$Nu_D=0.027 Re_D^{4/5}Pr^{1/3} \left(\frac{\mu}{\mu_s} \right)^{0.14}$ $0.6 \le Pr \le 16700$ $Re_D \ge 10000$ $L/D \ge 10$ where, $\mu$ is fluid viscosity at bulk temperature $\mu_s$ is fluid viscosity at heat transfer surface temperature. Note that this is implicit and require iteration. But it is more accurate than Dittus-Boelter