SU840706A1 - Method of measuring aerosol concentration - Google Patents

Description

(54) METHOD OF MEASURING THE CONCENTRATION OF AEROSOL

The invention relates to methods for studying the physical and chemical properties of substances, specifically to methods for determining the concentration of the dispersed phase in two-phase flows, and can be used to control the dust content of industrial emissions in the field of environmental protection. A method for measuring the concentration of aerosol, including preliminary charge, is known. corona particles and the subsequent registration of the current transferred by the particles. The current or charge of the particles is measured with an electrostatic electrode inductively charged particles are determined. The method has low sensitivity and is applicable in a narrow range of concentrations, mainly for measurements in habitable rooms and atmospheric air. A known method for measuring large concentrations of aerosol, which includes recording changes in the corona discharge current, shielded by initially uncharged particles moving in the aerosol stream at a known rate of 2. In this method, the flow rate is so small that the particles in the discharge field acquire an ultimate charge, so the difference in currents with and without particles is determined by the concentration of particles, regardless of speed. When the speed increases when the time of flight of the particles of the discharge region, (1) where E is the size of this region along the flow in meters; V is the velocity of the particles, becomes on the order of 0.1 si less, the particles acquire a charge of 90% of the limiting and less (j). In this case, to determine the concentration

introduce an appropriate correction to the measured current, depending on the speed nOTOtCBt

The known method is carried out with a device containing corona electrodes installed in a nozzle connected by a pipeline path with a thrust rod i

However, the method has a measurement error due to random pulsations of the initial (zero) current in the dust-free gas. The causes of these pulsations are numerous, these include fluctuations of the chemical and physical parameters of the dispersion medium (gas), as well as abrasive and corrosive wear of the surface of the discharge electrode. This error reduces the accuracy of the measurement. To eliminate this error, it is necessary to perform a zero current calibration periodically. The known method is used only for displaying the flow, and not for measuring, moreover, in the initially dust-free air, therefore the value of 1gule current is known. In industrial ducts there is no possibility of creating dust-free gas of the same chemical composition and physical state, therefore, with the expansion of the field of application of the known method, the measurement accuracy is unacceptably reduced. ;

The purpose of the invention is to improve the accuracy by periodically checking the zero current.

The goal is achieved by the fact that in the method of measuring the concentration of an aerosol, which includes recording changes in the corona discharge shielded by initially uncharged particles moving in an aerosol flow at a speed that charges the particles, at the time of the Zero current calibration, the flow rate increases to exclude charging. particles in the flow of aerosol and register the difference of the currents measured at two flow rates.

The method can be carried out by a device containing corona discharge electrodes installed in a nozzle connected by a pipeline path to a pull actuator, in which a flow chamber of a given volume is inserted into the path with two pairs of parallel connected chokes, from which the first pair of chokes are distinguished diameter of holes located at the entrance

into the chamber, and the second pair of identical chokes - at the exit from the chamber, and simultaneously being combined at the entrance and exit along one choke of different diameters.

The drawing schematically shows a device for implementing the method.

In the dust nozzle 1 there is a precipitating 2 and a corona 3

electrodes connected by appropriate cables to a high-voltage direct current source 4 and a recorder of 5 corona current changes. Nozzles 1 are pneumatically connected by a pipeline path 6 with a flow chamber 7 and a propulsion rod, such as an ejector 8. At the inlet and outlet of the chamber 7, two pairs are connected in parallel to

chamber 7 are throttles 9 and 10, and the throttles 9 have a larger through-hole than the throttles 10. Throttles 9 and 10 are connected to the path 6 by the commutator I1, equipped with a mechanical

drive 12 periodic action.

In the process of measuring the nozzle 1, due to the diffusivity of the intake aperture, isokinetic selection of the aerosol under investigation is provided

with the help of ejector 8 with high voltage source 4 and recorder 5 turned on. In the corona discharge field between electrodes 2 and 3, the particles acquire an electric charge, reducing the field strength and the recorded current in proportion to its concentration, or rather the total surface of the particles per unit volume of gas with a known

flow rates. At this time, the actuator 12 sets the switch 11 in the position shown in the drawing, where the throttle 10 is connected to the entrance of the chamber 7 with a smaller opening, and

Inlet - choke 9 with a large hole. The significant resistance of the input throttle provides in chamber 7 the greatest discharge corresponding to the capabilities of the ejector 8.

Claims (2)

The actuator 12 periodically switches the switch 11 to the position when the throttle 9 is connected to the input of the chamber 7, and the throttle 10 is connected to the output. The small resistance of the throttles 9 at the input leads to a rapid filling of the chamber 7 with aerosol and a given increase in the flow velocity in the area of the corona discharge. The measured current of the discharge bit at a higher rate corresponds to zero, which takes place in the dust-free gas due to the fact that the particles did not have time to acquire a charge. Thus, the desired concentration is proportional to the difference of the currents at two speeds, i.e. variable component. The duration of the calibration is determined by the constant time of leakage in chambers 7, depending on the volume of this chamber and the hydraulic resistance of the throttles of villages 9 with a sufficiently large resistance of throttles 10. The error in determining the zero current can be estimated depending on the flow rate, considering the kinetics of charging particles corona field m tj-t-1 where q is the charge acquired by the aerosol particle; q is the limiting charge of a particle at a given intensity of the electric field and an unlimited charging time; t 0.01 s is the charge time constant for air under normal conditions. At a known speed, using the formula (1), it is possible to determine the charging time, then by the formula (2) - the charge of the particle, and the calculated particle concentration is determined from the calculated charge and the detected current of the corona. If you increase the flow rate to M 7 / S 1 m / s, then the charging time. particles will become t lO. From formula (2), it can be calculated that the charge of the particle in this case is less than 1% of the limiting one, which causes. error of zero current determination. In the developed device layout, the electrode 2 has a diameter of 0.01 m and a length along the stream, indicated in the drawing, 0.01 m, which determines the size of the discharge region. The flow velocity at the time of verification is 100 m / s. With a chamber volume of 7-10 liters, the calibration time is slightly more than 0.002 s. Claims. A method for measuring aerosol concentration, which includes recording changes in corona current shielded by initially uncharged particles moving in an aerosol stream at a rate that ensures the charge of a particle, characterized in that, in order to improve accuracy by periodically checking a zero current, at the time of calibration by -. The flow rate is increased to a value that excludes charging of particles in the aerosol flow and the difference in currents measured at two flow rates is recorded. Sources of information taken into account in the examination 1. I. Vereshchagin, V. Levitov, G. Mirzabek, G. 3., Pashin M. M, Fundamentals of electro-gas dynamics of disperse systems. M., Energie, 1974, p. 167. 2. The patent of the USA 3932851, cl. Q 08 17/10, 1974 (prototype).