SU661297A1 - Method and rotary viscosimeter for determining rheological parameters of non-newtonian liquids - Google Patents

Description

differences of tangential stresses arising on both sides of the measuring cylinder, it is necessary to create a torque proportional to this difference acting on the dynamometer. For this reason, when examining highly viscous liquids, a dynamometer can be subjected to heavy loads, leading to a loss of initial elasticity (which necessitates repacking) or even to the destruction of its sensitive element (torsion and the like). In the study of Newtonian liquids, the liquid layers located Hbie from different sides of the measuring cylinder, 1 | pa, are subjected to tangent, deformation with shear rates of one sign by rotating the drive cylinders in one direction. In the study of non-neo-Ton in Bingham fluids, these elephant fluids undergo deformations with shear rates of different signs by rotating, driving cylinders in opposite directions, J Then, based on the measured shear rates ej and Eo of the total torque M (which is opposite to Signs 6 and 6 represent the so-called R & GOST moment of forces acting on both sides of the measuring cylinder. Parameters of the rheological equation describing the dependence tangential voltage (found from measured M) of shear rate. In the case of the study of Bingham liquids, such an equation is the linear Bingham equation of -yy-Gy-PE: with the parameters -t and,. These parameters are the desired values. The cedar table of known methods consists in the fact that in the study of liquids that differ greatly in viscosity, the dynamometer is subjected to varying loads over a wide range, which results. . to the resolution of its sensitive element (torsion), etc., due to material fatigue or occasional excessive loads; the loss of the initial stiffness (elasticity) of the torsion, which. necessitates the re-calibration. In addition, to low sensitivity, and, consequently, to the accuracy of the dynamometer, as it must be made with the expectation of a wide range of loads, including large ones. It is also necessary to note the limitations and narrowness of the ranges of tangential stresses that can be measured by the known method. When implementing this method, it becomes necessary to load the dynamometer with a difference in torques, which, in the study of highly viscous liquids, can be so large that it exceeds the limit allowed for this particular dynamometer. In connection with this, when investigating in accordance with a known method of liquids significantly differing in rheological properties, it is necessary to replace the forces in the dynamometer, i.e. to change their rigidity and elastic limit - with the aim of expanding the range of measured stresses. . The purpose of the present invention is to expand the measurement range and ensure that it is possible to determine the rheological parameters of liquids having a non-linear rheological flow curve. For this, the layers of the test liquid are set at different levels, the deformation of the blunt layers is carried out first with the shear rates of the same magnitude and sign, and then with the opposite of the shear rates, which are different. corresponding sequel. .p) the occurrence of the same series of values, but with a constant difference on the interval of this series, while maintaining a torque equal to zero, after which a number of tangential stress values corresponding to m shift, according to the formula f 7 -) S + -1 P. P2 where tTj, is a tangial napr of 5s, shear; n is the number of accepted values of the tangiocial shear stress; the height of the levels of the layers of the investigated liquid. The goal is also achieved due to the fact that in the rotational viscometer, the overflow devices are installed with the possibility of independent displacement relative to each other in a direction parallel to the axis of the cylinders. The drawing shows a diagram of the rotational viscometer. . The cylinder 2 of the bell type connected to the dynamometer I is installed. In the annular space between the coaxial cylinders 3 and 4, an independent pilot and each other are connected to the drive (electric motor) through two independent reverse speed options (drive and speed options / in the drawing not shown) Cylinders 3 and 4 mate with a fixed cylinder 5 through seals 6, so that the annular spaces 7 and 8 between cylinders 2-3 and 2-4 can be filled with the test liquid. Between cylinders 2 and 5 there is a small vertical gap 9 through which fluid can flow from annular space 7 to space 8 or back. Cylinders 3 and 4 are installed with the possibility of independent movements along the vertical axis of the device, and they are equipped with a device for measuring the relative positions of their vertical edges and fixing the cylinders at specified positions (not shown) due to what the cylinder can work in biased relative to each other, it is set when their upper edges are at different levels h and h. In the lower part of the device, a tube 10 is installed, through which the test fluid can flow S viscometer. And in the upper part of the device there is a ring collector 11 and a funnel 12, along which liquid can be removed from. viscometer, overflowing over the upper edges of cylinders 3 and 4. Thanks to the device for feeding and removing liquid, the viscometer can work in a stream. Another variant of the overflow device is also possible, according to which the cylinders are not displaced relative to each other, and only the relative position of the overflow holes made in the walls of the inner and outer driving cylinders is changed (the holes in the drawing are not shown). To change the speeds of rotation of cylinders 3 and 4, each of them is equipped with a tachometer (pressure gauges ha in the drawing are not shown). The proposed rotational viscose meter works as follows. The determination of the rheological parameters of non-Newtonian fluids can be carried out according to a known method, which is as follows. Through tube 10, the test fluid is fed into the working gaps formed by bell 2 and driven by cylinders 3 and 4, from which it flows through the internal and external overflow devices into the funnel. 12 and ring tray. Measurements can be made even if there is no flow of the test liquid from the bottom up. There are annular working gaps, as in conventional non-flowing laboratory-type viscometers. The drive through speed variators rotates with given speeds n and front, cylinders 3 and 4, which, in turn, through the liquid under study

