It does look like calculations were used for the graph. The data point for the immersion being below the counterflow is counterintuitive. You could e-mail Zymurgy and ask the question there, and I suspect the author would respond. Worked for me a while back when I had a question.
Too many theoretical variables. You okay at that
I'm okay with the time it takes to chill. But the study in Zymurgy says they're getting it done in 10 minutes vs. my 14 minutes.
They chilled 5 gallons, I did 5.5.
They used a 46'x3/8" coil. I use 2 separately-fed 25'x3/8" coils. Theoretically, this should give mine an advantage, at least enough to make up for the slight difference in volume.
We both used 65f water to chill.
I circulate the wort continuously, in the opposite direction of chiller flow.
My chiller flow rate is 3 gpm. So is theirs.
So how do they chill so much faster? Or do they? Perhaps the article is based strictly on calculations, with no scientific data, and is really just theoretical bs?
i have not read the full article, but i don't find it counterintuitive. if they recirculated the wort with a paddle briskly around the immersion coils the heat transfer gradient could be significantly higher, including th e tranfer at the air interface and the wort kettle interface. in fact, an argument could be made that this is significantly better than that from pumping a laminar layer through a counter flow or even a cross flow heat exchanger.