CN106290069A - Coefficient of viscosity measurement apparatus and measuring method - Google Patents

Abstract

The liquid viscosity coefficient measuring device of the present invention comprises a support platform, a cylinder, a small ball and a string, and the liquid to be measured is stored in the cylinder; it is characterized in that a dotting timer is placed on the support platform, and a paper dotting timer is arranged in the dotting timer. Belt, the edge of one side of the support table is provided with a fixed pulley, the cylinder is fixed under the fixed pulley in the form of opening upward, and a funnel with an opening facing downward is placed at the opening of the cylinder, and the axis of the funnel and the axis of the cylinder are in the On the same straight line; the small ball is located in the funnel, one end of the string is fixed to the small ball, and the other end passes through the funnel, bypasses the fixed pulley and is fixed to the paper tape. The measuring device and method of the present invention ensure that the small balls always fall along the central axis of the cylinder through the funnel, so that the influence of the cylinder wall on the small balls is minimized and the measurement accuracy is improved. The uniform motion state of the ball can be identified through the dot timer, which further ensures the measurement accuracy of the viscosity coefficient of the liquid.

Description

Liquid viscosity coefficient measuring device and measuring method

technical field

The present invention relates to a liquid viscosity coefficient measurement device and measurement method, more specifically, to a liquid viscosity coefficient measurement device and measurement method which utilizes a dot timer to measure speed and can ensure that the ball falls along the central axis of the liquid .

Background technique

In a stable flowing liquid, due to the difference of each layer of fluid, there is a force between the two layers of liquid in contact with each other, and the force is called viscous force. The viscous force is different between different liquid wave layers because they have different viscosity coefficients. Therefore, the measurement of liquid viscosity coefficient has become a very important subject in university physics experiments. Commonly used methods for measuring the viscosity coefficient of liquids are the falling ball method, the torsion pendulum method, the rotating cylinder method and the capillary method. In the experiment, the capillary method is commonly used for liquids with small viscosity coefficients, such as water, ethanol, carbon tetrachloride, etc.; for liquids with large viscosity coefficients, such as castor oil, glycerin, etc., the falling ball method or rotating drum method is commonly used.

In the falling ball method, when the ball moves in the liquid, it will be subjected to frictional resistance opposite to the direction of motion, and this resistance is the viscous force. It is caused by the friction between the liquid layer adhering to the surface of the ball and the adjacent liquid layer, not the friction between the ball and the liquid. If the speed of the ball is very small when it falls, and the liquid is infinitely vast, and the ball does not generate vortices during its movement, according to Tox’s law, the viscous resistance on the ball is:

F=6πηrv (3)

In the formula: η is the viscosity coefficient of the liquid, v is the falling speed of the ball, and r is the radius of the ball.

After the ball falls into the liquid, it is affected by gravity, buoyancy and viscous resistance, and these forces act in the vertical direction. Gravity is down, buoyancy and viscous drag are up. When the ball just fell into the liquid, the vertical downward gravity is greater than the sum of the vertical upward buoyancy and viscous force, so the ball accelerates. As the speed of the ball increases, the viscous force also increases. When the falling speed of the ball reaches a certain size, the resultant force on the ball is zero, so the ball falls at a uniform speed. From formula (3) can get:

4/3πr³(ρ-ρ ₀ )g= 6πηrv (4)

In the formula: ρ is the density of the ball; ρ ₀ is the density of the liquid.

From the above formula:

η=2(ρ-ρ ₀ ) gr²/9v (5)

Because the liquid is placed in the container, it is not infinitely extended. If the ball falls along the cylinder with the inner radius R ₀ and the height of the liquid in the cylinder is h, considering the influence of the container wall, then:

η=2(ρ-ρ ₀ ) gr²/[9v ₀ (1+2.4r/R ₀ )(1+3.3r/h)]

=(ρ-ρ ₀ )gd²/[18v ₀ (1+2.4d/2R ₀ )(1+3.3d/2h)] (6)

In the formula: d is the diameter of the ball, and the unit of η is Pa*s.

Under the conditions of d<<R ₀ and d<<h, the liquid can be regarded as infinite extension, and the formula (5) can be obtained. Thus, the viscosity coefficient of the liquid can be obtained.

