Hydrodynamics and transfer speed: will fatter tubing help?

[sibelman]

Hey, hydraulic engineers and physicists, I don't understand fluid flow. Please help me with some basic education.

I've been using 5mm ID EVAbarrier tubing, with swivel-flare ends, to transfer from fermenter to keg. I'm wondering whether switching to 6.3mm ID EVAbarrier tubing will increase flow rate. The ID of the flare fittings is only about 5mm -- does that mean that increasing the tubing size won't matter 'cuz the flare fittings (not to mention the ball-lock disconnect and keg poppets!) are bottlenecks that limit the flow?

 

[doug293cz]

Yes, the larger ID tubing will speed transfer. The fittings offer a fixed amount of flow resistance, and the tubing adds a variable amount of resistance depending on ID and length. Each tubing type has a characteristic flow resistance per foot, which is different for different ID's. The longer the tube, the more resistance, and the smaller the ID the more resistance per foot. The flow rate at any given head pressure is determined by the sum of the fitting resistance and the tubing resistance - higher resistance -> slower flow. Thus reducing the tubing resistance will reduce the total resistance, and increase flow rate. You will get into diminishing returns once the tubing resistance becomes less than the total fitting resistance.

The physics is explained here.

Brew on