JP3934520B2 - Measuring method of elastic force of fluid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for measuring the elastic force of a viscoelastic fluid in a high strain rate region.
[0002]
[Prior art and problems to be solved by the invention]
Since the elastic force of a fluid is different from dimensions and cannot be measured directly, various values are obtained indirectly by observing various behaviors. There are many measurement methods in the low strain rate region, but there are many problems in measuring the elastic force of the viscoelastic fluid in the high strain rate region.
[0003]
One such method is to measure the bulge of the jet diameter when the fluid is discharged from the nozzle and calculate the elastic force. Because this method is performed in air, the measurement value is affected by surface tension and gravity, and even if the jet flows out of the narrow tube, it does not swell immediately. Had drawbacks.
[0004]
The method of measuring the drop in thrust due to the elastic force of the fluid by discharging the jet into the air can measure under the high pressure conditions required for high-concentration polymer solutions, but if the outflow speed is low, measure the thrust In addition to being difficult, it was similarly affected by gravity and surface tension from releasing the jet into the air.
[0005]
On the other hand, the method of measuring the drop in the reaction force due to the elastic force of the fluid by discharging the jet into the liquid is not affected by surface tension or gravity, but it was difficult to apply high pressure due to the structure of the device. .
[0006]
Conventionally, in order to measure a normal stress difference which is one of elastic forces of a viscoelastic fluid, a cone / plate type rheometer is used. However, this apparatus can only measure in the low shear rate region, and cannot measure in the industrially important high shear rate region. In addition, a device that can withstand practical use has not been devised for measuring the tensile stress, which is another elastic force. For this reason, a simple apparatus that can measure both normal stress and tensile stress, particularly in a high strain rate region, has been eagerly desired.
[0007]
The present invention provides a measuring means which can eliminate the influence of surface tension by discharging a fluid into a liquid and can stably measure elastic force even in the case of a jet having a high pressure and a low flow velocity. That is, an object of the present invention is to provide a practical apparatus for mechanically measuring the elastic force of a fluid, particularly in a high strain rate region. Here, the elastic force includes the first normal stress difference in the shear flow and the extension stress in the extension flow.
[0008]
[Means for Solving the Problems]
The gist of the present invention will be described with reference to the accompanying drawings of Embodiment 1.
[0009]
The nozzle 2 for allowing the fluid to flow out in the liquid 5 is immersed in the container 4 containing the liquid 5, and the force applied to the container 4 is measured by the measuring device 6 to discharge the fluid from the nozzle 2. Using a mechanism that discharges when the fluid discharge (outflow) becomes steady, shuts off the fluid discharge with the shut-off valve 3, and calculates the elastic force using the difference in the observed force before and after the shut-off. The present invention relates to a fluid elastic force measuring method.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The preferred embodiment of the present invention (how to carry out the invention) will be briefly described with reference to FIGS.
[0011]
When the total force of the force (jet thrust) due to the fluid constantly discharged into the container and the gravity of the fluid accumulated in the container is continuously measured, the force increases linearly with time. To do. In other words, the force measured by the measuring device 6 when the fluid flows out is obtained by adding the thrust of the outflow jet in addition to the gravity due to the total mass of the container and the liquid that has been put in advance and the inflowing fluid. Therefore, if the flow is stopped at a certain moment, the force displayed so far by the measuring instrument is not constant at that value, but it is slightly lowered and constant as shown in FIG. Since the reduced amount corresponds to the jet thrust, the jet thrust can be determined by measuring the reduced amount. The thrust T of the outflow jet measured in this way is determined by the law of momentum between the outflow momentum per unit time of the outflow jet (hereinafter referred to as outflow momentum) M and the elastic force E of the fluid.
