JPH03186717A - Cryogenic flowmeter - Google Patents

Abstract

PURPOSE:To decrease the thermal disturbance or the flow resistance to a fluid, and also, to decrease the measurement error simply and at low cost by measuring a time difference by which the temperature variation or the pressure variation of the fluid heated by a heating means passes through two points of the downstream side. CONSTITUTION:When a current is allowed to flow to an induction heat coil 2 by pulse discharge from a pulse power source, part of a piping 1 is heated, and the temperature of a fluid flowing through the inside of the piping 1 rises. Also, propagation speed of a temperature variation of a liquid can be put so as to be equal to a flow velocity by taking a distance L between two points A, B to a value which can disregard a temperature rise in the longitudinal direction caused by thermal conduction of the piping. As a result, a flow velocity (v) can be given by v=L/t2-t1=L/DELTAt by putting as t2-t1=DELTAt. In this regard, t1 and t2 denote the time when a temperature variation of the fluid is generated. Subsequently, when the flow velocity (v) is measured, temperature and pressure of the fluid can be measured by a thermometer 5 installed between A and B and a pressure sensor attached to the tip of a connecting tube 6, and a material value in its state can be known.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a cryogenic flowmeter for measuring the flow rate of cryogenic fluid.

(Prior technology) When measuring the flow rate of cryogenic fluids such as liquid nitrogen or liquid helium, there are two methods: the differential pressure measurement method that measures mechanical quantities using an orifice or venturi, etc., and the heat pulse method that measures thermal quantities. and heating methods.

The heating method is described in Cryogenic Engineering Vol. 12.16. Na 3 (1
As shown in p. 144 to p. 146 of 1981), this method calculates the flow rate from the following equation by heating a part of the piping through which the fluid is flowing and measuring the amount of heating and the resulting temperature rise of the refrigerant.

G=Q/CpΔT (1) where G: Mass flow rate of fluid (kg/h) Q: Amount of heating
(KcaQ/h)Cp: Average constant-pressure specific heat of the fluid in the heating section (KcaIl/kg-K)ΔT: Temperature difference of the fluid between the heating and inlet ports (K) (Problem to be solved by the invention) As described above Each flow rate measurement method has the following drawbacks and inconveniences.

In general, even if the fluid flow rate is large in a cryogenic area,
Because the temperature is low, the density of the fluid is high and the flow velocity is extremely low. For this reason, an orifice or venturi that measures differential pressure, which is a dynamic quantity, cannot obtain sufficient hydrostatic pressure, making it difficult to measure the flow rate. Also, because the hydrostatic pressure to be measured is small.

The dimensions of the orifice or venturi used for measurement are
Ultra-compact and high-precision processing is required. If the flow rate is even lower, measurement becomes increasingly difficult and measurement errors increase. Furthermore, in this method of flow path measurement, it is necessary to provide a flow resistance for generating a pressure difference in a part of the fluid flow path.

On the other hand, when determining the flow rate Δ1 by the heating method, it is not necessary to provide a flow resistance in a part of the fluid flow path, but if the heating amount Q is not entirely transmitted to the fluid, the flow rate cannot be accurately determined <8 ( In addition, in order to measure the flow rate from the enthalpy change of the fluid, it is necessary to accurately measure the temperature and pressure of the fluid at the entrance and exit of the heating section.In particular, if the heating jtQ is small, the temperature change between the fluid entrance and exit is small, and the measurement error becomes large.For this reason, the amount of heating is required to be above a certain value, and thermal disturbance to the fluid increases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cryogenic flowmeter that minimizes thermal disturbance or flow resistance to a fluid, is simple, inexpensive, easy to replace, and has little measurement error.

[Structure of the invention]

(Means for Solving the Problems) That is, the cryogenic flowmeter of the present invention includes a heating means attached to a pipe through which cryogenic fluid flows, and a thermometer or pressure gauge attached at two points downstream of the heating means. The configuration is equipped with a meter.

(Function) In the cryogenic flowmeter of the present invention, the flow rate is determined by measuring the time difference in which the temperature change or pressure change of the fluid heated by the heating means passes through two points on the downstream side.

