Spindle cooling requirement, basics of calculation.


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    Lightbulb Spindle cooling requirement, basics of calculation.

    Hello,

    After reading couple threads about cheap Chinese water cooled spindles I came to conclusion, most people here have no idea how much cooling does your spindle need, so in here we will calculate:
    How much water flow do you need?
    How large radiator/much air flow you need?

    Here we will use school level thermodynamics, so everybody should understand what we discuss.

    Here we go, we will analyze how much water flow does a 2.2KW spindle need.

    Assumption1 spindle is 80% efficient, so 20% directly goes to heat. Or 0.44KW is needs to be absorbed by water. In reality your spindle is not ruining 100% load all the time, so these are worst case numbers.

    Wasted_power = 440W

    Water_specific_heat = 4200J*kg/C How much heat does 1kg water need to absorb to rise temperature by 1C.

    Water_temperature_rise = 20C We assume that water after spindle heats by 20 degrees. 20C is very conservative, in reality it can be up to 60C

    Water_flow = Wasted_power / (Water_temperature_rise * Water_specific_heat * Water_density) =440W / (20C * 4200J*kg/C * 1kg/l )= 0.005l/s or 19l/h so any water flow is enough for this spindle

    That is under 20 liters per hours for 2.2kW spindle under FULL LOAD



    For a diy machine we will use a cheap 120mm PC water cooling radiator.

    Water_temperature_rise = 20C

    Air_flow = 100m3/h = 0.028m3/s In reality 120mm fan has air flow similar to 130M3/h, but lets assume that radiator provides some air resistance.

    Air_specific_heat = 1000J*kg/C

    Air_density = 1.3kg/m3

    Air_temperature_rise = 0.5 * Water_temperature_rise = 10C

    Power_dissipation = Air_flow * Air_specific_heat * Air_density * Air_temperature_rise = 0.028m3/s * 1000J*kg/C * 1.3kg/m3 * 10C = 360W

    A 120mm pc radiator with fan will dissipate 360W of power if you are ok with spindle temperature 20C above room. Or a 120mm pc radiator with fan will cool a 2.2kW spindle, under FULL LOAD, with temperature rise of 25C above room temperature.

    In reality 40-60C above room temperature is safe for most spindles.


    PS: hope this sticks.

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  2. #2
    Member wtwoods_az's Avatar
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    Default Re: Spindle cooling requirement, basics of calculation.

    Know this is old, but if u r still out there, thanks for this.
    (A) The cheap pumps that come with the spindles say 3500 LPH (925 GPH) LOL. Yeah right.
    (B) I knew they would in reality require a lot less seeing as some of us never even hook the cooling up. I was about to figure it out, thanks for doing it already.
    Given all this, I found a good deal on JUST the spindle and inverter not all the extra junk. Going to get a small pump from HD or Amazon.
    Thanks again.....



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    Member davida1234's Avatar
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    Default Re: Spindle cooling requirement, basics of calculation.

    Interesting post.

    I did the same as you and did purchase just a 2.2kW water cooled spindle for my "David's New Desk Top Router" build thread.

    I used two 80mm radiators in series driven by a small 4.2W (about 400 milliAmp) pump. Plenty of circulation with that tiny pump. The biggest input/output temperature delta I measured was about 18-20 degrees F (about 10 degrees C).

    BryggaCNC.com


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    Default Re: Spindle cooling requirement, basics of calculation.

    I clamped a few turns of 1/8" bore copper tube tightly around the uncooled spindle and used an inexpensive pump from ebay and a large tub of water from the local HW store. No radiator at all. Works fine. Pump was sold as spindle pump for CNC too!
    Spindle cooling requirement, basics of calculation.-8428-jpg
    Bit of gal steel and some hose clamps to hold the copper tube tightly in place.
    Silicone rubber hose for the water.

    Cheers
    Roger



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Spindle cooling requirement, basics of calculation.

Spindle cooling requirement, basics of calculation.

Spindle cooling requirement, basics of calculation.