IF his flow rates were correct, the 2ed row would have to have a negative contribution
- added second row decreases fluid velocity by 50%, fluid spends 2X time in tube
- the shrowded second row = warmer air, less direct tube exposure; affecting 50% of the flow
so IF Joe's air flow/velocity is constant then the 1st row would replicate the Pro (assuming that halving the flow rate did not materially affect the coolant/tube heat transfer) and the second would be rather less due to the lower coolant/air temp differential; averaging the 2 streams together will result in a lower dT than the Pro alone
there is a bit more than this going on, which is why higher air flows can reverse this ratio
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