RU2589454C1 - Method of measuring viscosity of gas - Google Patents

Abstract

FIELD: physics; measurement technology.

SUBSTANCE: invention relates to technical physics, particularly to methods of measuring viscosity of gases, and can be used in various industries and in laboratory practice. Method of measuring viscosity of gases is realised by its extraction and its filling tank, passing through capillary at constant pressure drop, measurement of time of change of pressure in reservoir by given value. At that, additionally container capacity is changed, pressure is measured before and after throttle and viscosity of gas is determined from product of pressure and time of gas outflow at moment when pressure in container reaches specified value.

EFFECT: high accuracy and reliability, as well as enabling analysis of gases at pressure close to atmospheric pressure without using special gas flow rate activators and controls.

1 cl, 1 dwg

Description

The present invention relates to the field of technical physics, in particular to methods for measuring the viscosity of gases η, and may find application in various industries and in laboratory practice.

A known method of measuring the viscosity of gases (see Zalmanzon L.A. Aerohydrodynamic methods for measuring the input parameters of automatic systems. - Moscow .: Nedra, 1973. S. 122-126), according to which gas with a constant flow rate is passed through a capillary, the pressure drop is measured at it, by which viscosity is judged.

The disadvantage of this method is the low measurement accuracy associated with the influence of gas density on the measurement result.

The closest in combination of features is the method of measuring viscosity, implemented in a device (AS USSR No. 972325, IPC G01N 11/06), in which a gas sample is taken, it is passed with a constant pressure drop through the capillary, the time of pressure change to the capillary is measured by a given value, the value of which is used to judge the value of viscosity.

The disadvantage of this method, adopted as a prototype, is the lack of accuracy in measuring the viscosity of the gas.

The purpose of the invention is to increase the accuracy of measurements by reducing methodological errors and providing the ability to measure the viscosity of the gas at pressures close to atmospheric.

This goal is achieved by the fact that in the method of measuring the viscosity of gases by taking and filling it with a tank, passing it through a capillary with a constant pressure drop, measuring the time the pressure in the tank changes by a predetermined amount, they additionally change the volume of the tank, measure the pressure before and after the throttle and about the viscosity gas is judged by the product of the average pressure and the time of gas outflow at the time the pressure in the tank reaches the set value.

In FIG. 1 is a diagram of a device that implements a method for measuring gas viscosity.

Gas for analysis is fed to input 1 of a three-way valve 2, to the input 3 of which a variable volume tank 4 with a piston 5 is connected. A pressure gauge 7, input 8 of valve 9 and pressure repeater chamber 10 are connected to input 6 of valve 2. Spring 12 is placed in chamber 10 and screw 13 for compressing it. The input 14 of the crane 9 is connected to the input of the capillary 15, the input of which is connected to the chamber 16 of the repeater 11. In the chamber 16 there is a spring 17 and a nozzle 18 connected with the atmosphere. The piston 5 is equipped with a rod 19. Between the chambers 10 and 16 of the repeater 11 is a membrane 20. A pressure gauge 21 is connected to the chamber 16.

The implementation of the method is as follows. At the initial moment of time, the three-way valve 2 is brought into a state in which the gas supply line for analysis is connected to the cavity of the tank 4 of variable volume, the piston 5 in which is in its lowest position. The valve 9 installed at the inlet of the capillary 15 is closed. The selection of gas is carried out by moving the piston 5 to the level of N ₀ . The state of the gas entering the tank 4 is described by the equation

where P ₀ is the absolute pressure of the gas in the tank 4 having an initial volume of V ₀ , after the selection of the analyzed gas; Θ ₀ is the amount of gas; R is the gas constant; T is the absolute temperature of the gas.

After that, the valve 2 is transferred to a state in which the container 4 is connected to the pressure gauge 7 and the repeater chamber 10. The gas is compressed by moving the piston 5 using the rod 19 to a predetermined level H ₁ . The volume of the tank 4 will decrease by ΔV, and the pressure P ₀ - will increase by ΔP.

