3 General principles
3.1 Measurement principle
FLUXUS F60*
2017-10-16, UMFLUXUSF60xV5-0EN
14
Acoustic calibration factor k
a
k
a
=
The acoustic calibration factor k
a
is a transducer parameter which results from the sound
speed c within the transducer and the angle of incidence. According to Snell's law of re-
fraction, the angle of propagation in the adjoining fluid or pipe material is:
k
a
=
=
=
Fluid mechanics correction factor k
Re
With the fluid mechanics correction factor k
Re
, the measured value of the flow velocity in
the area of the sound beam is converted into the value of the flow velocity across the
whole cross-sectional pipe area. In case of a fully developed flow profile, the fluid me-
chanics correction factor only depends on the Reynolds number and the roughness of
the inner pipe wall. The fluid mechanics correction factor is recalculated by the transmit-
ter for each new measurement.
Mass flow rate
= ·
ρ
The mass of the fluid that passes through the pipe per unit time. The mass flow rate is
calculated from the product of the volumetric flow rate and the density
ρ
.
Transit time difference
∆
t
Is the transit time difference of the signals. In the TransitTime principle, the transit time
difference of the signals in and against the flow direction is measured, in the NoiseTrek
mode, the time difference of the signal from the transducer to the particle and vice versa.
The flow velocity of the fluid flowing in the pipe is determined from the transit time differ-
ence.
Volumetric flow rate
= v · A
The volume of the fluid that passes through the pipe per unit time. The volumetric flow rate
is calculated from the product of the flow velocity v and the cross-sectional pipe area A.
Heat flow
The heat quantity that is transferred per unit time. For the calculation of the heat flow see
chapter 21.
c
sin
------------
c
sin
------------
c
sin
------------
c
sin
-----------
m
·
m
·
V
·
V
·
V
·
V
·