Coldest possible home storage - Page 1
Forum section: electronics / projects

author: akis
author_rank: Frequent Contributor
timestamp: October 24, 2017, 10:22:09 am
content: I would like to store some tissue and it needs to be really cold so it lasts. What is the coldest freezer I could potentially buy? My home freezer is set at -23C but that's only good for a couple of months. Is it possible to have a home freezer at, say, -80C which is dry ice territory?The alternative solutions are liquid nitrogen (LN) at -196C and dry ice at -78C.LN requires special storage containers but they leak around 0.2l/day therefore I would need to refill very frequently. In addition because I live in the UK and they typically have their heads up their a*ses, they will not sell or deliver LN to a residential address, only to a business. So, even purchasing the LN will be impossible, and I presume very expensive.Dry ice is great but it evaporates and only lasts a day, so that is not a good solution either. Unlike LN, I can readily buy a 10kg polystyrene container of dry ice for £45 - but it will only last 1 day. I am not sure if I put it in the -23C freezer, how long would it last there. But it will not be very long I suppose.Therefore it seems the best solution might be an electrical freezer but one that can go down to -80C or even lower, if such a thing even exists.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 24, 2017, 10:36:53 am
content: "Lasts for a day" in what insulation? If you want long term storage, get yourself a Dewar at least!If you can't make your own company and/or afford the operating cost of such a freezer, you might consider finding a cold storage company that does. I have NO idea how many of these there are, and how competitive (cheap) their services might be... but I imagine they exist.An electric powered freezer/cryo is still going to be a capital+operating cost, so fits into the same mold. (They do definitely exist!) Get quotes and figure out if it's better than the alternatives.On that note, you can probably find a used or broken one for not too much. Several YouTubers have done so (Applied Science comes to mind, maybe Mike too I forget?, some others I don't remember anymore).Tim

author: amyk
author_rank: Super Contributor
timestamp: October 24, 2017, 10:51:00 am
content: Search for "cryocoolers". They can get far colder than -80C!

author: Jeroen3
author_rank: Super Contributor
timestamp: October 24, 2017, 10:56:29 am
content: Liquid nitrogen does require refills indeed, but it's not "very frequently". You can get subscriptions delivery to get refills every two weeks or so, but it can last longer, depending on the size and pressure of the container.The problem is keeping the containment cold enough to not get overpressure. However, in order to keep something cool with liquid nitrogen, you have to keep it boiling, in other words, escaping.Regulating valves for this will be expensive and difficult to get, which might shorten the length of your supply.Dry ice can be mailed. It's almost the correct temperature for you, and it comes in little grains. I suggest you use this. It's 2.4 euro per kilo in a shop I could find so far.There aren't many companies selling liquid nitrogen, but your local hospital could sell it to you, did you ask them?You can also find multi stage freezer.

author: akis
author_rank: Frequent Contributor
timestamp: October 24, 2017, 11:15:33 am
content: Apparently dry ice is C02 and it evaporates so you cannot store the pellets/slices in an airtight thermos. I was told that I cannot store it in the freezer there is no benefit (I cannot understand it but the dry ice suppliers said so).Even making my own company (which I have), it needs an industrial address, again something difficult to organise. Another chemical company says "we do not sell to individuals or to companies with residential addresses".I have since found there are "laboratory freezers" that go to -80C but cost like £6,500... Maybe a second hand one as you said but it would still be in the many thousands I imagine.That video is great BTW wish this guy was my neighbour.

author: Jeroen3
author_rank: Super Contributor
timestamp: October 24, 2017, 11:20:21 am
content: The evaporation is what makes it cold. If it does not evaporate, it's not cold.Putting it in a better isolated container (a freezer) will reduce the energy available to make it evaporate, thus will make it last longer. In theory.Practice might be that 20 degree to -10 degree do not make much of a difference.I mean, how much faster would water boil when you put the oven 30 degree higher?

author: AndyC_772
author_rank: Super Contributor
timestamp: October 24, 2017, 11:35:57 am
content: Quote from: akis on October 24, 2017, 10:22:09 amAssurance is hereby requested that "tissue" isn't a euphemism for a deceased friend or relative, or some part thereof.

