RU2500997C1 - Method of determining viscosity of nonlinear viscous liquids and apparatus for realising said method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: in the method of determining viscosity of nonlinear viscous liquids, the viscosity sensor used is a frequency-controlled drive in a set with an asynchronous electric motor of a mixer, whose synchronous supply frequency and motor voltage are stabilised. Viscosity is calculated from the mixer shaft speed and temperature of the liquid using the relationship: ν = b₀(Ω,t)+b₁(Ω,t)ω+b₂(Ω,t)ω², where ν is polymer viscosity, ω is motor shaft speed, t is polymer temperature, Ω is stabilised synchronous motor frequency, b₀, b₁ and b₂ are coefficients which depend on synchronous frequency and temperature. The apparatus for determining viscosity of nonlinear viscous liquids has a measuring vessel with a thermometer and a mixer rotated by an asynchronous motor which is controlled by a frequency converter with controlled frequency and voltage. A magnet is attached to the shaft of the mixer, wherein movement of the magnet is detected by a Hall sensor and an oscilloscope, signals from which are transmitted to a computer.

EFFECT: method of determining viscosity of non-Newton liquids on a stream, where spatial structure of the liquid medium should not be disrupted during measurement.

2 cl, 3 dwg

Description

The invention relates to methods for determining the viscosity of nonlinearly viscous liquids.

A feature of such liquids is that when the speed of the mixer changes, the viscosity changes. Moreover, there is a threshold value of the rotational speed of the mixer, at which the viscosity changes almost abruptly. The viscosity value also depends on the temperature of the liquid. That is, the flow curve of such liquids is not linear, i.e. viscosity is not constant, but depends on shear rate or on the history of deformation of the material. Such fluids are classified as non-Newtonian fluids, since they do not obey Newton's laws.

Several methods for measuring viscosity are known: capillary, vibration, rotational and ultrasonic.

The method of capillary viscometry [Malkin A.Ya., Chalykh A.E. Diffusion and viscosity of polymers. Measurement methods. - M .: Chemistry, 1979] is based on the Poiseuille law on a viscous fluid, which describes the laws of fluid motion in the capillary and is applicable only to Newtonian fluids.

The principle of operation of vibrational viscometers [Malkin A.Ya., Isaev A.I. Rheology: concepts, methods, applications / Transl. from English - St. Petersburg: Profession, 2007] is based on changing the parameters of the forced vibrations of bodies of regular geometric shape. The disadvantage of these devices is that they do not provide information about the degree of preservation of the spatial structure of a nonlinearly viscous medium.

Rotational method of viscometry [Malkin A.Ya., Isaev A.I. Rheology: concepts, methods, applications / Transl. from English - St. Petersburg: Profession, 2007] consists in the fact that the test fluid is placed in a small gap between two bodies, necessary for the shift of the test medium. One of the bodies throughout the experiment remains stationary, the other, called the rotor of the rotational viscometer, rotates at a constant speed, i.e. the rotational movement of the rotor of the viscometer is transmitted to another surface. Thus, the rotational moment of the rotor of a rotational viscometer is a measure of viscosity. The disadvantage of these devices is the need to select the appropriate spindles when changing the rotor speed, which leads to its discrete nature. In addition, it is not possible to take into account the effect of shaft speed on viscosity.

Ultrasonic method for measuring viscosity [Malkin A.Ya., Chalykh A.E. Diffusion and viscosity of polymers. Measurement methods. - M .: Chemistry, 1979] is based on measuring the rate of attenuation of oscillations in a plate of magnetostrictive material immersed in the medium under study. The main disadvantage of this method is the narrow measurement range due to the material properties of the device.

Today there is a measurement of viscosity on the stream (express method), related to indirect measurement methods, which are based on the principle of measuring the correlation between the specific viscosity of the polymer and the Mooney viscosity [Methods for the study of the structure and properties of polymers: Textbook. allowance / I.Yu. Averko-Antonovich, R.T. Bickmullin; KSTU, Kazan, 2002, 604 pp.]. The disadvantage of this method is the violation of the correlation due to the influence of various factors not taken into account by the equation, for example, the effect of the polydispersity of the polymer on the Mooney viscosity.

One of the features of determining the viscosity of rubbers according to the Mooney method is the evaluation of the polymer properties, the resistance of the polymer to premature vulcanization [Determination of the Mooney index of the polymer in latex SKMS-30ARKPN viscosity / N.D. Veyseyskaya, V.A. Ryzhov, B.S. Nedelkin, V.O. Reichsfeld // Industry SK, M., 1976, No. 7. - S.20-21].

The closest in technical essence and the achieved result is a method implemented in a device for measuring the viscosity of fluids [RF patent No. 2152022] using a measuring chamber in which the rotor of an induction motor is installed, and the information signal generating unit is made according to the AC bridge circuit, in the shoulders of which are included capacitors of variable capacitance, formed by the electrodes of the stator of the tachometer and at least one pole of its rotor, which through a capacitor of constant capacity, nny induction motor rotor and the wall surface of the viscosity of the sensor housing, is connected to one pole of the supply generator bridge, the other pole is electrically connected to the common point of resistors of different bridge arms.

