Changes In Gas Velocity Research Articles

Numerical Simulation Study on Rotary Air Preheater Considering the Influences of Steam Soot Blowing

The ash deposition is a general problem that needs to be solved effectively for the rotary air preheater of the coal-fired boiler. Taking the rotary air preheater of a 600 MW power station as the object, the mesh model of the flue gas side of the air preheater, considering the influences of steam soot blowing, is established using the Gambit 2.4.6 software. Based on the SIMPLE algorithm, the velocity field and the temperature field in the air preheater under varied working conditions are simulated using the software of Ansys Fluent 2021R1, and the influences of the boiler load, the operation parameters of the steam soot blower, and the running and outage of the soot blower on the flue gas velocity distribution in the depth direction of the corrugated plates, the soot-blowing coverage area, the inlet flue gas velocity, and the inlet flue gas temperature of the corrugated plates are analyzed. Under the base working condition, the flue gas velocity on the axis of the steam nozzle first decreases rapidly with increasing the corrugated plate depth (Z < 1.0 m), and then it decreases slowly with an almost equal slope. The longitudinal flue gas velocity has a positive correlation with the boiler load. The longitudinal flue gas velocity obviously decreases when the boiler load is decreased, and its reduction increases as the corrugated plate depth increases. It is one reason that the ash deposition is prone to occur on the cold end surface of corrugated plates under the condition of low boiler load. The longitudinal flue gas velocity increases with the soot-blowing steam velocity increasing when the corrugated plate depth is less than 1.5 m, but after that, it is almost not affected by the change in soot-blowing steam velocity. The soot-blowing coverage area has a negative correlation with the boiler load but a slight positive correlation with the steam velocity of the soot blower on the whole. The inlet flue gas velocity of the corrugated plates has a positive correlation with the boiler load and the inlet steam velocity of the soot blower. The average inlet flue gas velocity decreases by 21.7% when the boiler load is reduced by 50%. For every 5 m/s variation in the inlet steam velocity, the inlet flue gas velocity changes by about 10–14% whether the steam soot blower is put into operation or not, which has an obvious effect on the inlet gas velocity of the corrugated plates. The inlet flue gas temperature of the corrugated plates is, respectively, positively correlated with the boiler load and the inlet steam temperature of the soot blower. When the boiler load is reduced from 100% BMCR to 50% BMCR, the average inlet flue gas temperature of the corrugated plates is reduced by 44.2 K; however, when the soot-blowing steam temperature varies by 20 K, the average inlet flue gas temperature of the corrugated plates varies by only about 1.8 K. It means that it is difficult to enhance the cold end flue gas temperature of the corrugated plates only by raising the soot-blowing steam temperature at low boiler load. Adding a soot blower using high-temperature steam or hot air at the outlet of the corrugated plates may be an option to solve the ash deposition of the corrugated plates.

Study on Erosion Wear of Single- and Double-Orifice Throttling Tools for Underground Coal Gasification

In underground coal gasification, as a choke regulating the formation gas lift pressure, the throttling tool can effectively reduce the production cost, the number of ground heating and insertion equipment, and gas consumption. Because in this process, the coal is transformed into composite synthetic gas through a series of technical treatments, the throttling tool is in a working environment with high temperature and pressure. In the process of transportation of combined synthetic gas, the pulverized coal parts produced by incomplete coal combination move with the gas in the throttling tool. The high temperature and high-pressure gas carrying large-diameter pressed coal parts will cause serial erosion and wear to the throttling device, resulting in failure and well-controlled safety risks. Therefore, according to the Joule–Thomson effect, this paper independently designs downhole throttling tools with single- and double-hole structures. According to actual field conditions, the erosion wear of throttling tools with different systems in high-temperature gas–solid two-phase flow was simulated and predicted, and the internal flow field characteristics of throttling means were analyzed. The difference between the wall wear distribution, wall collision position, and wall erosion effect of different structure throttling mechanisms with the change in gas velocity was investigated, which guides the practical use of the subsequent throttling tools.

