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Author: Subject: Mini-Fridge -> Proccess Chiller
CaliusOptimus
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cool.gif posted on 23-9-2011 at 23:50
Mini-Fridge -> Proccess Chiller


I've had my mind on this for a while, but I never thought it would be this easy. The fridge I have was made in 1987 by Montgomery Ward, and it really couldn't have been more perfect for my plan.

Here's the evaporator after about 1 minute of disassembly. There was a little door up top that popped out by hand, and the evaporator was simply held on by a plastic clip in each corner. They were kind enough to leave me some slack in the refrigerant lines too!






One trash can later.... and it's complete! Aside from my choice in a circulating pump.




This alone could be very useful, but it won't suit me as-is. The first problem I see is the thermostat. The warmest setting has the pure water freezing before the compressor shuts off. I decided to go straight for a digital temp controller. Here's my choice:

http://www.omega.com/ppt/pptsc.asp?ref=CN4000_SERIES

These are very programmable, and when coupled with an RTD probe should suit my needs.

I'm also going to need an easy way to connect my 3/8" OD tubing. Ideally I'll add a pair of spigots with push-to-connect fittings and a valve on each. Unfortunately I couldn't find exactly what I wanted at the hardware store, so that will have to wait.
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blogfast25
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[*] posted on 24-9-2011 at 04:13


One problem I can see is that the evaporator isn't designed for agressive chemicals like acids and bases. It looks made mainly of aluminium. Careful with pitting holes in the refrigerant tubes...



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bbartlog
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[*] posted on 24-9-2011 at 04:18


Cool project, it's always nice to see pics of the home hardware! Curious though: what are you planning to run for so long a period of time that it wouldn't make more sense to just freeze some kilos worth of ice (ahead of time) and plop that in the water? Easy temp control to 0C and really quite a lot of cooling.
Also, I would try to get the evaporator positioned a little bit lower in the can (you have little margin right now for liquid loss of any kind) and maybe tilt it slightly so that chilled fluid doesn't tend to pool on top of it before being carried down by convection. If freezing is a problem, or if you just want lower temperatures, you could try adding enough CaCl2 to make a nice low-freezing brine. Might also avoid the need for a temperature controller, which for most applications (this is going to be used to run fluid through a condenser, right?) seems like overkill. Even if the water around the evaporator freezes into a solid chunk of ice when you use the thermostat you have, that shouldn't be more than an inconvenience so long as the pump is at the bottom of the trash can.
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Endimion17
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[*] posted on 24-9-2011 at 06:30


I'd use this as a reliable heat exchange system for refluxing procedures that last several hours, especially if the reaction flask is large. Just connect the cooler tubing to a small water pump and this bucket. The evaporator chills the water which is circulated by the pump from the bucket to the cooler. It eliminated the worries about adding ice and spilling water.
Those pumps can be found in those $20-50, small, indoor "fountains" or mini waterfalls. You know, that indoor "babbling brook" stuff.
Or, you can buy just the pump. Here's a really cheap adjustable pump. It can go all the way down to 20 gallons per hour (1.26 liters per minute) which should be tolerable for most systems. Only for $14.67 plus $4.95 shipping, weee! LOL :D

Smaller systems could use a 12 V power supply, mini waterfall pump, small styrofoam heat exchanger and a Peltier element.
Huh, now I'd like to try that myself. :)




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CaliusOptimus
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[*] posted on 24-9-2011 at 17:36


@blogfast

i wont be putting any chemicals in there. maybe something to drop the freezing point, but thats it.

@bbartlog

this is on-demand hassle free chilled water for very little effort, and in my case, without touching my wallet. why use ice? is the real question! :)

also, i will add something to lower the freezing point, no big deal, but i still want better temp control.

@Endimion17

i beat you to it on the peltier chiller, and i gota say it wasnt a worthwhile thing. i jumped through hoops to get it going....i machined a little heat exchanger, used a massive heatsink, and i thoroughly insulated the cold side. still it was only able to take a gallon of water from 75F to 65F in about 2 hours, with the water container in open air. this was with a single 120w junction. sure you could add more devices and get some cold water.... but have fun getting rid of all that heat. 10% efficiency just isnt my style. my mini fridge only takes 100w.
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CaliusOptimus
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[*] posted on 24-9-2011 at 21:18



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Neil
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[*] posted on 25-9-2011 at 03:17


Fridges & freezers are designed to operate within there intended temperature range.

