overall heat transfer coefficient for sphere based heat exchanger

Hello everyone

I'm currently working on my thesis to obtain my mechanical engineering degree. I'm designing a thermal energy storage system which basically works as follows:

- during a refrigeration system´s off peak hours, cold water-glycol solution (-10°C) passes through a cylindrical container filled with around 5000 plastic spheres, each sphere contains water/glycol solution.
- this water freezes the solution inside each sphere (these contain a lower glycol concentration in order to achieve freezing at -8°C)
- During on peak hours, hot water at about -6°C passes through the cylindrical storage and must exit at -8°C

All this work is theoretical of course, which brings me to my problem. I've been stuck for some time now trying to figure out the overall heat transfer coefficient of the whole cylinder/spheres arrangement In order to see if the amount of spheres that i've considered will be enough.

To (hopefully) simplify the problema I want to assume that the spheres move very little or not at all as water passes through the thermal storage (in the same fashion water flows through a tube bank)

Can anyone recomend some literature on the subject that might help me? or maybe a software of some sort? Any help will be highly appreciated.

Sorry for my writting and spelling, english is not my first language hehe.

Thanks everyone!

Hi, juicetavo :)

Quote:

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Originally Posted by juicetavo

Hello everyone

I'm currently working on my thesis to obtain my mechanical engineering degree. I'm designing a thermal energy storage system which basically works as follows:

- during a refrigeration system´s off peak hours, cold water-glycol solution (-10°C) passes through a cylindrical container filled with around 5000 plastic spheres, each sphere contains water/glycol solution.
- this water freezes the solution inside each sphere (these contain a lower glycol concentration in order to achieve freezing at -8°C)
- During on peak hours, hot water at about -6°C passes through the cylindrical storage and must exit at -8°C

All this work is theoretical of course, which brings me to my problem. I've been stuck for some time now trying to figure out the overall heat transfer coefficient of the whole cylinder/spheres arrangement In order to see if the amount of spheres that i've considered will be enough.

To (hopefully) simplify the problema I want to assume that the spheres move very little or not at all as water passes through the thermal storage (in the same fashion water flows through a tube bank)

Can anyone recomend some literature on the subject that might help me? or maybe a software of some sort? Any help will be highly appreciated.

Sorry for my writting and spelling, english is not my first language hehe.

Thanks everyone!

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Maybe this will be of some help to you ...
I do believe some other members will contribute with other better links ...

http://en.wikipedia.org/wiki/Heat_transfer_coefficient

http://www.thermopedia.com/content/1007/

http://www.cdeep.iitb.ac.in/nptel/Me...ain/2.6.3.html

http://www.syvum.com/cgi/online/serv.../heat1001.html

http://wwwme.nchu.edu.tw/Enter/html/.../chapter_3.pdf

http://www.scribd.com/doc/22016082/H...s-1-conduction

Best regards, Josip :)

Thank you Josip, the info you provided is great but unfortunately is a bit basic, I'm looking for something a little more applied to the specific arrangement of spheres. I found some info on a book called Heat exchanger design by Arthur Fraas, but it was only an online preview of the book and I haven't been able to find it anywhere online.

Hi, juicetavo :)

Quote:

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Originally Posted by juicetavo

Thank you Josip, the info you provided is great but unfortunately is a bit basic, I'm looking for something a little more applied to the specific arrangement of spheres. I found some info on a book called Heat exchanger design by Arthur Fraas, but it was only an online preview of the book and I haven't been able to find it anywhere online.

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I know this all is a basic, but all the best things are simple and very close to the basic ...

here you can read reduced preview ....
http://books.google.hr/books?id=1A_Y...page&q&f=false

seems a good book and I think it is not that much expensive ... from 22 to 150 US$
http://www.amazon.com/Heat-Exchanger...N%3D0471628689


another online link is here ... http://hedh.begellhouse.com/
http://hedh.begellhouse.com/toc/#page=10.html

this one is good ... try to search to download separate pages ...
http://www.wlv.com/heat-transfer-databook/
http://www.scribd.com/doc/137117392/...r-Data-Book-II

http://www.chemstations.com/content/...cles/shell.pdf
http://www.slideshare.net/rijumonibo...ngers-12606868

Good handbooks you can download from here ...
http://www.swep.net/en/products_solu...handbooks.aspx


Your idea is basically a good concept (similar to ice banks) of two phase HE and only good suggestion I can give to you is to try to obtain enough time and flow of your primary solution (/10*C) around all spheres to achieve capacity ... it is all about internal construction of HE ...

Hope this will be of some help to you ...

Best regards, Josip :)

http://wwwme.nchu.edu.tw/Enter/html/.../chapter_4.pdf

You are dealing with none steady state conditions on both the freezing and the harvest cycle but the temperature difference within the spheres should be pretty near nothing in both directions....considering the heat being exchanged is largely latent. If the outside fluid flow is the same during heating as during cooling, the analysis will be simpler but you will always have a slow-decay process in both directions.

Hope this helps. I believe you will end up employing the approximating process of Pages 23-27.