Gas Flow Velocity Research Articles

NOX EMISSION ON RECIPROCAL FILTRATION COMBUSTION OF BIOGAS: A CASE STUDY

Filtration combustion is an effective technique for dealing with low-calorific value fuels, such as derivative fuels from biomass, and simultaneously reducing pollutant emissions. In this study, combustion of biogas (22% of CO2) was investigated theoretically and experimentally by utilizing a reciprocal flow porous burner with heat exchangers inserted in the porous medium. Combustion of lean biogas-air mixtures is stabilized in a naturally transient process, in which a lean equivalence ratio range (0.1 ≤ Φ ≤ 0.9) and gas flow velocities of 0.2 and 0.3 m/s were employed, periodically switching gas flow direction. Reciprocal flow combustion has been compared with unidirectional combustion, using technical methane as reference gas. In this context, predicted temperature profiles inside the burner, as well as experimental results, have shown that the reciprocating system plays an important role in the combustion process, significantly improving flammability limits, efficiency, and emissions. As result, trapezoidal temperature distribution profiles have been obtained with peaks between 1200 and 1600 K, reaching high efficiency up to 90% and ultra-low emission of nitrogen oxides (≤ 2ppm).

Gas flow enhanced mass transfer in vacuum membrane distillation

Developing cost-effective methods to enhance the mass transfer (i.e. water vapor flux) in vacuum membrane distillation (VMD) is of vital significance. In this study, we propose and demonstrate a simple but highly effective method to enhance the water vapor flux in VMD by introducing a gas flow on the vacuum side. The effect of the gas flow rate on the mass transfer performance in VMD was investigated by experimentation and computational fluid dynamics (CFD) simulation. Both experimental and modelling results confirm that gas flow on the vacuum side can effectively enhance mass transfer in VMD by minimising the boundary layer effect. A higher gas flow velocity results in a lesser boundary layer effect and reduced temperature polarization, thereby achieving a much higher water vapor flux. Specifically, when the gas flow rate is 10 L/min, the water vapor flux is eight times higher than that without gas flow (45.5 vs. 5.8 g/m2 h) on the vacuum side in VMD under the same vacuum pressure of 10 kPa. This study provides a cost-effective method to enhance the water vapor flux in VMD. It offers significant insights into understanding the mechanisms of vapor condensation and mass transfer in thermally-driven membrane processes.

A Vertical Fountain Dryer Adjusted for Sawdust and Wood Chips Drying

This article presents the preliminary results on the drying process in a fountain dryer designed and adapted to drying waist sawdust and/or chips of various morphology and moisture content. In terms of drying technology, it is important to reduce the demand for heat and electricity. The phenomena occurring during the drying of sawdust in a fountain dryer were analyzed. Modifications of a typical fountain dryer were proposed in order to dry the chips, to obtain appropriate moisture and quality suitable for the process of their further granulation for the production of pellets. The test stand and the most important properties of the fountain dryer were described and discussed. Such characteristic aims of the device, i.e., efficiency, combustion, air and exhaust gas flow measurements, among others, were presented. The characteristics of the sawdust drying curves as a function of temperature were also determined. Computer simulations of heat exchange, air, and exhaust gas flow velocities were also performed and compared with the results obtained directly from the modified test stand. The maximum combustion of sawdust measured during startup of the furnace was 0.14 m3/h, which is 0.46 m3 of the fuel consumption for the production of 1000 kg. Drying times of wet sawdust is relatively short and takes ~50 s for (weight of wet sawdust 4.75 kg, with moisture of 35%) the relatively low air temperature of 175 °C.

