RU2548948C1 - Method to detect viscosity of non-newtonian liquids - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: method to detect viscosity of non-Newtonian liquids includes their pumping via a channel, and viscosity is detected on the basis of the expression $${\eta }^C=\frac{N^{С}\cdot \left(r-r_{AV}\right)}{2\cdot \pi \cdot r_{AV}\cdot {\left({\vartheta }_{AV}^{С}\right)}^3\cdot t},$$

, where: η^C - viscosity of non-Newtonian liquid, Pa·s; N^C - useful power spent for second shift, W; r - radius of inner surface of pipe, m; r_AV - average radius of non-Newtonian liquid flow, m; $${\vartheta }_{AV}^{С}$$

- average speed of water suspension flow, m·s^-1; t - time of suspension jet leak from attachment, s.

EFFECT: simplified method to determine viscosity of non-Newtonian liquids mainly due to use of values of power spent for second shift and produced with the help of measurement equipment as input parameters.

Description

The invention relates to measuring equipment, and in particular to methods for measuring the viscosity of liquids.

A known method of measuring the viscosity of a liquid, including determining the time of expiration of its fixed volume through a capillary with a given diameter of the living section [1].

The disadvantage of this method [1] is the inability to measure the viscosity of non-Newtonian fluids.

A known method of measuring the viscosity of a fluid, including pumping fluid through a channel of known diameter, determining stress and shear rate on the channel wall [2].

The disadvantage of this method [2] is the impossibility of measuring the dependence of viscosity on shear rate at a given fluid velocity.

, где: η - вязкость жидкости, Па·с; τ(x) - напряжение сдвига, Па; γ′(x) - скорость сдвига, с^-1; x - текущая координата вдоль оси канала, м [3].A known method of measuring the viscosity of non-Newtonian fluids, including pumping them through a cylindrical channel, determining shear stress, shear rate, distribution profile of flow rates in the channel cross section and the dependence of viscosity on shear rate from the expression

where: η is the fluid viscosity, Pa · s; τ (x) is the shear stress, Pa; γ ′ (x) is the shear rate, s ^-1 ; x is the current coordinate along the axis of the channel, m [3].

The disadvantage of this method [3] is the complexity, high complexity and duration of the process of determining shear stress, which requires quite expensive hardware.

, гдеThe closest in technical essence is a method for determining the viscosity of non-Newtonian fluids, including pumping them through the channel, calculating the second flow rate and average flow rate, while the viscosity of non-Newtonian fluids is determined from the expression

where

η ^в - viscosity of water (Newtonian fluid, taken according to the reference data), Pa · s;

η ^s - viscosity of the suspension (non-Newtonian fluid), Pa · s;

- средняя скорость потока воды (расчетная величина), м·с^-1;

- average water flow rate (calculated value), m · s ^-1 ;

- средняя скорость потока водной суспензии (неньютоновской жидкости, расчетная величина) м·с^-1 [4].

- the average flow rate of an aqueous suspension (non-Newtonian fluid, calculated value) m · s ^-1 [4].

и, как следствие этого, с целью их нахождения, в введении дополнительных операций в цепочку основных.The disadvantage of the method [4] is the need to use rheological parameters of the intermediate Newtonian fluid (water) η ^B ,

and, as a consequence of this, in order to find them, in the introduction of additional operations in the main chain.

The invention solves the problem of simplifying the method for determining the viscosity of non-Newtonian fluids, with the creation of prerequisites for improving the express method for its implementation, in relation to production conditions, for example, during the processing and transportation of low-consistency wood-based fiber suspensions through technological pipelines.

The technical result consists in simplifying the method for determining the viscosity of low-consistency non-Newtonian fluids [4], mainly due to the use of the power spent on the second shift obtained by measuring technique as input parameters.

, гдеTo ensure a technical result, in a method for determining the viscosity of non-Newtonian fluids, including pumping them through a channel, calculating the second flow rate and average flow rate, according to the invention, the viscosity is determined from the expression

where

η ^C is the viscosity of a non-Newtonian fluid, Pa · s;

N ^C is the net power spent on the second shift, Pa · s;

r is the radius of the inner surface of the pipe, m;

r _SR - the average radius of the flow of non-Newtonian fluid, m;

- средняя скорость потока водной суспензии, м·с^-1;

- the average flow rate of the aqueous suspension, m · s ^-1 ;

t is the time of expiration of the jet of suspension from the nozzle, sec.

