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  1. #21
    Hi ecat,

    Thanks for the info, like the kit at the end but trying to spend less than that if possible. I've done some calcs to get used to the sort of numbers involved in all this, and came up with this quick spreadsheet to work out how long it would take to heat up a certain quantity of water (assuming no heat loss from the reservoir).

    I also had another look at the inlet and outlet barbs screwed into the end of the spindle. Given that 3/8" (~10mm) ID pipe is quite popular for CPU cooling, I was disappointed to find the following rough dimensions on these barbs:
    The thread into the spindle end itself is around 7-8mm (I've emailed the supplier for the exact size)
    The barb which screws into this thread has a hole around 4.5mm at one end, and a hole about 2.5mm where the pipe connects.

    This is quite a reduction! I repeated the 'blowing into it test' with and without these barbs connected and it made a big difference. When I find out what size thread these barbs are they are going to be replaced! If they are G1/4 (popular CPU cooling size), I'm hoping I can put some proper cooling mod parts in instead and increase the hole size from 2.5mm to 10mm at the pipe end.

    Failing all that I guess the spindle endplate could be removed and the holes re-tapped. Feeling much better about this now since the flow will be so much better if I can open these restrictions up.

    By the way, I've asked the supplier if the internal channels are aluminium.
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    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #22
    ecat's Avatar
    Location unknown. Last Activity: 08-02-2014 Has been a member for 6-7 years. Has a total post count of 157. Received thanks 5 times, giving thanks to others 8 times.
    Impressive spreadsheet!

    If I were the pedantic sort I'd remind you to add in the heat load from the pump, but I'm not so I wont ;)

    The entry holes do look a bit piddly. Thin tube is more bendy (showing my full engineering acumen here) which may be a nice feature when connected to the moving head. I wonder how 12mm ID 19mm OD tube will fair after 2 weeks of constant bending and twisting?

    The reduction in diameter sounds significant and may well be a design feature used to increase the velocity of the water over the cooling part:

    1) Higher velocity means less laminar flow ie it minimises the occurrence of slower moving 'layers' of water near the boundaries which effectively 'insulate' the metal from the main cooling flow.

    2) The common sense of many tell them that the longer the water is in contact with the metal, the more heat the water will take up, or give up if in a radiator. This is of course pants, in and out asap is the way to maximise the amount of energy transferred..... Unless achieving a satisfactory velocity requires a 200w pump ;)

    Jet Plates!! Sounds good, lol

    Hehe, extra points to anyone who can tell me what the 'Blank' jet plate is for :)

  3. #23
    Hi ecat,

    Yes, didn't bother with the heat from the pump itself as it's quite small and this is a rough calc. By the way, I'm assuming you can ratio specific heat capacity values of water and Propylene Glycol in the proportion they are added to the mix.

    Since I'm going to mount all this on the router plate there is no pipe bending and movement between the spindle and water cooling system. If you see my build log you'll see the router plate is long enough with space above the spindle to mount the cooling bits. It's all been worked out - well, package protected for anyway!.

    I follow your point about narrow inlet/outlet increasing flow velocity, which it will, but immediately after the barbs (i.e. just inside the spindle) it opens out again which will slow it back down again. So I think this is effectively just a local bottleneck. My blow tests with and without the barbs back this up.

    Thinking about your maximum heat transfer point, I guess this is like the wind chill effect where a windy day will cool you down more than a calm day. The rate of transfer of heat is proportional to the difference in temperature between the 2 parts. Hot stuff (relative to the surroundings) cools quicker. As it cools, it cools slower and slower. Therefore you want to keep putting fresh cold water next to the hot bits to maximise the transfer rate. Possibly.

    I'm sure there are many factors involved, but to be honest I don't want to go down that long road - just want it to work so can get back to my hobby!

    Blank jet plates - CNC machine your own?!
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  4. #24
    ecat's Avatar
    Location unknown. Last Activity: 08-02-2014 Has been a member for 6-7 years. Has a total post count of 157. Received thanks 5 times, giving thanks to others 8 times.
    Blank jet plates - CNC machine your own?!
    To smart you be, yes. Indeed, drill your own holes :)

  5. #25
    Hello friends!
    Not bother with containers, radiator, and pump! I connected a hose cold water, and the sewage will water the flowers!

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