RU2582805C2 - Device for gas sampling in high-enthalpy plants of short-term action and method of measuring flow gas rate with use of said device - Google Patents

Abstract

FIELD: gas industry.

SUBSTANCE: invention relates to a technique of investigation of properties and composition of working gas in high-enthalpy plants of short-term action. Device for sampling gas in high-enthalpy plants of short-term action includes tightly connected sampler with sharpened front edge and expanding inner channel. Device also includes a pyro-valve, piston valve arranged in housing, a unit for connection of control of high-voltage wires for blasting powder charge and bypass opening in cylinder for gas collection and storage. Cylinder for collection of samples is equipped with a piston, and in channel of sampler there is a heat-conducting insert with a developed area of inner surfaces. Unit for connection of control of high-voltage wires for blasting powder charge is installed in wind shadow pyrotechnic valve and is additionally equipped with two-electrode system, and housing is provided with a drain hole to release pressure of powder gases. Method for determining gas flow rate with use of said device comprises evacuation of gas dynamic path and device cavities to a pressure of 10^-2 mmHg and through bypass port of sampler filled with a gas cylinder for sampling. Piston of cylinder is locked in far right position, and then sealed with overflow hole. Gas filled cylinder is allowed to cool to room temperature T_b, cylinder pressure is measured using a pressure gauge or pressure sensor. Knowing value of cylinder volume V and bypass opening pressure p_b in cylinder cavity, time t_b = t_b2 - t_b1 stay in open position opening bypass, determined by mass of gas (G_b)_e, released to tank in a time t_b (G_b)_e=Vp_b/(RT_b), where R - specific gas constant, t_b1, t_b2 - start and end of cylinder filling, calculate estimated value of mass that must sag in bottle for a time t_b.

EFFECT: invention provides high reliability of gas sample, preservation of cylinder, and also provides possibility of simultaneous measurement of gas flow rate.

3 cl, 1 dwg

Description

The invention relates to techniques for studying the properties and composition of the working gas in high-enthalpy installations of short duration.

For a number of works performed, for example, in pulsed high-enthalpy installations, it is necessary to know the composition of the working gas flowing around the model.

Thus, when studying gas-dynamic models with combustion, the question arises of the oxygen content in the air flowing around the model, since its fraction decreases due to oxidation of structural elements during electric arc heating in the prechamber. When using chemical energy to increase the plant's energy, it is necessary to know how completely the chemical reactions in the prechamber are completed and what composition the working gas has at the nozzle exit. When studying various schemes of direct-flow engines with heat and mass supply, it is desirable to know the composition of the combustion products at the exit of the nozzle, etc.

In addition, having experimental data on gas flow in the working part of a short-acting high-enthalpy wind tunnel (operating time ~ 100 ms) and comparing them with the calculated results, it is possible to increase the reliability and accuracy of the studies.

Known devices for obtaining information about the gas composition by sampling from a moving at a supersonic speed potentially chemically active medium using an expanding channel for freezing the sample and its further chemical analysis (Rozhitsky S.I., Strokin V.N. To the method of sampling gas from supersonic reactive flow. // Combustion and Explosion Physics. 1974. V. 10, No. 4. P. 492-498) [1]; (USSR author's certificate No. 463029, class G01n 1 / 22.1972) [2].

The disadvantages of these devices is the inability to use them in aerodynamic installations with short-term operating modes of ~ 100 ms for the following reasons:

- with a wind tunnel operating time of ~ 100 ms, the time for gas extraction and locking in a cylinder is several tens of milliseconds, which is clearly not enough to use these devices;

- to bind the sample to the changing flow parameters, tight synchronization of the sampling system with the installation mode is required;

- the volume of the cylinder into which the sample is collected is not arbitrary, but is determined by a compromise between the pressure in the cylinder, which should be much less than the total pressure in the channel of the sampler to prevent locking and disruption of the flow into the sampler, the sampling time and the minimum mass of gas necessary for chemical analysis in the cylinder;

- due to the short time of the regime, the pressure of the sample taken in the cylinder is much less than atmospheric, which creates serious problems when taking a gas sample.

