JP2009085639A - Noncontact-type viscometer and viscosity-measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noncontact type viscometer capable of readily measuring the viscosity from the displacement of a liquid surface. <P>SOLUTION: This viscometer is equipped with a measuring mechanism 301 for measuring the existence period, until vanishment of a recessed part 2 generated on the liquid 1 surface by a gas jetted out from a nozzle 21, arranged obliquely with respect to the liquid 1 surface; a proportional relation storage module 201 for preserving a proportional relation between the existence period and the viscosity of the liquid 1; and a viscosity calculation mechanism 302 for calculating a measured value of the viscosity of the liquid 1, based on the measured value of the existence period and the proportional relation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a physical property evaluation technique, and more particularly to a non-contact viscometer and a viscosity measuring method.

Conventionally, there are contact type viscometers that measure the viscosity of a liquid by directly contacting the liquid to be measured, such as a vibration viscometer, a rotary viscometer, a capillary viscometer, a falling body viscometer, and a cup viscometer. It was. However, the contact viscometer may cause contamination in the liquid to be measured. Therefore, a viscometer has been proposed in which a displacement generated on a liquid surface by irradiating a sound wave on the liquid surface is measured with a laser displacement meter, and the viscosity of the liquid is calculated from the measured displacement (see, for example, Patent Document 1). . However, the displacement of the surface of the liquid caused by irradiating the sound wave is very small and difficult to detect.
Kobayashi, Tai, Ito, “Non-contact viscometer using aerial acoustic waves”, Ultrasonic TECHNO, Nihon Kogyo Publishing, May-June 2007, p5-8

  An object of the present invention is to provide a non-contact viscometer and a viscosity measuring method capable of easily measuring the viscosity from the displacement of the liquid surface.

  The features of the present invention are: (a) a measurement mechanism that measures a life cycle until a recess generated on the surface of the liquid disappears due to a gas ejected from a nozzle disposed obliquely with respect to the surface of the liquid; A proportional relationship storage module that stores a proportional relationship between the life cycle and the viscosity of the liquid; and (c) a viscosity calculation mechanism that calculates the measured value of the viscosity of the liquid based on the measured value and the proportional relationship of the life cycle. The gist is that it is a contact viscometer.

  Other features of the present invention are: (a) a step of ejecting gas at a constant speed from a nozzle disposed obliquely with respect to the surface of the liquid; and (b) a recess formed on the surface of the liquid by the ejected gas. Measuring the life cycle until disappearance, and (c) measuring the life cycle and calculating the measurement value of the viscosity of the liquid based on the proportional relationship between the life cycle and the viscosity of the liquid. The gist is the method.

  According to the present invention, it is possible to provide a non-contact viscometer and a viscosity measuring method capable of easily measuring the viscosity from the life cycle until the concave portion generated on the liquid surface disappears.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

(First embodiment)
As shown in FIG. 1, the non-contact viscometer according to the first embodiment includes a nozzle 21 disposed obliquely with respect to the surface of the liquid 1, and a gas ejected from the nozzle 21 at a constant pressure and speed. Is provided with a detection device 31 for detecting the recess 2 generated on the surface of the liquid 1 and a central processing unit (CPU) 300. The CPU 300 includes a measurement mechanism 301 that measures the life cycle until the recess 2 generated on the surface of the liquid 1 disappears. A data storage device 200 is connected to the CPU 300. The data storage device 200 includes a proportional relationship storage module 201 that stores a proportional relationship between the life cycle from the generation of the recess 2 to the disappearance thereof and the viscosity of the liquid 1. The CPU 300 has a viscosity calculation mechanism 302 that calculates the measured value of the viscosity of the liquid 1 based on the measured value of the life cycle from the generation of the recess 2 to the disappearance and the proportional relationship stored in the proportional relationship storage module 201. In addition.

