Thermal Storage Calculation

Hi Everybody,

I am looking for a reference for thermal storage (ice on bare tubes) calculations.

There is a table at the end of Dossat book (third edition) which shows the U factors for bare tubes but calculating with these figures give a very high pipe lengths????!!!!

Does anybody know a good reference which at least gives one numerical example?

Thanks a lot.

Cheers

Hi lana
I have only seen plastic tubes used on this application. For the outside wall of storage container it should be (for a cylender) 1D:2L roughly - this gives maxamim volume with minamum surface area, calculated with differentiation maxima/minima. As for a reference site I don't know sorry.

I am also looking for a similar calculation. I require a thermal storage tank for some projects of mine. In case I get something I shall definately share.

Thanks guys.

There are some companies here who make these storage machines but I would like to know about the design which they don't share!! Of course if they know it anyway???!!!

All of them told me that this is completely experimental but I know it is not true.

Hope to get something useful.

Cheers

Now this sounds like fun! I would be interested in finding more information also. Going from memory the US manufacturers of ice builder use a maximum ice thickness of 2.5" on a pipe coil that looks eerily like a coil for an evaporative condenser.

This is the old school way it was/and is done for industrial refrigeration. The plastic tube type construction mentioned by Tesla (I like that screen name BTW) would be considered more of a commercial application that was developed by Calmac.

Ibrahim Dincer wrote a book on thermal storage, however I do not have a copy of it to say for sure whether it has these calculations or not Lana. His books are generally complete and offer some very good detail.

This is the most recent text I am aware of on this subject. Any other source is probably ancient:o.

If curiosity doesn't kill the cat, it will cause him many sleepless nights Lana.:D

There are some people in our country who are making these Ice Builders. Unfortunately no one has a design. It is just gues work , but it works. I myself am interested in the same and as you said the Ibrahim Dincer has something on the same, I shall .try to find the same.

I made an ice water bath for rapid cooling of cooked hot food packed in plastic bags. It has 5/8" copper tubes. DX. I found it to have a capasity of roughly 100W per meter tube at -8C evaporating and roughly 14mm ice thicknes. (44mm diameter of the ice.) One loop is 24 meter long and has a capasity of roughly 2,5kW. I have a very low superheat, only roughly 4K.

Thanks Iceman
BTW I will be at the Tesla museum next month.
Lana thinking outside the square the ultimate storage vessel would comprise of a spiral type plate heatexchanger, which is configured in such a way as to minimise natural convection currents (like a capacitor). This would allow max heat xfer durring cooling and minimum heat xfer whilst storring. It's in my head but hard to put on the computer. Construction would cost more but the efficiency would be better than a tube in shell.

Quote:

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Originally Posted by Tesla

Thanks Iceman
BTW I will be at the Tesla museum next month.

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I am sooo jealous. That should be a very interesting visit.

Thank you all for replying.

Actually I did the calculations but I would like to have a reference to check it with.
Why not check it with you guys.:rolleyes:

Assume 3000 kg of milk is delivered to the dairy factory. They need to cool this milk from 25°C to 4°C in 1 hour.
Now the cooling load required would be nearly 62 kW.
This means 62kWh energy (=53310 kcal). Thermal storage must store this energy in the form of ice which have 80kcal of latent heat.

53310/80 = 666.4 kg of ice must be stored.

Now, the economical situation is when we have ice on the pipe with the thickness of 3D (D is the tube diameter). I have read this somewhere but don't ask where:confused:.


Now when we calculate the weight of ice in every meter of any diameter pipe then we can have our tube Length.
For example if we use 7/8" tube then we need 237m of tube in our water sump.

This is as far as my brain processes :D.

Hope I did not put you to sleep.

Any comment from the experts would be highly appreciated.

Cheers

lana,

The heat load is comprised of not only the process load (cooling) but also the parasitic heat of the piping, ice tank, pump heat gain, and agitation. So you need to add these to make sure you have adequate cooling capacity in the ice bank.

I suspect you would have to also add some length to the tubing to allow for superheating if you use a TXV. I doubt the superheat section will form ice at the same rate as the true cooling section where a phase change occurs in the tubing.

Thank you US Iceman,

You are completely right. what I mentioned is a very rough calculation without any safety factors.

Of course no system is 100% efficient and there is always heat loss.

I would like to know whether the basis is correct.

Thanks again.

Cheers

HI lana,

I agree with your method.

Total cooling load / time rate / latent heat of ice = total mass of ice to meet the total cooling load in the time rate available or desired.

The next issue becomes one of time available for building the ice and the refrigeration system capacity. Since your process load is being cooled in 1 hour, do you then have 23 hours available to re-form the ice? Or perhaps less time limited to off-peak electrical charges?

That would determine the per hour cooling capacity required to size the refrigeration system.

Another consideration is the effect of increasing ice thickness on the tubing which reduces the heat transfer from the outer radius of the ice to the refrigerant in the tube.

I know I have seen a curve for this somewhere but I don't think I have a copy of it.:o

I have ordered the Dincer book mentioned earlier. It should be here next week. I will quickly review it and see what sort of magical answers it holds.;)

Hello to All,

this may not be a very scientific, but may help. Might put you in the right area for capacity etc., something to back calculate.

A 5000 litre bulk milk tank (Gasgoinge / Fullwood type) (ice bank type) generally has in the region of a 4HP condensing unit.

Typically a 4HP semi running on R404A will produce in the region of 8kW @ -8 deg / 44 condensing.

These produce a good crop of ice approx 1" thick in under 10 hours.

Billy Ray

lana,

Here is a link that may prove helpful to you. See page 65. This is not the same curve I was thinking of, but it should prove beneficial (I hope).

http://books.google.com/books?id=WkN...hl=en#PPA71,M1

Happy reading.:D

Hi everybody,

Sorry for late reply, I was so busy last three weeks.

Many thanks for the replies.

Dear US Iceman, thank you for the link. It is not possible to copy that link but I read some parts and might get some points from it.

Thanks a lot for your time.

Cheers

Dear Sir,

Thermal ice storage is based on 16- 20 hrs compressor operation.

as rule of thumb for 32 NB black pipe the ice storage is 7.5kg per mtr with a 50 mm ice thickness.

The ice production is depends upon the SST and operation hours.

The above is based on (-) 10deg C SSt and 16 hrs operation.

We are manufacture the same.


raj