author: max_torque
author_rank: Super Contributor
timestamp: October 24, 2017, 11:39:00 am
content: How big are the samples?Ive successfully used a peltier cooler in a freezer to generate a local, smaller, very cold zone!

author: akis
author_rank: Frequent Contributor
timestamp: October 24, 2017, 11:46:18 am
content: I was just reading about peltier. If you could cascade the hot-cold-hot-cold then maybe the coldest plate might reach the -100C that we require, I was thinking. If each peltier plate can do a 20C difference then with 6 peltier plates and keeping the hottest at room temperature we should be able to get the -100C.

author: cowana
author_rank: Frequent Contributor
timestamp: October 24, 2017, 11:58:14 am
content: Quote from: akis on October 24, 2017, 11:46:18 amThat's that hard part with Peltier elements. If the peltier's heatsink is at room temperature, there will be no thermal difference - so no heat transfer away from the heatsink (meaning it will heat up).The hotter a heatsink is, the faster it can dissipate heat; commonly between 20 and 40 degrees C above ambient is the best you can obtain with high power peltier elements.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 24, 2017, 12:00:02 pm
content: Insulation is everything in long-term storage. Invest on that. Thick polyurethane sheets for house insulation is relatively low-cost. Make all the joins, especially the outside walls, completely air and water vapor tight so that you won't get condensation inside the structure.In theory, if you only store something, and don't need to open it up frequently, then if the thickness of the insulation reaches infinity, the cooling energy required goes near zero.Also, both liquid nitrogen and CO2 ice are just means to store and transport "cooling energy", analogous to shipping a fully charged battery pack. The energy is "put in" when they make the product. Most likely, if your need is long-term, it will be cheaper to do the cooling yourself.If you get the insulation right, the cooling power required is so small that it makes the design much cheper and opens up many possibilities. Just to give you an example, it's trivial to reach -80 deg C using a triple-stage Peltier for about $30-40 in parts, but only with negligible cooling power. But if, thanks to good insulation and "hardly ever opening the box", you onlyneed that negligible power, one of the options would be to run a conventional freezer compressor that can go to about -30 deg C, then two-stage Peltier to get to -80 deg C:Freezer compressor 30W cooling power @ -30 degPeltier 1 10W cooling power, 30W heat generated @ -55 degPeltier 2 3W cooling power, 10W heat generated @ -80 deg.(Using Peltier, a poor technology choice, as an design example since I have no experience with cryocoolers. In any case, I guess they have the issue of poor efficiency and huge cost if you try to get high cooling power - hence the need for insulation!)This can be done in Excel. Get the insulation datasheets for thermal conductivity. Generate an expression to calculate the heat flow from the box, with the wall thickness as a variable; make it calculate the cost, too. Then calculate the cost of the cooling device per power needed (the power escaping through the insulation).

author: Siwastaja
author_rank: Super Contributor
timestamp: October 24, 2017, 12:03:56 pm
content: The issue with Peltiers is that, even if you do everything right, you'll get about 30% efficiency at dT = 25 deg C. And this is quite optimistic in my experience!If you work out the math of multiple stages, you'll find that big temperature differences lead tohugeamount of heat generated at the end of the last stage, while minimal cooling is provided.Think about this approximation:Cool to -80 at 1W: 4W heat generated at -55Cool to -55 at 4W: 16W heat generated at -30Cool to -30 at 16W: 64W heat generated at -5Cool to -5 at 64W: 256W heat generated at +20Cool to +20 at 256W: 1kW heat generated at +45Cool to +45 at 1 kW: possible with carefully designed liquid cooling block and a big radiator.All this needs to be designed in a compact way with extraordinary (probably aerogel required) insulation so that heat from the +45 degC "kilowatt" side does not flow sideways near the Peltier modules.That's why I recommended a standard household freezer as the first stage, since it can do dt = 50 deg C without any issues, at good efficiency, at meaningful cooling power. The Peltier kludge "only" needs to do 50 degC then.Optimum solution would be to use some kind of modified freezer with better suited refrigerant / pressures etc., so you would go lower than -30 deg C. However, I don't know enough about this to help you on this.I have experience on Peltiers, and while totally unoptimal, theycanprovide the required 50 deg C dT (to go from -30 to -80) in a two- or three-step configuration, but that's already pushing the limits.

