RU2289103C2 - Gas flow meter - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: gas flow rate comprises two tanks that are connected with main pipelines for supplying and discharging gas through the tree-composition control valves. The tanks are provided with top pressure-tight lids, and the volumes of the tanks are the same. In addition, the flow meter has unit for control of valves, two relays connected with the control unit, devices for closing the contacts of the relay secured to the floats mounted in each tank, and pipe that interconnects the tanks. The ends of the pipelines for supplying gas and pipe are submerged into the tanks. The depth of the pipe ends is higher or equal to the depth of the ends of the pipelines for supplying gas. The ends of the pipelines that connect the tanks with the main pipelines for discharging gas are mounted above the levels of liquid in the tanks.

EFFECT: enhanced accuracy of flow measuring.

1 dwg

Description

The invention relates to measuring technique and can be used to measure gas flow.

A bubble meter for measuring gas flow rate is known, comprising a measuring burette, in the lower part of which is a vessel filled with a liquid with a surfactant dissolved in it, and a gas supply pipe connected to the burette in such a way that a water seal forms between the tube and the burette ( Kremlevsky P.P. Flowmeters and counters of quantity. 3rd ed., Revised and supplemented by L.: Mechanical Engineering (Leningrad Branch), 1975, p. 619). The gas entering the tube in a water seal passes through a thin layer of soapy solution and rises along the burette in the form of bubbles covered by a solution film. The flow rate is determined by measuring the transit time of the film between the two marks on the burette and then dividing the volume of the burette between these marks by the measured time.

The disadvantages of such a flowmeter include the discreteness of measurements caused by the need to measure the travel time of the marks of only one arbitrarily selected film, a small upper measurement limit, limited by the fact that stable formation of a soap film is possible only with small diameters of the burette and a low rate of formation of gas bubbles, as well as a decrease measurement accuracy when gas is saturated with water vapor when it passes through a water lock, which leads to an increase in gas volume in the measuring burette.

A well-known gas-type gas flow meter, including a reservoir with liquid, gas supply and discharge lines with control valves, pipelines communicating the tank with the mains. In the reservoir with the liquid is a bell suspended on a compensation tape with a counterweight. After opening the control valve in the supply line, gas through pipelines enters the space under the bell, while the latter begins to emerge under the action of Archimedean force. After filling the control volume under the bell, the valve on the supply line closes and the valve opens on the gas discharge line from under the bell. The flow rate is calculated according to the measured time of gas displacement from the control volume (A.S. No. 987399, 1983. Bell-type discrete-dynamic installation for accurate reproduction and measurement of gas flow, published 07.01.83. Bulletin No. 1).

Such a device has the following disadvantages:

- the device performs discrete measurements of gas flow, since during the ascent of the bell the gas outlet line is closed;

- due to changes in the Archimedean force during the immersion of the bell, inertia and the presence of friction in the balancing system due to the presence of moving parts in the flowmeter, the gas pressure under the bell continuously changes, changing the hydraulic resistance of the flowmeter, therefore the flow rate is variable at constant pressure values in the line gas supply and hydraulic resistance in the gas discharge line, which complicates the processing of experimental data and reduces the accuracy of measurements.

The technical task of the invention is to remedy these disadvantages, namely:

- providing the possibility of continuous measurement of gas flow and quantity without loss of accuracy due to the use of two alternately filled and emptied gas volumes by automatically switching three-way valves in the gas supply and discharge lines;

- ensuring a constant flow rate at constant values of the pressure in the gas supply line and hydraulic resistance in the gas discharge line by maintaining a constant hydraulic resistance of the flowmeter, which is achieved by the absence of moving parts in the device and the organization of constant backpressure for the gas introduced into the tanks.

The solution of the technical problem is achieved by the fact that the gas flow meter includes a reservoir with liquid, gas supply and discharge lines with control valves, pipelines communicating with the mains.

