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?!