author: akis
author_rank: Frequent Contributor
timestamp: October 24, 2017, 01:14:48 pm
content: I have no experience with peltiers. Looking at the TEC1-12708 on ebay, it's about 80W and produces, if I understand it correctly, 60C difference on its plates. So we feed it 80W of power, we mount it on an infinite heatsink so the hot side is at 20C ambient, and the other side will be 20C - 60C = -40C. Is that correct? So we have expended 80W of power plus the power we need to dissipate it (fans etc) to try and keep it close to ambient, and for all that trouble we will get a 40mm x 40mm plate at -40C. I cannot assign a wattage on that cold plate?edited the -60C to the correct -40C

author: Siwastaja
author_rank: Super Contributor
timestamp: October 24, 2017, 01:39:29 pm
content: Quote from: akis on October 24, 2017, 01:14:48 pmNo. You'd need to look at the actual datasheet curves.Even assuming that you can get the datasheet, and the Ebay product conforms to it (highly unlikely), you are interpreting the datasheet headlines wrong: as usual, the numbers that sound good seldom hold up at the same time! Instead, the describe different cases.Those specs mean that it provides 60 degree C difference atzero cooling power(think about a perfect insulator at the cool side with a temperature sensor; not very useful!). Alternatively, it provides 80W cooling power atzero delta t, this is not very useful either, except whenstartingto cool down something.Between these two points, it's, at best, quite linear, i.e., if it's good and up to specs, it's going to cool at 40W at 30 deg C dt. But do check the actual curve, it's in the datasheet.Although, the full power (80W headline) is usually not included in the "quite linear" region. So, most likely, you are cooling at about 30W at 30 degC dt. At best.And by the way, to cool at this 30W, you still need to feed it 80W, which means you need to dissipate 110W from the hot side! And dissipating 110W from a 4x4cm area without its temperature rising at all is impossible. So your "30 degree dT" is not actually 30 degrees between theenvironmentand the cold side. Use a very carefully designed water cooling block with extremely good thermal coupling to minimize dT between the Peltier hot side and the environment, and maybe you have 20 degree "real" dT left.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 24, 2017, 02:51:49 pm
content: There may be some "normal" frezers that can run a little colder than -23 C, maybe reach -30 C if you are lucky.With dry ice the consumption depends on the insulation, just like with liquid nitrogen. As the temperature is higher, the heat for evaporation can also be a little higher. So it might be more economic than liquid nitrogen, though refilling could be a bit less simple.

author: Old Don
author_rank: Regular Contributor
timestamp: October 24, 2017, 06:54:44 pm
content: If you go with dry ice or liquid N then be sure you vent the area to the outside. CO2 is heavier than air and can displace air in a layer below which everything dies - pets, small children or adults down on the floor.

author: Jeroen3
author_rank: Super Contributor
timestamp: October 24, 2017, 07:15:58 pm
content: Fair warning, should have been known already though. Nitrogen is called "suffocation substance" (stikstof) for a reason in Dutch.Besides, I was incorrect. Dry ice does not evaporate, it sublimes.

author: max_torque
author_rank: Super Contributor
timestamp: October 24, 2017, 07:58:35 pm
content: AS mentioned, the thing to remember with peltiers is that the heat ejected from the device is the heat flux from the thing you are trying to cool AND the power you are feeding to the peltier to move that heat flux.As they are pretty low efficiency, as highlighted previously, the power drive a sensible amount of heat is large, which then has to come out the hot side!I have found that with a conventional domestic freezer, i could get down to around -35 degC(ish) but at quite low efficiency / power, and then putting multiple peltiers in PARALLEL i could get down to around - 70 degC. By putting the devices in parallel, i was reducing the heat flux through each device to maximise its DeltaT, and relying on the power of the freezer to remove the total heat flux from the system.Multistage Lab / Medical freezers are available, and can pop up on ebay occasionally, and the larger ones can be cheaper as they are less useful to most people than the smaller bench top ones. These use staged dual or triple refrigerant loops, using a different spec fluid in each loop where the average temperature of the working fluid is matched to the high efficiency region of its operation (the phase change point).