The Stokes formula (3) is derived from the universal motion equation of the fluid in an ideal state (no vortex). To do this, we need to modify the Stokes formula for correction. The corrected result is:

η1=(ρ-ρ ₀ ) gd²/[18 v ₀ (1+2.4d/2R ₀ )(1+3.3d/2h)]-3ρ ₀ dv ₀ /16

=η-3ρ ₀ dv ₀ /16 (7)

The existing device and method for measuring the viscosity coefficient by the falling ball method still has the following problems and deficiencies, specifically as follows: the falling of the small ball tends to deviate from the axis direction, and the influence of the wall of the oil cylinder on the movement of the small ball is increased. In the experiment, it is required that the ball should fall along the axis of the cylinder as much as possible, so as to minimize the influence of the oil cylinder on the movement of the ball. However, in the experiment, students rely on self-assessment to estimate, and often cannot determine the direction of the axis. Moreover, improper tools for picking and placing the ball will cause the trajectory of the ball to deviate from the axis when the ball is released into the oil tank, thereby increasing the impact on the motion state of the ball, resulting in a large error, and sometimes the ball cannot be guaranteed due to operational errors. Starting to fall from rest, with a horizontal initial velocity when falling, this has caused many unnecessary errors.

In the existing experiments, it is necessary to adjust the upper and lower lasers of the experimental stand, and perform alignment treatment on them. This process requires careful operation and is extremely cumbersome to operate. When the ball first enters the upper and lower laser areas, we think that the ball starts to move at a constant speed from blocking the upper laser, which is not accurate, and we cannot determine when the ball starts to move at a constant speed after entering the liquid.

The original experimental instruments can only measure the viscosity coefficient of the liquid at the current room temperature. However, in real life and scientific research, it is more meaningful to study the change of the viscosity coefficient of the same liquid at different temperatures. .

Contents of the invention

In order to overcome the disadvantages of the above-mentioned technical problems, the present invention provides a liquid viscosity coefficient measuring device and a measuring method.

The liquid viscosity coefficient measuring device of the present invention comprises a support platform, a cylinder, a small ball and a string, and the liquid to be measured is stored in the cylinder; it is characterized in that: a dotting timer is placed on the support platform, and a dotting timer is arranged in the dotting timer. Paper tape, a fixed pulley is arranged on the edge of one side of the support table, and the cylinder is fixed under the fixed pulley with the opening facing upwards. A funnel with an opening facing downwards is placed at the opening of the cylinder. On the same straight line; the small ball is located in the funnel, one end of the string is fixed to the small ball, and the other end passes through the funnel, bypasses the fixed pulley and is fixed to the paper tape.

In the liquid viscosity measuring device of the present invention, an outer cylinder is arranged on the periphery of the cylinder, and circulating water for heating and keeping warm the liquid to be measured in the cylinder is stored in the outer cylinder.

The liquid viscosity coefficient measuring device of the present invention includes a temperature control device for adjusting the temperature of the liquid to be measured in the cylinder. The temperature control device is composed of a temperature controller, a heating barrel, an input pump, an output pump, and a temperature control device arranged in the cylinder. Composed of sensors, the heating barrel is equipped with a heater to heat the circulating water in the heating barrel; the circulating water in the heating barrel is pumped into the outer cylinder through the input pump, and the circulating water in the outer cylinder is pumped into the heating barrel through the output pump; The temperature controller measures the water temperature in the cylinder through the temperature sensor, and maintains the measured liquid in the cylinder at the set temperature by controlling the switch status of the heater, input pump and output pump.

The measuring method of liquid viscosity coefficient measuring device of the present invention is characterized in that, realizes by following steps:

a). For equipment placement, place the dotting timer on the support platform, and put the paper tape into the dotting timer; place the cylinder under the fixed pulley, buckle the funnel upside down on the opening of the cylinder, and ensure that the funnel The axis and the axis of the cylinder are on the same straight line, and the string for hanging the balls is fixed on the paper belt around the fixed pulley; the outlet on the heating barrel is connected with the water inlet of the outer cylinder through the input pump, and the outlet on the outer cylinder The water port is connected with the upper inlet of the heating barrel through the output pump; b). Lower the ball, turn on the dotting timer, and then release the ball to make the ball drop along the central axis of the cylinder; c). Calculate the uniform velocity value and wait for After the ball descends to the bottom of the cylinder, turn on the dot timer and take out the paper tape, identify the area where the ball moves at a uniform speed, and read the distance between the two dots, and then calculate the speed value of the ball when it is moving at a constant speed. is v ₀ ; d). Calculate the viscosity coefficient, assuming that the radius of the inner cavity of the cylinder is R ₀ , the height of the liquid to be measured in the cylinder is h, the density of the ball is ρ, the radius is r, the liquid to be measured is The density is ρ ₀ ; the friction coefficient of the fixed pulley is c; the viscosity coefficient η of the liquid to be measured is calculated by the formula (1):

