EFFECTS OF REGIME PARAMETERS ON THE HYDRODYNAMICS OF THE INVESTIGATED VORTEX APPARATUS

ABSTRACT

The effects of regime parameters on the hydraulic resistance of a hollow vortex apparatus with a tangential swirl of gas and liquid flow are considered. To determine the energy consumption for carrying out gas purification processes from dust and harmful substances, contact heat exchange, absorption purification of gases and other processes carried out in gas-liquid systems, it is necessary to take into account pressure losses in the vortex apparatus. At the same gas velocity, the hydraulic resistance of the investigated vortex apparatus is much less than the pressure drop in hollow, nozzle and poppet apparatuses and does not exceed the resistance of highly efficient vortex-type apparatuses of other designs. The hydraulic resistance of hollow vortex apparatuses with tangential vortices is determined by the velocity of the gas phase, the flow rate of the liquid and the design parameters of the apparatus, as well as the physical properties of the working media. The optimal operating modes of the developed vortex apparatus have been established, from the position of the pressure drop in the apparatus.

АННОТАЦИЯ

Рассмотрены влияния режимных параметров на гидравлического сопротивления полого вихревого аппарата с тангенциальным завихрителем потока газа и жидкости. Для определения энергозатраты на проведение процессов очистки газа от пыли и от вредных веществ, контактного теплообмена, абсорбционной очистки газов и других процессов, осуществляемых в системах газ-жидкость необходимо учитывать потери давления в вихревом аппарате. При одной и той же скорости газа гидравлическое сопротивление исследованного вихревого аппарата намного меньше, чем перепад давления в полых, насадочных и тарельчатых аппаратах и не превышает сопротивления высокоэффективных аппаратов вихревого типа других конструкций. Гидравлическое сопротивление полых вихревых аппаратов с тангенциальными завихрителями определяется скоростью газовой фазы, расхода жидкости и конструктивными параметрами аппарата, а также физическими свой­ствами рабочих сред. Установлены оптимальные режимы работы разработанного вихревого аппарата, с позиции перепада давления в аппарате.

Keywords: tangential swirler, vortex apparatus, centrifugal force, twist coefficient, energy consumption, gas velocity, hydraulic resistance, irrigation density, resistance coefficient, fluid flow.

Ключевые слова: тангенциальный завихритель, вихревой аппарат, центробежная сила, коэффициент крутки, энергозатраты, скорость газа, гидравлическое сопротивление, плотность орошения, коэффициент сопротивления, расход жидкости.

Introduction

To date, the problem of cleaning harmful gases of industrial enterprises is becoming the most urgent task. Purification of industrial gases from suspended particles into gas cleaning plants is carried out by artificially changing the technological parameters of the gases being cleaned to match the optimal characteristics of the gas cleaning devices used.

Atmospheric air is a vital factor for the surrounding nature and human habitat. In modern production, the development of many industries is often inextricably linked with the problem of separation of dust-containing streams, which in turn releases a large amount of dust into the atmosphere. This dust is a significant danger, as it has an adverse effect on human health.

Harmful emissions from industrial enterprises are an urgent problem for all developing countries today. The main task of the industry is the development of modern efficient high-performance equipment that combines the solution of environmental problems of production. In industrial enterprises, existing dust and gas cleaning plants require improvement. At the same time, the problems of industrial emissions and energy savings are being solved.

Harmful emissions from industrial enterprises are an urgent problem for all developing countries today. The main task of the industry is the development of modern efficient high-performance equipment that combines the solution of environmental problems of production. In industrial enterprises, existing dust and gas cleaning plants require improvement. At the same time, the problems of industrial emissions and energy savings are being solved [1].

The study of current methods of gas purification in a two-phase medium reports that one of the ways to intensify the interaction of multiphase systems is the implementation of phase contact in a centrifugal field. Due to rotation in the multiphase layer, significant centrifugal forces arise, which ensure high dispersion and stability of the multiphase system, large specific contact surfaces and relative phase velocities. To intensify a number of gas-liquid processes, it is advisable to use vortex-type apparatuses. Their gas capacity can be hundreds of thousands of cubic meters per hour, and the hydraulic resistance of one unit ranges from 392 Pa to 1470 Pa.

Vortex-type devices have a number of advantages, which distinguishes them favorably from other "wet" cleaning devices. Joint purification of gases from gaseous and dispersed inclusions is possible. They have a large gas throughput capacity, which makes it possible to clean large-tonnage emissions. Vortex apparatuses work steadily in wide ranges of gas and liquid workloads, have small dimensions and a relatively simple design [2].

However, at present there are no theoretical and experimental foundations for hydrodynamic studies, the structure of flows and mass transfer in an apparatus with rotational-vortex interaction of phases, brought to practical application, which constrains their widespread use in industry.

In this regard, conducting research in order to expand the scope of application and increase efficiency, competent design and skillful use of vortex devices is relevant, as it is of both scientific and practical interest.