  A pump 25 that sends out gas such as air is connected to the nozzle 21 via a blower pipe 23. The liquid 1 is stored in a container 101 such as an open petri dish. The container 101 is disposed on a stage 102 that can move in the horizontal and vertical directions. When a gas is blown obliquely onto the surface of the liquid 1 at a constant pressure and speed, a recess 2 is formed on the surface of the liquid 1 due to the momentum of the gas, as shown in FIG. Next, due to the momentum component parallel to the surface of the liquid 1, the recess 2 moves laterally on the surface of the liquid 1 as shown in FIG. When the recess 2 moves the same distance as the radius of the recess 2, the momentum component perpendicular to the surface of the liquid 1 is not given to the recess 2, so the recess 2 disappears due to the buoyancy of the liquid 1, as shown in FIG. At the same time, the next recessed portion 3 is newly generated on the surface of the liquid 1 by the continuously blown gas. In addition, although it is preferable that the atmospheric | air pressure of gas is constant, a highly accurate fixed property is not required.

  In this way, when an air flow is ejected toward the surface of the viscous liquid 1, a shearing force acts on the surface of the liquid, and the position of the liquid near the surface and the position of the internal liquid begin to shift. However, due to the viscosity of liquid 1, the positional deviation is local. Furthermore, if the gas is continuously blown at a constant atmospheric pressure, the local positional deviation becomes a vortex near the liquid surface, and recesses are periodically generated on the surface of the liquid 1 from one to the next and disappear. become. Here, the time from the generation of one recess 3 to the disappearance is defined as the “life cycle” of the recess 3. The life cycle of the recess 3 is strongly influenced by the inertia of the liquid 1 such as surface tension when the viscosity of the liquid 1 is low, and is strongly influenced by the viscosity of the liquid 1 when the viscosity of the liquid 1 is high.

  Referring to FIG. 5, the momentum p of gas per unit time sprayed on liquid 1 is given by the following equation (1).

p = m _A × u… (1)
Here, m _A represents the mass of the gas per unit time, and u represents the velocity of the gas. When gas is sprayed onto the liquid 1 from the opening of the nozzle 21 having the radius r, the surface area S of the opening of the nozzle 21 is given by the following equation (2).

S = πr ² (2)
Thus the mass m _A of the gas is given by the following equation (3).

m _A = ρ _a × u × S = ρ _a × u × πr ² (3)
From equations (1) and (3), the momentum p of the gas is given by the following equation (4).

p = ρ _a × πr ² × u ² … (4)
The traveling direction of the gas, when the angle between the surface liquid 1 and theta, the horizontal component p _h momentum p of the gas has on the one second is given by the following equation (5), and impulse f _h of 1 sec equal. The vertical component p _v of the gas momentum p is given by the following equation (6).

p _h = p × cosθ = ρ _a × πr ² × u ² × cosθ = f _h … (5)
p _v = p × sinθ = ρ _a × πr ² × u ² × sinθ… (6)
Here, when a sphere having a radius r moves in the liquid 1 at a velocity v, a viscous resistance force f _v given by the following equation (7) is applied to the sphere according to Stokes' law.

f _v = 6π × η × r × v = k × v (7)
Here, η is the viscosity of the liquid 1, and k is a constant. When establishing the equation of motion of a sphere, the density of the liquid 1 must be used as the inertial mass, not the density of the gas. Therefore, assuming that the spherical bubbles move forward at the speed v, and that the liquid having the same shape as the spherical bubbles moves backward at the speed v, the equations (5) and (7) The following equation (8) is derived.

m _W (dv / dt) = f _h -f _v = f _h -k × v… (8)
Note that m _W is the mass of the liquid having the same shape as the spherical bubbles, and is given by the following equation (9), where ρ _W is the density of the liquid 1.

m _W = {(4πr ³ ) / 3} × ρ _W … (9)
The following equation (10) is obtained by solving the differential equation for the velocity v in equation (8) by variable separation.

dv / (f _h -kv) = dt / m _W
-(1 / k) log (f _h -kv) = (t / m _W ) + C ₁
f _h -kv = C ₂ × exp (-kt / m _W )… (10)
Here, C ₁ and C ₂ are constants. From the boundary condition that v = 0 when t = 0, the velocity v of the spherical bubble is given by the following equation (11).

v = (f _h / k) [1-exp (-kt / m)]… (11)
The spherical bubbles are accelerated by the force f _h applied in the horizontal direction by the blown gas, but as shown in Fig. 6, the terminal velocity v _F given by the following equation (12) is instantly determined by the viscous resistance force f _v And move at a constant speed.

