CN101923033A - Method for measuring viscosity of low-viscosity liquid and rheometer - Google Patents

Abstract

The invention relates to a method for measuring the viscosity of low-viscosity liquid and a rheometer. The method for measuring the viscosity of low-viscosity liquid comprises the following steps of: S10, measuring cylinder radius (r), surface area (S) of cylinder immersed liquid and liquid density (rho); S20, measuring an idle-load mechanical spectrum comprising values of a storage modulus (k) and a loss modulus (k') in a system complex modulus (k+ik') as well as system rotary inertia (I); S30: adding measured liquid into a sample groove, applying stress with oscillation frequency (omega) to a system, measuring a phase difference (delta) of the stress and the strain of the measured liquid and drawing a phase difference-frequency curve; and S40, applying a stress to the system and measuring the phase difference by selecting the frequency corresponding to a phase difference peak value according to the phase difference-frequency curve of the S30 step and calculating the viscosity (eta) of the measured liquid according to the following formula. The invention ensures that high measurement accuracy which can not be achieved by other similar equipment near resonance frequency is obtained by skillfully using the characteristics of k-Iomega2-0 under system idle-load resonance frequency. In addition, the invention also discloses a rheometer which uses the measuring method.

Description

The measuring method of viscosity of low-viscosity liquid and flow graph

Technical field

The present invention relates to a kind of measuring method of viscosity of low-viscosity liquid, and utilize this method to measure the rotational rheometer of ground viscous liquid viscosity.

Background technology

The rheological properties of soft material, particularly viscosity, all very important to its production, accumulating and use.The classical instrument of measuring the behavior of soft material viscoelasticity comprises: viscosity meter, flow graph, dynamic mechanical analysis instrument (DMA) etc., also develop in recent years and some perturbation measuring methods, realize the accurate measurement of small power and miniature deformation based on little rheology and atomic force microscope (AFM).

The key instrument of measuring the behavior of liquid viscoelasticity at present remains flow graph.The basic structure of flow graph is a lot, but its ultimate principle all is that sample is applied a dynamic shearing field, with the dynamic stress that applies relatively, obtains the phasing degree of the modulus and the modulus of sample.Rotational rheometer for example, its principle are to adopt motor to drive anchor clamps to give the sample stress application, measure strain or the rotating speed that produces with the optics demoder simultaneously, and obtain sample viscosity by corresponding calculated.

What set up is the shearing shear wave of decay rapidly because liquid is inner when measuring, and can't directly determine ess-strain numerical value, and this shows as the fluid that existing kinetic measurement flow graph is difficult to accurate measurement low shear modulus.The device of traditional measurement viscosity such as falling ball method viscosity meter, capillary viscosimeter etc. when measuring, when particularly measuring low viscosity material, often need very long Measuring Time on the other hand.

In sum, existing measurement means can't accurately be measured the rheological properties of low-viscosity (mobile) liquid.

Summary of the invention

First technical matters that the present invention solves provides a kind of measuring method of comparatively accurately viscosity of low-viscosity liquid.

Second technical matters that the present invention solves provides a kind of flow graph that is used to measure viscosity of low-viscosity liquid, makes this flow graph can more accurately measure the viscosity of low-viscosity (mobile) liquid.

For solving first technical matters, first technical scheme that the present invention adopts is:

A kind of measuring method of viscosity of low-viscosity liquid, this method adopts and rocks the type flow graph as survey instrument, and this flow graph comprises that it comprises cylinder, sample cell, it is characterized in that this measuring method may further comprise the steps:

S10: the surface area S, the fluid density ρ that measure cylinder radius r, cylinder immersion liquid;

S20: measure the mechanoscopy when unloaded, comprise moment of inertia I and the storage modulus k among the complex modulus k+ik ' of system and the value of loss modulus k ' of system;

S30: in sample cell, add measured liquid, system is applied the stress that vibration frequency is ω, and measure the phase differential δ of the strain of stress and measured liquid, and draw phase differential-frequency curve;

S40: according to phase differential-frequency curve of step S30, the frequency that makes applied stress is calculated the viscosities il of tested body fluid near the resonant frequency of system and measure phase difference then according to following formula:

$\mathrm{\η}=\frac{{[(k-I{\mathrm{\ω}}^2)\·\tan \mathrm{\δ}-k^{\′}]}^2}{2\mathrm{\ρ}{\left(r^{2}S\right)}^2\·{\mathrm{\ω}}^2}$

As one of improvement of first technical scheme: in step S30, at first draw out unloaded phase differential-frequency curve, and the frequency of phase differential peak value correspondence when sample estimates are measured in view of the above, poor according to the frequency of the phase differential peak value correspondence of estimating then to system's stress application and measurement respective phase, simultaneously according near the phase differential-frequency curve the measurement result drafting peak value.

