Ice cream mobile freezer

[raynerd]

Evening
I've got a summer fate coming up and I've decided to make an ice cream box for the front of our pashley trike and try and earn some money for the school. I'll obviously have it then for using on the trike for myself as well. The trike has been my latest project and needs a little more work but is nearly there. I am looking for suggestions as to the best design for a freezer box to run mobile and keep ice cream frozen for at least 3 hours, ideally 4+.

Commercial trike freezers are now 12v mobile units that run on a battery, hidden in the bottom of the unit. However, these run at £1200+ and are far far too expensive for such little use, even if I use it after the fate for my own use (which I won't that often!!)
http://www.veloelectrique.co.uk/wp-content/uploads/VendorX-parasol-frame.jpg

The old pashley freezer boxes were insulated boxes with eutetic plates:


Now this exact one was on ebay for £350. I nearly went for it but decided it was still too expensive. The owner actually suggested I made one as he has in the past. His suggestion was 9mm ply lined with 100mm kingspan insulation board and fitted with 2-3 eutetic freezer plates.

Making my own insulation lagged box would be fun and certainly doable. I'm just not sure how to fit a lid and the functionality of it. If you look at the old ones, they had a master lid and two little openings to limit heat exchange when opening to take ice creams out.

I also don't know anything about eutetic plates other than then being glorified freezer blocks! Are they genuinely better than a stander cooler freezer block?

Do you think the whole design would keep my ice cream cold for 3+ hours? Should the inside insulation be lined again with more ply or aluminium. Would adding a few bags of ice to the bottom help?

The outside box size would be a max of 640mm x840mm and 800mm high. Inside would be big as possible after insulation!
I'm looking forward to the thoughts of the madmodders.

Chris

[awemawson]

 Good insulation and a block of 'dry ice' ie solid carbon dioxide would be much more effective than any electric unit you can struggle to carry batteries for I reckon.

[russ57]

I agree ; 50 years ago,  a canvas 'box'  probably insulated with kapok was able to keep icecream frozen in the Aussie summer for several hours using dry ice.  I'm sure that expanded polystyrene will be far better.  Since cold drops,  I'd not be complicating the lid too much.

[vtsteam]

Yes, like Andrew, I'm thinking the batts would be a concern. Best way to tell is to check the wattage of the eutectic plates, figure how many plates you need, and then plan on them running continuously, which might be likely, even though mfr. says not. Figure your draw, and then work out what batts you'd need, and their weight and the cost of a good charger.

While everybody says dry ice, it's great if you can source it, but uncool if you can't! I think it would indeed be the perfect simple solution, and traditional, too.

[raynerd]

Morning, yes, the issue with dry ice is sourcing it.

I think I should clarify, my plan is to have nothing to do with batteries. The eutetic plates I talk about would be frozen over night and then stuck in the box before the journey starts.

I'll look into dry ice today.

[David Jupp]

Another low tech approach is to use ice sprinkled with salt - salt reduces the melting point, the latent heat of fusion has to be supplied from somewhere (by pulling heat from the surroundings) - this results in a temperature drop.

Might be OK if you can get hold of plenty of ice.  I think I might want to include a small drain in the bottom of the box if using this approach.

[Edited for silly error]

[awemawson]

http://www.dryiceuk.com/  (Next day delivery)

http://www.green-gases.com/ (On line purchasing)

[vtsteam]

I quess we didn't know what was meant by eutectic plates! 

We use similar packs for keeping food cool (but not frozen), and the ice cream maker uses a freezable metal liner/container that is similar to freeze ice cream. Older ice cream makers used the salt and ice method, but that does depend on melting the ice to create the cold temps, so must have a drain and ice additions over time.

I do wonder if any of these will be enough to maintain frozen ice cream over the time reguired. But ye never know til ye try!

I aways like to do a small scale experiment first in this type of thing, to get an estimate for how to build the real thing. It's usually cheaper by far, quick to do, and quantifies things. Plus it's fun.....

[Noitoen]

35 years ago, in South Africa, dry ice was also the method. We used to buy ice cream in the afternoon and beg the vendor for some bits of ice for experiments. Exploding plastic Coke bottles was our favourite pastime  

[nrml]

How about going low-tech and using a polystyrene foam box and frozen hot water bottles (is that an oxymoron? ) as ice packs? They are water tight (no drainage problems like with ice blocks), elastic enough to allow expansion while freezing, come in a variety of sizes and above all are cheap. You can even flog them off on ebay when you are done with them.

[RodW]

Freezers are usually set to -15 degrees will easilly last 3 to 4 hours without opening. Years ago, faced with a house relocation of 700 km, i bought some dry ice and whacked in the top of my chest freezer. I never did it again despite doing similar moves. Just exclude the air with crumpled newspaper.

Agreed however dry ice is the way to go and it won't matter what the container is as it is -196 ○C. But I do remember the old canvas icecream bags packed with dry ice when we had Christmas tree events with no power 90 miles from town as a kid in the 70s. Alternatively, look for a 12 volt Danfoss comlressor and add a car battery to power it.

[RussellT]

I agree the key to this is good insulation but I've had a couple of thoughts that no one's mentioned so I thought I'd throw them into the melting pot to confuse the issue.

At school dry ice was made by discharging a CO2 fire extinguisher into a canvas bag - probably an expensive way to get it but would give the possibility of recharging.

Caravan fridges have freezer boxes and are gas powered and are quite cheap secondhand.  Could you build your box around the works?

Russell

[tom osselton]

Co2 fire extinguisher works well on beer too! 

[raynerd]

Hi guys, I work in a science department and we do discharge a co2 cylinder with a special cap in it to make dry ice. Takes about half the co2 cylinder to make a pellet and is not economical. Cheapest dry ice supplier is £25 (for way too much). You can't store it and having to preorder each day before you went out wouldn't work either. Although it may be the best freezing solution, I don't think its a practical or economical one. Interesting replies...keen to hear more.

[Bluechip]

Hmmmmm

Got a Street Traders License ??

Got a Food Hygiene Certificate ???

Had your Food Preparation Facilities inspected and approved ??

You MAY need them ... 

I don't think it applies for fresh fruit / veg. so radishes on a cocktail stick may well be OK.

DAMHIK.

Dave

[raynerd]

yes, and my mum is on speed dial if anyone gets ill.

street Traders License - NO I'm on private land
Food Hygine Certificate - No legal requirement to sell prepacked ice cream
Area Approved - No, this would be a requirement if on public area and even this is a grey area not always requested by the council.

I do intend to hold a pedlars certificate with my wife so in summer we can sell icecream on hot days in our village but that's a different story for a different day. I'm currently using the ice cream trike to make money for a school...

[joshagrady]

...Cheapest dry ice supplier is £25 (for way too much). You can't store it and having to preorder each day before you went out wouldn't work either. Although it may be the best freezing solution, I don't think its a practical or economical one.

Chris, do welding suppliers in the UK not stock dry ice?  It might be worth giving the local Air Liquide (or similar) a ring and asking prices.  I know that in the US dry ice from a welding place is just barely more expensive than a bag of frozen H2O.

[rowbare]

Your local grocer or fish monger might have dry ice from their deliveries.

bob

[nrml]

Your local grocer or fish monger might have dry ice from their deliveries.

bob

Health & safety / Food hygiene would probably frown upon reusing ice from the fish monger (and possibly the grocer also).