Dry ice in the fridge

[Supine Being]

It's always hard to keep the fridge cool on a small boat, especially if you're staying away from marinas and shore power. Packets of ice work, but they only last a couple of days and create a bit of a mess. So I was wondering if anyone here has ever used dry ice? There are companies that will deliver it, and it should last a while linger and create little mess. On the downside, I'm thinking that it might be just too cold for anything that is very close to it in the fridge.

Any thoughts?

 

[VicS]

It's always hard to keep the fridge cool on a small boat, especially if you're staying away from marinas and shore power. Packets of ice work, but they only last a couple of days and create a bit of a mess. So I was wondering if anyone here has ever used dry ice? There are companies that will deliver it, and it should last a while linger and create little mess. On the downside, I'm thinking that it might be just too cold for anything that is very close to it in the fridge.

Any thoughts?

I think I would be concerned about CO₂ accumulating below

 

[Pinnacle]

We used it in the Fastnet race in 1981. It worked. We didn't die!

 

[Jcorstorphine]

I think I would be concerned about CO₂ accumulating below

1kg of Dry Ice will sublime to produce 500 litres of CO2 but it will be evolved over a period depending on the insulation of your ice box.

 

[Border Terrier]

My domestic set up includes 300 ah battery capacity and a 75 thingy solar panel.

With constant and successful use over time, I am confident to leave my fridge on
line while away from the boat.

My fridge is 20 years old with a noisy fan; rather like Maria Sharapova. 'Nough said.

 

[maby]

It will work and, provided your fridge is reasonably well insulated the evaporation will be sufficiently slow that you will not suffocate provided you have a reasonable amount of ventilation.

You do need to handle it with a reasonable amount of care - contact with your skin for more than a few seconds will cause a painful burn and there have been some nasty accidents using it to cool food where small pieces have got mixed into things like ice cream and been swallowed - causing some nasty internal injuries.

 

[JumbleDuck]

Dry ice sublimates at -78.5C. If you want your coolbox to stay at 5C, that means you get the enthalpy of sublimation (571kJ/kg) plus the specific heat required to bring the gas up through 83.5K (83.5 x 0.819[1] = 68.4 kJ/kg) for a total available coolth[2] of 639.4kJ/kg

If you get ice at -10, let it melt and then have the water drain away you have the specific heat change for the ice (10 x 2.1 = 21 kJ/kg) plus the enthalpy of fusion (334kJ/kg) for a total of 325 kJ/kg coolth.

Per kilogram, therefore, you get twice as much cooling from dry ice as from the normal stuff. Volumetrically it's even better: as dry ice is 50% more dense than water ice, you get three times as much cooling from a given volume.

Just two caveats. First of all, it won't be anywhere near that good if you just dump dry ice into a normal coolbox. If you do whole coolbox interior will head for -80C, and the increased thermal gradient across the walls will drive in much more heat[3]. If the outside air temperature is 20C, the water ice cooled version is at 5C and the dry ice cooled one is at -55C on average, you have five times the thermal gradient and, roughly speaking, five times the heat flow in, so your twice as much cooling power will only last 2/5 = 40% as long. You could get round this by insulating the dry ice well so that it didn't cool down the coolbox too fast.

Secondly, cooling wrappings, bottles and so on to -78.5 might not be a sensible thing to do. Brittle materials break easily.

Summary: it would work if done carefully, but probably isn't worth the bother.

[1] cp at stp is 0.819kJ/kgK. I'm guessing it will be roughly the same down to -80
[2] I worked in cryogenics
[3] i.e. let the coolth[2] escape

 

[balladsailor]

When I was a student, back in 1966, I drove an ice cream van. The 'fridge' was a giant cool box that we loaded with dry ice ...... Worked really well, kept ice cream solid all day and there was always plenty left at the end of the day.

 

[William_H]

Still the best bet for the OP is to freeze water in plastic bottles the bigger the better. (comensurate with the space available in home freezer). If the bottles are clean the resulttant water can be used for cooking washing etc. If they melt too quickly then try putting the frozen bottles in an insulated bag then into the fridge.(icebox). good luck olewill

 

[Supine Being]

Thanks for all the replies. Maby makes a good point about the risks of pieces of it getting into food, which I hadn't thought about. I think that plonking a 1kg slab into the box might be too much (JumbleDuck, that is an amazingly detailed reply). I think that I would get the smallest slabs possible and insulate it to slow down sublimation and avoid turning the cool box into a freezer.