η=2(ρ-cρ-ρ ₀ ) gr²/[9v ₀ (1+2.4r/R ₀ )(1+3.3r/h)] (1)

Considering that there is a vortex phenomenon when the ball falls in the cylinder, the calculated viscosity coefficient η is corrected by formula (2):

η1=η-3ρ ₀ dv ₀ /16 (2)

Among them, d is the diameter of the ball, d=2r.

In the measurement method of the liquid viscosity coefficient measuring device of the present invention, in step a), if the viscosity coefficient of the liquid at a specific temperature needs to be measured, the temperature controller is turned on, the temperature is set at the corresponding temperature, and the temperature controller is set to After the liquid in the cylinder is heated to the set temperature, the next step of measurement is performed.

The beneficial effects of the present invention are: the measuring method of the liquid viscosity coefficient measuring device of the present invention, by setting an inverted funnel on the upper end of the cylinder, and the axis of the funnel is on the same straight line as the axis of the cylinder, during the experiment, it is guaranteed that the small ball It always falls along the central axis of the cylinder, which minimizes the impact of the cylinder wall on the ball and improves the measurement accuracy of the viscosity coefficient of the liquid. The falling process of the ball in the liquid is recorded by the dot timer, which can effectively identify the uniform motion state of the ball in the liquid, which is more accurate than the ball moving speed obtained by the laser measurement method in the past, and further ensures Measurement accuracy of liquid viscosity coefficient.

Further, by setting a temperature control device that can adjust the temperature of the liquid in the cylinder, the liquid in the cylinder can be heated to a set temperature according to the requirement, which is convenient for analysis experiments with different viscosity coefficients of liquids at different temperatures.

Description of drawings

Fig. 1 is the structural representation of the liquid viscosity coefficient measuring device of the present invention;

In the figure: 1 supporting table, 2 cylinder, 3 small ball, 4 funnel, 5 fixed pulley, 6 string, 7 dotting timer, 8 paper tape, 9 outer cylinder, 10 temperature controller, 11 input pump, 12 output Pump, 13 heating barrels, 14 heaters, 15 temperature sensors.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the structural representation of the liquid viscosity coefficient measuring device of the present invention is provided, which includes a support platform 1, a cylinder 2, a small ball 3, a funnel 4, a fixed pulley 5, a string 6, and a ticking timer 7. The paper tape 8 and the temperature control device. The supporting table 1 shown in the figure plays a role of fixing and supporting. The supporting table 1 is at a certain height from the ground. 8. It is used to record the movement information of the ball 3. The shown fixed pulley 5 is fixed on the right side of the support platform 1 , the cylinder 2 is placed under the fixed pulley 5 , and the funnel 4 is buckled upside down on the upper end of the cylinder 2 .

Bead 3 is tied on an end of string 6, and string 6 passes funnel 4 and is tied on the paper tape 8 after going around fixed pulley 5, and before experiment, bead 3 is positioned at the height position of funnel 4 place. The central axis of the funnel 4 is on the same straight line as the central axis of the cylinder 2, so that the ball 3 always falls along the direction of the central axis of the cylinder 2 during the falling process, so that the inner wall of the cylinder 2 is opposed to the movement of the small ball 3. impact is minimized.

During the experiment, after the ball 3 falls to the bottom of 2, by identifying the dot spacing on the paper tape 8, the time period of the uniform motion of the ball 3 in the liquid can be identified, and the ball can be calculated according to the dot spacing. 3 Velocity when moving at a constant speed in a liquid. Compared with the previous use of two lasers to identify the time point of the appearance of the ball, the time period of the uniform motion of the ball 3 can be identified, and the accelerated falling process just entering the liquid is excluded, making the speed measurement more accurate.

