JP2914534B2 - Liquid viscosity measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a liquid viscosity. More specifically, the present invention relates to a liquid viscosity measuring method that can easily and surely improve the accuracy of viscosity measurement by automatically selecting a flow model corresponding to a liquid whose viscosity is to be measured, without requiring skill.

[0002]

BACKGROUND OF THE INVENTION It is well known that the viscosity of blood depends on the health condition of the individual, and therefore, measurement of blood viscosity is an important and effective factor indispensable for treatment and prevention of diseases. is there.

Conventionally, a rotational viscometer has been used to measure blood viscosity. In this rotational viscometer, the same blood must be used many times with varying shear stress. It is necessary to take the logarithmic derivative of the numerical value, the calculation is complicated, errors are easy to occur, special unstable flows such as Taylor vortices occur as the rotation speed increases, heat generation due to viscosity occurs, Blood cells may be displaced due to centrifugal force.It takes a long time to measure one sample.After the measurement is completed, wash with water to remove blood,
Then, after the apparatus is dried, the next sample is measured, so that the operation is complicated.

In order to overcome the disadvantages of the conventional rotational viscometer, the applicant of the present invention has previously proposed a liquid viscometer capable of performing simple, quick and accurate measurement and requiring a small amount of liquid such as blood. A method and a liquid viscosity measuring device that is small, easy to move, and inexpensive to manufacture are proposed (Japanese Patent Application No. 2-418855). This liquid viscosity measurement method uses a sealed tubular container depressurized to a predetermined internal pressure, one end of which is communicated with the other end of the thin tube immersed in the liquid into the tubular container, and utilizes the pressure difference between both ends of the thin tube. The liquid is introduced into the tubular container through the thin tube, and the time-dependent change in the pressure in the tubular container is measured by a pressure sensor connected to the inside of the tubular container. To decide.

[0005]

In the measuring method proposed above, the shear stress and the shear rate of the liquid are calculated based on the time-dependent change in the pressure in the tubular container, and the ratio between the shear stress and the shear rate is calculated. To determine the viscosity.
In this case, a flow model such as an exponential law model or a Newton model is selected according to the type of the liquid, and the viscosity is determined according to a mathematical expression corresponding to each model.

[0006] However, apart from the case where the flow model to be applied to the liquid is known in advance, in the measurement method proposed earlier, the calculated shear rate and shear stress are plotted on a graph (this is a personal computer or the like). The flow model to be applied was determined from the distribution of the obtained plots. This judgment is
There is a problem that it takes time and experience and skill.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid viscosity measuring method capable of easily and instantly selecting a flow model and measuring the viscosity of a liquid in view of the circumstances described above.

[0008]

According to the liquid viscosity measuring method of the present invention, a liquid is introduced into a decompression container through a thin tube, and the liquid viscosity is measured based on a change in the pressure in the decompression container and the flow rate of the liquid flowing through the thin tube with time. A liquid viscosity measuring method for calculating the shear stress and the shear rate at the inner wall of the thin tube and calculating the viscosity of the liquid from the obtained values of the shear stress and the shear rate, including a step of selecting a flow model to be applied to the liquid. So
And use the calculated shear stress and shear rate
Structural viscosity index of a law model and Newton model,
Power law model, Bingham model and caisson model
Determine the correlation coefficient and obtain the obtained structural viscosity index and correlation coefficient.
Is used to select the flow model .

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a liquid viscosity measuring method (hereinafter, simply referred to as a measuring method) of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic explanatory view of a liquid viscosity measuring apparatus which can be suitably used in the measuring method of the present invention, and FIGS. 2 and 3 are flowcharts of one embodiment of the measuring method of the present invention.

The liquid viscosity measuring device 10 shown in FIG. 1 receives a tubular container 12, a puncture needle device 20, a communication connection device 32, a pressure sensor 40, and an output signal from the pressure sensor 40,
An AD converter 42 for converting it into a digital signal;
Computer 44 to which the output signal from converter 42 is input
, A liquid storage tube 50, and a thermostat 54 as main components. Details of each component are as follows.