When tested in high-enthalpy installations of short duration for determining the parameters of the working gas flowing around the model, there is a limited number of measured quantities. This limited set of values does not allow experimentally determining the required set of flow parameters, such as speed, static pressure and temperature, etc. We have to use a number of assumptions, which, together with the measured values, allow us to create a closed system of equations that ensures that in the working part the calculated parameters of the gas incident on the model are obtained.

The correctness of this approach to determining the parameters of the working gas in the working part (verification of the method for determining the parameters) is verified in special experiments by comparing any measured flow characteristic with its calculated value. The deviation of the calculated characteristic from its measured value serves as an assessment of the accuracy of determining the parameters of the working gas in the working part of the installation. Such a characteristic may be the mass of gas flowing in the working part of the installation through the cross section F ₀ for a fixed time.

A device is known that allows under specific conditions of a short-acting high-enthalpy installation to determine the flow rate of a gaseous medium passing through the channel cross-section (Korolev A.S., Boshenyatov B.V., Druker I.G., Zatoloka V.V. Impulse pipes in aerodynamic studies Novosibirsk, Science, Siberian Branch, 1978. 80 p.) [3], p. 60.

The principal disadvantages of this device are as follows.

- the need to take into account the real properties of the gas associated with high temperature and pressure;

- the need to lower the gas temperature in front of the measuring nozzle in order to reduce the dynamic component of the error in the readings of thermocouples, which makes it necessary to install a heat exchanger-cooler in front of the measuring nozzle;

- inertia in the readings of thermocouples measuring the temperature of the gas in front of the measuring nozzle, which casts doubt on the correctness of the temperature measurement and, therefore, leads to gross errors in the flow measurement.

The closest adopted for the prototype is the device described in the article (Shumsky V.V., Yaroslavtsev M.I. Composition of the working fluid in the working part of the high-enthalpy plant // FGV. 2012. T. 48, No. 1. P. 28- 37) [4], for the selection of gas from the working part of the impulse pipe, taking into account the above features of the high-enthalpy wind tunnels mode, allowing gas to be taken from a supersonic or hypersonic flow for subsequent chemical analysis.

The device contains a sampler that is tightly connected with a pointed front edge and an expanding internal channel, a pyrovalve in the body of which a piston is placed, a connection unit for controlling high-voltage wires to detonate the powder charge, and a bypass hole is made into the volume for collecting, storing and sampling gas from it.

The disadvantages of the device described in [4], in the case of gas extraction for chemical analysis, are as follows:

- at gas flow inhibition temperatures in front of the sampler opening greater than 2000 K, a drop in the temperature of the sample taken in the supersonic part of the sampler (lowering the static temperature when the sample is expanded, heat dissipation into the channel walls) is not enough to guarantee the absence of secondary chemical reactions in the device channels;

- a significant part of the temperature drop should occur at a subsonic speed along the length from the point of transition of the supersonic flow into the subsonic flow (from the pseudo-jump to the camera). In this device, heat removal is carried out only in the walls of the channel, which is not enough;

- the large length of the channels of the device from the beginning of the pseudo-jump to the cylinder does not provide at high temperatures for the sample taken the requirement that the transit time of a sample of this length be less than the time of induction of possible secondary reactions;

- the pyrovalve undermining unit is located on the front of the device, which at high temperatures and gas flow pressures causes malfunctions due to large heat fluxes in the area where the control conductor is connected to the pyrovalve.

- the presence of one (positive) igniting electrode (device body is minus) leads to the appearance of electroerosion on the surface of the valve piston and device body, which violates the tightness of the sample gas cylinder.

The objective of the invention is to expand the experimental capabilities of the device by increasing the limiting temperatures and pressures at which the device can be used in high-enthalpy installations of short duration as a device for sampling gas to determine the composition and measure gas flow.

This object is achieved in that the device for gas sampling and flow measurement in high-enthalpy installations of short duration contains the actual sampler, pyrovalve, connection unit for controlling high-voltage wires to detonate the powder charge, a bypass hole in the cylinder for collecting and storing gas samples.