Numerical simulation of the influence of operating parameters on the inner characteristics in a hydrogen-enriched shaft furnace

The hydrogen-enriched shaft furnace faces the challenge of insufficient heat due to the endothermic reaction involved in hydrogen reduction of iron ore. The optimization of operating parameters is crucial in maximizing the utilization of energy, leading to enhanced gas utilization rate and metallization rate. This work established a 2D shaft furnace model based on an actual MIDREX shaft furnace to examine the impact of operating parameters on the reduction process. The findings reveal that reducing the gas velocity leads to a decrease in Fe concentration but an increase in CO utilization coefficient. The H2 utilization coefficient, however, shows less sensitivity to changes in gas velocity. Increasing the gas temperature enhances the Fe concentration and improves the gas utilization coefficient increases. An increase in central supply gas velocity results in a decline in Fe concentration, an increase in the CO utilization coefficient, while only slightly affecting the H2 utilization coefficient.

Simulation of a continuous fluidised bed dryer for paddy

A model for simulating the drying of paddy (Oryza sativa L.) in a continuous fluidised bed dryer was employed. Equipment and material models were applied to describe the process. The equipment model was based on the differential equations obtained by applying mass and energy balances to each element of the dryer. In the case of the material model, mass and heat transfer rates in a single isolated particle were considered. Simulation results were verified by comparison with experimental data from the literature. There was a very good agreement between experimental data and simulation. The effects of gas temperature and velocity, particle diameter, dry solid flow, and solid temperature on the drying process were studied. It was found that the changes in gas velocity, dry solids flow, and solid temperature had essentially no effect on the drying process.

Simulation of a continuous fluidised bed dryer for shelled corn

In this study, a mathematical model to simulate the drying of shelled corn in a continuous plug-flow fluidised bed dryer is presented. Equipment and material models were applied to describe the process. The equipment model was based on the differential equations obtained by applying mass and energy balances to each element of the dryer. In the case of the material model, mass and heat transfer rates in a single isolated particle were considered. Calculation results were verified by comparison with experimental data from the literature. There was a very good agreement between experimental data and simulation. The effects of gas temperature and velocity, particle diameter, dry solid flow and solid temperature on the drying process were investigated. It was found that the changes in gas velocity, dry solids flow and the solid temperature had essentially no effect on the drying process.

Fluidization dynamic characteristics of carbon nanotube particles in a tapered fluidized bed

These picture shows the energy contribution of micro-, meso- and macro-structures at different operating conditions in the TFB without distributor. Energy contribution of micro-, meso- and macro-structures at different particle size. In this work, a tapered fluidized bed (TFB) without a distributor for fluidizing carbon nanotube (CNT) was applied for improving the dead zone, blockage, and fracture of distributor, which occurred in actual production. Experiments were performed under different superficial gas velocities, static bed heights, CNT agglomerate size, and positions of pressure probe. To obtain multi-perspective and multi-scale understanding of fluidization dynamics of gas–CNT flow in the TFB without a distributor, the standard deviation, skewness, kurtosis, wavelet decompositions and homogeneous index analysis methods were adopted. Some noticeable phenomena were observed. Particle movements including inter-particle, gas–particle and particle–wall dominate dynamic characteristics. The amplitudes of pressure fluctuations of coarse agglomerated multi-walled CNT were more sensitive to the gas velocity than that of fine agglomerated multi-walled CNT. The sensitively of energy contribution of the meso- and macro-structures was that the sensitivity of the measured position was less than the sensitivity of the energy contribution by the changes of particle size, and the sensitivity of the energy contribution by the changes of particle size was less than the energy contribution by the changes of gas velocity. The fluidization quality of coarse agglomerated multi-walled CNT was better than that of fine agglomerated multi-walled CNT, which was verified by the skewness and wavelet analysis.

Temperature estimating method for exhaust gases in valveless pulsejet engine

The article describes the problem of measuring the temperature in a pulse combustion chamber. The object of the study is a valveless pulsejet. The problem is analysed on the example of exhaust gases temperature measurement. The measurement in these conditions requires the use of a sensor resistant to large changes in gas velocity and temperature and at the same time with adequatly low inertia. This excludes the use of fast and precise yet thin, resistant wire sensors or ultrafast thin film thermocouples. Finally, a temperature measurement system based on sheated thermocouples was chosen. During each test the thermocouple has its own temperature which is different from the medium temperature. In order to properly determine the measured temperature of flowing media it is necessary to take the sensor time characteristics into account. In this article the iteration method is proposed to solve this problem.