v _F = (f _h / k)
= (ρ _a × πr ² × u ² × cosθ) / (6π × η × r)… (12)
The relationship between the velocity u of gas ejected from the nozzle 21 and the flow rate U is given by the following equation (13).

u = (U / πr ² )… (13)
Therefore, the terminal velocity v _F is given by the following equation (14) from the equations (12) and (13).

v _F = {ρ _a × πr ² × (U / πr ² ) ² × cosθ} / (6π × η × r)
= (ρ _a U ² × cosθ) / (6π ² × η × r ³ )… (14)
Since the distance that one recess 2 shown in FIGS. 2 to 4 moves on the surface of the liquid 1 during the life cycle can be empirically assumed to be equal to the radius r of the opening of the nozzle 21 shown in FIG. The life cycle t _C is given by the following equation (15).

t _C = r / v _F
= r / {(ρ _a U ² × cosθ) / (6π ² × η × r ³ )}
= (6π ² × η × r ⁴ ) / (ρ _a U ² × cosθ) (15)
By transforming the equation (15), the relationship between the life cycle t _C of the recess 2 and the viscosity η of the liquid 1 is given by the following equation (16).

η = {(ρ _a U ² × cosθ) / (6π ² r ⁴ )} × t _C … (16)
Incidentally, the relaxation time tau _F up to the terminal velocity v _F is given by the following equation (17).

τ _F = m _w / k = (2r ³ ρ _a ) / (9η)… (17)
In the equation (16), the gas density ρ _a , the flow rate U, the angle θ, and the radius r of the nozzle 21 each take values determined by the apparatus, so the life cycle t _C of the recess 2 and the viscosity η of the liquid 1 Is in a first-order proportional relationship.

As the detection device 31 fixed to the jig 103 shown in FIG. 1, a photoelectric sensor can be used. The detection device 31 is arranged toward the surface of the liquid 1. The detection device 31 detects a change in light intensity caused by the formation and disappearance of the recess 2 from the next to the next on the surface of the liquid 1. Further, the detection device 31 photoelectrically converts the detected light intensity and outputs an electrical signal as shown in FIG. A measurement mechanism 301 shown in FIG. 1 receives an electrical signal from the detection device 31. Further, the measurement mechanism 301 calculates the period of the electric signal as a measured value of the life cycle t _C of the recess 2 by performing, for example, fast Fourier transform (FFT) on the electric signal.

The data storage device 200 stores an equation representing the relationship between the life cycle t _C of the recess 2 and the viscosity η of the liquid 1 shown in the above equation (16). The viscosity calculation mechanism 302 reads the above equation (16) from the data storage device 200 and receives the measurement value of the life cycle t _C of the recess 2 from the measurement mechanism 301. Further, the viscosity calculating mechanism 302 calculates the known value of the gas density ρ _a , the flow rate U, the angle θ, and the radius r of the nozzle 21 and the measured value of the life cycle t _C of the recess 2 in the equation (16). Substitute and calculate the measured value of viscosity η of liquid 1.

  An input device 312, an output device 313, a program storage device 330, and a temporary storage device 331 are further connected to the CPU 300. As the input device 312, a keyboard, a mouse, or the like can be used. As the output device 313, a monitor screen using a liquid crystal display (LCD), a light emitting diode (LED), or the like can be used. The program storage device 330 stores a program for causing the CPU 300 to execute data transmission / reception between devices connected to the CPU 300. The temporary storage device 331 temporarily stores data during the calculation process of the CPU 300.

  Next, a viscosity measuring method according to the first embodiment will be described using the flowchart shown in FIG. Note that the calculation results by the CPU 300 shown in FIG. 1 are sequentially stored in the temporary storage device 331.

(a) Gas is sent from the pump 25 in step S101, and the gas is jetted from the opening of the nozzle 21 onto the surface of the liquid 1. Due to the ejected gas, the recesses 2 are periodically generated from the next to the surface of the liquid 1 and disappear. In step S102, the detection device 31 detects a change in light intensity caused by the generation and disappearance of the recess 2 from one to the next, and outputs an electrical signal as shown in FIG. In step S103, the measurement mechanism 301 shown in FIG. 1 receives an electrical signal from the detection device 31, and calculates a measured value of the life cycle t _C of the recess 2 from the electrical signal.

