For a fully developed flow through a pipe, how will the heat transfer coefficient (h) change, when the mean flow rate is doubled with all other conditions remaining the same?
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The exponent 0.8 in the Dittus-Boelter equation is key for turbulent flow problems:
- If flow velocity doubles ($2\times$), then $h$ scales by $2^{0.8} \approx 1.74 \implies 74\%$ increase.
- Note: If the flow field were fully developed *laminar*, the Nusselt number would be constant ($Nu = 3.66$ or $4.36$), meaning $h$ would not change with flow rate. The options here clearly indicate a turbulent flow context.