Multi-scale characteristics and gas-solid interaction among multiple beds in a dual circulating fluidized bed reactor system

To investigate the gas-solid mixing and interaction among reactors of Dual Circulating Fluidized Bed Reactor (DCFBR), the detecting methods of acoustic emission and pressure fluctuation are employed to study the effects of operating parameters including riser gas velocity, bubbling bed gas velocity and pot-seal gas velocity on the gas-solid behavior and multi-scale characteristics of the DCFBR system. The experimental results demonstrate that gas disturbance makes bed particles fully mixed and the intensity of inter-particle mixing increases as gas disturbance intensifies. Meanwhile, inter-particle mixing can also cause changes in voidage. Therefore, gas and solid phases in the reactor have a mutual effect on each other. In addition, the particle circulation rate varies as the operating gas velocity changes, which in turn causes variations in both particle and bubble behaviors in the riser and the bubbling bed with particles and bubbles interacting with each other. By combining the methods of Hurst and fractal dimension analysis, the multi-scale variation of acoustic signals in the upper and lower parts of the riser under fast fluidization is obtained. As the results reveal, there are certain differences in particle clusters and bubble phase behaviors between the upper and lower parts of the riser. The larger the particle cluster size, the more uneven the flow inside the bed, indicating an intensified effect of the inter-granular particle cluster. Moreover, the size of particle cluster, which is related to particle concentration, increases as the concentration intensifies.

Combustion state monitoring of premixed heating appliances with flame ionization current and chemiluminescence

ABSTRACTThe development of a combustion operating point control system has received interests from gas boiler manufacturers in order to ensure optimized performances despite variations of natural gas composition. Fully premixed burners are widely used in these boilers and the equivalence ratio is a key parameter to control. Experiments are carried out in this study for CH4/air fuel blends diluted by N2 or CO2 or enriched by H2, C2H6, or C3H8. Two low cost solutions for monitoring the equivalence ratio based on the flame ionization current and the chemiluminescence signal are investigated on a laboratory laminar conical flame. The behavior of the ionization current with changes of gas velocity, fuel composition, and equivalence ratio is shown to be mainly related to the size of the dead space between the flame base and burner rim. In a second stage, changes of the chemiluminescence signal is studied and the use of CH*/OH* intensity ratio as an equivalence ratio indicator is verified. Numerical 1-D premixed flame simulations are performed to support the experimental results on the flame chemiluminescence. Finally, a third equivalence ratio sensing method is proposed, coupling both techniques and the three strategies are compared.

Performance evaluation of different approaches for early detection of defluidization

Identifying the onset of an agglomeration phenomenon at an early stage in processes utilizing gas-solid fluidized beds that operate under the influence of cohesive interparticle forces affords enough time to apply counteractive strategies and avoid a disastrous agglomeration of particles potentially leading to complete bed defluidization. In this paper, we compare the performance of different leading approaches proposed in the open literature for the advanced detection of defluidization. The approaches include the single-signal-monitoring of evolutions of total bed pressure drop, standard deviation of pressure signals, or S-value from the attractor comparison analysis as well as the simultaneous-monitoring of temperature and in-bed differential pressure signals during the process. The results show that the simultaneous-monitoring of temperature and in-bed differential pressure signals provided the best prediction of the onset of agglomeration while it demonstrated the least sensitivity to the changes in gas velocity, operating temperature, and bed inventory.

Schlieren imaging investigation of the hydrodynamics of atmospheric helium plasma jets

This work investigates the hydrodynamic characteristics of a coaxial double-ring electrode helium plasma jet by means of a “Z-type” Schlieren imaging system. The Schlieren images and visual optical photographs made show that a transition point from a laminar region to a turbulent region exists for gas flow without plasma when the helium flow rate exceeds a certain value. After plasma ignition, the laminar region shrinks with voltage increases, and the maximum length of the plasma plume is confined to the laminar region. The heat transfer equation and the spectral broadening of the He I 667.8 nm were used to estimate the increased gas temperature in the plasma jet, and the change in gas velocity by ionic momentum transfer was found by application of a double sphere collision model. As a result, gas heating is considered to be the dominant factor for the earlier onset of turbulence after plasma ignition, whereas the role of ion momentum transfer to neutral gas molecules is comparatively weak. The hydrodynamic behaviors of the plasma jet at the impact region for organic glass and silicon substrates are also researched. The ionization front propagates along the organic glass surface and contracts at the impact point on the silicon surface. More visible vortices are observed from Schlieren images with silicon substrates than with organic glass substrates. Possible mechanisms related to the different treatment effects are discussed.

Fundamentals of Trapped Ion Mobility Spectrometry Part II: Fluid Dynamics.