A lattice Boltzmann model for simulating gas transport in coal nanopores considering surface adsorption and diffusion effects

The gas flow in coal is extremely complicated as a combined results of multiple flow mechanisms and complex pore structures. Comprehensive understanding of gas flow behaviors in coal is of great importance for the prediction of coalbed methane (CBM) production and the elimination of gas-induced disasters in coal mines. Based on the lattice Boltzmann method (LBM), this study constructs a LB model considering surface adsorption and diffusion effects, which involves multiple mechanisms of gas flow, including viscous flow, enhanced gas slippage (gas slippage is enhanced by surface diffusion) and surface diffusion. The results show that in micropores (<2 nm) and mesopores (2–50 nm), under the effect of adsorbed gas, bulk gas flow velocity increases at a low pressure but decreases at a high pressure. Adsorbed gas surface diffusion permeability, enhanced gas slippage permeability and viscous flow permeability decrease with the rise of pore pressure. In nanopores in coal reservoirs, surface diffusion more significantly enhances gas slippage at a low pressure and in smaller pores. Besides, in the flow calculation, gas slippage without the considering effect of adsorbed gas and Knudsen diffusion can replace each other. According to the results from the LB model, the apparent diffusion coefficients of gas in coal particles decreases with the increase of pore pressure in smaller pores(<10 nm) but increases in larger pores(>10 nm). The study further investigates flow mechanisms controlling the CBM extraction yield in different extraction stages. In the early stage of extraction, the CBM extraction yield is controlled by Darcy seepage in fractures; in the middle stage, it is controlled by viscous flow in larger matrix pores; in the late stage, it is controlled by gas diffusion induced by the superposition of surface diffusion and enhanced gas slippage in matrix micropores and mesopores.

A prediction model for new well deliverability in an underground gas storage facility using production data

Natural gas is a naturally occurring fluid mixture consisting mainly of methane. Natural gas flows in the porous medium of a tight gas reservoir storage facility (TGRSF), factors such as a short operating period, high gas flow velocity, and small gas drainage radius could lead to apparent changes in the rock's physical properties, such as pressure and permeability. Porous media with changing petrophysical parameters will experience changes in fluid flow. The failure of existing methods to consider these factors has led to significant errors in predicting the deliverability of a new well in a TGRSF. In this study, a prediction model for the deliverability of new wells in a TGRSF that considers the stress-sensitive effect of permeability is proposed. The semi-analytical solution of the model is achieved via mathematical methods, such as the Laplace transform and perturbation theory, and verified by an industrial simulator (Ecrin-KAPPA). The solution results show that the dimensionless pseudo-pressure has a linear relationship with the dimensionless time in the late asymptotic solution. The material balance time is redefined based on this linear relationship, which can be used to calculate the equivalent relationship between producing at a constant rate and a variable rate. Combined with the equivalent relationship, we draw a series of typical curves to fit the petrophysical parameters within the gas drainage radius of existing wells and extract the petrophysical parameters of the new well. The model successfully predicts the deliverability of a new well (QK3) in China's TGRSF, with a peak deliverability of 18.76 million m3. The research results obtained in this paper can provide theoretical guidance for the optimal design of the number of new wells and required investments in the TGRSF.

Development and experimental investigation of the narrow-gap coated electrostatic precipitator with a shield pre-charger for indoor air cleaning

We designed and evaluated a two-stage electrostatic precipitator with a shield pre-charger and a narrow precipitator for indoor air cleaning. Unlike the conventional ESP-type air cleaner, the ion generation and particle charging regions were separated by a perforated plate with bias voltage. The electrical energization was achieved by connecting a large resistor in series with the shield electrode. A narrow-gap plate-plate precipitator was placed after the pre-charger for a strong electric field and a high specific collection area. The performance of the shield pre-charger, the narrow precipitator and their integration in lab-scale of 62 m3/h and pilot-scale of 500 m3/h were evaluated. The overall collection efficiency was 98.6 % and 75.5 % for gas flow velocities of 0.4 m/s and 1.2 m/s, respectively. The ozone concentration was around 0.2 ppm for a 24 h continuous operation. Our study showed a close relationship between particle charging and shield voltage with charging current, and a relatively stable performance under high gas flow velocity. The particle collection efficiency was 2.5 times higher than that of a conventional ESP-type air cleaner of similar size at a gas velocity of 1.2 m/s.

