Originally Posted by SankePankey
Cool. Thanks very much for the explanation.
So, looking at say the Medium 20 and Small 40 since they are pretty close in surface area... If you are doing a recirculating plate chill like I will be, you will get better performance out of a higher flow unit like the Small 40. With a straight into primary method, you'd be better off with the Medium 20 since it's actually more efficient.
With the former, the higher flow would make up for the less efficiency. Right? (Lets assume, as in my case, 5 gallons per minute on both hot and cold.) Anyhoo, can't wait to try it for myself when she gets here.!
It's really going to depend on the application. if you're running high flow rates, those extra plates will be better off than having a longer unit with fewer plates.
if you take a look at my wort chilling performance chart,http://www.dudadiesel.com/files/wortchart.pdf
, you'll find the medium 20 palte (B3-23A 20 plate) is 50% better than the small 40 plate. So with such a higher performance rating, that slight drop in pressure on the cold fluid is not going to hinder the performance enough to where it's better to use the one with less restriction. In the case of gaining 50% more heat transfer, it will take some serious flow reduction before this matters much, so the longer one is definitely better.
To put some numbers into perspective for you, using 5 gpm on the small 40 plate has a pressure drop of 0.5 psi. the medium 20 plate is 3 psi drop. Both numbers are very small amounts. I'd need to bust out some engineering data to find the actual flow loss from this, but it's not much at all.