A fluid flows over a heated horizontal plate maintain at temperature $T_{W}$. The bulk temperature of the fluid is  $T_{\infty }$ . The temperature profile in the thermal boundary layer is given by:

$$T=T_{W}+\left ( T_{W}-T_{\infty } \right )\left [ \frac{1}{2}\left ( \frac{y}{\delta _{t}} \right ) ^{3}-\frac{3}{2}\left ( \frac{y}{\delta _{t}} \right )\right ],\:\:\:\:\:0\leq y\leq \delta _{t}$$

Here, $y$ is the vertical distance from the plate, $\delta _{t}$ is the thickness of the thermal boundary layer and $k$ is the thermal conductivity of the fluid.

The local heat transfer coefficient is given by

1. $\frac{k}{2\delta _{t}}$
2. $\frac{k}{\delta _{t}}$
3. $\frac{3}{2}\frac{k}{\delta _{t}}$
4. $2\frac{k}{\delta _{t}}$