Method of determining liquid physical properties

FIELD: physics.

SUBSTANCE: gas is fed to the inlet of a gas-carrying pipe immersed at a given depth into the monitored liquid. Maximum pressure in the pipe is then measured. Repetition periods of gas bubbles are also measured at two different gas flow rates into the gas carrying pipe. Further, surface tension, density and viscosity of the monitored liquid are then determined from the value of maximum pressure in the pipe and repetition periods of gas bubbles.

EFFECT: higher accuracy of determining surface tension of liquid and broader functional capabilities of the method through possibility of determining density and viscosity of the liquid.

1 dwg

 

The invention relates to the field of measurement technology, in particular to pneumatic control surface tension and density of liquid, and can find application in various industries such as petroleum, chemical, microbiological, food, etc.

There is a method of determining the coefficient of surface tension of a liquid by the method of "supine" drops (Adimon. Adhesion of fluids and wetting. M, Chemistry, 1974, p.52-55), which consists in determining the shape and size of the droplets lying on the wafer using optical systems, such as a microscope.

The disadvantages of the method are the complexity of determining the characteristic sizes of the drops and the dependence of the measurement result of the density.

Know the definition of the coefficient of surface tension of liquid by way of the isolation rings, earrings or plates from the liquid under study (method Du-Nui) (Surface phenomena and surfactants. Handbook edited Arm. L., Chemistry, 1984, s-168), which consists in measuring the force required for detachment of the ring from the surface of the liquid. The disadvantages of this method are the low accuracy due to contamination of the surface of the ring, and the inability to ensure the continuity of the dimension.

Closest to the proposed technical essence is the way I determine the surface tension of liquids by the method of maximum pressure in the bubble (test Methods aqueous solutions of surfactants. The overview. Part 1. Compilers: Iketani and Liebovich. M, NITAI, 1965, p.39-50), which consists in determining the highest pressure in the bubble of air blown out of the capillary immersed in the test liquid to a predetermined depth.

The disadvantage of the method adopted for the prototype, is the dependence of the measurement result from the depth of immersion of the capillary and viscosity of the fluid.

The technical problem is to increase the accuracy of determining the surface tension of viscous liquids, as well as expanding the functionality of the method by providing the possibility of determining the density and viscosity of the fluid.

The technical problem is solved by the fact that for the determination of density, surface tension and viscosity in controlled liquid immersed to a predetermined depth gas supplying tube of known diameter, serves gas with a predetermined flow rate to the input of a gas-feeding tube, measure the maximum value of pressure in the tube and additionally measure the repetition period of gas bubbles, then change the value of the gas flow to a specified value, and again measure the repetition period of the bubbles, as a result, values for the maximum pressure in the tube and the periods of repetition of the bubbles corresponding to different values of gas flow, in judging the density, surface tension and elm are the spine of the controlled fluid.

Figure 1 shows the block diagram of the device for the implementation of the proposed method for determining physical properties of a liquid.

To the input of a gas-feeding tube 1, is immersed in a controlled liquid 2 to a depth of N, via the pneumatic resistance 3 the gas is supplied with a specified flow rate from the source 4. To the input of the gas-feeding tube 1 is connected to the pressure transducer 5. The output of the inverter 5 is connected to the input of the frequency meter 6 for measuring the period of pressure fluctuations in a gas-feeding tube, i.e. the repetition period of the bubbles. The outputs of the inverter 5 and the counter 6 is connected to the inputs of the computing unit 7, the output of which is connected to the input of the secondary device 9.

When the gas in the gas supplying tube 1 at its output produces a gas bubble, the diameter of which increases up until the lifting force is Fa=Vng(ρWg), where Vn- the volume of the bubble at the moment of separation, g - acceleration of gravity, ρWthe density of the fluid ρgthe density of the gas becomes equal to the sum of the forces of viscous friction Fη=6ηWπν1rnand forces resulting from adhesion of the bubble Fσ=πσWd0sinθ, where ηWis the dynamic viscosity of the fluid, ν1the velocity of the center of the bubble when the gas in the tube with a constant flow rate of Q1, rn- OBJImport at the time of separation, σW- the surface tension of the liquid, d0- tube diameter, θ is the wetting angle.

Assuming that the center of the bubble moves uniformly and its separation occurs when the distance between the center of the bubble and the end of the tube is equal to 2rn, the moving speed of the ν1can be found by the formula

where T1the repetition period of the bubbles when the gas in the tube with a flow rate of Q1.

At constant flow rate of Q1tear the volume of the bubble Vnis determined by the expression

Taking into account (1) and (2) and provided sinθ=1 the balance of forces acting on the bubble at the moment of separation, will be written in the form:

When changing the gas flow in a gas-feeding tube from the values of Q1to Q2equation (3) takes the form

where T2the repetition period of the bubbles when the gas in the tube with a flow rate of Q2.

At the same time for viscous liquids the maximum gauge pressure Pandin the bubble is determined by the expression

where H is the depth of immersion of the tube in the liquid, Pa- excessive pressure above the liquid surface.

Taking into account (1) the expression (5) when Q1=const takes the form

Equation(3), (4) � (6) constitute a system deciding which is relatively σW, ρWand ηWget the expression to determine σW, ρWand ηWon the measured values of Pand, T1and T2when Q1, Q2, g, d0, H=const.

where

the coefficients of proportionality.

Thus, the dimension of Pand, T1and T2allows you to define the equations (7), (8) and (9) surface tension σWthe density ρWand the viscosity of the liquid ηW.

In the measurement process when Q1=const pressure in a gas-feeding tube 1, increasing with the growth of a gas bubble, fed to the inlet of the pressure transducer 5, which measures the pressure Pandin the tube at the time of separation bubble. At the same time the pulse output signal from the Converter 5 is fed to the input of the frequency meter 6 for measuring the repetition period of the bubbles T1which signal together with the signal transformed into the La pressure 5 enters the computing unit 8. Then change the gas flow rate of Q1to Q2and to the input of the computing unit 7 of the counter 6 receives the new value of the repetition period of the bubbles T2corresponding to the flow rate Q2. In the last phase computing unit 7 on the basis of the measured Pand, T1and T2by the formulas (7), (8) and (9) defines the values of the surface tension σWdensity ρWand the viscosity of the liquid ηWand generates the signals received at the input of the secondary device 8.

In the proposed method produces measuring the maximum pressure in the bubble and periods adherence of gas bubbles at two different values of the flow, allowing you to determine the viscosity and density of the fluid and to increase the accuracy of determination of surface tension by accounting for the effects of viscosity and density on the measurement result.

The method of determining physical properties of a fluid, according to which conduct the gas to the gas supplying inlet tube is immersed to a predetermined depth in the controlled fluid, and measure the maximum pressure in the tube, characterized in that it further measure the periods of repetition of gas bubbles at two different gas flow in a gas-feeding tube and the magnitude of the maximum pressure in the tube and periods adherence of gas bubbles is judged on the surface of the nom tension, density and viscosity of the controlled fluid.



 

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