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  1. #1
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    Very Cold R14 Expansion Tank Design Strategy



    I'm diving into a small 3 stage cascade for a project we are working on. I'm a newb at refrigeration (but a pretty good Mechanical Engineer, I must say ) and that's a lot to get into, but I don't have a choice - it's gotta get done!

    Anyway, I've been reading that its highly recommended to have a good size expansion tank on the coldest stage to help with start up. I agree with this on the basis that without one the pressure inside the system when turned off (ie system entirely at atmospheric temperature) could get huge.

    The only other way I can imagine to avoid using an expansion tank is to have over-sized pipe for the low pressure vapor side.

    Here is my design strategy:

    After the system is designed fully I plan to solve for the mass of R14 in the system at steady state operation. Essentially this just means finding the volume of liquid between condenser inlet and evaporator outlet, and the volume of gas everywhere else. Now that I know how much R14 I know I need to run the system, I need to find out how much pressure all this R14 would build to at ambient temperature - which is likely very large without a tank!

    Then I will add an expansion tank to the system whose volume is large enough so that at ambient temperature the pressure is within my safe limit.

    I plan on locating it just in front of the suction side of the compressor. The reason for this location is that this is where the low pressure gas is at its warmest point (and thus lowest density in the whole system) and therefor less R14 will be in there during operation. (If I located this tank prior to the evaporator, for example, it would do the opposite of what I want it to do - it would require much more CF4 to operate because it would hold liquid during operation and then evaporate all of that during shut down.)

    Any flaws in that approach?



  2. #2
    Brian_UK's Avatar
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    Re: Very Cold R14 Expansion Tank Design Strategy

    Have a look at page 9 of this document and the preceeding diagram it may help...
    http://www.accessengineeringlibrary....5884_ar021.pdf
    Brian - Newton Abbot, Devon, UK
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  3. #3
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    Re: Very Cold R14 Expansion Tank Design Strategy

    Excellent link, Brian! Thank you very much.

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