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Semi-Disposable Package Heater

For transport of cold-sensitive cargo
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Sending things to places is at an all-time popularity high. Many things, like pencils, can be confidently shipped with minimal regard for any potential temperature swings*. Other products, such as perishable food or lab supplies are shipped cold, packaged in an insulated box with plenty of dry ice. So long as your package arrives with any unsublimated CO2, you know it has been at -78C for the entire journey**. Dry ice is a robust solution that maintains temperature with 100% reliability and no mess.

There are, however, situations where minimum temperatures must be maintained. For example, if you wanted some pretty blue shrimp sent to you and the 1000 miles between origin and destination averages -15C. Here, the thermal buffering capacity of water and styrofoam insulation help, but often not enough. Some mitigate the problem by adding small disposable, chemical heating pouches designed for gloves etc. but these are unregulated and success is guesswork.

So, a niche has been identified. What we need is temperature regulation. So let's start by solving the problem with the Mk1 bs0 Sure-Temp Package Cosy.

Simply take a PID temperature controller, an RTD sensor, a 25W silicone-encased heating element and a 3-cell Li-Ion pack of about 20 AmpHr capacity. Link it all up with a voltage-regulator & charging circuit, a microcontroller with logging, possibly wireless data. Done. That was easy! I reckon you could mass produce that for less than $150!

Ok, so accounts & sales aren't happy and FedEx has vetoed the extra lithium cells. Let's iterate with a little value engineering. Take 2 alkaline cells. A positive temperature coefficient (PTC) heater and a switch. Done! That get's you ~20 hours of 2W heating, which inside insulation should be good. Getting PTC at the right range accurately isn't easy, or at least easy and cheap at the same time... but we're on the right track with the rest.

We can lower cost with a dumb heater if we get the sensing/control done reliably. For this I'm going with a wax-motor thermistor type doodad. Wax is reliable, like dry ice, you're relying on a fundamental physical property of wax&temperature. Wax expands, moves potentiometer, current to heater changes. The heater is just the cheapest wire available. Then we need a switch***, a low voltage LED and a bit of silicone casing. Done.

You can get fancy, color code various models for 20C/25C/30C and so on, there's applications outside living things, chemical solutions that precipitate etc. For safety, maybe add a tiny PTC thermistor to the heater to prevent thermal runaway, which isn't spectacular with standard cells. Your package recipient will know by looking at the LED to see if the cells are almost completely done. The key is to keep it cheap, so even the voltage indicators on the side of some cells could replace the LED.

There, someone build and mass-produce this so I don't have to wait for spring.

*keep below 250C or package in nitrogen **if no dry ice remains, add some and leave it for someone more junior to test. *** think a bit of removable plastic between two contacts.

bs0u0155, Jan 03 2020

**** https://xkcd.com/325/
[hippo, Jan 04 2020]

Steamer duck https://en.wikipedi...g/wiki/Steamer_duck
Hotter than your average duck .. ? [8th of 7, Jan 04 2020]

Radioisotope Heating Unit https://en.wikipedi...isotope_heater_unit
Scalable for this application? [Chairborne Hero, Jan 05 2020]

On including animals in the package to maintain a suitable temperature http://www.todayifo...st-soviet-invasion/
mainly for 8/7 [Loris, Jan 05 2020]

Pipefish https://en.wikipedia.org/wiki/Pipefish
They might have been designed for the job ... [8th of 7, Jan 06 2020]

[link]






       // . Other products, such as perishable food or lab supplies are shipped cold, packaged in an insulated box with plenty of dry ice. So long as your package arrives with any unsublimated CO2, you know it has been at -78C for the entire journey**. //   

       "And from that moment on, the BorgCo team working on the design and development of the new Schrödinger cat-carrier box knew that success was assured... "   

       We will bun the idea for the inspiration it has provided, but also because it is in fact a good idea. However, the same effect of a near-constant low level heat source could be achieved, without any wiring, by using a suitably sized block of radioisotope; glassfied waste would be fine, as long as the heat output per unit mass was known.   