The processes of dust collection are largely determined by the hydrodynamics of the apparatus, including the total hydraulic resistance of individual elements and the entire apparatus as a whole.

The total resistance of hollow vortex apparatuses consists of pressure losses:

for friction along the length in the tangential inlet pipes-swirlers;

for friction along the length and for creating a twist of the gas-liquid flow in the vortex tube itself;

for friction in the separation chamber and hopper of the apparatus;

friction in the gas outlet pipe from the apparatus, as well as at the entrance to the working chamber and exhaust pipe and at the exit from them.

At the same time, losses in swirlers, where the gas velocity is high, will prevail. The pressure losses in the swirlers depend on its geometric characteristics and the degree of swirling of the gas flow. The losses at the gas outlet from the apparatus depend on the twist in the vortex zone and the degree of compression of the flow at the outlet of the apparatus [3-4].

Objects and methods of research

Experimental studies have been carried out to determine the pressure drop and to increase the efficiency of dust collection in a vortex apparatus in a "wet" way. The influence of the dimensions of the working elements of the apparatus, the velocity of the gas phase and the flow rate of the liquid on the efficiency of the dust collection process is determined. Optimal values of the size of the apparatus, gas velocity and fluid flow are selected in terms of the magnitude of the hydraulic resistance of the apparatus and the intensity of dust cleaning. Based on the results obtained, the design of a highly efficient dust collector was developed, introduced into industry and tested.

To study the hydrodynamics and efficiency of dust collection of a vortex apparatus with a swirling gas flow, an experimental installation was manufactured and installed (Fig. 1). The study of the total hydraulic resistance of an experimental vortex apparatus was carried out according to a generally accepted method. The experimental setup consists of a direct-flow vortex apparatus 1 with swirling downward flows of gas and liquid, a fan for moving gas 5, a centrifugal pump for liquid circulation, shut-off valves, measuring and control devices. The dimensions of the working part of the experimental vortex apparatus have the following values: diameter D = 0.056-0.1 m, height 0.5-1 m. Atmospheric air, sand dust and tap water are used as working media.

Air was supplied by a fan 5 to the upper part of the apparatus through tangential swirlers of the gas flow 2. Water was also supplied by a centrifugal pump from the flow tank to the upper part of the vortex apparatus through tangential swirlers of the liquid flow 3. To ensure hydrodynamic stability, rotating gas and liquid flows in the apparatus, tangential supply of both gas and liquid was performed with their rotation one way. The exhaust air is discharged through the duct into the atmosphere.

Figure 1. Scheme of the experimental setup:

1 – working chamber of the vortex apparatus; 2 – tangential gas swirlers; 3 – tangential swirlers of liquid; 4 – separator; 5 – fan; 6 – air flow meter; 7 – water flow meter; 8 – U-shaped water diffmanometer

The gas phase flow rate was measured using a vortex flowmeter of the Prowirl type. The total hydraulic resistance of the vortex apparatus was measured by a U-shaped water diffmanometer 8, one end of which was connected to the inlet tangential pipe, and the other to the gas outlet pipe.

The liquid flow rate was measured by rotameters of the PC 7 type, regulated by valves installed on the liquid supply line and on the pump bypass line.

Studies of the total hydraulic resistance of the vortex apparatus were carried out with a small excess gas pressure on the air-water system under isothermal conditions, when the temperature of the gas and liquid were almost equal and amounted to 20 ± 2 ℃, the excess pressure did not exceed the hydraulic resistance of the apparatus and the supply gas line, and amounted to 5-6 kPa.

The experiments covered the following range of parameter changes:

the twist coefficient: А=F_ap/F_sh=2,1÷3;

the gas flow velocity in the short circuit swirlers in the range of 20 = 60 m / s;

the average flow rate of the axial gas velocity in the working area of the apparatus  =10÷60 m / s;

the Reynolds number for gas Re =10000÷200,000;

the ratio of the mass flow rates of liquid and gas entering the vortex apparatus in the range L/G = 0.3 ÷5.

The results of experimental studies of hydraulic resistance obtained in a vortex apparatus with diameter of D = 0.1 m, the height of the working zone H_w = 1.0 m, the twist coefficient A = F_ap / F_sh = 2.1 at the following operating parameters are presented:

average exhaust gas velocities w₀=12=28 m/s;

the ratio of mass flow rates of liquid and gas L/G = 0.36÷4.4.

A specially made recording device - dispenser was used to feed sand dust into the gas stream. The used dust dispenser made it possible to create dustiness of gas (air) up to 0.5 kg/m³.

С _entrance - dust concentration at the entrance to the device:

                                             (1)

where m₁- is the mass of dust placed in the dispenser, kg;

τ - is the time of the complete outflow of dust from the dispenser, h;

V_air - volumetric air flow, m³/h.

At the outlet of the apparatus, the dustiness of the air was determined by sampling on a straight section of the flue.