E = MT (1)
The relationship holds. Since M can be obtained by calculation from the velocity distribution of the outflow jet if the flow rate is known, E can be obtained by measuring T. Here, the momentum M of the fluid is expressed by M = (fluid density) × (outflow flow rate) × (outflow velocity). Actually, the fluid flowing in the narrow tube or the like does not have a constant outflow velocity but has a velocity distribution, so it is necessary to perform integration corresponding to M. In any case, the actual M is obtained from the velocity distribution of the flowing fluid. Can do. For example, in the case of a Newtonian fluid (low molecular liquid such as water or oil) that flows out from a thin tube, M = 1.33 (fluid density) × (outflow flow rate) × (average outflow velocity) = 1.33 (fluid density) × (Outflow flow rate) ² ÷ (capillary cross-sectional area).
[0012]
Further, the rate of increase in force measured before the flow is interrupted corresponds to the flow rate. Therefore, M obtained from the flow rate before the interruption and the decrease T of the force (the difference between the observed forces before and after the interruption). Can be used to obtain the elastic force of the fluid, which is the difference between M and T, using equation (1). Since the above measurement can be performed in a fluid, the influence of gravity and surface tension on the measurement of elastic force can be eliminated.
[0013]
However, when the influence of gravity or surface tension is sufficiently smaller than the elastic force, it is not necessary to immerse the nozzle in the liquid.
[0014]
【Example】
Specific embodiments of the present invention will be described with reference to the drawings.
[0015]
The force that is reduced by letting the fluid flow out from the capillary tube, the orifice, or the nozzle into the liquid stored in the container installed on the load cell, and then suddenly blocking the flow is measured using the load cell. The elastic force of the fluid is calculated from the thrust, and this method makes it possible to measure the elastic force in a high strain rate region that is industrially important.
[0016]
In addition, the present invention is used for measurement and quality control in the fields of polymer melts, polymer solutions, viscous fluids, glass, various films, inks, paints such as paint, adhesives, magnetic material mixed liquids, etc. By measuring the elastic force of the solution, various problems caused by the elastic force can be solved.
[0017]
Example 1
In this example, the test fluid is allowed to flow out of the capillary tube. At this time, the liquid is allowed to flow out into the same kind of solution in a container placed on the outflow side or into an easily available liquid such as water or oil. It is assumed that the outflow rate is known in advance by means such as using a flow meter or using a fluid pumping method using a quantitative pump. Or you may obtain | require from the inclination before the flow interruption | blocking of FIG. When the container is placed on the load cell and the fluid is allowed to flow out in a steady state, the output value of the load cell increases at a constant rate due to an increase in the amount of liquid in the container. At this time, the value measured by the load cell is the sum of the weight of the container and the solution accumulated in the container and the thrust of the outflow jet. Now, when the flow is stopped suddenly by a solenoid valve or the like, the value of the load cell decreases by the thrust of the outflow jet and becomes a value indicating the weight of the container and the solution accumulated in the container. Therefore, the thrust of the outflow jet can be measured from the decrease in the load cell value.
[0018]
The measured value of the thrust of the outflow jet described above is smaller than the jet thrust theoretically calculated from the outflow momentum if the liquid has an elastic force, corresponding to the elastic force (see Equation (1)). ). Therefore, the elastic force can be calculated from the difference between the thrust calculated from the outflow momentum and the measured jet thrust. If an orifice or nozzle is used instead of a thin tube, the extension stress can be measured. Further, the strain rate corresponding to the measured elastic force can be obtained by calculation from the velocity distribution if the flow rate is known.
[0019]
Therefore, it is possible to measure an elastic force including normal stress and tensile stress in a high strain rate region, which has been difficult to measure by a very simple and inexpensive apparatus. The amount of the test fluid is small, and the measurement can be performed in a short time.
[0020]
Specifically, for example, as shown in FIG. 2, a load cell 6 having a full scale of 100 gf and a resolution of 10 mgf is used as a measuring device, and the nozzle 2 is suspended so as to be immersed in the aqueous solution 5 of the polyethylene container 4 containing the 500 ppm PEO aqueous solution 5. The solution introduced from the inlet 1 was discharged at a flow rate of 4 gf / second for 1 second, and then shut off by the solenoid valve 3. During this time, the electrical output from the load cell 6 was almost as shown in FIG. 1, and the decrease in the force corresponding to the thrust was about 0.55 gf. Since the force just before blocking the fluid is about 73 gf, the measured drop value is reliable. If the total mass is reduced by reducing the amount of the liquid 5 put in the container 4 in advance, the accuracy of the measured value can be further improved. When the electromagnetic valve 3 is shut off, an instantaneous output peak appears due to the vibration of the device. However, such noise can be reduced by devising such as installing a damper. As in this method, since the same solution is discharged into the 500 ppm PEO aqueous solution 5, it is not necessary to consider the influence of gravity and surface tension as compared with the case where it is released into the air.