For solving second technical matters, second technical scheme that the present invention adopts is:

A kind of flow graph that is used to measure low-viscosity (mobile) liquid, it comprises cylinder, fixed mount, torsion wire, magnet, field coil, sample cell, LASER Light Source, catoptron, four-quadrant photodiode, and data analysis disposal system, this data handling system comprises the viscosity calculations module, it is characterized in that: the computing formula that described viscosity calculations module adopts is:

$\mathrm{\η}=\frac{{[(k-I{\mathrm{\ω}}^2)\·\tan \mathrm{\δ}-k^{\′}]}^2}{2\mathrm{\ρ}{\left(r^{2}S\right)}^2\·{\mathrm{\ω}}^2}.$

The principle of the present invention's first scheme and alternative plan is:

The equation of motion that at first rocks:

$I\stackrel{\widetilde{\·\·}}{\mathrm{\θ}}=\tilde{M}+{\tilde{M}}_L-(k+i{k}^{\′})\widetilde{\mathrm{\θ}}---\left(1\right)$

Wherein I is the moment of inertia of system,

Be external force moment (being magnetic field moment),

Be the viscous coupling torque on the solid-liquid interface, k+ik ' is the complex modulus of torsion wire,

Be t displacement constantly.

The phase differential δ that above-mentioned analysis can obtain ess-strain satisfies:

$\tan \mathrm{\&delta;}=\frac{k^{\&prime;}+r^{2}S\sqrt{\mathrm{\&rho;\&eta;}}{\mathrm{\&omega;}}^{\frac{3}{2}}\sin \frac{3\mathrm{\&pi;}}{4}}{k-I{\mathrm{\&omega;}}^2+r^{2}S\sqrt{\mathrm{\&rho;\&eta;}}{\mathrm{\&omega;}}^{\frac{3}{2}}\mathrm{<figure-callout\; id="3"\; label="cos"\; filenames="HSA00000195011500011.png"\; state="\{\{state\}\}">cos</figure-callout>}\frac{3\mathrm{\&pi;}}{4}}---\left(2\right)$

Wherein r is the cup radius, and S is for immersing the surface area of liquid, and ρ is a fluid density.

When instrument was unloaded, we can think

Be 0, at this moment:

$\tan \mathrm{\&delta;}=\frac{k^{\&prime;}}{k-I{\mathrm{\&omega;}}^2}---\left(3\right)$

The relation of phase differential δ and vibration frequency ω can obtain k and k ' when measuring zero load, brings (2) formula into, and we can solve the relation between viscosities il and the phase differential δ:

$\mathrm{\&eta;}=\frac{{[(k-I{\mathrm{\&omega;}}^2)\&CenterDot;\tan \mathrm{\&delta;}-k^{\&prime;}]}^2}{2\mathrm{\&rho;}{\left(r^{2}S\right)}^2\&CenterDot;{\mathrm{\&omega;}}^2}---\left(4\right)$

Phase differential δ during by measurement different frequency ω, we just can obtain the viscosities il of sample.And according to (4) formula, when system at unloaded resonant frequency (k-I ω ²When measuring → 0), the minor alteration of sample viscosities il all can have bigger reaction, tan δ k-I ω in other words on phase differential δ ²→ 0 makes that the measuring error of δ is reduced.

For the liquid of certain viscosity, there is " sensitivity " peak value in its phase differential-frequency curve, and at the frequency band away from peak value, the absolute value of measured value changes less; Viscosity is more little, and " sensitivity " peak value moves to high frequency more, the unloaded resonant frequency of infinite tendency; Viscosity is more little, and " sensitivity " peak is sharp-pointed more.This shows: after probably determining sample viscosity, can calculate " sensitivity " peak value of sample correspondence, use the frequency measurement near peak value, just can improve the precision of viscosity to greatest extent.The present invention has utilized k-I ω under the unloaded resonant frequency of system cleverly ²→ 0 characteristics make to have the inaccessiable high precision of other like devices in measurement near resonant frequency.

Description of drawings

Fig. 1 is a flow graph synoptic diagram of the present invention;

Fig. 2 is a Theoretical Calculation full rate measurement result, and the reaction viscosity differences is to the influence of phase differential;

Fig. 3 is that the measurement result that the glycerine water solution of several variable concentrations measures compares, and difform curve is represented variable concentrations, is respectively 0%, 30%, 80%, 95%;

Fig. 4 becomes the viscosity measurement value of process distilled water and the comparison of theoretical value: open circles is the phase differential that experiment obtains; Filled circles is the viscosity that calculates according to experimental result, and curve is theoretical viscosity number curve.

Embodiment

The measuring method of viscosity of low-viscosity liquid of the present invention adopts and rocks the type flow graph as survey instrument.As shown in Figure 1, this flow graph comprises cylinder (1), fixed mount (2), torsion wire (3), magnet (4), field coil (5), sample cell (6), LASER Light Source (7), catoptron (8), four-quadrant photodiode (9), and data analysis disposal system (figure does not show).

