Question

Consider a hydrodynamically fully developed laminar flow through a circular pipe with the flow along the axis (i.e., z direction). In the following statements, T is the temperature of the fluid, Tw is the wall temperature and Tm is the bulk mean temperature of the fluid. Which one of the following statements is TRUE?

• A. For a thermally fully developed flow,$\frac{\partial T}{\partial z}=0$, always.
• B. For constant wall temperature of the duct,$\frac{dT_m}{dz}=$constant.
• C. Nusselt number varies linearly along the z direction for a thermally fully developed flow.
• D. For constant wall temperature (Tw > Tm) of the duct,$\frac{dT_m}{dz}$ increases exponentially with distance along z direction.

Answer 1

Answer: (D)

For constant wall temperature (Tw > Tm) of the duct,$\frac{dT_m}{dz}$ increases exponentially with distance along z direction.

Answer 2

The correct option is (D): For constant wall temperature (Tw > Tm) of the duct,$\frac{dT_m}{dz}$ increases exponentially with distance along z direction.