new ice making idea

Hi guys, I am a chem eng student and just had an idea and was wondering if it is correct or stupid. My dad is a dairy farmer and as far as i can tell there are 2 milk refrigeration systems. One is the direct expansion system where refrigerant is used to cool the milk directly and the 2nd is where ice is made overnight using cheap electricity and this ice is used to cool the milk when it is placed in the tank. The benefit of the ice building system is that it uses cheap night rate electricity. The disadvantage is that it is much less efficient. As far as i can tell the main reason for this inefficiency is the low rate of heat transfer from the refrigerant to the water. Refrigerant is passed through coils which cools the water outside the coils and ice builds on the outside of the coils. As ice has a low coefficient of heat transfer, very little heat gets through the ice and it takes much longer to transfer the desired amont of energy, causing a reduction in efficiency.
My idea was to use a second fluid which doesnt freeze until a temperature significanly below 0C, which doesnt mix with water and which also has a different density to water. Oil might fill these criteria. The oil could be cooled to a temp below 0C by the refrigerant and as it would be in the liquid phase, the rate of heat transfer would be much higher( an agitator could be used to increase turbulence. THe oil could then be passed into the bottom of a container of water. As oil has a lower density than water it would rise through the water and would transfer heat to the water. The water would then freeze. The oil could then be recyled after it comes to the top of the container.
I was hoping somebody might be able to tell me if this was tried before or whether there is some flaw in my logic which i have missed.

Hi Ice Builder:)

nice to see a new face:)

Oil has been used for process engineering as a secondary refrigerant, but it is quite thick and suffers from pumping losses.

What you are thinking about is thermal storage.

You can buy a product called christopia balls, this is basically a sealed ball inside a tank of glycol, with brine inside it, cool it beyond the latent phase and you have a very good thermal store.

Kind Regards. Andy:)

Hi Ice Builder,

Welcome to the RE forum.

That was certainly an interesting question to start with.

I agree with Andy. Also, the use of oil may not be acceptable due to potential milk contamination. The higher viscosity will also require increased pumping power, so some of the energy savings will be lost.

The use of the Christopia Balls is a good idea as you will have a lot more surface area for heat transfer.

One thing to keep in mind with energy efficiency and electricity costs. The ice builder may be less efficient than some other system, but you also have to recognize the total cost of operation.

BY using off-peak electric rates the ice builder may actually cost less to operate than some other system which may be more "energy efficient".

Another form of thermal storage is like an ice machine. The ice is continually harvested off of the evaporator surface so the suction pressure can be considerably higher than a static ice builder. This way you get both benefits; more efficient and thermal storage.

You are thinking about the right things and a degree in Chemical Engineering will go a long way in helping you to sort these issues out.

Hello Ice Builder,

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I was hoping somebody might be able to tell me if this was tried before or whether there is some flaw in my logic which i have missed.

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1. The point is to use a very small refrigeration equipment to build up ice bank (thermal store) over night. It is small and cheap like you said but working for many hours it must be efective

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The disadvantage is that it is much less efficient. As far as i can tell the main reason for this inefficiency is the low rate of heat transfer from the refrigerant to the water.

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2. Please check your refrigeration equipment (missing refrigerant, wrong set points....)

3. Having primary refrigerant+secondary+ second secondary your COP will be like this:

COP= copR1 (*****) x copR2 (oil) x copR3 (water) = 0.99 x 0.99 x 0.99= this is only an example of heat transfer

4. You can use some low temperature glycol also, but then you should have milk fat stick to the tank walls :) instead in milk :(


Best regards,

Josip:)

The big advantage of making ice is exactly the phase change of water where you can store a lot of energy in the ice.
With oil, you can't pass a phase change.

Packo, a well known European mill cooler manufacturer (and located in my backyard) has as system with fuzzy-logic which makes not more ice then necessary by comparing outside temperature, milk entering temperature, time to cool it down,..
So the ice thickness is not the same each day.
But, even with a lower efficiency and running at a very cheap night rate, it's still more economic to do this with ice.
Consider also that if you don't make ice, you will need a much larger unit which will cycle much more on and off.

In theory, you could use a condenser unit to condense CO2 from a large holding tank into a large receiver during the night, and open a solenoid valve during the day.
Of course, the cost of the equipment will likely overshadow any savings.

I suppose that hydrogen energy storage is another idea except the technology for that is just coming and will take a very long time to become practical.

Ice thermal storage is probably the most practical technology available to you.

Hi Peter. Thank you for your comment but i thing you might of misunderstood me slightly. My idea was to create ice but to do so in a different way. The refrigerant would cool the oil and then the oil would be used to cool the water until it freezes. the idea was that this might be more efficient given that heat could be transfered much quicker.

US Iceman and Andy : thank you for your comments but i can find nothing on the net about christopia balls.

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Originally Posted by ice builder

Hi Peter. The refrigerant would cool the oil and then the oil would be used to cool the water until it freezes. the idea was that this might be more efficient given that heat could be transfered much quicker.

US Iceman and Andy : thank you for your comments but i can find nothing on the net about christopia balls.

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Hello Ice Builder,

Try to find some article about indirect heat transfer and see about efficiency.

Indirect heat transfer is always less efficient and slower then direct, but in some cases we have to use it mostly due to safety regulations otherwise it is simply waste of energy.

Best regards,

Josip :)

Hi ice builder,

Here is a link to the Cristopia Energy Systems website:

http://perso.wanadoo.fr/cristopia/en...dproducts.html

You probably could not find the site since we spelled the name incorrectly. :o

Here is a research report on phase change material for thermal storage that may be of some interest to you.

http://www.fskab.com/annex17/FINAL%20REPORT.pdf (4.8 Mb file size)

Best Regards,
US Iceman

Hi:)

it was me who spelt cristopia with a h.:D

Might know a little about refrigeration, but I can't spell:o

Kind Regards. Andy:)

Andy, Don't feel bad. I did the same also.:o

I use the spell checker in the Google toolbar which is quite handy, but it still has some limitations.

English is my natural language and I have problems with it.:D

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Originally Posted by US Iceman

Andy, Don't feel bad. I did the same also.:o

I use the spell checker in the Google toolbar which is quite handy, but it still has some limitations.

English is my natural language and I have problems with it.:D

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Hope, inspite to all your language problems ;) , you can fully understood what others want to say:)

for example, me;)

(Don't even try to think about my fight with spell checkers and with dictionaries :) )

Best regards,

Josip

This is a previous link http://www.refrigeration-engineer.co...ight=cristopia

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Originally Posted by US Iceman

English is my natural language and I have problems with it.:D

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I'ms o glad I' mnot the only one.... :p