       Since the BorgCo design already includes a radioisotope source, little modification is needed.
8th of 7, Jan 03 2020
  

       //could be achieved, without any wiring, by using a suitably sized block of radioisotope;//   

       All we need is a way of modulating radioactive decay at will to match the demands of the changing environment. I've put in a request with the physics dept. marked "action this day". If they can't crack it, I reckon I can put together some kind of pile with reactor-control rod mechanism based on those bimetallic strips that so consistently produce perfect toast.
bs0u0155, Jan 03 2020
  

       Your wax-pellet thermostat is the answer there; have it open ventilation louvres when the cargo reaches optimum temperature. The system will then self-regulate, presuming that you don't get the isotope blocks close enough and in sufficient quantity for prompt neutrons to cause... problems.
8th of 7, Jan 03 2020
  

       This all sounds very complicated.   

       Instead, just use a bunch of those chemical handwarmers (the ones that crystallize and release heat). The handwarmers are usually activated by pressing a rough metal disc - the local stresses are enough to initiate the crystallization, which then propagates thoughout the pounch, releasing warmthness.   

       So, suppose you want your tropical shrimp kept above 25°C. You just need a chemical heater in which the metal disc is replaced by one of those disc-shaped bimetal things, that "pops" when it gets below 25°C. Hey presto, as soon as the temperature falls too low, the chemical heater delivers a burst of heat.   

       Now, a single heater will be a once-only warmer. However, if you put several of them into the polystyrene box (each one capable of warming the water by maybe 3°C), they will all activate at slightly different temperatures due to inherent inaccuracies. So, when the water temperature dips below 25.2°C, the first one will fire, heating the water to 28.2°C. When the water cools to 25.1°C, another one will fire, restoring 28.1°C. Etc etc until all have been used.   

       As a bonus, you can re-set all the heaters by popping them in boiling water, and use them again next time.
MaxwellBuchanan, Jan 03 2020
  

       Which one triggers the mechanism that breaks the vial of poison ?
8th of 7, Jan 03 2020
  

       Cats are widely believed to be homeothermic, and therefore don't require in-transit heating. And no, it's not worth trying it to find out for sure.
MaxwellBuchanan, Jan 03 2020
  

       // homeothermic //   

       Really ? Gay cats ? Who knew, huh ?
8th of 7, Jan 03 2020
  

       Other cats, presumably.
MaxwellBuchanan, Jan 03 2020
  

       Yes, but they tend to keep it to themselves.
8th of 7, Jan 03 2020
  

       //thermal runaway, which isn't spectacular with standard cells//   

       What about standard cells surrounded by a flammable hydrocarbon, such as wax? Would they get more spectacular then?
Voice, Jan 04 2020
  

       Carbon disulphide ?
8th of 7, Jan 04 2020
  

       No thanks, I've just had a coffee.
MaxwellBuchanan, Jan 04 2020
  

       I agree with Max - most animals self-regulate temperature pretty well, so just ship your package inside a larger package which contains a cat, fox, raccoon, bobcat****, dingo, mountain lion, or hyena, depending on the size of package and what animals are locally available and this will ensure a constant temperature
hippo, Jan 04 2020
  

       Technically speaking, most animals are not homeothermic (there are, for instance, an awful lot of nematodes in the world, and a shocking number of beetles). However, including a mammal in the shipping container is a commendable idea.   

       It would be convenient, if shipping tropical fish, to include an aquatic mammal or bird - preferably one not known to eat tropical fish. A krill-eating whale, or even a dolphin (with its beak glued shut) would meet the need. Ducks could be used for small packages, with the bonus of being edible after use.
MaxwellBuchanan, Jan 04 2020
  

       It would be important to select the right species, though; use a Steamer duck <link> by mistake, and the package might boil dry by the time it's delivered...
8th of 7, Jan 04 2020
  

       //if shipping tropical fish,//   

       Why limit this to shipping, by simply building a smaller tank inside my existing aquarium, I could add a suitable rodent and remove the need for a heater. A small tube could be used to supply the creature with the relatively negligable volumes of water they drink, although some sort of valve is advised as starting a syphon could make a mess.
bs0u0155, Jan 04 2020
  

       Rather than using a rodent, you would be better off with a Water Otter ...
8th of 7, Jan 04 2020
  

       You need to think bigger, [bs]. Build a whale tank, and then have a smaller aquarium in the middle for the shrimp and guppies.   

