Heat Transfer · External and internal convection
Atmospheric air at Ti = 20 °C enters an aligned tube bank with 8 rows of tubes in the…
Problem
Atmospheric air at Ti = 20 °C enters an aligned tube bank with 8 rows of tubes in the flow direction and 6 tubes per row. Each tube has D = 20 mm, Ts = 100 °C, and longitudinal and transverse pitches SL = ST = 40 mm. The upstream velocity is U∞ = 5.0 m/s and the bank width is 0.24 m. Air properties may be evaluated at the arithmetic-mean temperature Tm = (Ti + To)/2, iterating if needed. Use the Zhukauskas form Nu_D = C Re_{D,max}^m Pr^{0.36} (Pr/Prs)^{1/4} with C = 0.27 and m = 0.63 for aligned tubes at 10^3 ≤ Re_{D,max} ≤ 2 × 10^5. The maximum velocity is Umax = [ST/(ST − D)] U∞. Determine the air outlet temperature To and the total heat-transfer rate from the bank.
Hint
U_max = [S_T/(S_T − D)] U_∞ for an aligned square pitch, and Zhukauskas uses Re_{D,max}.
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