Numerical modelling of raw materials atomization and vaporization in a heat carrier gas flow in technical carbon production based on the Euler approach

Previously, the authors of this article proposed a 3D Euler-Eulerian model of raw materials spraying and evaporation in the heat-carrier gas flow in the carbon production reactor. The raw materials' droplets fragmentation and evaporation are considered as the carrier and dispersed phase interaction. The continuous phase is a heat carrier gas whose motion is described by the Navier-Stokes equations. Dispersed phase (droplets of raw material and products of its evaporation) motion is described using a non-uniform convective-diffusion equation for the particle concentration. The model was tested with water as a raw material. In this work, hydrocarbons are specified as raw materials. It is proposed next to solve the inverse problem with the target functional providing zero contact of the unevaporated raw materials with the reactor wall. Then the number of solid coke particles in the final product will be minimal. An analysis is made of the unevaporated raw material area sensitivity to the inlet velocity of the heat-carrier gas flow. This parameter has the most impact on the distribution area of the unevaporated raw materials and is assumed to be varied in the optimization problem.

Numerical study of particles removal from dusty gas in separation device with straight arc-shaped elements

The paper presents an original design of the separator with straight rows of arc-shaped elements, which allows efficient separation of solid particles without significant abrasive wear of the device’s surfaces. A three-dimensional model of the device is developed, and the principle of its operation is described. In this paper, a numerical study of the capture of solid particles from a gas flow in the separation device is performed. It is found that at a relatively low inlet gas velocity (1 m/s), the separation efficiency of particles with a diameter of 20 to 100 μm is on average 78.9%. An increase in the inlet velocity of the dusty gas flow results in a decrease in the efficiency of the device for particles ranging in size from 25 to 80 μm. The pressure drop of the separator at a velocity of 1 m/s ranges from 45.5 to 95.4 Pa, and at a gas velocity of 4 and 7 m/s – from 740.8 to 4652.1 Pa. An increase in the number of straight arc-shaped elements from 4 to 12 and an increase in particle density from 3400 to 10000 kg/m3 leads to improved separation efficiency.

Effect of total dissolved gas supersaturation and flow velocity on survival and swimming ability of juvenile Schizothorax prenanti

Abstract Although developing large-scale hydropower cascades in the upper Yangtze River effectively improves the hydropower resource utilization, it produces total dissolved gas (TDG) supersaturation. In the flood season, the high level of TDG supersaturation (TDGS) frequently occurs in the downstream of dams, causing migratory fish to suffer from gas bubble trauma (GBT) and reducing their survival and swimming ability. Currently, there is a deficiency in particular approaches to evaluate the ecological hazard posed by TDGS on migratory fish as they traverse different flow velocities within their migratory routes. This study assessed the vulnerability of juvenile Schizothorax prenanti (S. prenanti) to GBT from the static setting to 9.0 BL/s during exposure to nominal levels of 100%, 110%, 120% and 130% TDG. The mortality occurs when the flow velocity surpasses 6.0 and 7.5 BL/s in 100% and 110% TDG levels, respectively. For fish exposed to 120% and 130% TDG levels, the relationship between survival time and flow velocity is an approximately inverse bell-shaped curve with increasing velocity. The optimal velocity of maximal survival time of juvenile S. prenanti is 3.0 and 4.5 BL/s in 120% and 130% TDG-supersaturated water. Both TDG level and flow velocity significantly affect burst swimming speed (Uburst) and critical swimming speed (Ucrit). The cases involving GBT showed substantial declines in Uburst and Ucrit, exceeding 6.0 BL/s and TDG levels greater than 120%. The results may contribute to formulating a specific management strategy for hydropower operation during the migratory period and conserving vulnerable species in the Yangtze River.

A Magnetic Field Induced Cold Atmospheric Pressure Air Plasma Jet

Cold atmospheric pressure plasma jets (APPJs) using air as working gas are of particular interest and desirable but with significant challenge. In this article, an air APPJ induced by an external radial magnetic field is reported. The experimental results show that with the external magnet, an air plasma jet can be obtained with a length of 7 mm and a width of 10 mm. While without the external magnet, the plasma only exists in the dielectric tube. The dynamic behavior shows that its propagation velocity is close to the gas flow velocity. The plasma jet appears no difference when it is in contact with a ground conductive object. On the other hand, optical emission spectrum shows that they are dominated by the N2 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{N}_{2}^{+}$ </tex-math></inline-formula> emission. The electrical characteristic shows that the peak of the discharge current and the breakdown voltage increase when the magnet is used. The gas temperature of the plasma jet is about 310 K. Laser-induced fluorescence measurement shows that high concentration of OH radicals appears along the plasma jet. In the sterilization experiment, the application of external magnetic field has increased the sterilization effect by about two times

