Hoffer Flow Controls HP Series User Manual page 21

A consequence of using center line positioning in medium diameter pipes is
that a scaling factor, relating the average flow to the center line flow, must be
included in determining the calibration constant of the metering section. In
general, the profile scaling factor (PF) relates to the shape of the velocity
profile under a given set of fluid conditions (i.e., Reynolds Number (Rn)). In
large diameter pipes the profile scaling factor (PF) is equal to one since the
turbine is located at the average velocity point.
It is necessary to consider the effects of the flow profile (PF) within the line as
well as the obstruction that the stem and well assembly present to the fluid flow
(OF).
The profile scaling factor may be obtained from measured data or by utilizing
empirical equations derived from fluid mechanics of the fluid profile shape as a
function of Reynolds Number.
Table B lists the profile scaling factor derived from one such empirical
equation. To choose the correct profile scaling factor, determine the Reynolds
Number corresponding to the anticipated minimum and maximum flow rates
using the following equation:
for Liquid Service:
3160
=
Rn
ID
where
Q - flow in US gallons
per minute
ID - pipe bore in inches
 - viscosity in Centistokes
From Table B obtain the profile scaling factors corresponding to the
approximate Reynolds Number.
Calculate the mean profile scaling factor using the following equation:
HP-208

Q


+
PF
=
MAX
PF
2
AVE
Page 15 of 17
for Gas Service:
Rn
where
Q - flow rate in SCF/sec
D - density in #/ft3
ID - nominal pipe ID in inches
µ  - viscosity of gas in
PF
MIN
4
 
Q D
=
 
 
ID
#/in-sec
HP Insertion Meter