Question: A particular heat exchanger is built of parallel plates, which serve to separate the two fluids, and parallel continuous fins, which extend between the plates so as to form rectangular flow passages. For one of the fluids the plate separation is 1 em and the nominal fin separation is 2 mm. However, manufacturing tolerance uncertainties lead to the possibility of a 10 percent variation in the fin separation. Consider the extreme case where a 10 percent oversize passage is adjacent to a 10 percent undersize passage. Let the flow be laminar and the passages sufficiently long that an assumption of fully developed flow throughout is reasonable. For a fixed pressure drop how does the flow rate differ for these two passages, and how does it compare to what it would be if the tolerance were zero?