JPH063393B2 - Flow measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fluid flow rate measuring device.

[Prior art and its problems]

Conventionally, various types of fluid flow rate measuring devices have been put to practical use, but there is still no highly reliable device for measuring the flow rate of a cryogenic fluid. For example, incorporating a rotating mechanism or the like for measuring the flow rate in the flow path of the cryogenic fluid causes a large heat loss due to the inflow of heat, and thus is not feasible. Some strain gauges are used, but the operating temperature range is limited and reliability is poor.

[Means for solving problems and their effects]

The present invention provides a fluid flow rate measuring device that solves the above-mentioned problems of the prior art, and has a structure in which a pipe having a known pipe friction resistance value of a fluid flowing inside is separated in the axial direction thereof. A means for detecting the fluid pressures P ₁ and P ₂ at only two points and a means for detecting the temperature T of the fluid are provided, and
The density ρ of the fluid is obtained from the relationship between the average value of the pressures P ₁ and P ₂ and the temperature T, and the density ρ and the pressures P ₁ and P _{2 are determined.}
It is characterized in that a calculation means for obtaining the flow rate from the relationship with the difference of is provided.

In this device, the pressure and temperature of the fluid flowing in the pipe are measured, and the flow rate is calculated from the values, so there is little heat loss associated with the measurement, and a wide operating temperature range,
It is possible to perform reliable flow rate measurement.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1 and 2 show a fluid flow measuring device according to an embodiment of the present invention. In the figure, 1 is a pipe through which a cryogenic fluid flows, and 2 is a connecting flange provided at both ends thereof. In order to prevent radiant heat from flowing into the outer circumference of the pipe 1, a super insulation 3 having a surface with a high emissivity is wound, and the outer circumference of the pipe 1 is covered with a spacer 4 made of a resin having a high heat insulation property. The outer tube 5 is arranged. The space between the pipe 1 and the outer pipe 5 is evacuated and kept vacuum after the device is installed in the pipeline.

Further, the pipe 1 is provided with pipes 6 and 7 for pressure detection at predetermined intervals in the axial direction thereof. The pipes 6 and 7 are led out of the outer pipe 5 and connected to a pressure gauge (not shown). Further, as shown in FIG. 2, a temperature measuring element 8 such as a carbon resistance or a platinum resistance is closely arranged on the outer circumference of the pipe 1, so that the temperature of the fluid passing through the pipe 1 can be detected. There is.
Although not shown, the lead wire of the temperature measuring element 8 is connected to an external measuring instrument.

Now, assuming that the pressures in the pipes 6 and 7 are P ₁ and P ₂ , and the distance between them is the inner diameter of the pipe 1, the following relationship is established.

However, λ: pipe frictional resistance value of fluid ρ: density of fluid v: flow velocity (1986 mechanical engineering handbook A-5 fluid engineering edition A5-74
(From equation (239) on page) The pipe frictional resistance value λ is a coefficient determined by the shape, surface condition, etc. of the pipe 1, and is therefore measured beforehand.

On the other hand, the flow rate Q of the fluid flowing in the pipe 1 is given by the following equation.

Therefore, according to the equations (1) and (2), the flow rate Q is P ₁ ,
It can be calculated from P ₂ and ρ.

The problem here is the existence of the density ρ that changes with temperature and pressure. The relationship between the density ρ, the temperature T, and the pressure P is to be obtained in advance by experiments.

For example, in the case of helium, the relationship can be expressed by the following equation.

ρ = e ^{(1.0233LnP + 3.9046)} × T− ^{0.0045LnP + 1.0033)} (3) However, the unit of temperature T is K (Kelvin) and the unit of pressure P is
atm. The pressure P can be calculated by the following equation. That is, P ₁ . It is the average value of P ₂ .

P = (P ₁ + P ₂ ) / 2 (atm) (4) The use range of the equation (3) is a range in which 0.5 atm ≦ P ≦ 10 atm 15K ≦ T ≦ 1000K are compatible.

Pressure (1.0 atm, 5.0 atm, 10 atm
When changing in the range of 15K to 1000K, the density ρ of helium actually measured, the density ρ _MA calculated by the equation (3) from the values of the temperature T and the pressure P, and its error rate (ρ / ρ _MA − 1) is as shown in Tables 1 to 3. The calculated value ρ _MA agrees well with the measured value ρ, and it can be seen that the accuracy is sufficiently usable.

Therefore, the pressure P _{1 of} helium passing through the pipe ₁ . P
₂ and the temperature T are measured, and the density ρ is calculated from these values by an arithmetic means such as a micro computer using the equations (3) and (4), and further the equations (1) and (2) The flow rate can be measured with high accuracy by performing the calculation for obtaining the flow rate Q by utilizing.

[Advantages of the Invention] As described above, according to the present invention, the pressure and temperature of the fluid flowing in the pipe are measured to obtain the flow rate, so that the heat loss of the device is small and the operating temperature range is wide. Moreover, since the structure is simple, a highly reliable and inexpensive flow rate measuring device can be obtained.

[Brief description of drawings]

1 is a vertical sectional view of a flow rate measuring device according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line II-II of FIG. 1-pipe, 3-super insulation, 6.7
-Pipe for pressure detection, 8-Temperature measuring element.

Claims (2)

[Claims] _1. A means for detecting the fluid pressures P ₁ and P ₂ at two points separated in the axial direction and a means for detecting the temperature T of the fluid in a pipe of which the friction resistance value of the fluid flowing inside is known. And the density ρ of the fluid is determined from the relationship between the average value of the pressures P ₁ and P ₂ and the temperature T, and the flow rate is determined from the relationship between the density ρ and the difference between the pressures P ₁ and P _2. A flow measuring device, characterized in that it is provided with a computing means. 2. The device according to claim 1, wherein the fluid to be measured is helium, and the density ρ of the fluid is obtained from the following equation. ρ = e ^{(1.0233LnP + 3.9046)} × T ^{− (0.0045LnP + 1.0033) where} T is absolute temperature (K) P = (P ₁ + P ₂ ) / 2 (atm)