# How to know a pipe is partially full ?

# What is the liquid height and equivalent diameter ?

1.
Introduction

2. Pipe full or partially filled ?

3. Height of liquid in the pipe
calculation

4. Equivalent diameter calculation

## 1. Introduction

It happens that pipes are not actually full, for example in some
return pipes, condensate...etc... then the assumption that they are
full can lead to some erroneous calculations. [Brannan] is reporting a
method proposed by Durand in order to know if a pipe is totally full
or not.

## 2. Pipe full or partially filled ?

To know if the pipe is full or not, it is necessary to calculate **Q/d**^{2.5}

- If ≥ 10.2 it means the pipe is
full

- If < 10.2 the pipe may be
partially full only, further calculations are required to know the
height of liquid in the pipe and the equivalent diameter

With :

Q = flow rate in gpm

d = pipe diameter in in

## 3. Height of liquid

The method is proposing to have x
= ln (Q/d^{2.5})

Then calculate H/D =
0.446+0.272x+0.0397x^{2}-0.0153x^{3}-0.003575x^{4}

^{
}

With :

H = height of liquid in the pipe
in ft

## 4. Equivalent diameter calculation

The equivalent diameter can be
calculated from the following correlation :

D_{e}/D = -0.01130+3.040
(H/D) -3.461 (H/D)^{2} +4.108 (H/D)^{3 }-2.638 (H/D)^{4}

With :

D = pipe diameter in ft

De = equivalent diameter in ft

Source

Rules of thumb for Chemical
Engineers, Brannan, Elsevier, page 5

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