Tubular container 12: The tubular container 12 is a glass or resin-made circular tube main body 14 having both ends opened, and a rubber-like elastic body (preferably, Butyl rubber). The inside of the tube main body 14 is exhausted to a predetermined pressure (for example, -380 mmHg based on the atmospheric pressure) in advance, and the reduced pressure is maintained by the pair of sealing stoppers 16 and 18.

Puncture needle device 20: The puncture needle device 20 includes a puncture needle 22 provided with a hub 30 at a portion near a needle tip 23a of a metal (preferably stainless steel such as JISSUS 304 material) cannula 23; The main member is a bottomed tubular holder 24 for easily and reliably performing an operation for puncturing the puncture needle 22 into the sealing stopper 18 of the tubular container 12. Holder 24 is the pipe body
It is shorter than 14 and has an inner diameter that can easily receive the end of the tube body 14. The puncture needle 22 has its needle tip 23
a is screwed into a female screw hole provided at a substantially central position of the bottom wall 26 of the holder 24 at a hub 30 formed as a male screw body so that a protrudes into the holder 24. It is designed not to move in the axial direction.

Communication connection device 32: The communication connection device 32 includes a metal hollow puncture needle 34 having a hub 38, and one end of which is connected to the hub 38.
And a pressure guiding tube 36 that can accurately transmit the pressure in the tube body 14 to the pressure sensor 40. The other end of the pressure guiding tube 36 is connected to the pressure sensor 40 in an airtight manner.

A pressure sensor 40, an AD converter 42, and a computer 44 are connected to each other by wires 46, 48 in the aforementioned order. In these, the pressure value measured by the pressure sensor 40 is input to the AD converter 42 and input to the computer 44 as an electric signal.
The computer 44 is set in advance by inputting the following mathematical expressions.

Liquid storage tube 50, thermostatic chamber 54: As the storage tube 50 for containing the test liquid 52, a commercially available test tube is suitably used. The constant temperature bath 54 is for maintaining the storage tube 50 containing the test liquid at a constant temperature in order to test the test liquid 52 at a desired temperature.

Next, the measuring method of the present invention performed by using the above-described apparatus will be described.

First, an outline of the principle of the measuring method of the present invention is as follows. A hollow puncture needle which can penetrate a first sealing member at one end of a tubular container and penetrate one end thereof into a tubular container is preferable. , One end of which is immersed in a liquid and the other end of which is a depressurized tubular container (eg,
When it is in communication with the tubular container reduced in pressure to -380 mmHg based on the atmospheric pressure), the inside of the thin tube is changed according to the differential pressure between the static pressure of the end of the thin tube immersed in the liquid and the pressure of the tubular container. The liquid flows and flows into the tubular container. The speed of the liquid flowing through the capillary depends on the viscosity of the liquid. The change in pressure in the tubular container while the liquid is sucked into the tubular container is measured by a pressure sensor, and the liquid viscosity is determined from the measured value by a mathematical model. The determination of the liquid viscosity is suitably performed by a computer. The determination or selection of the mathematical model is automatically performed by a computer.

The following values are input to the computer in advance.

P _A : Atmospheric pressure Vo: Volume of the inner volume of the tubular container plus the volume of the portion connecting the tubular container and the pressure sensor R: Inner radius of the thin tube L: Length of the thin tube Next, FIG. The method of using the device shown in FIG.

First, a communication connecting device 32 is connected to the sealing stopper 16 of the tubular container 12 fixedly fixed by a holding device (not shown).
Through the sharp end of the puncture needle 34 (see FIG. 1). Before or after this operation, the liquid storage tube 50 containing the test liquid 52 is inserted into the thermostat 54. Then, puncture needle device
The free end side of the puncture needle 22 at 20 is the solution to be tested in the reservoir 50.
Insert into 52.

After the computer 44 is activated and waits for a predetermined time, the degree of negative pressure in the tubular container 12 is measured via the communication connection device 32, and if the negative pressure is less than the specified value. For example, the hollow puncture needle 22 is projected (see FIG. 2).

