Disposable Cool Storage

No matter how you do this... "cheap" will not fit its description.

I would start with some simple experimentation and measurement of the amount of heat transfer this flask experiences in a room, temperature stabilized to 25° C first. This will determine if just insulation or active cooling will be needed. You will then have to codify better the nominal conditions of the three months. Keeping anything at 0° C for the three months of June, July and August on Antarctica will likely require heating and not cooling. [I know that's an absurd example but it does make my point.]

The enthalpy of the phase change for ice to water should also be considered as a possibility. Ice and styrofoam insulation make a good combination.

If your entire envelope to work within is that of a one litre flask I see some serious tech issues. Having enough room for the proper volume of insulating vacuum is essential and based on the volume and type of material you intent to chill (liquid or solid).

Of course if you had a single gel cap to chill it would be more feasible than say.. a liter of liquid medicine.

More details. I like the compressed gas idea, but a small pressure vessel? ..define small?

I imagine you'll need a much larger flask. It's an amazing request of you. good luck

The trouble with a trapped gas for cooling is this precludes air travel for this package.

The unknowns in this design is precisely why I recommend testing first. Presumably this chilled drug requires some sterile packaging that itself will be both a thermal mass heat sink and thermal barrier to the drug. Knowing how many Joules of energy it will take to reach ambient temperature and how many watts per difference in temperature will be the only way to properly design this.

Are those watts at 120V or 240V?

Peltiers aren't very inefficient, they are horribly inefficient.

You state no external power supply. What about putting it in another container, any limitations on that front?

What are the environmental conditions for the storage? Inside, outside, arctic, desert?

In addition to these... any human interface limitations during the three-month period?

The closest I can come is with a tiny dc powered compressor, a battery supply recharged by solar cells, cooling a vacuum flask...within a vacuum flask

http://www.aspencompressor.com/Download%20Pdf/IntlApplMfgArticle2009.pdf

http://www.sciencedirect.com/science/article/pii/S1876610215002933

ref...

http://www.electronics-cooling.com/2008/05/2u-rack-mountable-vapor-compression-cooling-system-for-high-power-electronics/

Thank you all for a great response, especially SolarEagle, the name says it all.

The solar power option we will chase up, no point in redesigning the refrigerator.

The storage is for antivenin in hot countries and it would only be accessed if someone got a snake/spider bite.

The phials are sealed and would be cooled and delivered in refrigerated transport.

The main problem is distance/time in an emergency.

I am still interested in whether the latent heat of liquefied gas is an efficient storage means.

Tony

http://www.portablesolarpower.biz/collections/12v-portable-solar-fridge-freezers

Cylindrical Dewar Flask with Handle 1000 mL (Representative photo only) Click to enlarge

Something in a small dewar flask?

A Dewar is designed for much colder material than 0° C.

Redesign it.

Adapt it for warmer temperatures.

Use a different gas.

Discount it completely.

Just a thought.

Is human interaction allowed? Thermos flasks can maintain a liquid at a constant temperature for a very long time.

I'd chill the thermos flask first by putting it in a freezer uncapped. Once the inside surface has reached 0 C I'd put the material in it and cap it.

Then I'd wrap it in bubble wrap and place it inside a large styrofoam cooler surrounded by gel-filled chill packs that are also at 0 C.

Then I'd take a rod-type thermometer and poke it through the styrofoam lid so that its bulb is stuck deep among the gel packs. Periodically I'd check the temperture and if the thermometer begins to climb above 3 C I'd swap out some of the gel packs with cold ones.

Only one stage (I mean a vacuumed container) it might not be enough. See a configuration with double walls that encompasses your container. It would be easier to maintain a 0°C external to your first.

I'm curious what kind of compound needs that kind of temp. control anyway? Presuming that it's already sterile, what type of chemical reactions are you trying to avoid that will occur below 0 and above 5 Celsius?

A common question I ask novice designers... "Do you really need to hold that tight of a tolerance?"

Organs for transplant may be.

No power supply? That eliminates Peltier.

How about putting your flask in the center of a very large block of ice that is wrapped in insulation (styrofoam or something similar). Figure the mass of ice needed from the heat of fusion of water/ice and the R value of the insulation and ambient temperature (I am assuming it is higher than 0 deg C).