The measuring method of the liquid viscosity coefficient measuring device of the present invention is realized through the following steps:

a). For equipment placement, place the dotting timer on the support platform, and put the paper tape into the dotting timer; place the cylinder under the fixed pulley, buckle the funnel upside down on the opening of the cylinder, and ensure that the funnel The axis and the axis of the cylinder are on the same straight line, and the string for hanging the balls is fixed on the paper belt around the fixed pulley; the outlet on the heating barrel is connected with the water inlet of the outer cylinder through the input pump, and the outlet on the outer cylinder The water port is connected with the upper inlet of the heating barrel through the output pump;

b). Lower the ball, turn on the dot timer, and then release the ball to make the ball drop along the central axis of the cylinder;

c). Calculate the uniform speed value. After the ball drops to the bottom of the cylinder, turn on the dot timer and take out the paper tape, identify the area where the ball moves at a constant speed, and read the distance between the two dots, and then calculate the ball The velocity value when doing uniform motion is set to v ₀ ;

d). Calculate the viscosity coefficient, assuming that the radius of the inner cavity of the cylinder is R ₀ , the height of the liquid to be measured in the cylinder is h, the density of the ball is ρ, the radius is r, and the density of the liquid to be measured is ρ ₀ ; The coefficient of friction of the fixed pulley is c; Calculate the viscosity coefficient η of the liquid to be measured by formula (1):

η=2(ρ-cρ-ρ ₀ )gr²/[9v ₀ (1+2.4r/R ₀ )(1+3.3r/h)] (1)

Considering that there is a vortex phenomenon when the ball falls in the cylinder, the calculated viscosity coefficient η is corrected by formula (2):

η1=η-3ρ ₀ dv ₀ /16 (2)

Among them, d is the diameter of the ball, d=2r.

In step a), if it is necessary to measure the viscosity coefficient of the liquid at a specific temperature, turn on the temperature controller and set the temperature at the corresponding temperature. After the temperature controller heats the liquid in the cylinder to the set temperature, proceed The next measurement.

Comparative Test:

In the test, the liquid density ρ ₀ =9.54*10²kg/m³, the ball density ρ=7.74*10³kg/m³, the cylinder radius R ₀ =3.3cm, the height of the liquid (oil) in the cylinder h=35cm, the ball radius r =0.3cm.

As a reference group, the experimental data of the uniform velocity of the ball measured by the laser photogate and electronic timing instrument are shown in Table 1:

Table 1

frequency 1 2 3 4 5 6 often (s) 0.810 0.805 0.837 0.806 0.821 0.835

The distance between two laser lights L=10cm. Process the above data: the value of time t takes the average of 6 times, that is, t=0.819s. Therefore, η=0.738Pa*s can be obtained, and after correction, η1=0.608Pa*s.

At this time, the temperature in the laboratory was 30°C and there was no wind. The standard value of the viscosity coefficient of the liquid under this condition is 0.55Pa*s, and the error of the above result is 10.5%.

Adopt the test device of the present invention to test, the liquid and the bead are all the same, and the friction coefficient c=0.6 of the fixed pulley. By analyzing the paper tape, 5 points are a timing point, and the distance between the two timing points where the adjacent segments are equal is measured to be 0.5cm, and then the speed of the ball moving at a uniform speed is calculated as V ₀ = 0.05m/s.

The ball is also affected by the friction of the pulley during the movement, so the force analysis of the ball can draw the following conclusions:

[4πr ³ ρ(g-cg)]/3-4πr³ρ ₀ g/3=6πηrv (8)

Because the liquid is placed in the container, it is not infinitely extended. Considering the influence of the container wall, the viscosity coefficient of the liquid is calculated by formula (1):

η=2(ρ-cρ-ρ ₀ )gr²/[9v ₀ (1+2.4r/R ₀ )(1+3.3r/h)] (1)

Substitute the data into formula (1) to get the viscosity coefficient η=0.600Pa*s of the liquid.

Considering that there is a vortex phenomenon when the ball falls in the cylinder, the calculated viscosity coefficient η is corrected by formula (2):

η1=η-3ρ ₀ dv ₀ /16 (2)

Wherein, d is the diameter of the pellet, and η=0.546Pa*s is obtained.

Under this condition, the standard value of the viscosity coefficient of the liquid is 0.55Pa*s, and the error of the above result is 0.72%.

Through the comparison and analysis of the above data, we believe that:

(1) When the improved experiment and the original experiment are carried out in the same external environment, it can be seen from the results that the error of the improved measurement result is 9 percentage points lower than that of the original experiment, which can explain the use of the dot timer Measuring the velocity of the ball and using the top funnel to control the center axis of the ball has a great influence on the measurement of liquid viscosity.

Through the above analysis, our improvement of this experiment can significantly improve the measurement accuracy and reduce the occurrence of measurement errors.