What is new is that a heat-conducting insert with a developed surface area is installed in the sampler’s channel, and the gas collection and storage cylinder is equipped with a piston, due to the movement of which the pressure in the cylinder can be changed, while the connection point for the control high-voltage wires to detonate the powder charge is installed in the aerodynamic shadow a pyrovalve and is additionally equipped with a two-electrode system, and a drainage hole is made in the pyrovalve body to relieve pressure of the powder gases.

The same device allows you to implement a method for determining gas flow by comparing the mass of gas (G _b ) _e , which filled a chamber of known volume in experiments during time t _b with the value of mass (G _b ) _p , which should enter the chamber during time t _b at the calculated values of the velocity W _n and the specific volume v _{n of} gas in the working part of the installation. This indirectly determines the gas flow through the tube with a cross-sectional area F.

The technical result achieved in this case is an increase in the limiting temperature and pressure at which the device can be used in high-enthalpy installations of short duration, for example, in impulse pipes, increasing the reliability of the selected gas sample filling the chamber, and the possibility of simultaneously measuring the flow rate.

A diagram of a device for sampling gas and measuring flow in highly enthalpy installations of short duration is shown in the drawing.

The device includes: nozzles 1 of a sampler with a pointed front edge and an expanding internal channel, sampler 2, insert 3 of a material with high thermal conductivity (can be made of copper) and with a developed area of internal surfaces (porous), pyrovalve body 4, spring-loaded stopper 5 for fixing the piston 6 of the pyrovalve and the drain hole 7 to relieve the pressure of the powder gases. The connection node for controlling high-voltage wires for signaling to detonate the powder charge 8 (pyrocomposition) is installed in the aerodynamic shadow behind the pyrovalve and also contains a burning candle 9, the insulator of the candle 10 and two electrodes 11. An additional (negative) electrode 11 provides a controlled discharge between the electrodes, and not on the piston, as it was in the prototype. After several starts, traces of electrical erosion appeared on the surface of the piston and cylinder, and the system was not sealed. In the present embodiment, the system is not connected to the ground. The volume for collecting, storing and sampling gas samples - the cylinder 12 contains a piston 13, a screw 14 for moving the piston of the cylinder, a rubber plug 15 for sampling gas and a pressure sensor 16. The bypass hole 17 between the cavity of the sampler 2 and the cylinder 12 is closed by the piston 6 of the pyrovalve .

The device shown in the drawing, in the sampling mode, operates as follows.

Before the experiment, the device is in its original state, as shown in the drawing. When preparing the wind tunnel for start-up, the gas-dynamic path of the pipe is evacuated to a pressure of 10 ^-2 mm Hg. Together with the gas-dynamic path, the cavities of the device for sampling gas are evacuated: the channel of the sampler 2, the cavity of the pyrovalve body 4, the bypass hole 17, the cylinder 12. Using the screw 14, the piston 13 is retracted to the extreme right position and is locked to prevent its displacement due to pressure difference acting on the ends of the piston after the start of the pipe and depressurization of the working part of the installation.

After starting the pipe through the hole d ₀ there is a leakage of gas into the sampler. In the process of gas sampling using high-speed video recording, the shape of the shock wave at the sharp leading edge of the hole d _{0 is} controlled. The signal to detonate the pyrovalve is fed through the connection unit for the control high-voltage wires until the outgoing shock wave appears. Therefore, the timing of the pulse to detonate the pyrovalve is additionally controlled by a video camera.

After the signal to detonate the pyrovalve due to the rapid increase in pressure in the cavity 8, the piston 6 closes the hermetic bypass hole 17 of the sampler 2 through ~ 50-100 μs, the spring-loaded stopper 5 fixes the piston 6 in the extreme left position.

Thus, the cavity of the cylinder 12 is isolated from the gas-dynamic path of the pipe.

When determining the flow rate, the gas filling the cylinder is allowed to cool to room temperature T _b . Then measure the pressure in the cylinder by the pressure gauge or pressure sensor 16. Knowing the volume V cylinder 12 and the bypass openings 17, the pressure P _b in the cylinder cavity, the time t = t _b -t _{b1 b2} stay in the open state of the bypass openings 17, determine the mass gas entering the cylinder during t _b

(G _b ) _e = V _b / (RT _b ),

where R is the specific gas constant, t _b1 is the time of the beginning of the filling of the cylinder, t _b2 is the time of the end of the filling (activation of the pyrovalve after the signal to detonate the powder charge 8).

