Question

Explain the meaning and usefulness of the equivalent diameter, for the annular region in a double pipe heat exchanger.

Answer 1

Meaning :

Equivalent diameter for double pipe heat exchanger is calculated when the fluid is flowing through the annulus. In that case we need to calculate the daimeter of the pipe which is equivalent to the diameter of the annulus , that diameter is called the equivalent diameter.

Usefulness :

So in double pipe heat exchanger equivalnet diameter is useful for calculating the velocity of the fluid, Reynolds number, Nusset number.

Equivalent diameter for heat transfer is different than the equivalent diamtere for the pressure drop. So equivalent diamter for heat transfer is given by d which is given below.

Where

internal diameter of outer tube

external diameter of inner tube