(Example) Hereinafter, an example of the present invention shown in FIG. 1 will be described. An induction heating coil 2 is placed on the outer surface of the plumber on the upstream side through which the fluid flows. On the downstream side, a thermocouple 3 is placed at two points A and B that are spaced apart, and a temperature uniformity block 4 made of a metal with high thermal conductivity such as copper is placed between these two points A and B.
The thermometer 5 housed in the pipe 1 and the impulse pipe 6
The second step is installation. Further, a pressure sensor (not shown) is attached to the end of the pressure guiding pipe 6. A heat shield 8 is provided around these pipes 1 via a vacuum atmosphere 7 to reduce heat intrusion. On the outer peripheral side of the heat shield 8, an outer tube 9 for maintaining a vacuum atmosphere 7 covers the piping 1.

Next, a second explanation will be given of the operation of the present invention configured as described above.
This will be explained using figures. FIG. 2(a) shows the output voltage and its time change when the heating coil is applied when heat is input to the fluid by the induction heating coil. Figure 2(b) is
It shows the change in temperature difference (difference in thermoelectromotive force) over time at two points A and B.

Now, when a current is passed through the induction heating coil 2 by a pulse discharge from a pulse power source (not shown), a part of the pipe ↓ is heated, thereby increasing the temperature of the fluid flowing inside the pipe 1. Since the fluid is flowing from upstream to downstream with a certain flow velocity V, the temperature change of the fluid occurs at time 1.
, 1. and time t when the heating coil is applied. is as shown in FIG. In this case, the propagation speed of the temperature change in the fluid is.

By setting the distance between two points AB to a value that allows the temperature rise in the longitudinal direction due to heat conduction of the pipe to be ignored, it can be made equal to the flow velocity.

As a result, the flow velocity S is given by setting 12-1□=Δt. When the flow velocity is measured, the temperature and pressure of the fluid can be determined by Δ(q) using the thermometer 5 installed between AB and the pressure sensor attached to the tip of the impulse pipe 6.
It is possible to know the physical property values of the fluid in that state. As a result, the flow rate of the fluid is each volume flow + Jt: V (m'/
5) V=A-pi (4) Mass flow rate: G (kg/5) G=ρ ・V (5)=ρ
・A − v (given by e.

However, A: Channel cross-sectional area (1) Sa: Flow velocity (m/S) ρ: Average density of fluid (kg/m'). Here, for flow rate measurement, only a thermocouple and a heating coil, which are easy to install and are inexpensive, are used, and nothing that would cause flow resistance is interposed in the -cut flow path.

The feature of this embodiment lies in the means for measuring the flow velocity.

Rather than determining the flow rate from a thermal amount using a heat pulse method or a heating method, heating is simply a means of causing a temperature change in the fluid, and there is no need to accurately measure the amount of heating. The important thing is to measure the propagation speed of the temperature change in the fluid, and the temperature change between two points is used as a signal for this purpose.

In the description of this example, a thermocouple was attached between two points as a signal for measuring the propagation velocity, and one end was used in common to measure a relative amount rather than an absolute amount. This allows detection even if the amount of heating is small and the temperature rise changes only minutely. However, even if the absolute amount is measured, there is no problem in the operation of the present invention. For this reason, a resistance thermometer may be used instead of a thermocouple. In addition, in this example, we mainly explained propagation velocity measurement using a thermometer.
Propagation velocity measurements using pressure are also possible. Install a pressure tube and a pressure sensor instead of the thermometer at the A82 point mentioned above. When a fluid is heated and its temperature increases, the pressure of the fluid changes accordingly. The same effect can be obtained by measuring the propagation speed of this pressure change. In addition, temperature and pressure measurements to determine the average physical property values of fluids are no different from conventional measurement methods, but instead of being attached to the outside surface of the pipe as in this example, they are inserted into the pipe. By eliminating the influence of the surrounding air, the flow rate can be determined with even greater precision.

Further, the fluid heating means may be a resistance type heater wrapped around or inserted into the piping, in addition to the induction heating coil of the above embodiment.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a cryogenic flowmeter that is simple, inexpensive, easy to replace, and has little measurement error, while minimizing thermal disturbance to the fluid or flow resistance.

[Brief explanation of drawings]

The second construction drawing is a sectional view of a cryogenic flowmeter according to an embodiment of the present invention.
Figures (a) and (b) are diagrams explaining the present invention in detail. Engineering... Piping 2... Induction heating coil 3
... Thermocouple 5 ... Thermometer 6 ... Impulse tube

Claims (1)

[Claims] A cryogenic flow meter characterized by comprising a heating means attached to a pipe through which cryogenic fluid flows, and a thermometer or a pressure gauge attached at two points downstream of the heating means.