According to the protruding display, the tip 23 of the puncture needle 22
a into the sealing stopper 18. FIG. 1 shows that the puncture needle 22 is
The tip 23a is completely inserted through the sealing plug 18 and inserted into the internal space of the tube main body 14. From the moment of this penetration, the test liquid 52 in the liquid storage tube 50 is
The pressure difference between the pressure on the upper surface of the test liquid 52 (actually, the atmospheric pressure) and the pressure in the tubular container 12 reduced to the atmospheric pressure or less,
It is sucked into the tube body 14 through the cannula 23.

As the test liquid 52 enters the tubular container 12, the space volume in the container decreases and the pressure gradually increases. This internal pressure eventually becomes equal to the atmospheric pressure.

The time variation of the pressure P _i (t _i indicates a certain point in time) in the tubular container 12 is measured by the pressure sensor 40 at arbitrary time intervals. The pressure in the tubular container 12 is the static pressure at the tip of the puncture needle 22 in the test liquid 52 (when the test liquid is in the liquid reservoir in the atmosphere, it may be regarded as equal to the atmospheric pressure) P _When it becomes equal to _A , the flow of the test liquid 52 into the tubular container 12 stops. During this time, the shear rate of the test liquid 52 flowing through the puncture needle 22 changes from a certain value to zero. The pressure in the tubular container 12 is
, Or is continuously input to the computer 44 as an output value from the pressure sensor 40.

Based on the pressure change in the tubular container 12 input to the computer 44, the flow characteristics of the test liquid 52 are determined based on the following concept.

The pressure P _i and the volume V of the space inside the tubular container 12
The flow rate of the test liquid 52 at the time t _i is calculated from the change with time of the pressure under the assumption that the product with _i is constant and expressed by the following equation (1).

[0028] _{P o V o = P i V} i ...... (1) time _{t i} the volume _{V i} of the test liquid 52 in the tubular container 12 in
Is represented by the following equation (2).

V _i = V _o −V _i (2) Accordingly, the flow rate Q _i is obtained by the following equation (3).

Q _i = dv _i / dt (3) On the other hand, the pressure difference between both ends of the puncture needle 22 is expressed as follows.

The _{ΔP i = (P A + ρgh} i) - (P i + ρgH i) -ρgL where _{h i} and _{H i} is the length of each liquid inlet portion of the puncture needle 22 is immersed in the test solution 52 The length between the upper end of the puncture needle 22 and the liquid surface in the tubular container, and these values can be obtained in the process of calculating the flow rate if the thickness of the puncture needle 22 is ignored.

If the length of the puncture needle 22 is 260 times or more the inner diameter of the puncture needle 22, the inlet effect and the outlet effect exerted on the pressure difference between both ends of the puncture needle 22 are within 5%. Time shear stress (wall shear stress) in the puncture needle 22 inside wall at t _i tau _wi and shear rate g _ai is calculated by the following equation.

Τ _wi = ΔP _i R / (2L) g _ai = 4Q _i / (πR ³ ) In practice, the pressure difference ΔP _i and the flow rate Q _i are obtained as an average of the time interval Δt (Q _i = ( _{v i -v i-1) /} Δ
t). Therefore, the shear stress τ _wi and the shear rate g _ai are also average values of the time interval Δt. Thus, the following equation can be obtained.

Τ _w = ΔPR / (2L) g _a = 4Q / (πR ³ ) * where g _a is the apparent wall shear rate (or apparent velocity gradient).

G = −du / dr = 3 g _a / 4 + (τ _w / 4) (d g _a / dτ _w ) * where g is a general velocity gradient and r is a radial position inside the puncture needle 22.

The viscosity is determined by determining the ratio between the shear stress τ _w and the shear rate g _a at one point in the fluid that flows in a steady state. FIG. 5 is an example of a result showing a relationship between a wall shear stress and a shear rate obtained for human blood. Here, α is a proportional constant.

