Eutectic plates

Hello all

I have had a request from a customer to provide refrigeration to a box constructed from 75mm cool room panel.

His job is to deliver shopping around town and because of health regs he must refrigerate all perishable food while delivering.

I looked at the possibility of using a 12 volt dc compressor but could not get one big enough.

The customer wants to be able to remove the whole box so it must be self contained.I think the only way to do this will be to use a eutectic plate and a mains powered condensing unit that will be plugged in overnight.

Do any of the forum members know of a eutectic solution that will maintain 2-4 degrees in the refrigerated space.?
(I was told that 1 part methylated spirits to 4 parts water was about right.)

Thanks

Haven't got any real answer for you Temprite but did a Google on 'eutectic solution' and got some interesting answers; maybe worth having a look through there (if you haven't already !).

Is it possible to fit a pukka engine driven cooling system to the vehicle ? They come ready made.

Gday Brian

Had a quick look through yahoo search and found some results but most were for plates for sale and there wasn't a lot about mixtures of solutions.Havent tried google though.

Thought about an engine driven refrig system but this is a toyota hi ace, not much room and the system has to be self contained.The back of the van is open to the cabin so couldnt run the engine in there.

Peter knows a fair bit about this I have read some of his previous posts.I think he uses a salt/water mixture but I dont what strength and the only thing that bothers me about this is corrosion of the evaporator.

Thanks.

Yep, corrosion does seem to be a major problem, some of the google results did discuss solutions and solution strengths.

You could suggest this to your client....
www.chiltonindia.com/products.htm
and click on
Tricycle, UT Deep Freezers
he might need the exercise !!

Hello Temprite,

As you probably know, we have a client who makes vans to deliver perishable foods and large market trucks - mostly 12 m counter in it - for selling on the market.
We make +/-5 vans a year with eutectic plates.

Eutectic plates now...you must use a solution whit it's eutectic point +/- 10K lower then the desired cold room temperature. So in your case, -6° C to -8°C.

You can use stainless steel plates or even iron plates that have to be metalised afterwards.
Use at least a thickness of 1,5 mm, if possible 2 mm.
The inside coil is normal 1/2" copper, holded in the middle of the plate with spacers. We use meranti or oak wood for this. Use 2 oak pieces with a thickness equal at ½ of the inner height of the plates. Clamp them together and drill in the seem of the 2 oak pieces the holes of ½” for the copper coil. After drilling, you then clamp the spacers around the tubes which are then exactly in the middle of the plate and secure the 2 pieces with stainless steel screws. Each 50 cm a spacer.

The spacers also serve as zones when the plates are completely defrosted and the solution begins to move around and makes a terrible noise.

If you want to make them yourself or the work will be done by a contractor, pay attention that they remain as straight as possible. You will otherwise have troubles to attach them on the wall.
If they’re flat installed – like in a counter – they can be longer, we even made plates of 4 m.

When they're standing vertical, make them not higher then +/- 1,2 and a width not larger then +/- 1 m, otherwise the TIG seals will burst open after some time.

Tell your client the following. When freezing the plates, you have to evaporate at at least –12°C to –15° C cool them down beyond the eutectic point. Goods that are stored very close to these plates can become very cold while freezing the plates.
Tell also that a temperature regulation afterwards isn’t possible anymore. The temperature is determined by the eutectic solution. We very often hear the question that they need a temperature regulator on it. This isn’t possible (in some cases)

You need to install an SV after the liquid receiver, energised the same as the compressor or use a pumpdown system. Otherwise at standstill during the day, all the liquid will gather in the plates and this gives ‘strange noises’ when restarting the compressor. You know why.

You can use one TEV and connect al the plates in line. You then use only one plate – the last one- for the superheating of the gas. If you use for each plate a TEV, you then have each time a not used zone in the plates.
You also can use different solutions in the plates and freeze them to that temperature of the coldest plate. After disconnecting power, they all will rise in temperature to their own specific eutectic point.

We tried different solutions – at least 15 - in the freezer and the solution that last the longest is simple salt water, mixed in the right amount.
We calculate the amount of salt, pour it dry in the plates and then fill it up with water. While filling, we make that the plates are a little hollow (+/- 1 cm in the middle) so that they can expand afterwards. Secure the filling taps while the plates are still hollow.
Don’t be afraid of the salt: it preserves very well. They even found copper coins from the middle-ages in the sea. We have the practical experience that it works.
There even exists corrosion inhibitors but we never used it.
And you can sale it to your client as an expensive secret solution J

Removing the whole box you said: be ware of the weight of the plates and the whole system..
There also exists plates (made in plastic and available in different sizes) – we use those of Linum - which he can freeze in his freezer room at –20°C. Once frozen, he then installs them in his van and they increase very fast to the eutectic point. You don’t need a compressor for this and the weight will be lesser. This is only possible for a small space.

So, that’s all I can say for the moment and it covers most of the things we encountered during all these years now.

I don't understand whats the big fuss,
Just install one more compressor in the engine compartment, condenser at the bottom, insulate between the cabin and the back and add a small evaporator to keep the temp.

I like Peters idea but he is a pro in in this field while you need a solution for one vehicle.
The space you need to cool is small, only a few cubic meters.
and with eutectic plates, you still need the space for a condensing unit that rattle all day long when the truck is on the roads. It doesn't help it much.

Check all the options.

Chemi :)

The vans we install these plates are vendors that goes from door to door. So they shut off their car engine when they arrive at the client. They can't let it run continuous because of the noise and the exhaust gasses of the engine.
The van also shakes/vibrates more when on idle speed which is unwanted.

Even if they should let it run, it runs on idle speed and gives almost no cooling that moment.

