SU1420467A1 - Primary transducer of fluid viscosity - Google Patents

Abstract

This invention relates to a technique for measuring the viscosity of a fluid. To make it possible to study small amounts of samples, an electrochemical diffusion pO2 sensor is used as a primary viscosity converter. The measurements are based on the dependence of the established values of diffusion currents in the presence and absence of mixing of the test medium in the zone of the active surface of the sensor on its viscosity, all other things being the same. For analysis, no more than 10 -10 g of the test substance is required. 2 Il. (2 co

Description

4 1ЧЭ

about

four

Od

The invention relates to a technique for measuring viscosity, in particular, primary converters, serving for measuring the viscosity of liquid media.

The purpose of the invention is to provide the possibility of examining small amounts of samples.

; FIG. 1 shows schematically the pO2 sensor; in fig. 2 - curve of dependence of the ratio of the established values of 1 diffusion sensor currents in the presence and absence of mixing of the studied medium from its viscosity.

: The electrochemical diffusion sensor; Clarke's pO2 cell, which operates on the principle of measuring the oxygen reduction current, includes an electrode system consisting of the indicator polarizing: electrode (cathode) 1 and reference electrode; Yes 2 comparisons placed in an electrolyte 3. Electrode system is separated from the analyzed liquid 4 by a gas-permeable: polymer membrane 5. The mixing of the analyzed medium 4 in the working surface area of the sensor is carried out by an electric mixer 6.

To measure the viscosity of the test fluid, a voltage is applied to the electrode system of the sensor, which provides a polarization of the indicator electrode 1 for the potential value corresponding to the limiting current of the electrochemical oxygen reduction. The depolarization current of the indicator electrode due to the ionization of oxygen molecules on it by the reaction; Og + 2H2O + 4e -.40N (1) is proportional to the oxygen tension in the analyzed fluid 4:

..

ig k-pO2

(2.)

where pO2 is the oxygen voltage;

k - coefficient of proportionality. The magnitude of the proportionality coefficient characterizes the rate at which 02 molecules arrive at the active surface of the indicator electrode and is determined by the expression

p-f. s

 ,

RE RM RMN.S

Gz)

where n is the number of electrons involved in the electrochemical reaction;

F is the Farade number; S is the area of the indicator electrode;

, B, b is the thickness of the inner 55 electrolyte layer, the gas-permeable membrane and the diffusion region, respectively;

with

YU

20 o -J5

25

45

Ra, Ry, RN.S - gas permeability of the indicated components of the near-electrode area of the sensor.

When this diffusion through the membrane 5 and the near-electrode region of the electrolyte 3 in the sensor is mainly due to specific design parameters

with

sensor itself. Member: - expressions (3),

rti-c

taking into account the properties of the diffusion region, the convective transfer and the molecular diffusion of oxygen in the studied liquid are determined.

When the electric mixer 6 is turned on, convective transfer plays a decisive role, and when the mixer is turned off, the process of molecular diffusion of dissolved oxygen is played.

The convective component is the transfer of molecules into the ionization zone along with the flow of a fluid moving as it moves or is forced to circulate. In this case, the convective mass transfer is expressed by the equation

IKOHB Vn.crcO2, (4)

where vn.c. - volumetric velocity of the test fluid;

CO2 is the concentration of oxygen in it.

Molecular diffusion is due to the transfer of dissolved oxygen molecules under the action of a concentration gradient. Mass transfer due to molecular diffusion of oxygen in the liquid under study, directed to the reaction zone of the pOa sensor, can be expressed by the equation

Dig.Odr.sOg (5)

where D is the molecular diffusion coefficient;

 dissolved oxygen concentration gradient.

Since the oxygen concentration in the area of the working electrode of the pO2 sensor is close to zero due to its electroreduction in accordance with equation (1), the expression (5) with a small approximation can be written as

B "F O-SO2, (6)

The ratio of the flow of directional transfer in the presence and absence of mixing of the test liquid takes the form

IKOHB Vri.c.cO2, | Viii.c

1dnf D- с02D

(7)

At the same time, the resulting signal of the ratio of the output currents of the pO2 sensor in the presence and absence of mixing is practically independent of the effective value of the oxygen concentration.

The molecular diffusion coefficient of the analyzed gas in accordance with the known equation can be represented as

where K is a fluid constant;

W-activation energy;

k is the Boltzmann constant;

T is the temperature of the liquid.

The viscosity of a fluid varies according to its temperature.

T T e

Substituting equation (9) into equation (8), we obtain

D C-T / L (10)

and equation 7 takes the form

1 +

Ul.s

ct

l

those. The operation of the pO2 sensor, used as a primary viscosity converter, can be described by the following equation:

With.

mr

one.

Thus, at a controlled value of Vn.c./KT, the viscosity value of the liquid under study is determined by the ratio of the output currents of the pO2 sensor at n. and no mixing.

Shown in FIG. 2, the dependence of the ratio of the established values of diffusion currents of the electrochemical, roS sensor on the viscosity of the medium under study confirms the correctness of the conclusions made. Measurements were carried out on aqueous glycerol solutions with known tabular viscosity values.

The invention provides the ability to sample small volumes. This allows the invention to be extended in biology and medicine in the analysis of valuable and rare samples. At the same time, the amount of material required for analysis using the proposed converter is much smaller compared with the known devices and is determined by values of the order of 10 g.

15

20

25

Claims (1)

Invention Formula Pri.menenie electrochemical diffusion sensor partial pressure of oxygen as the primary viscosity converter of liquid media. WITH ue. f I I 2 J 5 6 e w fae. 2 I I I I I I 20 with / 7h