The state of the gas will change and equation (1) will take the form

(P ₀ + ΔP) (V ₀ -ΔV) = Θ ₀ RT,

since P ₀ + ΔP = P _4n is the pressure in the tank 4 at the beginning of the measurements,

V ₀ -ΔV = V _4n , then

From (1) and (2) based on the Boyle-Mariotte law, i.e. provided Θ ₀ RT = const,

From (3)

The measurement process begins after opening the valve 9 and turning on the stopwatch (not shown in the drawing). The pressure P _4n at the inlet of the capillary 15 at the initial time t _{0 is} fixed. The analyzed gas passes through the capillary 15 into the chamber 16 of the repeater 11, and then through the nozzle 18 into the atmosphere. The pressure drop across the capillary 15 during the measurement process is maintained at a predetermined level using a repeater 11.

In the equilibrium state of the repeater 11, the force F ₁₀ = F _P10 + F _CR12 acting on the membrane 20 from the side of the chamber 10 is equal to the force F ₁₆ = F _P16 + F _CR17 acting from the side of the chamber 16, where F _P10 = P ₁₀ S is the force arising under the action of pressure P ₁₀ on the repeater membrane 20 of area S; F _P16 = P ₁₆ S is the force arising from the action of pressure P ₁₆ on the repeater membrane 20 with an area of S; F _pr12 = c ₁₂ Δl and F _pr17 = c ₁₇ Δl are the forces from the action of compressed springs 12 and 17 with stiffnesses of ₁₂ and ₁₇ , respectively, with deformation by Δl.

In equilibrium

F ₁₆ = F ₁₀ or P ₁₆ S + c ₁₇ Δl = P ₁₀ S + c ₁₂ Δl, whence

or

P ₁₀ -P ₁₆ = (c ₁₂ -c ₁₇ ) Δl / S.

The value of Δl is adjusted using the setting element 13 of the repeater 11 with a shift.

Since P ₁₀ -P ₁₆ = const, the gas flow rate G ₁₅ by capillary 15 with a conductivity α = const

G ₁₅ = α (P ₁₀ -P ₁₆ )

will be constant, which is a prerequisite for the implementation of the measuring process.

When the gas flows from the tank 4, the pressure P _4n decreases. The gas outflow, and therefore the measurement process, stops as soon as P _4n -P _4k = P _ass , where P _4k is the pressure in the tank 4 at time t _to . In this case, the pressure values P ₁₀ and P ₁₆ are fixed in the chambers 10 and 16 of the repeater 11, as well as the time t _k . At the end of the process of expiration from the tank 4 of a given amount of gas ΔΘ = G ₁₅ Δt _to its state will be described by the equation

Δt _k = (t _to -t ₀ ) is the time of the expiration process, at t ₀ = 0 Δt _k = t _to .

Subtracting equation (4) from (1), we obtain

P _ass V _4n = G ₁₅ Δt _to RT, whence

The gas flow rate G ₁₅ during its laminar flow through the capillary tube 15 is determined by the Poiseuille formula for a compressible fluid (see, for example, Ibragimov I.A., Farzane N.G., Ilyasov L.V. Elements and systems of pneumatic automation. - M. : Higher school, 1985.)

where d, l is the diameter and length of the capillary 15, respectively; η is the dynamic viscosity of the gas.

Substituting the value of G ₁₅ from (6) into (5), we obtain

и

- среднее давление на момент времени t_к, которое не является постоянной величиной и уменьшается с увеличением времени истечения,Given that

and

- the average pressure at time t _to , which is not a constant and decreases with increasing expiration time,

During measurement

so

The essence of the considered method for measuring the viscosity of gas is that gas is passed through the capillary 15, the pressure P _{4n is} fixed at time t ₀ and pressure P _4k at time t _k , during which the pressure in the tank 4 changes by a predetermined value of P _ass , after what measure the average pressure on the throttle 15 and the time t _to , the product of which determine the value of the controlled value.

The proposed method for measuring the viscosity of gas allows the analysis of gaseous media without the use of special stimulators of gas flow and regulators. In the proposed method, the selection of gas for analysis can be carried out at pressures close to atmospheric. The method excludes a methodological error caused by a change in the average pressure at the ends of the capillary. The method is economical, its implementation is simple, reliable and can improve the accuracy of measurements.

Claims (1)

A method of measuring the viscosity of gases by taking it and filling it with a container, passing through a capillary at a constant pressure drop, measuring the time that the pressure in the container changes by a predetermined amount, characterized in that the volume of the tank is changed, the pressure before and after the capillary is measured, and the gas viscosity is judged by the product of the average pressure and the gas outflow time at the moment the pressure in the tank reaches the set value.

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