What is a hydraulic diameter how is it defined and what is i

What is a hydraulic diameter, how is it defined and what is its value or usefulness in solving real heat transfer problems involving internal flow situations?

Solution

The hydraulic diameter  is used for a fluid flowing in a pipe, duct or other conduit of any shape. This uses the perimeter and the area of the conduit to provide the diameter of a pipe which has proportions such that conservation of momentum is maintained.

D_h = 4A/P

A= CROSS SECTION AREA AND P= WETTED PERIMETER

Hydraulic diameter is mainly used for calculations involving turbulent flow. Secondary flows can be observed in non-circular ducts as a result of turbulent shear stress in the turbulent flow.

Hydraulic diameter is also used in calculation of heat transfer in internal flow problems.