EVALUATION OF THE EFFICIENCY OF A MULTI-CHANNEL DUST COLLECTOR USING NUMERICAL SIMULATION

Multi-channel dust collectors are based on previously known designs of vortex dryers for bulk products. However, their use for air dust removal is promising. In earlier studies of these devices using numerical simulations, the dust capture coefficient was not evaluated, although it is the most important indicator of their efficiency. In this article, the numerical simulation of MCDC is carried out. The first stage of modeling is the calculation of the gas flow velocity and pressure fields in the device under study. At the second stage, a large number of trajectories of dust particles of different diameters were calculated with subsequent statistical processing. Dust capture coefficients and hydraulic loss coefficients were calculated. It is shown that for the reliability of the results of the numerical experiment, the number of dust particles should be at least 2000. To determine the effect of the outer half-shells on the efficiency of the device, these half-shells were discarded, as a result of which the multi-channel dust collector turned into a cyclone. The comparison of characteristics showed that, other things being equal, the devices being investigated have some advantages over cyclones in capturing of small fractions of dust. The hypothesis that the capture of particles in curved channels occurs mainly due to particle collisions with the front edges of metal half-shells was put forward and refuted. The results of numerical modeling do not support the hypothesis that some dust particles rotate along closed trajectories and form a filter for other particles. The formulas of other authors, which do not take into account the parameters of dust particles, are recognized as unworkable. The speculations of some authors about the influence of the Ranque-Hilsch vortex effect on the process of dust capture cannot be taken into account due to the low subsonic air velocities under the operating conditions of the apparatus.

Numerical simulation of the heat transfer characteristics of the second and third superheaters in a coal-fired thermal power plant radiant boiler

Superheaters are essential components in a coal-fired power plant because they keep the highest tube wall temperature points in the radiant boiler. The pressurized steam flowing in the superheater tubes is heated via the thermal radiation and convection from the combustion gas. To prevent the bursting of superheater tubes caused by the thermal fatigue for stable and safe plant operation, precisely predicting complex heat transfer characteristics, and estimating the local temperature and heat flux of the superheater are necessary. In this study, a computational fluid dynamics model of the boiler and the second and third superheaters in a coal-fired power plant is developed using radiation model (DO model) and turbulence models (k-ε RNG model). In the second superheater installed near the burner, the influence of radiation from the combustion gas is strong, and the temperature and heat flux of the outermost tube are highest. In the third superheater, the tube wall temperature and heat flux becomes large in the upper and middle parts of the superheater, where the combustion gas flow velocity around the superheater is high, whereas those at the bottom of the superheater are significantly small due to the dead water region of the gas. Therefore, to consider the combustion gas flow is important for prediction of the heat transfer characteristics of the third superheater.

Характеристики прогрева и испарения капель реактивного топлива и его суррогатов

The paper presents the results of experimental study of heating and evaporation of TS-1 aviation kerosene and its surrogates (n-decane and SU4) in a high-temperature gas flow (gas temperature range is 450–750 K, gas flow velocity range is 0–6 m/s). The conditions for temperature and gas flow rate are established, under which it is possible to provide good agreement on the time of complete evaporation, the dynamics of changes in the sizes (radii) and average temperatures of droplets of traditional aviation fuels using the example of kerosene TS-1 and its surrogates (SU4 and n-decane). When processing videograms, we used our own image processing algorithms developed in the MATLAB software package.

COMPUTATIONAL ANALYSIS OF THE IMPACT OF BOUNDARY CONDITIONS ON A PARTICLE-LADEN FLOW: A CASE STUDY IN A PRESSURIZED OXY-COAL COMBUSTOR