Trapped ion mobility spectrometry (TIMS) is a new high resolution (R up to ~300) separation technique that utilizes an electric field to hold ions stationary against a moving gas. Recently, an analytical model for TIMS was derived and, in part, experimentally verified. A central, but not yet fully explored, component of the model involves the fluid dynamics at work. The present study characterizes the fluid dynamics in TIMS using simulations and ion mobility experiments. Results indicate that subsonic laminar flow develops in the analyzer, with pressure-dependent gas velocities between ~120 and 170 m/s measured at the position of ion elution. One of the key philosophical questions addressed is: how can mobility be measured in a dynamic system wherein the gas is expanding and its velocity is changing? We noted previously that the analytically useful work is primarily done on ions as they traverse the electric field gradient plateau in the analyzer. In the present work, we show that the position-dependent change in gas velocity on the plateau is balanced by a change in pressure and temperature, ultimately resulting in near position-independent drag force. That the drag force, and related variables, are nearly constant allows for the use of relatively simple equations to describe TIMS behavior. Nonetheless, we derive a more comprehensive model, which accounts for the spatial dependence of the flow variables. Experimental resolving power trends were found to be in close agreement with the theoretical dependence of the drag force, thus validating another principal component of TIMS theory.

Simulation of a continuous plug-flow fluidised bed dryer for rough rice

In this study, a mathematical model to simulate the drying of rough rice in a continuous plug-flow fluidised bed dryer ispresented. Equipment and material models were applied to describe the process. The equipment model was based on thedifferential equations obtained by applying mass and energy balances to each element of the dryer. Concerning the materialmodel, mass and heat transfer rates in a single isolated particle were considered. Mass and heat transfer within the particles wasdescribed by analytical solutions with constant effective transport coefficients. To simulate the dryer, the material model wasimplemented in the equipment model in order to describe the whole process. Calculation results were verified by comparisonwith experimental data from the literature. There was very good agreement between experimental data and simulation. Theeffects of gas temperature and velocity, particle diameter, dry solid flow and solid temperature on the drying process wereinvestigated. It was found that the changes in gas velocity, dry solids flow and solid temperature had essentially no effect ondrying behaviour.DOI: http://dx.doi.org/10.5377/nexo.v27i2.1947

Feasibility Studies of the Sequential Dewatering/Dry Separation of Chinese Lignite in a Vibration Fluidized-Bed Dryer: Effect of Physical Parameters and Operation Conditions

The combined dewatering process and dry separation in a vibration fluidized-bed dryer was developed to upgrade Chinese lignite in terms of moisture and ash for effective utilization in power plants. The influence of operational parameters (fluidizing gas velocity, vibration strength, bed height, and drying temperature) and lignite properties (particle size and moisture content) on the drying or separation characteristics of −6–1 mm lignite was examined in a laboratory-scale vibration fluidized-bed dryer. Both operational parameters and lignite properties had a significant effect on the drying and separation performance. The drying and separation behaviors of a vibration fluidized bed were both enhanced in comparison to the case without vibration under the same operating conditions. Moreover, with the change in gas velocity, the drying and separation processes could be combined in the same vibration fluidized-bed dryer. Both processes achieved promising results compared to those of the fixed gas velocity condition, which was confirmed by the low calorific value analysis. A sequential drying and separation system in a vibro-fluidized-bed dryer was also designed on the basis of the separation and drying characteristic results.

Detecting Sudden Changes in Fluidization by Wall Vibration

Vibrations of fluidized bed walls reflect the nonlinear characteristics of bed hydrodynamics in gas–solid fluidized beds. Experiments were carried out in a lab-scale, two-dimensional fluidized bed operated at ambient conditions for three particle sizes, various gas velocities, three aspect ratios, and different probe locations. The S-statistic method, which is, in fact, the comparison of attractors of two dynamic signals in the state space, was used to determine de-fluidization condition in the bed. Different scenarios were tested to evaluate whether this method is able to detect changes in the hydrodynamics fluidized bed based on the bed vibrations, including change in the bed mass, particle size, and gas velocity. The results showed that this method is capable of detecting the de-fluidization state in the bed as a result of changes in gas velocity, particle size, and bed mass. However, an important factor is the location of probe, which can dramatically affect the capability of this method for detecting the de-fluidization state.