[0021]
Note that the present invention is not limited to this embodiment, and the specific configuration of each component can be designed as appropriate.
[0022]
Example 2
The interruption of fluid discharge is not limited to the method of the first embodiment, and can be performed by the following method. As shown in FIG. 3, the fluid jet that is constantly discharged from the nozzle is momentarily blocked by a flow blocking plate attached to the tip of the support rod. As this means, as shown in FIG. 4, before the shut-off, the small plate is placed at a position away from the jet (dotted line position in FIG. 4), and at the time of shut-off, the small plate is moved under the nozzle by rotating the support rod. Shut off. In this case, since it is not necessary to stop the discharge of the fluid itself, the force measured by the load cell is as shown in FIG. The difference between the extension line of the straight line before breaking and the straight line after breaking shows the thrust. The above method is effective even when the nozzle is not immersed in the liquid. The small plate may be replaced with a flat plate.
[0023]
In the second embodiment, since the momentum of the jet is slightly lost due to friction with the surrounding liquid before the fluid flows out from the nozzle and reaches the small plate, the accuracy is slightly lowered as compared with the first embodiment.
[0024]
Example 3
When the fluid is discharged into the air, as shown in FIG. 6, the flow may be blocked by a small cup in the air, and the fluid may be stored in the small cup.
[0025]
Example 4
The small cup of the third embodiment may be replaced with a flow blocking cage as shown in FIG. 7, and the fluid may be guided out of the container.
[0026]
In the case of Examples 3 and 4, the measured force is as shown in FIG.
[0027]
【The invention's effect】
Since the present invention is configured as described above, if there is a fluid discharge mechanism having a simple force measuring instrument and a shutoff valve and a container for receiving the fluid, a wide range can be selected according to various conditions such as the type of fluid, flow rate, pressure, and temperature. The elastic force of the viscoelastic fluid can be easily measured.
[0028]
The method of the present invention is not limited to batch measurement, and can be easily applied to continuous monitoring in a plant or the like.
[0029]
Usually, the fluid to be measured is used as the liquid for dipping the nozzle, but a different liquid may be used.
[0030]
In addition, it can be safely measured in a sealed environment even when it is dangerous to expose to the air, or when sanitary considerations are necessary, so that it can make a great contribution to the entire industry.
[Brief description of the drawings]
FIG. 1 is a graph showing the principle of fluid thrust measurement in Example 1. FIG.
FIG. 2 is a schematic configuration explanatory view showing a measuring apparatus according to the first embodiment.
FIG. 3 is a front view illustrating a schematic configuration of a measuring apparatus according to a second embodiment.
FIG. 4 is a schematic configuration explanatory plan view showing a measuring apparatus according to a second embodiment;
FIG. 5 is an explanatory diagram for obtaining a thrust from a force measured in the case of the second embodiment.
FIG. 6 is a schematic configuration diagram of an apparatus that receives a discharged fluid with a small cup when the fluid of the third embodiment is discharged into the air.
FIG. 7 is a schematic configuration diagram of an apparatus for receiving a discharge fluid by scissors when discharging a fluid of Example 4 into the air.
[Explanation of symbols]
2 Nozzle 3 Shut-off valve (solenoid valve)
4 Container 5 Liquid
6 measuring instruments

Claims (1)

The fluid is allowed to flow out into the container containing the liquid, and the discharge of the fluid is momentarily interrupted while measuring the force that the container receives by the fluid discharge, and the difference in the observed force before and after the interruption is used. And measuring the elastic force of the fluid.

Images