С_exit - концентрация пыли на выходе из аппарата:

                                           (2)

In order to study the hydrodynamics of the vortex apparatus , the following parameters were determined by processing experimental data:

1) average flow rate related to the full cross-section of the apparatus, axial air velocity:

                                                                             (3)

where  - volumetric air flow, m³/s;

 - the cross-sectional area of the device, m².                                  

2) Reynolds criteria:

                                                                                           (4)

where ρ - air density;

  μ - dynamic air viscosity.

3) experimental value of the hydraulic resistance of the layer:

                                                                              (5)

where  - the difference in water levels in the U-shaped diffmanometer, mm. of water.

4) resistance coefficients:

                                          (6)

where  - the total hydraulic resistance of the vortex apparatus, Па;

 - axial velocity in the vortex chamber, м/с [5].

Results

Fig. 2 presents the obtained results of experimental data in the form of the dependence of the total hydraulic resistance of the vortex apparatus under study on the average discharge velocity of the gas. The pressure drop in the apparatus under consideration increases almost monotonously with increasing gas velocity in both dry and wet apparatus. In direct flow conditions, the hydraulic resistance in vortex chambers with irrigated walls depends on the actual gas velocity, which is related to the gas velocity over the full cross section and the thickness of the film. When the irrigation densities are the same under direct flow conditions, an increase in the gas velocity leads to a decrease in the film thickness. As the gas velocity increases along the full cross-section of the chamber, the film thickness decreases, the actual gas velocity increases, and the hydraulic resistance increases accordingly.

In both dry and irrigated apparatus, as the gas velocity increases, the pressure drop gradually increases and after a certain area becomes almost directly dependent on the gas velocity. With an increase in fluid flow, the bending of the curves of the dependence of hydraulic resistance on the gas velocity decreases.

Figure 2. Dependence of the hydraulic resistance of the vortex apparatus with the coefficient A = 2.1 on the air velocity at different L / G ratios: 1 - dry apparatus; 2 – 0,36; 3 – 1,6; 4 – 3,8; 5 – 4,4

From Fig. 2, it can be seen that an increase in the ratio of mass flow rates of liquid and gas from 1.6 to 4.4 at the same gas velocities leads to an increase in the pressure drop in the vortex apparatus by 50-55%, at the same air velocities. The dependence of the pressure drop in the vortex apparatus on the gas velocity w0 is almost linear. At the same time, with an increase in the gas velocity, ΔP increases more intensively. The nature of the dependence of hydraulic resistance on fluid flow at L/G > 1 and constant initial parameters of gas and liquid is almost the same: with increasing G, the growth of ΔP increases.

According to equation (4) and the graph of the dependence of the dependence Δp =f (w), a graph of the dependence of the hydraulic resistance coefficient of the vortex apparatus on the mode of gas movement in the working area of the apparatus is constructed. The Reynolds criterion is determined by the diameter of the pipe and the axial component of the swirling flow velocity.

The adjustment of gas and liquid flow rates made it possible to study the hydrodynamics of the apparatus at different ratios of liquid and gas loads. The influence of the ratio of mass flow rates of liquid and gas on the hydraulic resistance of the vortex apparatus can be established by Fig. 2. Analysis of these graphs shows that under constant gas loads, an increase in fluid flow leads to an increase in the hydraulic resistance of the vortex apparatus and the greater the greater the flow rate of the liquid phase. The hydraulic resistance of the irrigated apparatus characterizes the additional energy of the gas flow spent on turbulence of the liquid. At low values of fluid flow, the hydraulic resistance increases slightly.

When the gas flow is tangentially twisted, the flow "unfolds" in the channel with the transformation of the tangentially swirled flow into translational-rotational motion, which leads to a loss of total pressure. A large contribution to the hydraulic resistance of the apparatus at constant fluid load is provided by the flow rate of the gas phase. The hydraulic resistance of the dry apparatus differs significantly from the resistance of the irrigated apparatus. The pressure drop in the vortex apparatus is caused by the friction resistance between the air flow and the surface of the working pipe. The roughness (the average height of the roughness protrusions on the inner surface of the pipe) of the pipes we used exceeded 0.2 mm. 

Conclusion

 The obtained results of an experimental study of the pressure drop in a hollow vortex apparatus with tangential swirlers made it possible to identify the energy consumption of the investigated apparatus for the dust collection process, and it was also noted that with increasing gas velocity in both dry and irrigated apparatuses, the pressure drop in the investigated apparatus increases.

With an increase in fluid flow, the bending of the curves of the dependence of hydraulic resistance on the gas velocity decreases. An increase in the ratio of mass flow rates of liquid and gas from 1.6 to 4.4 at the same gas velocities leads to an increase in the pressure drop in the vortex apparatus by 50-55%, at the same air velocities.

If we compare it with the usual devices, we can conclude that the hydraulic resistance of the vortex apparatus under study does not exceed the resistance of foam, film, nozzle, poppet and other centrifugal devices.

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