author: Zero999
author_rank: Super Contributor
timestamp: October 24, 2017, 08:29:02 pm
content: The problem is, the greater the temperature differential between the hot and cold side of the refrigerator, the more energy is required to move the same amount of heat. The energy has to go somewhere, so it ends up at the hot side of the heat pump. See the Carnot cycle:https://en.wikipedia.org/wiki/Carnot_cycleHow much energy do you need to pump out of the object being cooled?I think the only way to do this is to use Peltier cooler and a domestic freezer, as mentioned above, but you need to be realistic about amount of energy/the size of the object you want to cool.

author: edavid
author_rank: Super Contributor
timestamp: October 24, 2017, 08:44:16 pm
content: You could send your "tissue" to KrioRus:http://kriorus.ru/en

author: Someone
author_rank: Super Contributor
timestamp: October 25, 2017, 12:46:52 am
content: Quote from: akis on October 24, 2017, 11:15:33 amHaving worked with these sorts of tissue storage appliances, they sure do look like regular freezers from the outside. Its common to have dry ice in a large insulated bin but as mentioned above they need appropriate ventilation and safety systems to ensure you don't kill anyone (or pets etc). Carefully stored a dry ice bin will sit for several weeks before its empty.But it probably wont be cost effective to build or buy a storage system for long term use with infrequent access on site, you should look at paying an existing business to store the samples for you as economies of scale favour huge installations (rooms full of freezers) over small ones.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 25, 2017, 01:46:07 am
content: Quote from: Siwastaja on October 24, 2017, 12:00:02 pmBut don't go crazy. Infinity is very big indeed, and needless to say, you'd also need infinite time for it to reach equilibrium.How fast does it go down, anyway? In fact, for a generally spherical sort of object, it goes as 1/r (and only worse for pointier shapes). So you have diminishing returns for OD >> ID. Choose the best insulation you can (vacuum dewar, foam, aerogel?), as that's your bigger challenge, once you have enough thickness.Tim

author: cdev
author_rank: Super Contributor
timestamp: October 25, 2017, 02:04:18 am
content: Are you planning on cryopreserving living cells? Like an unborn child's future umbilical cord blood (contains lots of stem cells) or doing cryopreservation experiments of some kind?Just curious.

author: technix
author_rank: Super Contributor
timestamp: October 25, 2017, 05:33:49 am
content: I think you can buy LN2.You can keep your frozen items inside a vacuum flask with LN2 in it. This way you can keep it at a nice cool 77-80 Kelvin for a few weeks, with a high quality vacuum flask at least.

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 25, 2017, 05:46:34 am
content: Maybe check with the overclockers who build refrigeration systems for breaking frequency records?http://www.xtremesystems.org/forums/forumdisplay.php?80-Vapor-Phase-Change-CoolingYou'll need a cascade design to get to -80C, but two stages will do it. A single stage with R410a can go down to about -50C, although that requires a special compressor designed for very high compression ratio. (A R152a/R410a cascade is a "hobbyist friendly" first cascade that can use common R134a compressors for both stages.)Not sure what would work well for a second stage that goes down to -80C, but R410a should work well for the first, targeting a mid stage temperature of about -30C.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 25, 2017, 08:09:56 am
content: The problem with stacking peltiers is that each stage needs to take not only the heat from the "load" , but also the waste heat from the peltier below. Ages ago I took apart a Sat-comms front-end that used 3 layers of peltiers to cool the front-end. From memory, the first was about 20x20mm, the second about 60x60, and the last about 200x300mm.

author: BradC
author_rank: Super Contributor
timestamp: October 25, 2017, 08:21:08 am
content: Quote from: NiHaoMike on October 25, 2017, 05:46:34 amEthylene works quite well. CO2 will work also if you add enough argon to stop it turning to dry ice in the evaporator but that turns out to be a pretty tricky problem.R23 is what you really want, but it's not very amateur friendly unless you happen to have either a license or a "mate".Plenty of info on building simple cascades in the overclockers forum. There are some neat auto-cascades also, but they are bordering on witchcraft and unless you've built yourself some decent refrigeration systems in the past probably well past your average skill level.