4.3 Flow through a pipe or tube

4.3.1 Turbulent flow
A classical expression for calculating heat transfer in fully developed turbulent flow in smooth tubes/pipes of diameter (d) and length (L) is given by Dittus and Boelter

(4.3)

where,

n = 0.4, for heating of the fluid

n = 0.3, for cooling of the fluid

The properties in this equation are evaluated at the average fluid bulk temperature. Therefore, the temperature difference between bulk fluid and the wall should not be significantly high.

Application of eq. 4.3 lies in the following limits

Gnielinski suggested that better results for turbulent flow in smooth pipe may be obtained from the following relations

When the temperature difference between bulk fluid and wall is very high, the viscosity of the fluid and thus the fluid properties changes substantially. Therefore, the viscosity correction must be accounted using Sieder – Tate equation given below