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  1. #1
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    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!



  2. #2
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    Re: overall heat transfer coefficient for sphere based heat exchanger

    Hi, juicetavo


    Quote Originally Posted by juicetavo View Post
    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!
    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

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    Don't ever underestimate the power of stupid people when they are in large groups.

    Please, don't teach me how to be stupid....
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  3. #3
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    Re: overall heat transfer coefficient for sphere based heat exchanger

    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.

  4. #4
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    Re: overall heat transfer coefficient for sphere based heat exchanger

    Hi, juicetavo

    Quote Originally Posted by juicetavo View Post
    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.
    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

    It's impossible to make anything foolproof because fools are so ingenious...

    Don't ever underestimate the power of stupid people when they are in large groups.

    Please, don't teach me how to be stupid....
    No job is as important as to jeopardize the safety of you or those that you work with.

  5. #5
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    Re: overall heat transfer coefficient for sphere based heat exchanger

    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.

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