(b) In step S104, the viscosity calculation mechanism 302 reads the equation (16) from the proportional relationship storage module 201. Also, known values of the gas density ρ _a , the flow rate U, the angle θ, and the radius r of the nozzle 21 are input to the viscosity calculation mechanism 302 from the input device 312. Next, the viscosity calculation mechanism 302 receives the measurement value of the life cycle t _C of the recess 2 from the measurement mechanism 301. Thereafter, the viscosity calculation mechanism 302 substitutes the known value of the gas density ρ _a , the flow rate U, the angle θ, and the radius r of the nozzle 21 and the measured value of the life cycle t _{C into} the equation (16), and the liquid 1 The measured value of the viscosity η is calculated. Finally, the measured value of the viscosity η of the liquid 1 is output to the output device 313, and the viscosity measuring method according to the first embodiment is completed.

  In the conventional non-contact type viscometer, the viscosity of the liquid is measured based on the displacement of the surface of the liquid caused by irradiating the sound wave. However, the displacement of the liquid surface caused by the irradiation of sound waves is minute and difficult to detect, and it is necessary to use an expensive device such as a laser displacement meter. Furthermore, since the output of the sound wave and the laser is high, there is a problem that it is dangerous when the human body is accidentally irradiated.

  In addition, there is a method in which a laser beam is irradiated on the liquid surface to generate a fine wave on the liquid surface, and the viscosity of the liquid is measured from the displacement of the fine wave. However, since the displacement of the fine wave generated by the laser light irradiation is very small, it has been difficult to measure the decay time of the diffracted light generated when the laser light is incident on the fine wave.

  There is also a method of measuring the viscosity of the liquid by placing a metal probe near the liquid surface, applying a voltage of 100 to 200 V to the probe to generate an electric field, and measuring the displacement generated on the liquid surface. there were. However, the displacement of the liquid surface was very small, and it was difficult to detect. In addition, when the liquid to be inspected is charged and ignitable, there is a problem in that there is a risk of explosion during measurement.

  On the other hand, in the non-contact type viscometer according to the first embodiment, the recess 2 is generated by continuously blowing gas to the liquid 1 at a constant pressure. Since the frequency of the gas sprayed on the liquid 1 is substantially zero, the frequency of the phenomenon generated in the liquid 1 by the sprayed gas is also low. Since the operation of applying mechanical energy to blow gas at a constant pressure shifts to a low frequency phenomenon on the surface of the liquid 1, the displacement of the liquid such as the depth of the recess 2 and the moving distance becomes large. Therefore, it can be easily detected by an inexpensive device such as a photoelectric sensor. In addition, air or the like can be used as the gas injected from the nozzle 21, so that it is not necessary to use an ignitable or toxic gas, and the viscosity of the liquid 1 can be measured extremely safely.

(First modification of the first embodiment)
It is experimentally verified that the life cycle t _{C of the} recess 2 shown in FIG. 1 and the viscosity η of the liquid 1 are in a first-order proportional relationship. First, the nozzle was placed at a height of 2 mm in the vertical direction from the surface of the liquid, the diameter of the nozzle opening was set to 50 μm, the flow rate of the jetted gas was set to 30 ml / min, and the pressure of the gas was set to 0.2 MPa. Next, the life cycle t _C of the recesses was measured for each of the silicone oil samples 5 to 13 manufactured by Shin-Etsu Kogyo Co., Ltd. shown in FIG. Then, as shown in FIG. 10, the viscosity of the silicone oil samples 5 to 13 and the life cycle t _{C of the} recesses showed a first-order proportional relationship. Although there is a difference from the theoretical line indicating the relationship between the life cycle t _C and the viscosity derived from the equation (16), the difference is that when the equation (16) is derived, the concave portion has the same radius r as the nozzle radius r. This is considered to be approximate to a sphere having

Also, when the diameter of the nozzle opening is set to 400 μm, the flow rate of the jetted gas is set to 114 ml / min, and the pressure of the gas is set to 0.2 MPa, as shown in FIG. The survival cycle t _C of the first-order proportional relationship.