New in the present invention is that the gas flow meter is equipped with a second tank, both tanks are equipped with sealed caps and the volume of the tanks are the same. The second tank is also communicated by pipelines through control valves, which are made three-position, with gas supply and discharge lines. The flow meter contains a valve control unit, two relays associated with the control unit, relay contact closure devices that are mounted on floats installed in each of the tanks. The gas flow meter also contains a tube communicating both reservoirs, while the ends of the gas supply pipelines and tubes are immersed in the reservoirs and the immersion depths of the ends of the tube are greater than or equal to the immersion depths of the ends of the gas supply pipelines, and the ends of the pipelines connecting the reservoirs with gas discharge lines are located above the upper fluid levels in tanks.

The drawing shows a diagram of the proposed gas flow meter.

The gas flow meter includes a reservoir 1 with a liquid and a reservoir 2 provided with sealed caps 3 and 4, while the reservoirs 1 and 2 have the same volumes.

The gas flow meter also contains a supply line 5 and a gas discharge line 6 in which three-position control valves 7 and 8 are installed. The gas supply line 5 has the ability to communicate with reservoirs 1 and 2 through the three-position valve 7 and pipelines 9 and 10, and the line 6 has the ability communication with reservoirs 1 and 2 through the control three-position valve 8 and pipelines 11 and 12. The flow meter contains a control unit 13 for valves 7 and 8, two reed relays 14 and 15 connected to the control unit 13, contact closure devices 16 and 17 p les 14 and 15 that constitute permanent magnets are fixed to the floats 18 and 19 mounted in each of the tanks 1 and 2.

The flow meter comprises a tube 20 communicating reservoirs 1 and 2. The ends of the gas supply pipelines 9 and 10 and the tubes 20 are immersed in the reservoirs 1 and 2, wherein the immersion depths of the ends of the tube 20 are greater than or equal to the immersion depths of the ends of the gas supply pipelines 9 and 10. Pipelines 11 and 12 of the gas outlet are connected to the caps 3 and 4 of the tanks 1 and 2.

The flow meter operates as follows.

When the liquid reaches the upper level (position "max") in the tank 1, when the valve 8 through the pipe 11 connects it to the gas discharge line 6, the mass m _{0 of} the gas in this tank is:

where ρ ₀ is the density of the gas in the tank 1 in the position "max", kg / m ³ ;

V _p - the volume of the gas cavity formed in the tank at the moment when the liquid in it is at the lower level (position "min"), m ³ ;

V _W - the volume of fluid in the tank, enclosed between the upper (position "max") and lower (position "min") levels, m ³ .

At this moment, the float 18 pops up, the magnet 16 mounted on it draws closer to the reed relay 14, which causes the contacts of the latter to close, and the control unit 13 puts the valves 7 and 8 in the position when the tank 1 is connected to the gas supply line 5 and disconnected from the line 6 gas discharge, and tank 2 - vice versa. The gas coming through the pipe 9 displaces the liquid through the pipe 20 from the tank 1 to the tank 2, and the gas located in the tank 2 is displaced by the fluid entering it through the pipe 12 and valve 8 into the gas discharge line 6. The pressure P _{K of the} liquid in the place of discharge of gas from the pipeline 9 (point "K" in the drawing) is the sum of the pressure P _{2 of the} gas in the tank 2 and the hydrostatic pressure of the liquid column with a height equal to its height in the tube 20:

where P ₂ is the pressure in the tank 2, n / m ² ;

ρ _W - the density of the liquid, kg / m ³ ;

g is the acceleration of gravity, m / s ² ;

N - the height of the liquid in the tube, m

The pressure P ₂ is determined by the hydraulic resistance of the gas discharge line 6. If it does not change during the entire time of liquid displacement from the tank 1 or the gas is discharged into the atmosphere, then the back pressure Р _K for the gas entering the tank 1 from the pipeline 9, in accordance with (2), remains constant. The hydraulic resistance of the flow meter, therefore, does not change, and with a constant value of the pressure in the gas supply line 5 and the hydraulic resistance in the gas discharge line 6, its flow rate will remain constant.

