Perhaps this is a question better suited to Ravi Dolwani and his technical staff (welcome to the forum, by the way). I'm also fairly new to the heat exchanger business, but there are somethings I'd like to understand, if nothing else then for my own curiosity.
I think of the radiator as I would a straighforward 2-circuit heat exchanger, crossflow. The air circuit is your 'cold' circuit, and the coolant running through the radiator is the 'hot' circuit. The radiator dissipates the heat stored in the fluid to the air. Correct? Pretty simple liquid-to-air heat exchanger.
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The design (inlet in the middle of tube that is seam brazed) increases the heat transfer surface area of the tube by approximately 15% over regular tubes. You get the efficiency of 2 smaller tubes vs. 1 large tube within the same space criteria. With "B-tubes" you are able to get "dual liquid laminar flow."
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Okay, so I'm on board with the increase in surface area, that's fine by me. I assume the 'B' part of the tube, is that done for structural support purposes, to give added safety to a large flat surface. I might be wrong on that, but I would hesitate to have a large flat surface without some sort of support. Then again, my background is in aerospace, so I may be over-exaggerating the details.
The real conundrum for me is that I am not understanding, from an engineering standpoint, the benefits of 'dual liquid laminar flow'. I take this to mean the both the air and liquid circuits have laminar flow on the heat transfer surface, correct? To me, I would consider having laminar flow (especially on the hot circuit) to provide a negative impact on the heat transfer. You have fluid that is, in a sense, 'adhered' to the heat transfer surface, so you are cooling a portion of the liquid, but the hot middle section of the liquid is never coming in contact with the heat transfer surface. I don't have an issue with the cold air circuit, which appears to be a straightforward plate-fin configuration.
In my experience, it's not altogether uncommon to see some sort of turbulating element in heat exchangers to increase the heat transfer capabilities of the unit. Long winded post short - I'm missing something, and I'd ask, what are the advantages to having a "dual fluid laminar flow"?
Again, my background is strictly in the aerospace industry, where requirements are probably far above what they are for automotive applications. If that's the reason why I am misunderstanding something, that's fine. But I hate being unable to reason out something for myself, and it doesn't help I can't physically see a unit, as that usually helps me in my comprehension. Any answers would be appreciated. Thanks!