Also, when the diameter of the nozzle opening is set to 50 μm, the flow rate of the jetted gas is set to 16 ml / min, and the pressure of the gas is set to 0.2 MPa, the viscosity and the concave portions of the silicone oil samples 2 to 8 are shown in FIG. The survival cycle t _C of the first-order proportional relationship.

Also, when the diameter of the nozzle opening is set to 50 μm, the flow rate of the jetted gas is set to 14 ml / min, and the pressure of the gas is set to 0.2 MPa, as shown in FIG. The survival cycle t _C of the first-order proportional relationship.

Therefore, the proportional relationship storage module 201 shown in FIG. 1 may store an approximate expression that approximates the proportional relationship between the life cycle t _{C of the} recess and the viscosity η of the liquid that is acquired in advance. In this case, the viscosity calculating mechanism 302 can calculate the measured value of the viscosity η of the liquid 1 by substituting the measured value into the variable of the life cycle t _C of the recess included in the approximate expression.

(Second modification of the first embodiment)
In the first embodiment, an example in which the detection device 31 illustrated in FIG. 1 is a photoelectric sensor has been described, but the present invention is not limited to this. For example, the detection device 31 may be a high speed camera. In this case, the measurement mechanism 301 may measure the life cycle t _C of the recess 2 from the image sent from the detection device 31. FIG. 14 shows an example in which the life cycle of the recesses generated on the surfaces of the liquids having a plurality of viscosities is measured by the photoelectric sensor and the high-speed camera, respectively. As shown in FIG. 14, even if any one of the photoelectric sensor and the high-speed camera is used as the detection device 31, no large error occurs in the measurement result.

(Second embodiment)
As shown in FIG. 15, the non-contact viscometer according to the second embodiment includes a thermometer 104 that measures the temperature of the liquid 1, and a viscosity calculation mechanism 302 based on the measured value of the temperature of the liquid 1. A temperature correction mechanism 303 for correcting the measured value of the viscosity η of the liquid 1 to be calculated is provided. The viscosity η of the liquid 1 decreases as the temperature increases. Further, the viscosity η of the liquid 1 increases as the temperature decreases. Therefore, for example, when the temperature of the liquid 1 is 30 ° C. even though it is set to measure the viscosity η of the liquid 1 at 20 ° C., the temperature correction mechanism 303 calculates the liquid calculated by the viscosity calculation mechanism 302. The measured value of viscosity η is multiplied by a number greater than 1 to correct the measured value of viscosity η. Further, for example, when the temperature of the liquid 1 is 10 ° C. even though it is set to measure the viscosity η of the liquid 1 at 20 ° C., the temperature correction mechanism 303 calculates the liquid 1 calculated by the viscosity calculation mechanism 302. The measured value of viscosity η is multiplied by a number less than 1 to correct the measured value of viscosity η. The other components of the non-contact viscometer according to the second embodiment are the same as those in FIG.

(Third embodiment)
As shown in FIG. 16, the non-contact viscometer according to the third embodiment includes a flow meter 105 that measures the flow rate of the gas injected from the nozzle 21, and a viscosity based on the measured value of the gas flow rate. A flow rate correction mechanism 304 for correcting the measured value of the viscosity η of the liquid 1 calculated by the calculation mechanism 302 is provided. As shown in FIG. 17, the life cycle of the recesses generated on the surface of the liquid 1 may differ depending on the gas flow rate. Therefore, the flow rate correction mechanism 304 receives the measurement value of the gas flow rate from the flow meter 105, and when the viscosity calculation mechanism 302 calculates the measurement value of the viscosity η of the liquid 1 using the equation (16), the flow rate correction mechanism 304 The viscosity calculation mechanism 302 is instructed to substitute the measured value into the equation (16). Other components of the non-contact viscometer according to the third embodiment are the same as those in FIG.