6 transmits torque momentum to bell 2 and dynamometer 1. When measuring Newtonian fluids, both cylinders rotate at the same speed in the same direction, and when measuring visco-plastic Bingham liquids, they rotate the cylinders 3 and 4 at different speeds of the anti-contractile directions. Then, on the basis of the measured M, p, and p, determine the parameters of the rheological equation, which describes the dependence of the angular stress of the stress on the shear rate c. When changes are made according to my method, the test liquid is slowly pumped from the bottom upwards through the working gaps of the viscometer formed by the driving and measuring cylinders. The free surfaces of the liquid in the layers located on opposite sides of the measuring cylinder should be at different levels hj, and h, which is achieved by displacing the overflow devices relative to each other in the vertical (parallel to the axis of the cylinders) direction. At the same time, these fluid layers are subjected to continuous tangential deformations with shear rates of the same or opposite signs — by rotating the driving cylinders in one or mutually opposite directions. In this case; first, these layers are deformed with the same (in magnitude and) constant shear rates by rotating both cylinders in the same direction with the same angular velocity n (rev / sec.). At the same time, the torque meter M of the tangential forces acting on the measuring cylinder from both sides is measured by a dynamometer, which, with a known radius: g of the cylinder, allows one to determine the voltage by the formula. ; m L2VrCH 2 The corresponding shear rate is limited by the following formula (using the well-known clause where d is the width of the gap between the bDviH actuator cylinders and the measuring gauge. N, the values of, and T. are the coordinates of the first point on the isome rheological flow curve. To reduce the load on the innometer It is advisable to choose a small value for n, at which, also, as a rule, is small. After determining the first point of the rheogram, the same liquid layers are deformed with mutually opposite shear velocities.

for which, without changing the direction and speed of rotation of one of the cylinders, the direction of rotation of the other cylinder is reversed, and its speed n is chosen such that the torque shown by the dynamometer Mj is equal to zero (M 2 0).

. Since / then and the voltage Tz acting on the inner and outer surfaces of the bell will also not be equal to each other {TRFTN AT MDO. In order to convince ourselves of this, we will find a variety of Td, and TC at M 2 O.

The moments of the forces acting on the inner and outer surfaces of the bell are equal

MgTnr li Tg ;. -.

LLN - 2 112 n DIFFERENCE of these moments, measured by a dynamometer

Mg Mg-Mj -eUr di tg-tiaTnl, with M 0.

V v-from where

, V and, since

, h.h, To-rg trH.

. Due to the fact that the velocity of the outer cylinder did not change and remained equal to n, then the voltage; TC will be the same, equal to the already well-known T,

Using formula (3), one can easily find tTg by the known ti. The corresponding shear rate of the horse is determined by the formula (12) on the basis of the known Pg measured by a meter at which Mg is 0. Thus, the second point of the desired curve is determined. from 6. Her coordinates: f g and Tg.

Then the rotational speeds of both cylinders are increased at the same time, and so that the speed of the outer cylinder becomes equal njf, and the internal speed is chosen so that the moment acting on the dynamometer remains zero (M J O). Let this speed be n, determined by a tachometer. Zn Tr is easy to find t by the formula (3)

(moreover, r - 3 bases n can easily be found, using formula (2). | This gives the third point (with coordinates e and f) of the desired

Continuing to increase the rotational speeds of the cylinders (and, consequently, the shear rate) and the voltage stepwise, in this way, a sufficient number of points of the desired curve are obtained and a complete

logical curve (or its section), the parameters of which are the desired rheological parameters of the fluid.

Depending on the type of curve, the most adequate equation describing it is selected.

As can be seen from the description of the proposed method, in the course of its implementation, the dynamometer is loaded only once, with a non-zero differential moment M (), which can be chosen very much if desired. Kalymy (in the presence of a highly sensitive dynamometer). During the rest of the measurement time, the load

The dynamometer is zero (;.. &) No matter how high the voltages and shear rates acting in the fluid are high,

At this time, the dynamometer does not need to perform its usual function - measuring the vulture, since it actually works only as an indicator of no load. This can be done much easier and more precisely, since a very sensitive indicator of zero load can be used, and its operation is also easy to automate. In addition, in connection with a small value of a single measurable non-zero moment M, it is possible to significantly reduce the scale of the dynamometer (i.e., the range of directly measured moments) with a very wide range of detectable values.

shear stresses.

