So long as you can fully drain the tun, then the efficiency of your batch sparge is what it is. The only way you can lower it is by not completely draining the tun. What that says, in a nutshell, is you could theoretically find the lowest point of a tun and drain from that point. So a SS scrubbie covering that point would work - IF - it didn't suck everything to that point and create a very slow flow - stuck mash. As was pointed out, you may speed the flow using a manifold or other method.
Yes, that is correct. But keep in mind that lautering is not necessarily the best place to chase efficiency. If you are batch sparging and are seeing poor efficiency it is most likely due to incomplete conversion of the mash. The beauty of batch sparging is that its efficiency is not determined by dynamic difficult to control factors but only by static parameters like: wort let in the tun after run-off, number of run-offs and size of run-offs.
Fly sparging doesn’t have the theoretical efficiency limits of batch sparging, which are actually well in the 80s for most beers, but takes more skill and better equipment to be done right. It’s not as easily modeled as batch sparging. John took a stab at it in his book and I assume that there is much more data out there since big brewhouse manufacturers are concerned about that. They want their mash tuns to lauter as efficiently as possible.
Here is a little piece of information that I found a while back. Did you know that the swan-neck design seen on the faucets feeding old lauter grants are there to reduce suction on the grain bed? They are designed such that the opening of the faucet will be at the same level as the false bottom. As a result the wort that is below the false bottom and in the pipes leading to the grant cannot suck on the grain bed since it has to travel up the swan-neck where it looses all that energy. Modern tun designs monitor the pressure in each of these drain pipes and use that to regulate the pump speed as well as the cut depth of the rakes. The latter is also controlled by the clarity of the wort.
D looks like the best braid technique. A Colman extreme 70 qt happens to be that profile.
Yes, that is true. But don’t expect big gains from that difference. Maybe 1-2% would be my guess.
You can check for dead spaces and in efficiencies by calculating the grain absorption A after draining completely:
A = (total water volume used – temp corrected wort volume collected) / grist weight.
It is generally between 0.1 – 0.12 gal/lb. If you’re in that ball park there is not much you can improve. I have had a few cases where the grain retained more and I don’t exactly know why.
Note that A is what I call apparent grain absorption. The true grain absorption is higher since dissolved sugars also contribute to wort volume. But you only have to consider that if you need to know the actual volume left in the grain and not just what appears to be left in the grain. Here is some info on that: True vs. Apparent Grain Absorption