(Other embodiments)
Although the present invention has been described by the embodiments as described above, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques should be apparent to those skilled in the art. For example, the gas injected from the nozzle 21 shown in FIG. 1 is not limited to air, and various gases such as nitrogen gas can also be used. Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

It is a schematic diagram of the non-contact type viscometer which concerns on the 1st Embodiment of this invention. It is a 1st photograph of the recessed part produced in the surface of the liquid which concerns on the 1st Embodiment of this invention. It is a 2nd photograph of the recessed part produced in the surface of the liquid which concerns on the 1st Embodiment of this invention. It is a 3rd photograph of the recessed part produced in the surface of the liquid which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the momentum given to the surface of the liquid which concerns on the 1st Embodiment of this invention. It is a graph which shows the speed of the crevice which arises on the surface of the liquid concerning a 1st embodiment of the present invention. It is a graph which shows the output of the detection apparatus which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the viscosity measuring method which concerns on the 1st Embodiment of this invention. It is a table which shows the list of the silicone oil which concerns on the 1st modification of the 1st Embodiment of this invention. It is a 1st graph which shows the relationship between the viscosity of the silicone oil which concerns on the 1st modification of the 1st Embodiment of this invention, and the lifetime of a recessed part. It is a 2nd graph which shows the relationship between the viscosity of the silicone oil which concerns on the 1st modification of the 1st Embodiment of this invention, and the lifetime of a recessed part. It is a 3rd graph which shows the relationship between the viscosity of the silicone oil which concerns on the 1st modification of the 1st Embodiment of this invention, and the lifetime of a recessed part. It is a 4th graph which shows the relationship between the viscosity of the silicone oil which concerns on the 1st modification of the 1st Embodiment of this invention, and the lifetime of a recessed part. It is a graph which shows the relationship between the viscosity of the liquid which concerns on the 2nd modification of the 1st Embodiment of this invention, and the lifetime of a recessed part. It is a schematic diagram of the non-contact viscometer which concerns on the 2nd Embodiment of this invention. It is a schematic diagram of the non-contact type viscometer which concerns on the 3rd Embodiment of this invention. It is a graph which shows the relationship between the flow volume of the gas which concerns on the 3rd Embodiment of this invention, and the lifetime of the recessed part which arises in the liquid.

Explanation of symbols

1 ... Liquid
2, 3… Recess
21 ... Nozzle
23 ... Blower pipe
25 ... Pump
31 ... Detection device
101 ... container
102 ... Stage
103 ... Jig
104 ... Thermometer
105 ... Flow meter
200 ... Data storage device
201 ... Proportional relationship storage module
300 ... CPU
301 ... Measuring mechanism
302… Viscosity calculation mechanism
303 ... Temperature compensation mechanism
304 ... Flow rate correction mechanism
312 ... Input device
313 ... Output device
330 ... Program storage device
331 ... Temporary storage device

Claims (9)

A measurement mechanism for measuring a life cycle until a recess generated on the surface of the liquid disappears by a gas ejected from a nozzle disposed obliquely with respect to the surface of the liquid;
A proportional relationship storage module for storing a proportional relationship between the life cycle and the viscosity of the liquid;
A non-contact viscometer comprising: a viscosity calculating mechanism that calculates a measured value of the viscosity of the liquid based on the measured value of the life cycle and the proportional relationship.   The non-contact viscometer according to claim 1, wherein a velocity of the gas ejected from the nozzle is constant.   The non-contact viscometer according to claim 1 or 2, wherein the pressure of the gas ejected from the nozzle is constant.   The non-contact viscometer according to any one of claims 1 to 3, further comprising a photoelectric sensor for detecting the concave portion.   The non-contact viscometer according to claim 4, wherein the measurement mechanism calculates the life cycle of the recess by performing signal processing on an electrical signal output from the photoelectric sensor.   The non-contact viscometer according to claim 5, wherein the signal processing is Fourier transform.   The non-contact viscometer according to any one of claims 1 to 6, further comprising a temperature correction mechanism that corrects a measured value of the viscosity of the liquid based on the measured temperature of the liquid.   The non-contact viscometer according to any one of claims 1 to 7, further comprising a flow rate correction mechanism that corrects a measured value of the viscosity of the liquid based on the flow rate of the gas. Ejecting gas from nozzles disposed obliquely to the surface of the liquid;
Measuring a life cycle until the concave portion generated on the surface of the liquid disappears by the jetted gas; and
And a step of calculating a measured value of the viscosity of the liquid based on the measured value of the life cycle and a proportional relationship between the life cycle and the viscosity of the liquid.