US 10,704,937 B2 · Critical flow nozzle flowmeter for measuring respective flowrates of gas phase and liquid phase in multiphase fluid and measuring method thereof

Abstract

A method for measuring respective flowrates of gas phase and liquid phase in a multiphase fluid using a critical flow nozzle flowmeter. The critical flow nozzle flowmeter includes a throttling nozzle having an inlet, an outlet and a throat, and the throat has a smallest flow area for flowing fluid; a gamma ray detector, including a gamma ray emitter and a gamma ray receiver, arranged in a way allowing the gamma ray emitted by the gamma ray emitter to pass through a cross-section at the inlet of the throttling nozzle in a diametrical direction to reach the gamma ray receiver; pressure sensors respectively configured for measuring the pressure P1 at the inlet of the throttling zone and the pressure P2 at the outlet of the throttling nozzle; and a temperature sensor configured for measuring the temperature T1 at the inlet of the throttling nozzle.

A method for measuring respective flowrates of a gas phase and a liquid phase in a multiphase fluid using a critical flow nozzle flowmeter, wherein the critical flow nozzle flowmeter comprises:

a throttling nozzle having an inlet, an outlet and a throat;
wherein the throat has a smallest flow area for flowing fluid compared with the inlet and the outlet;
and a cross-section area of the throat of the throttling nozzle is 1/10 to ½ of a cross-section area of the inlet of the throttling nozzle;
a gamma ray detector comprising a gamma ray emitter and a gamma ray receiver, and the gamma ray detector is arranged in a way allowing a gamma ray emitted by the gamma ray emitter to pass through a cross-section at the inlet of the throttling nozzle in a diametrical direction to reach at the gamma ray receiver;
and the gamma ray detector is a single-energy gamma ray detector;
pressure sensors respectively configured for measuring a pressure P1 at the inlet of the throttling nozzle and a pressure P2 at the outlet of the throttling nozzle;
and
a temperature sensor configured for measuring a temperature T1 at the inlet of the throttling nozzle;
and the method comprises the following steps:
a) measuring the pressure P1 at the inlet and the pressure P2 at the outlet of the throttling nozzle by using the pressure sensors, and measuring the temperature T1 at the inlet of the throttling nozzle by using the temperature sensor;
b) flowing the multiphase fluid through the critical flow nozzle flowmeter in a critical flow manner, wherein judging whether the multiphase fluid has reached a critical flow state according to the following method:
setting a symbol “r” as a ratio of the pressure P2 at the outlet to the pressure P1 at the inlet, and
r
=
p
2
p
1
;
measuring the pressure P1 and the temperature T1 to determine a density ρg1 of the gas phase;
measuring a mixed density ρm with the single-energy gamma ray detector to determine a gas mass fraction GMF according to a first equation:
GMF
=
ρ
l
-
ρ
m
ρ
l
-
ρ
g
⁢
⁢
1
,
and further defining
a
=
1
-
GMF
GMF
⁢
ρ
g
⁢
⁢
1
ρ
l
;
according to a characteristic, i.e., the gas phase flows in a sonic speed when the multiphase fluid reaches the critical flow state, defining a critical pressure ratio rc by a second equation
r
c
=
[
a
⁡
(
1
-
r
c
)
+
k
k
-
1
k
k
-
1
+
k
2
⁢
(
1
+
α
)
2
]
k
k
-
1
,
and with the second equation, determining the critical pressure rc by iterative solution;
when a measured pressure ratio r meets
r
=
p
2
p
1
≤
r
c
,
determining the multiphase fluid is a critical flow;
in case of a critical flow, through a third equation
s
=
1
+
ρ
l
-
ρ
m
ρ
l
-
ρ
g
⁢
⁢
1
⁢
(
ρ
l
ρ
g
⁢
⁢
1
-
1
)
⁢
(
1
+
0.6
⁢
⁢
e
-
5
⁢
GMF
)
,
calculating a velocity slip ratio between the gas phase and the liquid phase;
and
c) respectively calculating a total mass flowrate Qm of the multiphase fluid, a gas phase mass flowrate Qm,g and a liquid phase mass flowrate Qm,l according to the following equations:
the total mass flowrate:
Q
m
=
CA
2
⁢
ρ
g
⁢
⁢
1
⁡
[
α
⁡
(
1
-
r
)
+
k
k
-
1
⁢
(
1
-
r
k
-
1
k
)
]
GMF
⁡
(
r
-
1
k
+
α
)
⁡
[
GMF
+
1
s
⁢
(
1
-
GMF
)
]
;
the gas phase mass flowrate:
Qm=QmGMF;
and
the liquid phase mass flowrate:
Qm,l=Qm(1−GMF);
wherein:
Qm is the total mass flowrate, kg/s;
ρg1 is a density of the gas phase at the inlet of the throttling nozzle, kg/m3;
ρt is a density of the liquid phase, kg/m3;
GMF is a gas mass fraction;
A is the cross-section area of the throat of the throttling nozzle, m2;
C is a flow coefficient of the throttling nozzle and is a constant;
k is an adiabatic index of gas;
r is a ratio of the pressure P2 at the nozzle outlet to the pressure P1 at the inlet, and
r
=
p
2
p
1
;
and
s is a velocity slip ratio between the gas phase and the liquid phase.

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Critical flow nozzle flowmeter for measuring respective flowrates of gas phase and liquid phase in multiphase fluid and measuring method thereof

Life of this patent

Critical flow nozzle flowmeter for measuring respective flowrates of gas phase and liquid phase in multiphase fluid and measuring method thereof

Life of this patent

Abstract

Claims1