SU998931A1 - Method and device for measuring evaporation kinetics of liquid drop - Google Patents

Description

(54) METHOD OF MEASURING THE KINETICS OF EVAPORATION OF A LIQUID DROPS AND DEVICE FOR ITS IMPLEMENTATION

The invention relates to a measurement technique, in particular to the study of the kinetics of evaporation of liquid droplets, and can be used in an experiment for studying the evaporation of droplets. Clean liquids and solutions, heat exchange processes in aero-dispersive systems, as well as technological devices to control the size of liquid droplets in the processes of drying, extraction, etc.

Known are methods and devices for studying the kinetics of evaporation of a liquid drop, based on measuring the linear size of a drop using a measuring microscope. The method and the device provide for the creation in the working chamber of a gas medium with specified parameters, placing a drop in the focus of the optical microscope circuit, its illumination and determination of the linear size (height) using a calibrated measuring scale naCl microscope. However, the described method has significant drawbacks: small speed and accuracy size measurement, the measurement process is not automated.

 The closest technical solution to the present invention is a method that also provides for the formation in the working chamber of a vapor-gas 1 medium with predetermined parameters, the formation of a drop of liquid and its placement in the focus of the optical scheme of the camera, lighting the drop and photographing at certain time intervals determination of droplet size and calculation of evaporation characteristics 2.

The device implementing this method contains a working chamber with systems for pumping out and gas inlet, a system for monitoring parameters of the vapor-gas medium. The camera is equipped with optical inputs for illuminating and photographing a drop. a camera and a backlight system with a heat filter that serves to absorb the heat rays of the backlight. The use of such a device determines the availability of equipment for pro-. photographic film and making prints with imaging of 1Cash1I, measuring instrument, optical or mechanical, to determine the size of the drop | 22 by fingerprint. . The disadvantages of this method are low speed (from shooting to obtaining evaporation characteristics takes at least 1.5 hours), the complexity of the measurement process, the impossibility of it: automation Using this method leads to a decrease in measurement accuracy (in better samples the error is 0.01 MM ) linear size due to the blurring of the droplet borders in the image with inaccurate positioning in the focus of the camera, to the complexity of the installation due to the installation of optical inputs into the working camera for highlighting and photographing. It is also necessary to install heat filters on the backlight, so that the heating of a drop with rays of light does not affect the evaporation rate. The aim of the invention is to increase the efficiency and accuracy of measuring the linear size of a liquid drop, as well as to enable the automation of the measurement process. The goal is achieved by the method of measuring the evaporation kinetics of a liquid drop based on the determination of the change in linear size of a drop placed in the vapor-gas medium with specified parameters , the vapor-gas medium with the specified parameters is created between the electrodes of the electric capacitor, its capacitance is measured, then on one of the electrodes is placed liquid drops, the capacitance of the formed condenser is measured again and judging by the difference in the obtained values, the drop size is determined, and by the change in this difference in time, the evaporation kinetics. A device for implementing the method, comprising a vacuum chamber with a system for pumping out and gas inlet and a system for monitoring environmental parameters, contains a two-electrode planar electric capacitor included in the driver circuit of a high-frequency electric oscillator, the output of which is connected to an electronic frequency counter having a digital output. The capacitor electrode is filled into 31 as a metal capillary, at the end of which there is a measurable droplet, and the other is in the form of metal coaxial with the capillary matic drive, the capillary end and the surface of the disc are located in one plane, FIG. 1 shows the block-; installation heme | in fig. 2 - electric capacitor, rectangular isometry. The device contains a two-electrode plane capacitor 1, a working chamber 2, a generator 3 of high-frequency electrical oscillations1, a system 4 for pumping out and injecting a vapor-gas medium, a system 5 for monitoring environmental parameters, an electronically variable frequency meter 6 with digital output, a metal capillary 7, a metal disk 9, a droplet of liquid to be measured 8, an insulating gasket 10.. The device operates as follows: The planar two-electrode electric capacitor 1 (Fig. 1) is placed B to the working chamber 2 so that the working space of the camera is located between its electrodes, and is included in the task of the electric oscillator 3 with system 4, with holding a vacuum pump with a trap and cylinders with different gases, pumped-. The saiOT gas-vapor mixture from the working chamber is re-injected to the specified parameters (temperature, pressure), which are monitored by system 5 containing a thermocouple and a vacuum meter. The frequency of the generator 3 is then measured with an electronically counted frequency meter 6, which is turned on at the generator output and has a digital output that allows you to automatically measure the measured frequency. Next, on the end of the capillary 7 (Fig. 2), a drop of the investigated liquid 8 is formed, the capacitance of the capacitor, which determines the frequency of the generator, will be determined by the size of the drop. The electrodes of the sensor}, the capillary p 7 and the metal disk 9 coaxial with one, are electrically insulated from each other by a gasket 1O, the end of the capillary and the surface of the disk are located in one plane. The change in the hour with the evaporation time is recorded by a frequency meter. The droplet size is determined from the difference between the initial frequency and the current one using the calibration characteristic. By changing the difference in time, KajEW-B size changes determine evaporation parameters such as evaporation rate, etc.

Example. To measure the evaporation kinetics of a water droplet from a flat surface, a planar electrical capacitor is manufactured. One capacitor plate is made in the form of a capillary made of stainless steel Х18Н9Т with a diameter of 2.016 mm, and the second - in the form of a disk made of steel of the same brand with a diameter of 160 mm.

The butt end of the capillary on which a drop is formed, and the surface of the disk are located in a B-same plane. The plates are electrically insulated from each other using a Teflon gasket. KontsenSatorg. include in the driver circuit of the generator of electrical oscillations with a natural frequency of 1O MHz in such a way that changing the capacitance leads to a change in the generator frequency.

