$Nu_F = \lim\limits_{\xi \to + \infty} \left [ \frac{-4}{\int_0^1 u^* \left(\eta \right) \theta_2(\xi, \eta) \, d\eta} \left. \frac{\partial{\theta_2(\xi, \eta)}}{\partial{\eta}} \right|_{\eta=1}\right]= 7.54$.

效果图：