Designing an effective burner is vital for the development of coal combustion technologies. Because of high pressure, the volumetric fraction of the coal particles in the injected fuel in a pressurized oxy-combustion (POC) burner approaches or even exceeds the limitations allowed by the commercial computational fluid dynamics codes (e.g., Ansys Fluent). Consequently, for such high particle volumetric fractions, the interplay between the particles, the fluid flow, and the burner wall needs to be re-evaluated. The present computational work is a first step in a systematic analysis of the roles of various characteristics involved in the POC process, such as the method of particle release, its location, and the particle size. Specifically, pulverized coal is burned under an elevated pressure of 15 bar in an O&lt;sub&gt;2&lt;/sub&gt;/CO&lt;sub&gt;2&lt;/sub&gt; environment. A 100 kW, a POC combustor, is modeled with Ansys Fluent using the Reynolds-averaged Navier-Stokes approach. It is revealed that for this pilot-scale, pressurized burner, the gas phase flow velocity in the near-wall region exhibits anomalies. With the major focus on POC, this work aims to eliminate/reduce the impact of high particle loading on the gas-phase flow. To scrutinize the role of particle loading in the near-wall region and eliminate the impact of this velocity on POC downstream, the particle-gas interplay in the boundary layer is investigated by means of the computational simulations incorporating the coupling between the turbulent flow and the particles. It is found that the tuning of the particle release location makes the gas-phase flow velocity in the presence of particles consistent with the pure gas flow velocity profile. The particles size is also found to have a significant impact on the particle trajectory.

A computational analysis of the impact of boundary conditions on a particle-laden flow: A case study in a pressurized oxy-coal combustor

Designing an effective burner is vital for the development of coal combustion technologies. Because of high pressure, the volumetric fraction of the coal particles at the fuel inlet of the POC burner approaches or even exceeds the limitations allowed by the commercial computational fluid dynamics (CFD) codes (e.g., Ansys FLUENT). Consequently, for such high particle volumetric fractions, the interplay between the particles, the fluid flow, and the wall need to be re-evaluated. The present computational work is a first step in a systematic analysis of the roles of various characteristics, specifically, the method of particle release, its location, and the particle size. In the POC process, pulverized coal is burned under elevated pressure in an O2/CO2 environment. Specifically, a 15-bar, 100 kWth, POC combustor is modeled with Ansys FLUENT using the Reynolds-averaged Navier-Stokes (RANS) approach. It is revealed that for this pilot-scale, pressurized burner, the gas phase flow velocity in the near-wall region exhibits some anomalies. In order to scrutinize the role of particle loading in the near-wall region, the particle release location is investigated. The numerical simulations incorporate coupling between the turbulent flow and the particles. It is found that the tuning of the particle release location makes the gas phase flow velocity consistent with the pure gas flow velocity profile. Moreover, the particle releasing location also influences the flame stability. The particle size is also found to have a significant impact on the particle trajectory, flame stability, and temperature.

Influence of Exhaust Temperature and Flow Velocity of Marine Diesel Engines on Exhaust Gas Boiler Heat Transfer Performance

Due to the relatively cheap price of diesel, most Marine engines use diesel as Marine fuel, but its emissions contain a lot of carbon. To reduce carbon emissions, International Maritime Organization (IMO) has established an Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing-Ship Index (EEXI). Currently, a popular way is to reduce EEDI by optimizing the heat transfer performance of exhaust gas boilers on new ships, but there is little research on the EEXI index of existing ships. For operating ships, the thermal conductivity of exhaust gas boiler materials and other parameters has been fixed, so the main factors affecting the heat transfer coefficient of the exhaust gas boiler are exhaust gas temperature and flow velocity. Therefore, this paper studies the influence of engine exhaust temperature and flow rate on boiler heat transfer coefficients and optimizes it to achieve the EEXI value required by IMO. Firstly, based on the conservation of mass and energy as the basic equation, a heat exchange model of the exhaust gas boiler is established by using the hybrid modeling method and lumped parameter method. Secondly, for the given boiler, since other parameters are basically unchanged, the input temperature and flow rate of the model are changed by the control variable method, and the temperature of the boiler outlet is simulated by the test algorithm. Through the simulation operation of an Aalborg OC-type boiler, the results show that when the exhaust gas flow velocity is 15 m/s, 17.2 m/s, 22.4 m/s and 25 m/s, respectively, the heat transfer coefficient at each flow velocity increases first and then slowly decreases with the increase of temperature, and there is an optimal temperature at each velocity, which is 230 °C, 227 °C, 225 °C and 224 °C, respectively. The innovation of this study lies in the research on the inlet temperature and flow rate of the exhaust gas boiler of the operating ship based on the EEXI, and the relevant results are obtained, which provides theoretical guidance for the operation management of the exhaust gas boiler of the operating ship.