Further, you need a rather small compressor with plates because you can spread the charge cycle over the whole night while charging on low electricity rates and lower ambient temperatures.
Running on the engine needs a lot more fuel.

Some other systems we installed in the past:
System 1
(Hubbart system of the UK) A hydraulic pump mounted, driven by a belt of the car engine, engaged with an electrical coupling, almost the same they use in car AC.
The high oil pressure from this pump goes to a hydraulic motor in a separte compressor compartment that drives an open compressor. On the pulley of the compressor, there is also a second pulley with an electrical motor so that the unit can be connected to the main power supply. The special item in this system is in the hydraulic pump: it delivers already full pressure on idle speed and if speed increases of the car engine, an internal bypass valve bypasses the excessive oil pressure.
Disadvantage Consumes +/- 1 l more fuel and it’s expensive.

System 2
4 pieces 12VDC batteries of 240 AH connected 2 x 2 as one 24 VDC source.
On this batteries, a 24 VDC/220VAC converter/charger of 2500 Watt combination from Victron (The Netherlands) or Mastervolt. Batteries are charged through a special ‘diodesplitter’ via the car’s 24 VDC generator which charges the car batteries and the inverter batteries.
As soon the unit is connected to the main power, battery supply is electronically shut of and the compressor is connected to the main 240 VAC power supply without power interruption.
It’s rather expensive but you can use standard components.

I’m not the expert but we learned a lot trough our mistakes.
We always make our plates ourselves, always stainless steel, ½” coil, fed trough the sharp stainless steel wall via a small piece 5/8” pipe so that you become double wall thickness.

Be also aware of the position of a hermetic compressor in a van/car. But it’s possible. If it shakes too much, then the inner suspension bolts or springs will brake. We already had 3 such a replacements this year.

Peter

Thank you
Fantastic information better than anything I could source. :)

Just a few questions

1.To make a plate that will sit at about -8 deg c what proportion of salt will I need to use.After looking at a few graphs I think about 10 percent will be close.(I wonder what sea water is? I have plenty nearby :D )

2.Do I need any form of control on the system while freezing the plates? Just in case someone leaves the condensing unit running too long.

Chemi
This system has to be self contained.He wants to slide in and out of van.

Regards

What are the sizes of the box? I can help you in sizing the compressor. If it's only plate, then a 3/8, perhaps a 1/2 Hp is more than enough, even smaller will work.
Remember that the compressor will always start with a high evaporating temperature. So, if you use a LP compressor, use a MOP TEV (you don't need a type with external equalization) or a crankcase pressure regulator to avoid excessive current on start-up or use a HP compressor.

The only protection we install is a LP/HP and an SV, energized together with the compressor. The cut-off of the LP is important: let it cut-off +/- 10 to 12 K lower than the eutectic point and cut-in again at +/- 1 K lower than the eutectic point.
Run a test cycle and look if the plate freezes completely and if it melt equally.

10% salt of the total weight is indeed very close. (13% for -10°C)
Make 1 plate (total thickness +/- 4 to 5 cm) as great as the biggest surface, preferable the ceiling. Make sure it's very well attached to the ceiling, best is bolts through the ceiling.

Most of the vendors we installed these systems are fish vendors. So they're working the whole day with very cold fish and ice.
Especially during the winter, it's pleasant to have some hot water to wash their hands.
The compressor is then installed on a flat isolated stainless steel tank of +/- 50 to 70 l. In this tank, we installed a small copper 1/2" coil and the discharge gasses are fed in in this coil before they go to the standard air cooled condenser.
Furtehr a HP cut-off to maintain HP is because when we start, the water is too cold to maintain HP.
Also during summer is this system an advantage: the compressors suffers the most at start-up due to the high LP at that moment. The standard condensers are then mostly too small too condense low enough. With the aid of the cold water at start-up, this problem is also gone and we can then even use a LP compressor.
I think I have some pictures of this. HAve to serach them somewhere.

Just a few points to consider when looking at Eutectics when used in a light vehicle are the sheer weight of the damn things, One of our less successfull projects was to use Carrier Eutectic plates to cool a box mounted on the back of a GMC Sonoma pickup for the delivery of icecream (Using a box that I had previously designed to transport chilled goods only) The plates were so heavy that even without a load the vehicle was undrivable. another aplication that I had seen in Saudi was a system mounted in a far more suitable box (Again for icecream), but mounted on a Izuzu 1 ton pickup made the vehicle very unstable on corners. in both vehicles high humidity gave problems with the icing and insulation of the tubes and plates.

Thanks Karl
I have taken that on board.

Peter
Box is actually an old ice chest made from coolroom panel. 75mm including floor.

height 1230mm
width 660mm
length 1230mm

Hinged door at one end.
Still has a condensing unit on it.I will have a look tommorow at what size it is.I think 1/2 hp.

I should suggest 1 plate of 110 x 110 cm and 4 to 5 cm thick.
Pour 1,8 kg salt in the plate and fill it up with water.
Weight of the plate +/- 30 kg.
The compressor of 1/2 hp will do the job.

I forgot something to tell: we made already spaces which could be regulated in temperature even with eutetic plates.
The eutectic plate is then mounted against the wall.
A second thin insulated wall is placed +/- 1 inch before the eutectic plate. This second wall has on the bottom a small gap of +/- 3 inches and on the top of this plate is a small fan (12 VDC) which is controlled by a room thermostat. As soon room becomes too hot, the 'stored cold air' behind the plate is forced then to the top of the room and warm air enters at the lower part of the plates.

Just got an idea today of how much a stainless tank will cost to make.

Wow not to cheap are they.Will pass on information to customer.

Just like to thank Peter again for all his help.