       Whales seem to be a good choice for the enthusiastic aquarist. They don't seem to suffer from ich, and if you Google "problems with pet whales", you get very few hits.
MaxwellBuchanan, Jan 04 2020
  

       PID? RTD?
pertinax, Jan 04 2020
  

       QED.
MaxwellBuchanan, Jan 05 2020
  

       M O U S E
Chairborne Hero, Jan 05 2020
  

       NWAWWASBE   

       // whales seem to be a good choice for the enthusiastic aquarist. //   

       Is there a potential market to be exploited in the breeding and sale of bonsai cetaceans ?   

       After all, there is no upper limit to what aquarium-obsessed fanatics will spend money on, and a 20cm long orca would be a fascinating pet.
8th of 7, Jan 05 2020
  

       //You need to think bigger, [bs].//   

       After a little consideration, I realized that the aquarium seems to be built inside a large tempeature controlled mammalian habitat, strange how I didn't spot that.
bs0u0155, Jan 05 2020
  

       Well, be careful. Some mammals are quite toothy.
MaxwellBuchanan, Jan 05 2020
  

       //if shipping tropical fish// - surely it would be more efficient to deliver fish through the mains water network?
hippo, Jan 06 2020
  

       //a large tempeature controlled mammalian habitat// Planet Earth. You are proposing to set up a parcel delivery company that just puts the parcel on the ground and waits for the rotation of the Earth to carry it the distance required, and then contacts the recipient telling them that their parcel is ready to collect?
pocmloc, Jan 06 2020
  

       We fail to see the flaw in that. After all, it's impossible to be more than 20,000 km from any point on your planet's surface to any other point, which in astronomic terms (even in terms of your own planetary system) is "right on your doorstep".
8th of 7, Jan 06 2020
  

       //surely it would be more efficient to deliver fish through the mains water network?//   

       With a few tweaks, I can see this work. Firstly, the water quality here in the US will need to improve to support life. Heating to 23-24c. Solve the chlorine,Worse, is chloramine. Replace copper piping, it's acutely toxic to the invertibrates.North America is largely a rocky wasteland scraped clean by glaciation and as such there's a lot of dissolved rock/hard water. OK for the African cichlids but most tropical fish will need reverse osmosis on the front end and some strategic re-salting.   

       The last consideration would be the 2-3 paralell systems we'd require to separate the predator and prey fish. Apart from that, we're good.
bs0u0155, Jan 06 2020
  

       //separate the predator and prey fish// Not necessarily. Depending on the diameter of the pipes (and fish), they may not be able to turn around to eat one another.   

       You could probably find an incredibly bony, robust vegetarian fish to use as a buffer between predators and prey.
MaxwellBuchanan, Jan 06 2020
  

       We got your perfect species right here ... <link>
8th of 7, Jan 06 2020
  

       I'm not sure. To a predator, pipefish look an awful lot like breadsticks.
MaxwellBuchanan, Jan 06 2020
  

       Is there a predator that specifically targets breadsticks ?
8th of 7, Jan 06 2020
  

       Yes, although technically it's a weevil. However, imagine yourself as a piranha, confined in a seemingly endless pipe, and with something that looks crunchy and edible only an inch in front of you.
MaxwellBuchanan, Jan 06 2020
  

       //incredibly bony, robust vegetarian fish//   

       Take of the "fish" part, and that's just large snails. Failing that, the common pleco is big, armored and prefers wood to fish.
bs0u0155, Jan 06 2020
  

       // However, imagine yourself as a piranha, confined in a seemingly endless pipe, and with something that looks crunchy and edible only an inch in front of you. //   

       We're doing that.   

       We're starting to feel a strange affinity to Nicola Sturgeon ... very disturbing ...
8th of 7, Jan 06 2020
  

       Who the heck is Nicola Sturgeon? Did you make that up? WHOA - hang on a moment. This could explain something that's been puzzling me. I kept hearing this name mentioned on the radio during the run-up to the general election, and kept wondering why this Nicholas Tergeon never appeared on TV. Now it all makes sense.
MaxwellBuchanan, Jan 06 2020
  
      
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