The disadvantage of this technical solution is its inapplicability for non-Newtonian fluids, since the rotation of the rotor can violate the spatial structure of the liquid medium.

The objective of the invention is to develop a method for determining the viscosity of non-Newtonian fluids in a stream, characterized in that during the measurement process the spatial structure of the liquid medium should not be destroyed.

This problem is solved by the fact that in the method for determining the viscosity of nonlinearly viscous liquids, a frequency-controlled drive complete with an asynchronous electric motor of the mixer is used as a viscosity sensor, in which the synchronous power frequency and voltage of the motor are stabilized, while the frequency of rotation of the shaft of the mixer and the temperature of the liquid calculate the viscosity by the ratio:

$$\nu ={\text{b}}_{\text{0}}\text{(}\Omega \text{, t)}+{\text{b}}_{\text{one}}\text{(}\Omega \text{, t)}\omega +{\text{b}}_{\text{2}}\text{(}\Omega \text{, t)}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="00000004.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\text{2}}\text{, (one)}$$

where ν is the viscosity of the polymer, ω is the frequency of rotation of the motor shaft, t is the temperature of the polymer, Ω is the stabilized synchronous frequency of the electric motor, b ₀ , b ₁ and b ₂ are coefficients that depend on the synchronous frequency and temperature.

In terms of the device, the problem is solved in that in a device for determining the viscosity of nonlinearly viscous liquids, including a measuring tank with a thermometer and an agitator rotated by an asynchronous motor, which is controlled by a frequency converter of adjustable frequency and voltage, while a magnet is attached to the agitator shaft, the movement of which fixed by a Hall sensor and an oscilloscope, the signals from which are transmitted to a computer.

As a result of a series of experiments and statistical analysis of the obtained data, a functional relationship was revealed:

$$T(\nu ,\Omega ,t)={\text{a}}_{\text{0}}\text{(t}\text{,}\Omega \text{)}+{\text{a}}_{\text{one}}\text{(t}\text{,}\Omega \text{)}\nu +{\text{a}}_{\text{2}}\text{(t}\text{,}\Omega \text{)}{\mathrm{<figure-callout\; id="2"\; label="\nu "\; filenames="00000004.png"\; state="\{\{state\}\}">\nu </figure-callout>}}^{\text{2}}\text{, (2)}$$

where T is the time of one complete revolution of the drive shaft, ν is the viscosity, Ω is the specified frequency, t is the polymer temperature, and ₀ , a ₁ , and ₂ are the coefficients of the equation determined by the experimental method and depending on the synchronous frequency, temperature, and asynchronous characteristics engine.

The experimental results obtained at different given frequencies, but at a constant temperature and at one given frequency, but at different temperatures, are shown in figures 2 and 3, respectively. From formula (2), by means of algebraic transformations, formula (1) is obtained, where the frequency ω is determined after the time of one full revolution of the drive shaft T.

The figure 1 presents a diagram of a device for measuring viscosity on the stream.

The device includes a three-phase asynchronous motor 1 with a squirrel-cage rotor, a stirrer 2 and a variable frequency drive 3, in which it is possible to measure the current in the circuit and the voltage supplied to the electric motor. A magnet 4 is attached to the mixer shaft, the movement of which is recorded by the Hall sensor 5 and the oscilloscope 6. The temperature of the liquid 7, which is placed in the tank 8 of the water bath 9, is measured by a thermometer 10. The viscosity is calculated on the computer 11.

The device operates as follows. The measured liquid 7 is placed in a container 8 with a stirrer 2, rotated by an induction motor 1, which is controlled by a frequency converter 3 of adjustable frequency (synchronous frequency) and voltage. The motor shaft rotates with a frequency at which there is no destruction of the spatial structure of the liquid medium. This frequency is selected experimentally at the stage of collecting information and determining the coefficients of formula (1). The rotational speed is measured using a magnet 4 and a Hall sensor 5. When a magnet attached to the mixer shaft passes by the sensor, the sensor generates a voltage surge determined by the oscilloscope 6. Computer 11 determines the time intervals between adjacent surges and calculates the viscosity value as a function of synchronous frequency, shaft speed and temperature.

The claimed technical result of the invention is achieved by using the dependence of the slip and the rotational speed of the induction motor on the load on its shaft.

Claims (2)

1. A method for determining the viscosity of nonlinearly viscous liquids using a frequency-controlled drive as a viscosity sensor complete with an asynchronous agitator motor, in which the synchronous power frequency and motor voltage are stabilized, while the viscosity is calculated from the agitator shaft speed and fluid temperature by the ratio :
ν = b ₀ (Ω, t) + b ₁ (Ω, t) ω + b ₂ (Ω, t) ω ² ,
where ν is the viscosity of the polymer; ω is the rotational speed of the motor shaft; t is the temperature of the polymer; Ω is the stabilized synchronous frequency of the electric motor; b ₀ , b ₁ and b ₂ are coefficients depending on the synchronous frequency and temperature. 2. The device for implementing the method according to claim 1, comprising a measuring capacitance with a thermometer and an agitator rotated by an asynchronous motor, which is controlled by a frequency converter of adjustable frequency and voltage, while a magnet is attached to the agitator shaft, the movement of which is fixed by a Hall sensor and an oscilloscope, signals from which are transferred to the computer.

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