(2) We use a dot timer in the improved experiment, which saves students from the tedious process of aligning the light in the pre-experiment preparation process. In addition, using the top funnel, it is easy to control the ball falling from the central axis, and the precision is very high.

(3) By adding a temperature control device to the experimental instrument, we have achieved the measurement of the viscosity coefficient of the liquid at different temperatures. This is of great help to real life and scientific research.

The liquid viscosity coefficient measuring device of the present invention not only improves the test accuracy and reduces some complicated and tedious processes in the test process, but also allows us to understand the influence of temperature on the liquid viscosity coefficient.

Claims (5)

1. A device for measuring the viscosity coefficient of a liquid, comprising a support platform (1), a cylinder (2), a small ball (3) and a string (6), and the liquid to be measured is stored in the cylinder; it is characterized in that: the support platform A ticking timer (7) is placed on the top, a paper tape (8) is set in the ticking timer, a fixed pulley (5) is set on the edge of one side of the support table, and the cylinder is fixed under the fixed pulley with the opening facing upwards , a funnel (4) with the opening facing down is placed at the opening of the cylinder, the axis of the funnel is on the same line as the axis of the cylinder; the ball is located in the funnel, one end of the string is fixed to the ball, and the other end passes through The funnel is fixed with the paper tape after bypassing the fixed pulley. 2. The liquid viscosity coefficient measuring device according to claim 1, characterized in that: an outer cylinder (9) is arranged on the periphery of the cylinder (2), and there is stored in the outer cylinder to heat and keep warm the liquid to be measured in the cylinder. of circulating water. 3. The liquid viscosity coefficient measuring device according to claim 2, characterized in that it includes a temperature control device for adjusting the temperature of the liquid to be measured in the cylinder (2), and the temperature control device is controlled by a temperature controller (10) , a heating barrel (13), an input pump (11), an output pump (12) and a temperature sensor (15) arranged in the cylinder (2), and a heater (14) is arranged in the heating barrel so as to heat The circulating water in the barrel is heated; the circulating water in the heating barrel is pumped into the outer cylinder (9) through the input pump, and the circulating water in the outer cylinder is pumped into the heating barrel through the output pump; the temperature controller measures the temperature in the cylinder through the temperature sensor. Water temperature, by controlling the switching status of the heater, input pump, and output pump, the measured liquid in the cylinder is maintained at the set temperature. 4. a kind of measuring method based on the liquid viscosity measuring device claimed in claim 1, is characterized in that, realizes by the following steps: a). For equipment placement, place the dotting timer on the support platform, and put the paper tape into the dotting timer; place the cylinder under the fixed pulley, buckle the funnel upside down on the opening of the cylinder, and ensure that the funnel The axis and the axis of the cylinder are on the same straight line, and the string for hanging the balls is fixed on the paper belt around the fixed pulley; the outlet on the heating barrel is connected with the water inlet of the outer cylinder through the input pump, and the outlet on the outer cylinder The water port is connected with the upper inlet of the heating barrel through the output pump; b). Lower the ball, turn on the dot timer, and then release the ball to make the ball drop along the central axis of the cylinder; c). Calculate the uniform speed value. After the ball drops to the bottom of the cylinder, turn on the dot timer and take out the paper tape, identify the area where the ball moves at a constant speed, and read the distance between the two dots, and then calculate the ball The velocity value when doing uniform motion is set to v ₀ ; d). Calculate the viscosity coefficient, assuming that the radius of the inner cavity of the cylinder is R ₀ , the height of the liquid to be measured in the cylinder is h, the density of the ball is ρ, the radius is r, and the density of the liquid to be measured is ρ ₀ ; The coefficient of friction of the fixed pulley is c; Calculate the viscosity coefficient η of the liquid to be measured by formula (1): η=2(ρ-cρ-ρ ₀ )gr²/[9v ₀ (1+2.4r/R ₀ )(1+3.3r/h)] (1) Considering that there is a vortex phenomenon when the ball falls in the cylinder, the calculated viscosity coefficient η is corrected by formula (2): η1=η-3ρ ₀ dv ₀ /16 (2) Among them, d is the diameter of the ball, d=2r. 5. The measuring method of the liquid viscosity coefficient measuring device according to claim 4, characterized in that, in step a), if the viscosity coefficient of the liquid at a specific temperature needs to be measured, the temperature controller is opened, and the temperature is set to Set at the corresponding temperature, wait for the temperature controller to heat the liquid in the cylinder to the set temperature, and then proceed to the next step of measurement.