I do know that big piles of snow in Boston survived until summer, so the idea is doable.

If the contents are at the desired temperature,the only thing to consider is the heat

transfer from the outside of the vessel to the inside environment.

(Presuming that the outside is warmer than the inside.)

The 3 modes of transfer are conduction,convection,and radiation.

The greater the differential,the higher the transfer rate.

A vacuum effectively blocks convection and conduction,and the reflective layer blocks

radiation,which is why a vacuum bottle is such a good thermal insulator.

The weak points are where the ends of the bottle join together.

If you could enclose the vacuum bottle inside of another vacuum bottle,you could improve the insulation ability even more.

I would suggest a double-walled vacuum container,with a block of Pykrete (14% sawdust,86%water) surrounding it.This will help regulate the temperature to 0 C.

Pykrete has the same melting point as water,but melts much slower,due to it's low thermal conductivity.

I would put this double container inside of a picnic cooler filled with Pykrete,cast into a form fitting mold around the vacuum containers.

Pykrete expands when freezing,more so than water,so allow room for this when

freezing.

Also,the finer the sawdust in the formula,the better.

Storing the container in a shaded area will also extend the durability.

If you simply want to cool something to a smaller extent,try this simple,energy free way to drop the temperature up to 25 degrees F below ambient:

Get 2 unglazed clay containers,with one of them able to fit inside of the other.

Fill the space between them with sand and wet the sand.

Put the article of interest in the inner pot.

The slow evaporation of the water will bring the temperature down to around the

dew point of the surrounding environment.

Keep the sand moist,and you have a simple evaporative cooler.

A native African has a patent on this method,so research it before doing it.

Good luck.

Unless the rate of vapourization can be tightly regulated your drug will need thawing out before it can be used, as you will tend towards the boiling point of a pressurized gas.

I have to add my vote for styrofoam.

Wait until I make one for you.

Huh?

This is an interesting challenge. My refrigeration experience is at the large industrial level, ammonia mostly, so trying to scale it down could be iffy.

You have about 1 ft² of surface area to contend with, and a TD (temperature difference) of about 60dF. On a WAG, the insulation R-value of this set-up might be around 10 (could be better, but I'm trying to be conservative).

Q = (A TD)/R, which comes to 6 Btu/h of heat flow that must be counteracted. Three months = 2184 hr, so this will come to 13,104 Btu over the whole time period.

If you use an expendable refrigerant for this, 13,104/latent heat will give you how many pounds you need to last for the 3 months. For ammonia, as an example, ~22 lb.

That's only one way to go. I will try later to come up with a micro compression cycle to do this.

A vacuum thermos, within a vacuum thermos would have a low heatload....these instant icepacks placed inside the outermost container would work, but for how long is a question that can only be answered in practice....

http://www.uline.com/BL_6705/Instant-Ice-Packs?keywords=cooling%20packs

http://www.odec.ca/projects/2005/tena5t0/public_html/discussion.htm

Cryo-coolers are joule devices often used for cooling IR detectors for missile applications. They are powered only by compressed gas only. They might make a nifty solution to your problem. The only drawback I am aware of is that the nozzles can freeze.

Again thank you for some great ideas, some of which were:

• Using chemical reaction to produce cold
• Using Pykrete, a sawdust/water mix
• Investigate organ transplant boxes
• Using missile Cryo-coolers, I couldn't find any on eBay but I could buy a book on the subject for $600. Joking aside, it proves it can be done and a chemist friend agrees with that.
• Investigate the conditions of use and the competency of the users

I have some guidelines now: http://www.health.wa.gov.au/circularsnew/attachments/623.pdf

• The temperature needs to be 2-8°C
• It mustn't freeze the contents
• It needs to incorporate a data monitor

I need to find out:

• What price is acceptable
• The usable volume required
  
• The accessibility required and frequency
• What will be done to reduce ambient temperature
  
• What are the normal heat losses in the container
• What gases and cylinders are available, both disposable and refillable
• What suitable valves are available
  
• What the power consumption would be and a suitable battery
  
• How strong the unit needs to be

Thank you for a great response, Tony

Below is a link to a ZEER POT,as I mentioned previously,but I could not find a link at the time.