Often the material choice for the condenser and expansion lines are made with the assumption the fridge will only be on for X hours and will remain above or below X°.



moding them to run outside of this range often, but certainly not always, opens them up to attack on their plumbing joints which causes rapid premature failure.




Is that duct tap I see on the unfastened switch perched above the water bath...?
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[*] posted on 25-9-2011 at 22:46


I also have a couple of these still operating lying around in the workshop.I was thinking about a similar set up (using ethanol) as a cold trap for vacuum work acheiving maybe -20C ?.Do you think the plate could be bent to a cylinder without damage?
The logic being to maximise plate area to minimum container size and volume of coolant.




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CaliusOptimus
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[*] posted on 26-9-2011 at 17:40


Quote: Originally posted by Neil  
Is that duct tap I see on the unfastened switch perched above the water bath...?


clear heat shrink

Quote: Originally posted by starman  
I also have a couple of these still operating lying around in the workshop.I was thinking about a similar set up (using ethanol) as a cold trap for vacuum work acheiving maybe -20C ?.Do you think the plate could be bent to a cylinder without damage?
The logic being to maximise plate area to minimum container size and volume of coolant.


i wouldnt risk bending mine, mainly because the refrigerant lines are delicate. i do think i could be done though.

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Neil
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[*] posted on 26-9-2011 at 18:07


Ah! Heat shrink is good :D

Make sure you keep chlorides far away from your water bath ;)
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[*] posted on 27-9-2011 at 05:05


Nice work, this is precisely what I had in mind as well - I mentioned it in a few threads a while ago.

But you're in a particularly lucky position with an evaporator that can be so easily moved into the bucket.

I use ice, but it's annoying having to find space for it in the freezer and remembering to refill it. It's even more annoying when the bag runs out in the middle of something.

With regards to the 0C issue, add some antifreeze to the bucket. Use the maximum negative temperature guide on the pack and be sure to measure the two parts, so it doesn't turn into unpumpable slush or solid in the lines and pump.

I also had another idea, which was to drop lots of plastic drinks bottles into the sump. These could be filled with either water or some mixture of water + salt or water + antifreeze to solidify at a specific temperature. By having the solidifying mix in the plastic bottles, you keep the chemicals away from the evaporator and retain a liquid to pump. Squash the bottles a little before capping them so they don't pop, and use a bit of PTFE tape on the threads so the contents is well and truly sealed in place.

You might be interested in the table on this wikipedia page.

Most things that need low temperatures for condensation do not carry much heat with them and even a plain sump of liquid will not change it's temperature all that much.

But, by adding the plastic bottles, you then have a state change, which will absorb an order of magnitude more energy before changing it's temperature.

I can get my freezer down to -30C by leaving the super freeze on for a day or so, which essentially just shorts out the temperature control so the pump runs continually. It's a normal domestic freezer. If your's is from 87, it may not be able to manage -30 but it's worth checking out.

It's worth getting some form of digital controller on there as the standard controls have terrible hysteresis. I keep watching the temperature on my freezer - it's fairly new but uses a standard mechanical control - the temperature will drop to -18C (say) then float up to -16 or 14 before clicking back on.

Remember to use some insulated lines if possible, if only to stop condensation pouring off the hoses.

Congradulations on the cooler! It may not be perfect, but it's a darn site cheaper than the lab ones are new, and not that far off the mark. And it's recycling, see if the government will refund you on capital costs. :D

[Edited on 27-9-2011 by peach]




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Neil
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[*] posted on 20-1-2012 at 10:03


How is the chiller working? I'm most of the way through converting a water cooler but have found that I need to add a cooling fan to keep the compressor from over heating.
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[*] posted on 20-1-2012 at 12:45


Interesting post. I use a converted water cooler/ dispenser to act as a tiny refrigerator, using most of the existing hardware plus extra insulation around the cooler bucket. It can reach -26C. Ideal for cooling small beakers, flasks. Needs a digital controller but currently runs open loop. A fan on the heat exchanger helps in hot weather. I also crank up a disused refrigerator in the garage for bigger jobs - again, you can't get much below -25C, but freezing mixtures can, as Peach says above. And if you have some solid CO2, keeping it in the fridge really prolongs its useful life.

Regards,
Der Alte
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