Question

Consider a two-dimensional laminar flow over a long cylinder as shown in the figure below.

The free stream velocity is $U_{\infty }$ and the free stream temperature $T_{\infty }$ is lower than the cylinder surface temperature $T_s$. The local heat transfer coefficient is minimum at point

• A.
  1
• B.
  2
• C.
  3
• D.
  4

Answer 1

The correct option is B

2


1. $Re=500$
2. $Re={10}^4$
3. $Re=2\times {10}^5$
4. $Re=2\times {10}^6$

Experimental results for the variation of the local Nusselt number with $\theta$ are shown in the above figure for the cylinder in cross flow of air. The results are strongly influenced by the nature of boundary layer development on the surface. Starting at the stagnation point, $N{u}_{\theta }$ decreases with increasing $\theta$ as a result of laminar boundary layer development. $N{u}_{\theta }$ reaches a minimum at ${80}^o$ where separation occurs. So, at point 2, the local heat transfer coefficient is minimum.