My biggest fear would be suffocation, however. Even in summer we tend to have the washboards in overnight and even though we stay ventilated, I would worry about CO2 accumulating lower down. Food for thought, thanks all.

 

[oldsaltoz]

We used dry ice when racing long distance, works really well and lasted a long time. The trick is to wrap the dry ice in some cardboard to control the temperature.

Dood luck and fair winds.

 

[Keen_Ed]

Still the best bet for the OP is to freeze water in plastic bottles the bigger the better. (comensurate with the space available in home freezer). If the bottles are clean the resulttant water can be used for cooking washing etc. If they melt too quickly then try putting the frozen bottles in an insulated bag then into the fridge.(icebox). good luck olewill

How about freezing dry ice into plastic bottles of ice?

 

[Rigger Mortice]

Even if you could get the dry ice into the bottle, you would still need to let the CO2 escape.

 

[TheEcho]

How about freezing dry ice into plastic bottles of ice?

Congratulations, you have just made a dry ice bomb. You can google for videos of the explosion you get.

 

[owen-cox]

1kg of Dry Ice will sublime to produce 500 litres of CO2 but it will be evolved over a period depending on the insulation of your ice box.

But it is highly poisonous and heavier than air. I think it's a very bad idea. I work in breweries and it is a very serious risk there but in a brewery you can smell a beery smell so you know it's there. With dry ice you won't so may just go to bed and not wake up.

 

[RichardS]

But it is highly poisonous and heavier than air.

It's not actually poisonous at all, but it does cause suffocation by displacing oxygen. However, as soon as oxygen is re-introduced, recovery is immediate.

Richard

 

[owen-cox]

It's not actually poisonous at all, but it does cause suffocation by displacing oxygen. However, as soon as oxygen is re-introduced, recovery is immediate.

Richard

Not true. It can kill at much lower levels such as 7% which would not displace enough oxygen to kill.
http://en.wikipedia.org/wiki/Hypercapnia see here for details.

Here is an extract from the HSE website.
"CO2 is commonly thought of as posing a threat to life through asphyxiation when it displaces the oxygen in air down to dangerously low levels. For CO2 to reduce the oxygen concentration in air down to a level that is immediately dangerous to life, the CO2 concentration would need to be in the order of 50% v/v. Evidence shows, however, that CO2 does create an immediate threat to life at a concentration of only 15% in air due to the toxicological impact it has on the body when inhaled at this concentration.
In humans, CO2 is a normal component of blood gases at low concentrations, however, at high exposure inhalation levels it is lethal. In humans one of the most powerful stimuli known to affect the respiration is CO2 and this results in humans being very sensitive to changes in CO2 concentrations. The inhalation of elevated concentrations of CO2 can increase the acidity of the blood triggering adverse effects on the respiratory, cardiovascular and central nervous systems. Depending on the CO2 concentration inhaled and exposure duration, toxicological symptoms in humans range from headaches (in the order of 3% for 1 hour), increased respiratory and heart rate, dizziness, muscle twitching, confusion, unconsciousness, coma and death (in the order of >15% for 1 minute)."


CO2 exposure is also recognised by the HSE as a substance hazardous to health and in likely environments it must be monitored as a relatively low quantity over a long time can cause long term effects.
Personally when you consider it is used to stun animals before slaughter I would not want to encourage the use of it in a confined space like a yacht! I think it would be hard for immediate recovery from passing out while asleep with nobody there to introduce oxygen. But if you want to take the risk go ahead.

 

[Rigger Mortice]

Maybe it's OK on a fully crewed boat that is being worked 24hrs a day but I don't think I fancy risking it on a lightly crewed boat that is coastal hopping.
Apart from that, I wouldn't know how to get hold of the stuff. I've never seen it in the supermarkets alongside the ice.

 

[RichardS]

Wikipedia - "CO2 is an asphyxiant gas and not classified as toxic or harmful in accordance with Globally Harmonized System of Classification and Labelling of Chemicals standards of United Nations Economic Commission for Europe by using the OECD Guidelines for the Testing of Chemicals."

Irrespective of whether Wikipedia is to be believed or not, I certainly did not say that CO2 is not harmful. I have no intention of using it on my boat and neither have I evinced an intention to do so.

Richard

 

[[3889]]

Not advocating the introduction of CO2 in an enclosed space but, unlike CO, it is very unlikely CO2 would cause death whilst sleeping. Very modest elevation will induce hyperventilation which will wake you quickly.
I'm surprised to hear of it's use in stunning animals - I suspect this practice would not meet UK welfare standards and is an economic choice.