Simulation of aerolian sand transport with SPH-FVM coupled method

To overcome the drawback of discrete particle model (DPM) and Euler-Euler two-fluid model (TFM) in solving gas-solid two phase flow, a new method called SPH-FVM coupled method is presented, and then it is used to simulate aerolian sand transport problems. Based on a pseudo fluid model the smoothed particle hydrodynamics (SPH) is used to solve the discrete particle phase by tracing the movement of each individual particle, and the finite volume method (FVM) is used to discretize the continuum flow field on the stationary mesh by capturing fluid characteristics. Two phases are coupled through contributions due to the effects of drag, pressure gradient and volume fraction, and then the coupled framework of SPH-FVM is established. The properties of SPH are redesigned to be suited for the discrete phase named SDPH. The relationship between SPH particles and discrete particles is illustrated, and the SPH discrete equations of pseudo fluid are derived. Saltation processes of sands in aerolian sand transport, sand movement under free-air wind, and creeping processes of dune, are simulated; while the particle trajectories, the distribution characteristics of mean downwind velocity, and the changes of gas velocity under the sand reaction are analyzed. Through comparison with experiments, it is shown that the accuracy of the new method is high, and it can also reduce the computational cost. This indicates that the new method can be applied to aerolian sand transport even to other gas-solid multiphase flows.

Changes of Gas Velocities in Passing Through Flamelets in a Premixed Turbulent Bunsen Flame

A laser-Doppler velocimetry (LDV) system was employed to measure three components of velocity at a mid-flame point on the centerline of a propane/air flame of equivalence ratio 1.10 on a 26 mm-diameter Bunsen burner with fully developed turbulent pipe flow upstream at a Reynolds number of 6700. The LDV measurement volume was 1 mm below the leading electrode of a four-element electrostatic probe that provided the velocity and direction of motion of flamelets in the turbulent flame brush. It was found to be possible, during each flamelet passage, to rotate the coordinate system about a vertical axis so that the flamelet and all gas velocity vectors remained very nearly in the same vertical plane, thereby implying locally nearly two-dimensional motion, insofar as the influence of the gas expansion on the gas velocity is concerned. In the local plane of motion, the observed changes in gas velocity caused by flamelet passage exhibited a downward component for upward moving flamelets with the fresh mixture above the burned gas and an upward component for upward moving flamelets with the burned gas above the fresh mixture, consistent with the expected gas expansion through the flamelet. Moreover, within the accuracy of the LDV measurements, profiles of changes of the component of gas velocity normal to the flamelet agreed with velocity profiles calculated for steady, planar, unstretched, premixed laminar flames. These results indicate relatively little distortion of laminar flamelet structures in the turbulent flame brush at these turbulent intensities of about 5%.

The Optimization Design for Protection Plate Structure of Honing Measuring Head

In order to improve the pneumatic gauging precision of honing process, according to the pneumatic gauging characteristic of honing machine, the mathematical model of air current state in measurement process is established with oblique shock wave theory. Through setting up different fillet on protection plate, the air flow state of measurement process could be improved. The change of gas velocity, temperature and pressure was analyzed for different protection plate structure by fluid simulation software, the validity of the theoretical analysis was verified, which can provide the theory basis for structure optimization of the honing head.

Genetic Algorithm Study on the Flow Distribution Characteristics of Pneumatic Conveying in Pipe Network System

This paper mainly conducts experiments on distribution characteristics of the millet and hollow glass beads which have the same average particle diameter and different densities in horizontal T branch pipe, analyzing related data. At the same time it uses BP network optimized by genetic algorithm to conduct simulation prediction. The results show that the distribution fraction of any material in two branch pipes of the same resistance is basically the same, the fluctuation of the material with less density and larger particles is larger when the superficial gas velocity changes. When two control valves opening are not the same, and A control valve fully open, with the B’s reducing, the mass fraction which is assigned to the collection container B has larger overall decline, and the range of it gradually increases. It can be seen that the inflection point of fluid state changing in pipeline is related to density and has nothing to do with particle size. When the superficial gas velocity is smaller than the inflection point, with the decreasing of control valve opening in branch pipe B, the reduction extent of the mass fraction for the materials with less density and larger particles which is assigned to collection container B is larger. The comparison between the genetic algorithm predictive value and the experimental value shows that they are in good agreement. It has a higher prediction accuracy to simulate flow distribution characteristics by using genetic algorithm.

Flame-Flow Interaction in Turbulent Premixed Flames (Change in Gas Velocity across the Flamelet in Turbulent Premixed Flames)

Flame-Flow Interaction in Turbulent Premixed Flames (Change in Gas Velocity across the Flamelet in Turbulent Premixed Flames)