Burkert 8626 Instructions De Service page 39

For the selection of the MFC, the same principles apply as for the proportional
valves in the control mode. Depending on the data specified, the following two cases
can be distinguished:
a) If the pressure values p
desired maximum flow rate Q
value of the MFC is given by:
k = (Q
(1)
Vs max
or
k = (Q
(2)
Vs max
where
k is the flow index of the MFC with fully opened actuator in [m
Vs
Q is the desired maximum flow rate in [l
max
ρ
is the density of the medium in [kg/m
N
(1013 mbar, 273 K)
T is the temperature of the gas in K
p , p are the absolute pressures in [bar] up and downstream of the MFC
1 2
Type 8626.
b) If, on the other hand, the pressure values p
the overall installation and the desired maximum flow rate Q
required flow index of the overall installation k
of the equations (1) or (2). For determining the required k
according to
(1/k
(3)
the flow index k for the installation without the MFC must, however, be known or
Vs
determined, e.g. by short-circuiting the pipe at the point of installation of the MFC.
38
up and downstream of the MFC , in which the
and p
1 2
should be attained, are known, the required k
max
√
ρ ρ ρ ρ ρ
* T
N
/ 514) *
∆ ∆ ∆ ∆ ∆ p * p
2
√
ρ ρ ρ ρ ρ
* T
N
/ 257) *
p
1
2 ) = (1/k 2 ) + (1/k 2 )
Vtot Va Vs
for p > p /2
2 1
(subcritical flow)
for p < p /2
2 1
(supercritical flow)
3 /h]
/min]
N
3
] under standard conditions
and p at the inlet and outlet of
1 2
are given, the
max
may be calculated from one
Vtot
value of the MFC
Vs
Vs
Type 8626