It is cheap and simple,and can use readily available materials .

They can get down to 4.4 C under ideal conditions.

This will decrease the ambient temperature around the container,thereby reducing the differential temperature,and the heat gain of the storage device.

http://www.instructables.com/id/A-Practical-Zeer-Pot-evaporative-cooler-non-electr/

You could enhance the cooling of the ZEER POT by placing it in an open windy part of the vehicle during transport.

You could improve on this for your purpose by having a third inner pot surrounded by Pycrete,also easy to make,and the Pycrete melting point,like water,is always 0 C degrees. (0 C is the melting point of water,not the freezing point.)

As long as there is a thin layer of water surrounding your container,and chunks of Pycrete,the temperature will be stable.Thus it is self regulating.

All you have to do is make certain there is solid Pycrete at all times.

Temperature monitoring labels are available that can indicate temperature in real time,and also store an event if it goes out of a specified range.

These will allow you to monitor as well as indicate if the contents have been out of the desired range.

These labels require no power.

Link:

http://www.coleparmer.com/Category/Irreversible_Temperature_Labels_Indicators/6371

I am sure there are cheaper ones available,but I did not do an exhaustive search.

The company might even donate them to your project if you let them know the purpose.

For an audible alarm, a reed switch and magnet inserted into a hole bored in the Pycrete could trigger an inexpensive piezo chirp or buzzer,or LED.

If the Pycrte melts, they would fall out of alignment,and trigger the alarm.

Good luck

Speaking of ZEER pots, there are also BEER baskets. I have seen them in Africa used to chill and store beer. They are woven straw baskets that leak until they become wet with beer. Then the fibers expand, and the leaking almost stops completely. A small breeze is enough to promote evaporation and cooling.

I'm thinking using liquid nitrogen somehow. It is already used in to store cell cultures and tissue samples at -196 degrees, and it is readily available commercially. It lasts weeks in a very well insulated container.

If you put it into a sealed pressurized container, it could be kept at room temperature, and by releasing nitrogen gas from the container, it seems like you could adjust the container to any temperature between -196 and ambient temperature.

If the nitrogen container could be put into another insulated compartment inside the flask, maybe it could be used to keep the contents of the flask between 2 and 8 degrees, by automatic, controlled release of the evaporating nitrogen gas.

All that nitrogen has to escape somewhere. A few in a large warehouse wouldn't pose a threat. A couple thousand of those farting boxes in a semi trailer, and you might have to live up to your username!

That's right. We used to have a few of the big ones in a room in our lab, but there was good ventilation and they didn't actually outgas very fast at all, so I never had to keel over to let people know that the nitrogen had built up.

A warehouse full of them with poor ventilation would be a problem. I'm thinking though that if they are specifying a small, 1 liter flask, then they are not talking about mass storage. If they were they would just use a refrigerated warehouse at 2 - 8 degrees, or a refrigerator. Sounds like they need something portable.

Thank you Canary

I'm investigating available small cylinders in nitrogen and carbon dioxide and suitable control valves.

Tony

The devices are known as as Joule-Thomson coolers. They work with almost any gas if the gas has an appropriate J-T coefficient. This would include oxygen, nitrogen, etc. This means that the vented gas could be scuba air, which is not toxic, even in large quantities. The only gas you should exclude is water, because it can clog the gas passages.

The various expendable liquid/gas ideas have the advantage of simplicity, set off against the need of regulating temperature to avoid freezing the antivenin, and the weight of refrigerant required for the long term.

A closed mechanical compression/evaporation cycle could also be promising. A small bellows could serve as a seal-less compressor, coupled to evaporating and condensing coils of simple tubing.

For what it is worth, as a safety regulator, may I suggest that...

Before you spend allot of time working on any system then vents any type of non breathable gas, talk to a safety regulator in the target jurisdiction to see what they think of this idea.

Any device that lowers oxygen concentration in any type of closed area... say a vehicle for example, may be very much frowned upon.

I would hate to see you expend all sorts of effort coming up with a real cool gas based system only to have it shut down by the regulators.

From Perth I look at anti-venin as a worthwhile project.

It seems to me that air is the optimum refrigerant, it cooled Australia's first export fresh meat exports in 1879 and for air conditioning all todays airlliners.

