KROHNE CORIMASS MFC 85 EN User Manual
Page 10
10
C
M
100
However,
ρ
S
and
ρ
C
vary with temperature, T. This is compensated for by using the following
equation for both
ρ
S
and
ρ
C.
ρ
=
ρ
20
+ K
1
(T-20) +K
2
(T-20)
2
Equation 3
where:
ρ
20
, K
1
and K
2
are input by the customer for each component.
These parameters are entered via the Fct. 3.10 menus.
Menu
Comments
Fct. 3.10.1 SOLUTE R20
ρ
20
for the solid component
Fct. 3.10.2 SOLUTE K1
K
1
for the solid component
Fct. 3.10.3 SOLUTE K2
K
2
for the solid component
Fct. 3.10.4 LIQUID
Select either WATER or NON WATER
If WATER is selected then
ρ
C
is taken
from an internal lookup table of water’s
density versus temperature.
If NON WATER is selected then
ρ
C
is
calculated from Equation 3 using the
parameters in menus 3.10.5 to 3.10.7
Fct. 3.10.5 LIQUID R20
ρ
20
for the liquid component
Fct. 3.10.6 LIQUID K1
K
1
for the liquid component
Fct. 3.10.7 LIQUID K2
K
2
for the liquid component
Having computed the concentrations it is possible to estimate the flow rate of the individual
components. If m is the total measured mass flow rate of the mixture, then the flow rate of the
solid/solute, m, is given by :
m =
·
m
Equation 4
4.2
Concentration Of Miscible Liquids
When two liquids mix or dissolve together they are said to be miscible. The two components
may also have a strong chemical interaction. For such mixtures volumes do not add.
V
T
≠
V
S
+ V
C
Consequently equations 1 and 2 above only approximate to the true behaviour of the mixture.
The accuracy of this approximation varies from mixture to mixture and each case must be
individually assessed. Normally it is possible to achieve a good fit, although this may only be
over a limited range of densities.
Consider a mixture of ethanol and water as shown in the figure below. Clearly the true
characteristic does not follow the ideal case of the previous section. Ignoring temperature
compensation, (K
1
= K
2
= 0) the concentration software may be programmed with one of the
following data sets.
Fit 1
Fit 2
SOLUTE R20
0.85659 g/cm
3
0.83678 g/cm
3
LIQUID R20
0.99812 g/cm
3
1.01477 g/cm
3
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