Channeling- a function of sparge arm/grainbed depth?

Can someone explain to me (in very small words, please) channeling? Is this only an issue for someone with a braid, or for someone who doesn't keep an inch or two of liquid above the grain bed?

I have a false bottom (round Igloo cooler) and I've tried various sparge arm set ups. It seems like just running a piece of tubing into the MLT is easiest. I'm using a sparge arm today, which gently sprinkles on top of the grainbed. I have a couple of inches of liquid above the grainbed, and my sprinkle is more of a drip. To keep the flow slow enough, I had to turn it down to just the dripping. In order to keep a nice sprinkle, I have to open the ball valve too much.

Anyway, should I be checking for channeling, or am I pretty safe to assume that there isn't any channeling going on?

If you've got water above your grain bed and you're draining slow, you shouldn't have channeling. I think this happens more when your grain bed compacts and/or there's one place all of the sparge water runs to as it drains (doesn't happen w/ false bottom).

Lil' Sparky said:

If you've got water above your grain bed and you're draining slow, you shouldn't have channeling. I think this happens more when your grain bed compacts and/or there's one place all of the sparge water runs to as it drains (doesn't happen w/ false bottom).

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Thanks- that's what I was thinking too. But I consulted Palmer's book, and the appendix is filled with math calculations and fluid mechanics. Darcy's Law is WAY over my head.

Darcy's Law is WAY over my head.

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You're short, lots of things are.

Channeling happens when the wort takes the path of least resistance.

higher flow rates = channeling.

True channeling, the grain rearranging in a way that creates one or several lower resistance paths, is a function of flow rate.

With respect to using a braid to fly sparge, you can keep your flow rate low enough to prevent channeling, but for the sparge water to travel through the grains near the edges is a much higher resistance path so you just won't get much flow through that region, which creates dead/low efficiency spots.

Channeling isn't really affected by how you're adding sparge water, unless you're upsetting the grain bed. Its affected by how you're drawing off the wort.

flyangler18 said:

You're short, lots of things are.

Channeling happens when the wort takes the path of least resistance.

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Thanks. I'm taller than most other short people, though!

I am thinking that channeling would be far more likely in a MLT with a braid, then, right? Because of the laws of fluid mechanics, and Darcy's Law, even though I don't fully understand it. If the liquid is a couple of inches above the grainbed, the entering sparge water that comes in would be evenly distributed throughout the MLT in the liquid that's already in there, right? Not not go right from the center where it enters and drops right through to the bottom (channeling), if I understand this correctly.

I think it's more a combination of things that have been said already.

First, keeping water over the top of the grainbed does two things. It keep the bed more fluid which prevents clumping and non rinsed areas. It also ensures that there's equal pressure across the top with no drilling.

The flow rate has a lot more affect on channeling if the collection points are focused (small, single braid for example). In theory, a full coverage false bottom shouldn't care about flow rate because it will always pull the water/wort straight down.

Think of a single sheet of sparge water slowly descending through the bed and exiting the bed in the same flat plane. That would be ideal.

I am thinking that channeling would be far more likely in a MLT with a braid, then, right?

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Yes, because the wort is draining through that concentrated point on the braid as opposed to all through the grain bed in a false bottom or manifold assembly.