For a hydrodynamically and thermally fully developed laminar flow through a circular pipe of constant cross-section, the Nusselt number at  constant wall heat flux $(Nu_q)$ and that at constant wall temperature $(Nu_T)$ are related as

1. $Nu_q > Nu_r$

2. $Nu_q < Nu_r$

3. $Nu_q = Nu_r$

4. $Nu_q = (Nu_r)^2$