Topic: Heat Transfer
Which of the following is true for the scenario of a fluid flowing along a tube and a constant heat flux applied on the tube surface?
- A. The mean temperature of the fluid varies linearly along the tube length
- B. The surface temperature of the tube varies linearly along the tube length
- C. The difference between the tube surface temperature and mean fluid temperature remains constant throughout the tube length
- D. All of the above
Answer: D. All of the above
Explanation: Under constant heat flux boundary conditions in a fully developed pipe flow:
1. Heat added is constant, causing the fluid mean temperature $T_m$ to increase linearly with length $x$.
2. The convective heat transfer coefficient $h$ is constant. Since $q'' = h(T_s - T_m)$, the temperature difference $(T_s - T_m)$ must also remain constant.
3. Because $T_m$ is linear and $(T_s - T_m)$ is constant, the surface temperature $T_s$ must also increase linearly with $x$.