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  1. #1
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    Lightbulb Cold Storage project



    Greetings everyone,

    I'm not in the refrigeration engineering branch (yet) and I come from a Physics background. Lately I've been working on a project of cold storage (ice bank) in which I'm trying to project a low (specific) cost ice bank, in a prototype stage. Since I'm completely new to this I could use some help and this forum seemed perfect for it.

    Here are some details of the project:
    • 80cm*80cm*80cm insulated tank;
    • HDPE coil as an heat exchanger;
    • approximately 15kWh of storage;
    • internal melt system with water glycol (20% weight slycol concentration) solution as refrigerant;
    • water glycol start temperature around -6 degC;
    • DN20 coils (around 26.67mm OD) with around 1.9mm wall thickness;
    • 1.6m/s average velocity of water-glycol flowing in the tubes.


    The type of heat exchanger may be found here attached.
    ice_pipe_2geom_3D.png

    The part I'm in need of help is to project the type of chiller I need to chill down the return glycol solution and its pump. I don't know exactly the type of chiller I need and the required parameters I need to get to project that chiller and pump.

    If someone could help I'd be glad. Hope I was clear.

    Best regards,
    António Rocha



  2. #2
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    Re: Cold Storage project

    Hi António,

    Some answers and some questions,

    For that glycol temperature (-6ºC) you should'nt have only 20%, you should have something around 30 to 35% to not have a risk of freezing with the usual evaporating temperatures between -10 and -14ºC.

    If you want to have 1,6 m/s in a DN 20 tube (inox for instance) you need something like 2,3 m3/h and with a Dt of 4ºC (usual with a comercial chiller) you will need a chiller with something close to 11 kW, quite small but you can find some. The usual type is an air condensed chiller and you can find one easily.

    For that flow you can easily find a pump, and those kind of chillers may be asked with hidraulic kits including the needed pumps.

    Best regards,
    CDuque

  3. #3
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    Re: Cold Storage project

    CDuque, thank you for helping.

    Regarding the glycol concentration, probably you're right because the freezing point for 20% is around -12ºC. Thanks.

    About the chiller and pump, I understood what you said but I have some further questions. It seems it was quite straightforward to you to get the Dt of 4ºC and 11kW parameters. How did you reach such values? The other questiion is: shouldn't I think about the pressure drop for the pump as well? Or if I'm imposing a certain flow, the required pressure drop will be obtained?

    Again, thank you for your time (or obrigado maybe?)

    Best regards,
    António Rocha

  4. #4
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    Re: Cold Storage project

    Hi
    Is your pipes vertical or horizontal
    Looks like vertical
    To return oil in this type of design is nearly impossible
    So do horizontal .
    Also don't forget U trap

  5. #5
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    Re: Cold Storage project

    Hi mbc,

    Thank you for your answer. That design is still in a prototype version.

    Isn't the return oil a problem if my refrigerator is a gas-liquid type? In this case I would be using a water-glycol solution in that geometry to freeze ice around it (cold storage). Would return oil still be an issue?

    How would U trap be useful here?

    Best regards,
    António Rocha

  6. #6
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    Re: Cold Storage project

    Quote Originally Posted by AntonioRocha View Post
    CDuque, thank you for helping.

    Regarding the glycol concentration, probably you're right because the freezing point for 20% is around -12ºC. Thanks.

    About the chiller and pump, I understood what you said but I have some further questions. It seems it was quite straightforward to you to get the Dt of 4ºC and 11kW parameters. How did you reach such values? The other questiion is: shouldn't I think about the pressure drop for the pump as well? Or if I'm imposing a certain flow, the required pressure drop will be obtained?

    Again, thank you for your time (or obrigado maybe?)

    Best regards,
    António Rocha
    Hi AntonioRocha,

    the thermal balance is quite straightforward this time, since P = m * c_p * dT, where:
    P is thermal power, in kW
    m is the mass flow of water + glycol, in kg / s
    c_p is the average specific heat, in kJ / (kg * K)
    dT is the temperature difference, in K, between the entrance and the exit of the mixture at your coil

    Regarding pressure drop, you only have to take into account the one produced at the pipe. I'd use the Darcy-Weisbach formula (internet is plenty of charts for water and some other liquids, if you don't want to iterate for the friction factor) for the calculations.

  7. #7
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    Re: Cold Storage project

    cool-noob,

    That's what I thought it would be, after some research about it - for both the thermal balance and the pressure drop.

    I think I'm clarified for now. Your help was much appreciated.

    If i have further doubts on the project I will use this thread again.

    Best regards,
    António Rocha

  8. #8
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    Re: Cold Storage project

    Hi

    I thought this is your evaporator and refrigeration inside of that .
    Again in your design air should not be trap in your piping

    In all slap in piping air should be able to move free to go out of system.

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