temperature, do you run your genset once a day, twice a day and for how long, do you have space for 6" or 8" of insulation if you build the box.
An old chest freezer would work, just line the interior walls and floor with 3"-4" of polurethane board, 2" to the lid.
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Old 03-08-2009, 19:39   #52
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Originally Posted by chala View Post
It is on my note, they are fairly old but you are right it is looking like 20% of table salt I also experimented with glycol (-12C/10.4F and other) by the way the load also included the making of 2.25kg/4.96lb of ice.
That sounds better, 20% by weight NaCl is -16.5C freezing, 1.16 specific gravity.
What is the size of your compressor (Model #) and amp draw at 220 Volt and amp draw of invertor at 24 volts?
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Old 03-08-2009, 21:58   #53
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Quote:
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O K lets say I either build or reuse a large horizontal freezer box with really thick insulation and with a tight hatch door and good gaskets and that the inside space is about 10 cu ft and that power supply is not critical, I'm running a 20kw genset with house banks of 4 8d batteries, what do you recommend in the way of a cold plate kit or compressor. Bear in mind I'm neither a plumber or electrician but a mere numb nut carpenter, so a plug and play kit would be great.
Found a website which lists the energy use of refrigerators and chest freezers I foundthat a 10 cubic ft chest freezer uses depending on brand, etc. from 270 to 460 kwattHrs a year in a house. That is from 75 to 135 AmpHrs a day as drawn by an inverter at 85F. Any hotter and the unit way/will run continuously unless you turn the box temperature up.
In other words if you run your generator once or twice a day for say a total of 3-4 hours plus a "little" help from the batteries and inverter it may work withouy any costly conversions if you pick the most energy efficient freezer. You would also need a good air flow through the compartment it is in.
You would need the wattage of the freezer and its monthly or yearly energy use, then you could backtrack to operating hours a day. Then knowing the run time of the generator you can figure out the load on the batteries.
You would need to install a relay on the compresser so when the generator runs the freezer runs continuously, basically you are turning the contents of the freezer into your cold holdover plate.
I knew a guy years ago who was doing this on his boat. He ran his genset for 4 hours a day.
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Old 05-08-2009, 03:13   #54
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Freezer Off

Time..Box temp..lo..hi……..current A……….....volts V…………………ambient
………..C/F……………........fluke..shunt..inv W..inv..panel..fluke..digitor
10.15..-0.7/30.74..1C…….-0.3…0.0..…0.0….25.0..24.6..25.3…………27.5C

Inverter switched ON
…………………………..........…-0.6…-0.15
Freezer ON start current ….-54.4A, no fans
10.25..-.07/30.74..-25..49…-9.4
10.26..-6.6/20.12………….....-7.9…-6.4…160W..24.1
Fans on
10.40..-18.8/-1.84..-26..42…-6.7…-5.2…255W..24.1..23.8………24.3 at bat.
terminals.
10.55..-20.1/-4.18..-27..44….-6.4…-5.0…240W..23.7..26.0………24.3…30.6C
Freezer Off
10.56………………………..-1.7…-0.15…160W..24.5..24.5..25.05..24.9…….
Fluke remnance 0.25A
Average current for ½ hours 6.3A 24V including start up current.
Inverter switched Off: voltage at battery terminals, Fluke 25.18, Digitor 25.0. panel voltage 24.5,
Fluke model 83
Fluke DC/AC current probe 80i-410
Batteries 2 * AC Delco M27MF purchased 11 12 2003,
7.5A 10hrs, 15A 5.0hrs, 20A 3.6hrs, 25A 2.7hrs, weight 24 kg *2.
Inverter Excelsior Power ext 1100/24, 24V, 1100 W, surge power 3000 W, no load current < 0.15A, weight 2.8 kg.
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