Although blood has been referred to as Casson fluid, it exhibits properties of non-Newtonian fluids such as Bingham fluids and power law fluids except for regions where the shear rate is low, but it can be regarded as almost Newtonian fluids. As mentioned, for example, the following flow model can be used depending on the type of liquid including human blood.

Newton model

[0039]

(Equation 1)

Power law model

[0041]

(Equation 2)

Bingham model

[0043]

(Equation 3)

Caisson model

[0045]

(Equation 4)

In the measuring method of the present invention, a computer automatically determines which of the above-mentioned four flow models the liquid whose viscosity is to be measured corresponds to.

FIG. 4 shows a flow model selection flowchart.

First, the previously calculated τ _i and g
_{Using ai} , the structural viscosity index N _OS of the power law model, the correlation coefficient R _{C · NE of} the Newton model, the correlation coefficient R _{C · OS of} the power law model, and the correlation coefficient R _{C · BI of the} Bingham model
Then, the correlation coefficient R _{C · CA} of the caisson model is calculated.
The formulas for calculating these indices or coefficients are as shown below. Here, in Equations 5 to 17, CN is the number of data, τ is the shear stress, τ _r is the yield stress, τ _BI is the shear stress in Bingham, and τ _CA is the shear stress in the caisson.

[0049]

(Equation 5)

[0050]

(Equation 6)

[0051]

(Equation 7)

[0052]

(Equation 8)

[0053]

(Equation 9)

If N _OS is larger than 0.9 and 1.
If it is smaller than 1, it is determined that the model is a Newton model; otherwise, _{RC * OS} , _{RC * BI} and Rc
_{C ・} The magnitude relationship of _CA is examined, and the flow model with the largest value is selected.

When the model selection is completed, the viscosity is calculated according to the mathematical formula corresponding to each flow model.

The viscosity μ in the Newton model is calculated by the following equation.

[0057]

(Equation 10)

The viscosity μ in the power law model is calculated by the following equation.

[0059]

[Equation 11]

[0060]

(Equation 12)

The viscosity μ in the Bingham model is calculated by the following equation.

[0062]

(Equation 13)

[0063]

[Equation 14]

The viscosity μ in the caisson model is calculated by the following equation.

[0065]

(Equation 15)

[0066]

(Equation 16)

[0067]

[Equation 17]

[0068]

As described above, according to the measuring method of the present invention, the flow model of the test liquid can be instantaneously selected after the measurement without any skill, and other flow models can be applied. The viscosity of tobacco can be obtained instantaneously.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a liquid viscosity measuring device that can be suitably used in the measuring method of the present invention.

FIG. 2 is a flowchart of an embodiment of the measuring method of the present invention.

FIG. 3 is a flowchart of one embodiment of the measuring method of the present invention.

FIG. 4 is a flow model selection flowchart in the measurement method of the present invention.

FIG. 5 is a graph showing the relationship between wall shear stress and shear rate determined for human blood.

[Explanation of symbols]

 10 Liquid viscosity measuring device 12 Tubular container 16 Sealing stopper 18 Sealing stopper 20 Puncture needle device 22 Puncture needle 40 Pressure sensor 42 AD converter 44 Computer 52 Liquid under test

Claims (2)

(57) [Claims] 1. A liquid is introduced into a decompression vessel via a thin tube, and a shear stress and a shear rate on the inner wall of the thin tube are calculated based on a time-dependent change in a pressure in the decompression container and a flow rate of a liquid flowing through the thin tube. a liquid viscosity measuring method for calculating the viscosity of the liquid from the values of shear stress and shear rate is, the and Nde including the step of selecting a flow model to be applied to the liquid, the calculated shear stress and shear rate values
Of structural viscosity index and newt of power law model
Model, power law model, Bingham model and Caeso model
Of the structural viscosity index and the obtained structural viscosity index.
And selecting the flow model using a correlation coefficient . 2. The structural viscosity index of the power law model is 0.9.
If it is larger and smaller than 1.1, the liquid flow model
To select the Newton model
If not, the power law model, Bingham model and
And the correlation coefficient of the caisson model
2. The model of claim 1 is selected as a liquid flow model.
Measurement method.