With some 600ml of water/ice,a week between chilling seems likely.

A nylon or PTFE tube coiled around the anti venin capsules' enclosure with both ends through the dewar's lid will deliver the cooling required to refreeze the Water to ice.

The compressed air, via an appropriately chosen capillary (outside the dewar) can come from any convenient source.

Moisture in the air has to be considered, it can be desiccated, trapped or perhaps not freeze onto the tube's bore.

Deciding when to start and stop the chilling could be by the water temperature rising above zero (only a few hours to 5 C). The stop signal can be taken from the exit air's temperature which will fall as soon as all the water is frozen solid.

The expansion on freezing must be allowed for by the water being held in a latex bag centered by resillent packing.

Zaf and HiTekRedNek

Zaf, I was interested in air refrigeration, is the air at ambient temperature and what sort of pressures are we talking. If you have any references, I'll follow them up.

HiTekRedNek the pots were very interesting as were the labels and I learnt something new. I'm unsure if human intervention aspect and the performance in humid climates would be acceptable, we can experiment.

Thank you for your contributions. Tony

A note about the pot:

Their temperature can never go below the local dew point.

Sorry for the delay in my reply. I would contact the department of mechanical engineering at your university,they should be able to dimension the capillary and heat absorbing coil also the heat dissipating area between compressor and capillary. You havn't given the likely route and destination for this antivenine so your source of air could be anything from 10 to 1000 psi and the tubes' diameters chosen accordingly.

The water evaporation approach seems to be best used to minimize heating of the ice, extending the refreezing intervals. See Coolgardie safe, they were still in use in 1953 when I came to Perth. The compressed air could also be stored in a tank/bottle cooled in a Coolgardie safe improving energy efficency.

For storing numbers of flasks a 0C fridge seems logical. Happy progress!

Thank you Zaf

I've currently passed the information to PhD student who is trying to obtain funding. CO2 seems to be the simplest and as it can remain liquid at ambient temperature would seem the logical starting point.

Tony

Have your student research the endothermic reaction of water and urea(cheap).

I observed this very chilling reaction while working on the farm as a kid,rinsing out a

bucket where ammonium nitrate had solidified.

A simple drip control for the water and consequent cooling could be a medical I/V drip bag with a pinch regulator.

Once the amount of water required is determined,the rate should be fairly constant.

This combined with good external insulation and high thermal mass could be the economical answer you are looking for.

The resulting by product can be used as plant fertilizer.

Hi Tony,

A further possibility is LPG. Plain venting would be hazardous but flaming off could remove the hazard. The gas could be fed into a bag for later use (WWII petrol substitute style).

May the funding flow to the project.

Tom.

What are the size constraints of the container?Are you limited to the size of the thermal flask?

Presuming that you are not constrained by size,then a layer of carbon,in the form of compressed graphite will give a large thermal mass.

Carbon has almost twice the specific heat of water.

Put the flask in close intimate contact with the carbon to create as much surface contact as possible.

Now we need to stop radiation,conduction and convection from raising the

temperature of the carbon,and consequently the flask.

The outermost layer should be reflective,like perhaps Mylar or aluminum foil.

Then a layer of paper,then Mylar again.

I have found that alternating layers of aluminum foil and newspaper are surprisingly

efficient as a thermal insulator.(A serendipitous discovery when making a home made

capacitor for a small Tesla Coil.Even when exposed to high temperatures,the paper

will char and still function as a good thermal insulator).

Follow this by a layer of expanded Vermiculite(relatively cheap),which has a thermal conductivity of .021 W mK.

Or the more expensive Micro Therm,which has a thermal conductivity of only .04W mK.

Although used mainly for high temperatures,it is efficient down to cryogenic temperatures as well.

Good luck in your venture.

http://www.microthermgroup.com/high/EXEN/site/hightemperature-insulation.aspx

Thank you Tom and HiTek

LPG has been considered for about 3 minutes, I can imagine the lid being removed so they can make a cup of tea. At least with a CO2 leak they would die quietly.

Thank you for the insulation info. Regarding size, I'm still waiting for feedback, but my understanding is a 1Lt flask would be adequate.

Tony