The estimated value of the mass that must leak into the cylinder for a time t _b is determined from the expression

where W _n , v _n - calculated values of speed and specific volume in the working part of the installation, F ₀ - the area of the entrance to the sampler.

The value of δ = (G _{b p} -G _{b e} ) / G _{b e} characterizes the deviation of the calculated values from the experimental ones and, thereby, with the accuracy determined by δ, allows to determine the gas flow rate G = W _n F / υ _n through the cross-sectional area F in the working parts of the installation.

When taking gas to determine the composition, by conducting further chemical analysis, it should be borne in mind that the sample is frozen in three areas:

1) in section l ₁ with supersonic or hypersonic speed, at which, due to heat transfer to the cold walls of sampler 2, the sample temperature decreases;

2) in the area l ₂ with subsonic speed to the developed cold surfaces of insert 3;

3) to the cold walls of the cylinder 12 after the sample enters the cylinder.

The total cooling time of the sample during its passage from the inlet d ₀ to the cylinder 12 should not exceed the time of induction of a chemical reaction, which depends on the pressure and temperature in the sample. This induction time determines the choice of lengths l ₁ , l ₂ and the need to minimize the length of the section between the actual sampler 2 and the cylinder 12.

The gas cylinder is filled as described above, after the selected gas has cooled to room temperature, the piston 13 is moved to the left with the screw 14 in order to increase the pressure in the cavity of the cylinder 12 slightly above atmospheric. In this case, the pressure in the cylinder is monitored by pressure sensor 16. After that, a rubber plug 15 is punctured with a syringe and a sample is taken for chemical analysis, which ensures the proposed design of the gas sampler.

Information sources

1. Rozhitsky S.I., Strokin V.N. To the methodology for sampling a gas sample from a supersonic reacting stream. // Physics of combustion and explosion. 1974.Vol. 10, No. 4. S. 492-498.

2. USSR copyright certificate No. 463029, class. G01n 1/22, 1972

3. Korolev A.S., Boshenyatov B.V., Drucker I.G., Zatoloka V.V. Pulsed tubes in aerodynamic research. Novosibirsk Science, Siberian Branch. 1978. 80 p.

4. Shumsky V.V., Yaroslavtsev M.I. The composition of the working fluid in the working part of a highly enthalpy installation // FGV. 2012.V. 48, No. 1. S. 28-37.

Claims (3)

1. A device for sampling gas in high-enthalpy installations of short duration, containing hermetically connected the actual sampler with a pointed front edge and an expanding internal channel, a pyrovalve, in the body of which the piston of the valve is located, the connection unit of the control high-voltage wires for undermining the powder charge and a bypass hole is made in a cylinder for collecting and storing a gas sample, characterized in that the cylinder for collecting a sample is provided with a piston, t a heat-conducting insert with a developed area of internal surfaces, while the connection unit for controlling high-voltage wires to detonate the powder charge is installed in the aerodynamic shadow of the pyrovalve and is additionally equipped with a two-electrode system, and a drainage hole is made in the pyrovalve body to relieve the pressure of the powder gases. 2. The device according to p. 1, characterized in that the gas collection and storage cylinder is equipped with a piston displacement screw. 3. A method for determining gas flow in short-acting highly enthalpy installations using the device according to claim 1, characterized in that the gas-dynamic path and device cavities are evacuated to a pressure of 10 ^-2 mm Hg, a sample bottle is filled with gas through the sample port , wherein the cylinder piston is immobilized in its rightmost position, then sealed overflow aperture, filling the gas cylinder was allowed to cool to room temperature T _b is measured pressur e in the cylinder by the pressure gauge or pressure sensor, knowing the volume V bulb and the overflow aperture, the pressure P _b in the cylinder cavity, the time t _b = t _e2 - t _b1 stay in the open state of the bypass holes is determined the mass of gas (G _{b) e} entering the cylinder during time t _b
(G _b ) _e = V _b / (RT _b ),
where R is the specific gas constant, t _b1 , t _b2 is the start and end time of filling the cylinder, calculate the calculated value of the mass that must leak into the cylinder during t _b .

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