Development of Ultrasonic Pulsed Plasma Jet Source for Remote Surface Treatment

We have developed a supersonic pulsed plasma jet device capable of long-distance and high-speed processing, and investigated its basic characteristics for surface treatment applications, mainly in the material and medical fields. The developed apparatus is equipped with a mechanism to transport active species in the plasma to the object to be treated by jetting the generated high-density plasma outward with supersonic pulse jets, which allows the gas flow velocity to increase significantly during pulse jetting compared with plasma generation. This enables the active species in the plasma to reach the treatment target before deactivation, thereby realizing surface treatment at a distance. Measurements using the Schlieren method revealed that the velocity of the jet flow reached Mach 1.7.

Effects of gas flow parameters on droplet spatter features and dynamics during large-scale laser powder bed fusion

The droplet spatters generated by the laser induction directly affect the processing quality of the laser powder bed fusion (LPBF) process, gas parameters are a key factor in this process. In this work, the formation characteristics and dynamic behavior of process-by-products under different gas flow parameters were presented through high-speed imaging. A novel image processing method and spatters feature extraction algorithm were used to obtain the spatter number, the total spatter area, the spattering angle and the spattering velocity of 8 scenarios. With the comparative analysis, scan direction against the gas flow (SD-A) is proved to produce fewer droplet spatters than scan direction with the gas flow (SD-W), and the quantitative relationship between the gas flow parameters and the droplet spatter behavior is established for the first time. The maximum spattering velocity increases to 12.8 m/s as the gas flow velocity rise to 2.5 m/s. Finally, the mechanisms of the droplet spatter behavior influenced by gas flow parameters are discussed. The work provides a theoretically reference for the design and control of gas flow parameters during the large-scale LPBF.

Analysis and Modification of Motorbike Silencer for Noise Reduction by Experimentation and Analytical Equations

In this new era, noise pollution is very high. One of the reasons for this noise pollution is sound which is generated by the exhaust system of the motorbike. So, it is necessary to reduce the noise coming from the exhaust of the motorbike. In this paper, original silencer reverse engineering has been done, then three modification models of the silencer with its analysis have been done and from those results, one of the modified silencers was selected and it was sent for manufacturing. After fabrication of the silencer, two tests were conducted. First, the test was conducted with original silencer, then it was conducted with modified silencer. From that data, transmission loss of original and modified silencers was calculated and then compared with each other and from that, noise was reduced to 5db. Also, flow velocity of exhaust gas in original silencer and modified silencer were also measured. It concluded that modified flow was increased by 11% to original silencer and also PUC of modified silencer was checked and it was in limit as per the PUC norms.

Determination of the design velocity of the gas flow in coarse and fine filters with varying degrees of contamination in the paint booths

OBJECT. Determination of the design velocity of the gas flow in coarse and fine filters with varying degrees of contamination. METHODS. We carried experimental studies out to solve the problem. To exclude errors during the studies caused by marriage or other reasons, 3 samples of each of the coarse and fine filters (clean and used) were used. To determine the design speed, an experimental installation was assembled, presented in the work, which included an air duct, an air injection fan, a nozzle for measuring excess pressure in front of the filter under study, an air vent hole, filter samples, a ventilation grate and measuring instruments – a differential pressure gauge testo 510i and an anemometer testo 405i. RESULTS. The article describes the relevance of the topic, analyzes the change in the pressure drop in the duct when using spent and clean coarse and fine filters. They showed that an increase in their operational life is possible with the use of a multi-vortex separator, which can be installed as a preliminary stage of purification. CONCLUSION. The estimated gas flow velocity when using coarse filters is only 2 m/s. The estimated gas flow velocity when using fine filters is only 0.5 m/s. A comparison of the difference in the pressure drop in the duct when using coarse and fine (spent and clean) filters shows that coarse filters are more susceptible to dusty flow, i.e. the bulk of particles in the dusty flow at an enterprise with paint chambers are relatively large particles. Hydraulic resistance increases by 1.58 times.