The accuracy of the method. Is due to the fact that. during the determination of the rheological curve, they are changed and directly measured, mainly not

shear stresses (which is difficult to apply with greater accuracy), and the angular velocities of the cylinders, which can be measured more accurately, especially with tachometers, which work on the principle of discrete counting of the number of revolutions.

It should also be noted that the proposed viscometer can also be used with overflow devices installed at the same level (when h ;, hj). In this case, there is no need for the flow of the test liquid from bottom to top in the working gaps between the cylinders, and the viscometer can work as ordinary viscometers of stagnant type. However, this eliminates the possibility of reducing the torque during the measurement process to zero.

Proposed for this case

The measurement method is as follows.

Claims (2)

The free surfaces of the liquid in the layers located on both sides of the measuring cylinder are set at the same level h. First these 9. the layers are subjected to continuous tangential deformations with the same sign and magnitude of shear rates by rotating drive CILE Wood In the same direction with the same angular velocity n, and the torque of the M / tangential forces deformed from both sides is measured by a dynamometer on the measuring cylinder. This makes it possible to determine the voltage tr by the formula that is derived from the formula. {) If we set h. 2 h, h T- - h 1 and the corresponding shear rate - according to the formula (2). These layers are then deformed with mutually opposite shear rates, which change discretely by a step program, giving them such meaning that they go through the same series, starting with g, found from (2), and in this case, the constant would differ by one interval of this row. But the moment M, which is the moment difference (Ms-Mg), cannot be equal to zero in this case. It accepts various small values, proportional to the increments of the voltage of the G – D reacting at step increments of the velocity Shear d. After that, a number of shear stress values τ: are determined, corresponding to different shear rates 6, and any (n + 1) stress (Γ, + 1), starting with determined on the basis of th value (T) by the formula. In this case, the proposed viscometer also has an advantage over the known viscoseglars, which means that the rheological curve is any, including a curvilinear shape, and its parameters can be determined by loading the dynamometer with no large loads corresponding to the full force in the fluid. but only by the differences (increments) of these stresses arising from the formation of stepwise shear rates. These times the voltage spans and the proportional loads on the dynamometer can be chosen arbitrarily and be arbitrarily small (with a high sensitivity and accuracy of the dynamometer). The technical and economic effect of the present invention concludes with the fact that it allows a substantial increase in the operability of the dynomometer as a result of a significant reduction in the load on it and a reduction in its operating time at this reduced load; increase the sensitivity and, therefore, 7 and accuracy of the dynamometer, which becomes possible due to a significant reduction of its maximum load equal to M. With high sensitivity and accuracy of the dynamometer, it is possible to determine the rheological parameters of fluids of different rheological types, including those with non-linear characteristics. flow curves (known viscometer and method do not have this capability). It is also possible to significantly expand the range of detectable stresses, and, consequently, viscosities, with a significant reduction in the range of directly measured torques, since the stress range becomes independent of the maximum allowable load on the dynamometer; Therefore, when examining liquids that differ greatly in rheological properties, there is no need to change the stiffness of the dynamometer sensitive element (for example, torsion), i.e. move from one voltage scale to another, replace One torsion with another, etc. and at the same time change the measurement accuracy. In addition, it is easy to automate the viscometer and use it as a flow instrument installed on the process stream for the purpose of operatively monitoring the rheological properties of the flowing fluids. Claim 1. Method for determining the rheological parameters of non-Newtonian fluids with continuous shear deformation of the layers of the test liquid on both sides of the measuring surface with the elimination of their response to deformation by measuring the torque at the same time feeding the test liquid from the bottom up extending the measurement range and enabling the determination of the rheological parameters of liquids with a non-linear rheological flow curve; The liquid is set at different levels, the deformation of both layers is carried out first with the same shear rates and then shear rates that are mutually opposite in sign, which are discretely changed by the step speed corresponding to the successive passage of one and the same the same number of values, but with a constant difference on the interval of this series, maintaining the rotational moment equal to zero at this time, after which a number of tangent values are determined. (.... ff-ii ft t-:. ;;: I i i .. of the normal stress corresponding to different shear rates according to the formula / 7 - / 7, .L ntt- n -hj where T is the tangential shear stress; And - a number of accepted values of the tangential shear stress; Z is the height of the layers of the investigated liquid. 2. A rotary viscometer for carrying out the method according to claim 1, comprising two jaws with coaxial cylinders,. located in the annular cavity 12 between them is a measuring cylinder of the bell type, connected to a dynamometer, a device for supplying the test liquid to the annular cavity, external and internal overflow devices, and the fact that the overflow devices are installed with independent displacement relative to each other in a direction parallel to the axis of the cylinders. Sources of information taken into account in the examination 1. The author's certificate of the USSR 181873, class. C 01 N 11/14, 1966. 2. USSR author's certificate No. 269579, class C 01 N 11/14, 1970.