This measuring method may further comprise the steps:

S10: the surface area S, the fluid density ρ that measure cylinder radius r, cylinder immersion liquid;

S20: measure the mechanoscopy when unloaded, comprise moment of inertia I and the storage modulus k among the complex modulus k+ik ' of system and the value of loss modulus k ' of system;

S30: in sample cell, add measured liquid, system is applied the stress that vibration frequency is ω, and measure the phase differential δ of the strain of stress and measured liquid, and draw phase differential-frequency curve;

S40: according to phase differential-frequency curve of step S30, the frequency of selecting phase differential peak value correspondence is calculated the viscosities il of tested body fluid then to system's stress application and measure phase difference according to following formula:

$\mathrm{\&eta;}=\frac{{[(k-I{\mathrm{\&omega;}}^2)\&CenterDot;\tan \mathrm{\&delta;}-k^{\&prime;}]}^2}{2\mathrm{\&rho;}{\left(r^{2}S\right)}^2\&CenterDot;{\mathrm{\&omega;}}^2}$

Wherein, in step S30, can at first draw out unloaded phase differential-frequency curve, and the frequency of phase differential peak value correspondence when sample estimates are measured in view of the above, poor according to the frequency of the phase differential peak value correspondence of estimating then to system's stress application and measurement respective phase,, simultaneously according near the phase differential-frequency curve the measurement result drafting peak value.

For verifying the accuracy of above-mentioned measuring method, present embodiment has also been carried out confirmatory experiment.Storage modulus that preestablishes torsion wire and loss modulus that this experiment preestablishes torsion wire are made as 0.0008,0.5 respectively, corresponding unloaded resonant frequency 145.36Hz, and the viscosity of four kinds of fluid samples is respectively 0.01mPas, 1mPas, 0.1Pas, 10Pas.Calculate the measurement result of different frequency earlier, suppose that then viscosity reduces by 2 ‰, calculate the measurement result that makes new advances, the difference of two times result just can reflect the susceptibility of different frequency to viscosity.Simulated experiment in the result of frequency separation 110～160Hz as shown in Figure 2.

From this experimental result as can be seen, for the liquid of certain viscosity, there is " sensitivity " peak value in its phase differential-frequency curve, and at the frequency band away from peak value, the absolute value of measured value changes less; Viscosity is more little, and " sensitivity " peak value moves to high frequency more, the unloaded resonant frequency of infinite tendency; Viscosity is more little, and " sensitivity " peak is sharp-pointed more.This shows: after probably determining sample viscosity, can calculate " sensitivity " peak value of sample correspondence, use the frequency measurement near peak value, just can improve the precision of viscosity to greatest extent.

Fig. 3 utilizes the measuring method of present embodiment to obtain the relation curve of phase differential and frequency, and difform curve is represented the glycerine water solution of variable concentrations among this figure, and concentration is respectively 0%, 30%, 80%, 95%.

The viscosity of the distilled water that accompanying drawing 4 measures for the present invention under the varying temperature environment and theoretical actual viscosity ratio are, as can be seen from the figure, it is fairly good that experimental result and theoretical value meet, and illustrates that this measuring method can realize the accurate measurement of low-viscosity (mobile) liquid rheological properties.

In addition, flow graph of the present invention belongs to and rocks the type flow graph, and this flow graph has adopted the principle of above-mentioned measuring method, and the structure of the flow graph that adopts in its structure and the above-mentioned measuring method is essentially identical, does not repeat them here.In addition, the phase differential that this flow graph can be differentiated less than 0.0002 changes, and is that example is carried out analog computation with water, just corresponding to viscosity number 10 ^-6The variation of Pas.This is the theoretical boundary of measuring accuracy.

Claims (3)

1. the measuring method of a viscosity of low-viscosity liquid, this method adopts and rocks the type flow graph as survey instrument, and this flow graph comprises that it comprises cylinder 1 and sample cell 6, it is characterized in that this measuring method may further comprise the steps:

S10: the surface area S, the fluid density ρ that measure cylinder radius r, cylinder immersion liquid;

S20: measure the mechanoscopy when unloaded, comprise moment of inertia I and the storage modulus k among the complex modulus k+ik ' of system and the value of loss modulus k ' of system;

S30: in sample cell, add measured liquid, system is applied the stress that vibration frequency is ω, and measure the phase differential δ of the strain of stress and measured liquid, and draw phase differential～frequency curve;

S40: according to phase differential-frequency curve of step S30, the frequency that makes applied stress is calculated the viscosities il of tested body fluid near the resonant frequency of system and measure phase difference then according to following formula:

。

2. the measuring method of viscosity of low-viscosity liquid according to claim 1, it is characterized in that: in step S30, at first draw out unloaded phase differential-frequency curve, and the frequency of phase differential peak value correspondence when sample estimates are measured in view of the above, poor according to the frequency of the phase differential peak value correspondence of estimating then to system's stress application and measurement respective phase, simultaneously according near the phase differential-frequency curve the measurement result drafting peak value.

3. flow graph that is used to measure low-viscosity (mobile) liquid, it comprises cylinder (1), fixed mount (2), torsion wire (3), magnet (4), field coil (5), sample cell (6), LASER Light Source (7), catoptron (8), four-quadrant photodiode (9), and data analysis disposal system, this data handling system comprises the viscosity calculations module, it is characterized in that: the computing formula that described viscosity calculations module adopts is:

。

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