потока в трубопроводе, концентрации С. При известных значениях данных входных параметров, задача определения вязкости η^С неньютоновской жидкости существенно упрощается. Кроме того, для создания компактного экспресс-метода измерения вязкости неньютоновских жидкостей в производственных условиях в предлагаемом решении (по сравнению с известными способами [1, 2, 3, 4]) потребуется недорогое и в конструктивном отношении более простое приборное оснащение. Представленная формула определения вязкости η^С неньютоновских жидкостей выведена авторами аналитическим путем и подтверждена результатами эксперимента. Экспериментальное определение вязкости было проведено в проблемной лаборатории кафедры «Машины и аппараты промышленных технологий» СибГТУ.Unlike the known methods [1, 2, 3, 4], in the proposed solution, as the main input parameters, the values of the power N ^C spent on a second shift are measured, the time of the outflow of the jet from the nozzle t and the radius r of the inner surface of the pipe are calculated mean radius r _CP , mean velocity

flow in the pipeline, concentration C. For known values of these input parameters, the problem of determining the viscosity η ^{C of a} non-Newtonian fluid is significantly simplified. In addition, to create a compact express method for measuring the viscosity of non-Newtonian fluids under production conditions in the proposed solution (in comparison with the known methods [1, 2, 3, 4]), inexpensive and structurally simpler instrumentation will be required. The presented formula for determining the viscosity η ^{С of} non-Newtonian fluids was deduced by the authors analytically and confirmed by the experimental results. An experimental determination of viscosity was carried out in the problem laboratory of the Department of Machines and Apparatuses of Industrial Technologies of SibGTU.

As the studied liquids, aqueous suspensions of cellulose with a concentration of C = 0.5 were used; 1.0; 1.5%. Measurements were made with fixed input parameters: temperature t = 20 ° C; a fixed volume of the test fluid passed through the nozzle is V = 0.008 m ³ . The diameter of the channel cross section d = 0.02 m.

Example 1. The concentration of 0.5%. The operations were carried out in the following sequence:

и средний радиус r_СР потока по известным зависимостям;- calculated second flow rate Q, average speed

and the average radius r of the _CP stream according to known dependencies;

- measured the time t of the expiration of fixed volumes V of the studied liquids from the nozzle installed at the outlet of the channels and the power N ^C spent on a second shift.

The viscosity η ^{С was} calculated for the laminar regime of the suspension flow, since the results of the verification calculation showed that at concentrations C = 0.5% the flow regime in all working bodies of the installation is laminar (Re <2320).

Example 2. The concentration of 1%. The sequence of operations was carried out by analogy established in example 1.

The viscosity η ^{С was} calculated for the turbulent regime of the suspension flow, since the results of the verification calculation showed that at concentrations C = 1% the number Re was in the range of 14148 ... 16960.

Example 3. The concentration of 1.5%. The sequence of operations was carried out by analogy established in example 1.

The viscosity η ^{С was} calculated for the turbulent flow regime, since it was established that at concentrations C = 1.5% the number Re was the same as in Example 2, in the range 14148 ... 16960.

After substituting the calculation results and measurements in the presented dependence, the viscosity values of the studied aqueous pulp suspensions of Examples 1-3 were determined. The experimental results are shown in the table.

Thus, in comparison with existing methods [1, 2, 3, 4], the use of the proposed solution simplifies the process of determining the viscosity of low-consistency non-Newtonian fluids. Due to this, the prerequisites are created for monitoring this parameter in production conditions, for example, when grinding wood pulp entering the grinding stage in the form of low-consistency aqueous suspensions of cellulose.

In addition, it can be assumed that monitoring the viscosity of non-Newtonian fluids will prevent the possibility of emergencies that often occur when uncontrolled passage of the pulp through the mass pipe and the working cavities of the process equipment connected to it. Using the proposed solution improves the efficiency of technological processes.

Information sources

1. Tsvetkov V.N., Eskin V.E., Frenkel S.Ya. The structure of macromolecules in solutions. M .: Nauka, 1964.

2. Middleman S. The flow of polymers. M .: Mir, 1971.

3. SU No. 1716388, IPC G01N 11/04, application. 05/30/1989, publ. 02/29/1992, bull. No. 8.

4. RU No. 2441217, IPC G01N 11/04, application. October 28, 2010, publ. 01/27/2012, bull. Number 3.

Claims (1)

A method for determining the viscosity of low-consistency non-Newtonian fluids, including pumping them through a channel, calculating the second flow rate and average flow rate, characterized in that the viscosity is determined from the expression

where
η ^C is the viscosity of a non-Newtonian fluid, Pa · s;
N ^C - net power spent per second shift, W;
r is the radius of the inner surface of the pipe, m;
r _SR - the average radius of the flow of non-Newtonian fluid, m;

- the average flow rate of the aqueous suspension, m · s ^-1 ;
t is the time of expiration of the jet of suspension from the nozzle, sec.