Yokogawa digitalYEWFLO (DY) - Manual (Page 105)

<11. MAINTENANCE>
11-7
IM 01F06A00-01EN
(2) Flow Conversion Factor (U
k
)
Flow conversion factor U
k
is obtained by carrying
out the following computation depending on the
selection of the fl uid to be measured and the fl ow
unit.
(a) Steam
M (Mass fl owrate):
U
k
= ρ
f
× U ρ
f
× U
k (kg)
.... (11.9.1)
U
k
= ρ
f
× U
k (lb)
.... (11.9.2)
Q
f
(Flowrate at operation):
U
k
=U
k (m 3 )
.... (11.10.1)
U
k
=U
k (acf)
.... (11.10.2)
(b) Gas
Q
n
(Flowrate at STP):
U
k
= U
k (Nm 3 )
P
f
P
n
T
n
+ 273.15
T
f
+ 273.15
1
K
Ч Ч Ч
.... (11.11.1)
U
k
= U
k (scf)
P
f
P
n
1
K
(T
n
-32) + 273.15
(T
f
-32) + 273.15
9
5
9
5
Ч Ч Ч
.... (11.11.2)
M (Mass fl owrate):
U
k
= 
f
 U
f
× U
k (kg)
.... (11.12.1)
U
k
= ρ
f
× U ρ
f
× U
k (lb)
.... (11.12.2)
Q
f
(Flowrate):
U
k
=U
k (m 3 )
.... (11.13.1)
U
k
=U
k (acf)
.... (11.13.2)
(c) Liquid
Q
f
(Flowrate):
U
k
=U
k (m 3 )
.... (11.14.1)
U
k
=U
k (acf)
.... (11.14.2)
M (Mass fl owrate):
U
k
= 
f
 U
k (kg)
.... (11.15.1)
U
k
=7.481 
f
 U
k (lb)
.... (11.15.2)
Note: 7.481 is a conversion factor of U.S gal into acf
(d) User’s unit
U
k
=U
k (user)
................................................ (11.16)
U
ρf
: Density unit conversion factor
U
k(kg)
, U
k(Nm 3 )
, U
k(m 3 )
,
U
k(lb)
, U
k(scf)
, U
k(acf)
: Flow rate unit conversion
factor
(3) Mass Flow calculation
(a) Steam
In case of saturated steam, mass fl ow rate is
calculated from density values to temperature
measured by using saturated steam table.
In case of superheat steam, mass fl ow rate is
calculated from density values to temperature
measured by using steam table. In order to
measure superheat steam, it is necessary to
make constant pressure value. A pressure
values which is entered in parameter is used.
M = ρ
ft
× Q
f
.............................................. (11.17)
(b) Gas
In case of gas, Volumetric fl ow rate at
standard condition is calculated, so Pressure-
Temperature correction is carried out. It is
necessary to make constant pressure value.
A Pressure values at operational condition,
temperature and pressure value at standard
condition which is entered in parameter is used.
Q
n
= Q
f
Ч –– Ч –––––––––– Ч –– ........... (11.18)
(c) Liquid
In case of liquid, mass fl ow rate is calculated
from which used to calculate the secondary
function for the density value to the
temperature. A density value which indicated
by the order sheet is used.
M = ρ
n
× Q
f
× {1 + a
1
× (T
ft
– T
n
) × 10 -2 + a
2
×
(T
ft
– T
n
) 2 × 10 -6 } ....................................... (11.19)
[Footnote]
a
1
= {(k
1
– 1) × ∆T
2
2 – (k
2
– 1) × ∆T
1
2 }/
{( ∆T
1
× ∆T
2
2 – ∆T
2
× ∆T
1
2 ) × 10 -2 }
a
2
= {(k
1
– 1) × ∆T
2
– (k
2
– 1) × ∆T
1
}/
{( ∆T
1
2 × ∆T
2
– ∆T
2
2 × ∆T
1
) × 10 -6 }
k
x
= 1 + a
1
× ∆T
x
× 10 -2 + a
2
× ∆T
x
2 × 10 -6
∆T
x
= T
x
– T
n
(x = 1, 2)
P
f
T
n
+ 273.15 1
P
n
T
ft
+ 273.15 K