When the liquid reaches the lower level in the tank, the mass m _{1 of} the gas in it is equal to:

where ρ ₁ is the density of the gas in the tank in the "min" position, kg / m ³ .

The density ρ of the gas can be calculated from its pressure and temperature from the equation of state / 1 /:

where K is the compressibility factor, which is the ratio of the actual gas density to the calculated gas density in the same state, found according to the laws of an ideal gas (reference value);

R is the gas constant (reference value), J / (kg · K);

P is the gas pressure, n / m ² ;

T is the absolute temperature of the gas, K.

Accordingly, the gas density in any of the tanks in the "max" position is:

where P ₀ is the gas pressure in the tank in the "max"position; n / m ² ;

T is the absolute temperature of the gas in the tank, K.

The gas pressure P ₁ in one of the tanks in the “min” position is equal to the sum of the gas pressures in the second tank and the hydrostatic pressure of the liquid column with a height equal to its height in the tube 20. Since the second tank at this moment is in the “max” position ", then the gas pressure in it is P ₀ and pressure P ₁ is expressed by the sum of:

Accordingly, the density of the gas in the tank in the "min" position is equal to:

The mass of gas entering any of the reservoirs during the entire time of liquid displacement from it is equal to the mass difference m ₁ and m ₀ and, in accordance with (1), (3), taking into account (5), (7), is expressed by the formula:

where M is the mass amount of gas entering one of the reservoirs for the entire time the fluid is displaced from it.

The same amount of gas is displaced by the liquid during this time from an adjacent tank. Thus, in one cycle of the flowmeter, one of the tanks is filled with gas and gas is released from it. The half-cycle of the cycle is equal to the transition time of any of the tanks from the position "min" to the position "max" or vice versa. This time is equal to the interval between switching valves 7 and 8.

Mass gas flow is the ratio of the amount of gas passed through the flow meter when any of the tanks moves from the "min" position to the "max" position or vice versa, to the half cycle of the cycle:

where G is the mass flow rate of gas, kg / s;

t - half cycle of a cycle, s.

Thus, in order to determine the flow rate, it is necessary to know the temperature and pressure of the gas in any of the tanks at the moment when the liquid level in it is maximum, the switching time of the three-way solenoid valves and calculate using formulas (8), (9). Since the pressure and temperature of the gas in any of the tanks at the moment when the liquid level in it is maximum is equal to the pressure and temperature of the gas in the gas discharge line 6, they can be measured directly at any point in the line 6, therefore, instruments for measuring these parameters are not included into the flowmeter. If the gas is air and it is discharged into the atmosphere, as, for example, during calibration and calibration of industrial and laboratory flow meters, the gas parameters in the tank in the "max" position are equal to atmospheric and they are measured in the immediate vicinity of the air discharge site.

Bibliography

1. Methodical instructions. The consumption of liquids and gases. Measurement technique using special narrowing devices RD 50-411-83.

Claims (1)

A gas flow meter, including a liquid tank, gas supply and discharge lines with control valves, pipelines communicating the tank with highways, characterized in that the flow meter is equipped with a second tank, both tanks are equipped with upper sealed covers and the tank volumes are the same, the second tank is also connected by pipelines through control valves, which are made three-position, with gas supply and discharge lines, in addition, the flow meter contains a valve control unit, two relays associated with bl control window, relay contact closure devices that are mounted on floats installed in each of the tanks, a tube communicating both tanks, while the ends of the gas supply pipes and tubes are immersed in the tanks and the immersion depths of the ends of the tube are greater than or equal to the immersion depths of the ends of the gas supply pipelines and the ends of the pipelines connecting the tanks to the gas discharge lines are located above the upper liquid levels in the tanks.