Since you're interested in qualifications, I am an engineer that has done heat exchanger modeling, and have quite a bit of experience with air to water heat exchangers. You learn a lot when you learn to calculate things beyond just Reynolds Number... since you've been busy on google trying to find a place where I copied an argument from (and I didn't), I recommend you research Nusselt number and understand how it works.

Here's a simple explanation. Put your soup in the microwave to heat it. This represents a cross section of a tube in a heat exchanger. You run the microwave for 90 seconds, and you find that the edges are blazing hot and the center is cold. Why? The fluid is heating via conduction and not mixing (like laminar flow)... So what do you do? Stir it! Imagine if you could actually stir the liquid while microwaving - that would be efficient. Turbulent flow turns conductive heat transfer into convective heat transfer and greatly increases the heat transfer capacity of the system.