The condenser is placed on the lower flange of a vacuum-tight working chamber with a volume of 0.022 m, equipped with a system for pumping and filling gas-vapor mixture, a system for monitoring environmental parameters. -The system for pumping and inlet contains a fore vacuum pump VN-2MG with a nitrogen trap, cylinders with various gases and a system of taps that smooth pumping and gas inlet. the camera. The control system contains both a copper-constant thermocouple and ampervoltmeter FZOdl for measuring the temperature in the chamber, a mercury vacuum gauge for measuring pressure

Before starting the measurements, the vapor-gas mixture in it is pumped out of the chamber using a VN-2MG vacuum pump and dry pure nitrogen is pumped from a cylinder to a pressure of 740 mm, Hg. Art. The temperature in the chamber, measured by thermocouple, 19, bS.

Next, the frequency of the electric oscillation generator is measured with an electronically counted digital frequency meter ChZ-34A and a drop of distilled water is formed at the end of the capillary. If there is a droplet in the capacitor, its capacitance changes depending on the size of the droplet and the oscillation frequency of the oscillator is measured, which is also recorded by the frequency meter at regular intervals.

Electron-frequency counter through the input-output interface is connected to the computer-15BCM-5. Measurement information from the frequency meter in digital form, entering the computer memory and as it accumulates is processed according to a predetermined program.

From the difference between the initial and current frequencies, using the calibration characteristic, the size of the droplet is determined at specific time intervals (the height of the droplet 1i). The calibration characteristic has a Cd of 2.2429 1 + 4.1500h de f- the difference of frequencies without a drop in a condenser and with a drop of kGy; C - drop height, mm.

In the experiment, the time between measurements is O, 1 s. Measurement error is 0.004 mm (standard deviation).

By changing the size over time, the evaporation characteristics are determined by the formulas that describe this experimental situation (speed, evaporation coefficient).

Thus, the use of the proposed method and device for its implementation makes it possible to significantly increase the efficiency of research of the processes of evaporation of liquid droplets by increasing the speed of the measuring system (1 O measurements for 1 s or more, while the known method loses 1.5 to obtain a result), increase the accuracy of the measurement of l / 2.5 times compared with the known method (the measurement error is reduced to 0.004 mm). The application of the method and device will allow to fully automate the process of measuring and processing the experimental data. as the frequency of electrical oscillations of the generator. Carrying information about the size of the drop, about the change in size, can be automatically measured by a frequency meter and in digital form either recorded automatically on paper or directly transferred to a computer memory.

In addition, the design of the experimental setup is greatly simplified by eliminating the need for mounting optical backlight and photography inputs and, accordingly, heat filters.

These advantages allow the use of the method and device for the study of the processes of temperature and mass transfer of droplets of various liquids and solutions, especially fast processes, in aero-dispersed systems. Automating the measurement will allow effective control over the size of droplets in various technological devices, such as chemical industry. Formula and 1. A method for measuring the kinetics of evaporation of a liquid kappa, based on determining the change in the linear size of a drop, placed B a vapor-gas medium with predetermined parameters, characterized in that, in order to improve the efficiency and accuracy of measurement, it is also a deferred size In order to automate the measurement process, a vapor – gas medium with a given parameter is created between the electrodes of an electric capacitor, its capacitance is measured, then a drop of liquid is placed on one of the electrodes, s measured capacitance formed by the capacitor and the difference values obtained is judged on the linear dimension of a drop, and the change in time difference zachey kinetics of evaporation. 2s A device for implementing a method comprising a vacuum chamber with a system for pumping out and gas inlet and a system for monitoring environmental parameters, which is also contained in that it contains 9 1 two-electrode-plane electrical-. The capacitor is connected to the master circuit of a high-frequency electric oscillation generator, the output of which is connected to an electronically charged meter that has a digital output. In this case, one capacitor electrode is made in the form of a metal capillary, on the end of which is a measured droplet with a metal disk capillary, with the end of the capillary disk surface located in the same plane. Sources of information taken into account in the examination 1. Dunsky V. F., Yankov Yu. V. Slow evaporation of a solution droplet. Engineering Physics and Journal, Vol. HHH1U, 1978, No. 2, p. 205-211. 2. Shimansky Yu. I. et al. Experimental investigation of the rate of evaporation of water droplets in an atmosphere of air and carbon dioxide under the conditions of thermostatisation of the surface of a drop. - Ukrainian Physical Journal, vol. 17, 1972, No. 9, p. 1528-1534 (prototype).

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Claims (2)

The formula of the invention neither I 1. A method of measuring the kinetics of a liquid droplet, based on the laziness of changing the linear size of a droplet mixed in a vapor-gas medium with predetermined parameters, characterized in that, in order to increase the efficiency and accuracy of measuring the linear droplet size, as well as to enable automation of the measurement process, a vapor-gas a medium with given parameters is created between the electrodes of the electric capacitor, its capacity is measured, then a drop of liquid is placed on one of the electrodes, the capacitance of the formed cone is again measured the nasator and the difference in the obtained values are judged on the linear size of the droplet, and on the change in this difference in time - jg on the kinetics of evaporation. 2. 'A device for implementing the method, comprising a vacuum chamber with a system for pumping and admitting gas and a system for monitoring environmental parameters, characterized in that it contains 998931 8 two-electrode planar electric. a capacitor included in the master circuit of a generator of high-frequency electric oscillations, the output of which is connected to an electron-counting frequency meter having a digital output, and one capacitor electrode is made in the form of a metal capillary, at the end of which there is a measured drop, and the other in the form of a metal capillary coaxial with the capillary the disk, with the capillary end face ", the surface of the disk is located in one plane.