Airflow Field Research Articles

A Method for Estimating Ship Surface Wind Parameters by Combining Anemometer and X-Band Marine Radar Data

The steady airflow field on a ship is affected by structure and motion and challenged by phenomena such as the low measurement accuracy of the wind field caused by the occlusion of the anemometer. In this work, an improvement in the accuracy of wind measurements affected by structure is proposed, and a method for combining anemometer and X-band marine radar (RCRF) data is designed to further obtain wind parameters. The first step is to use the multivariate bias strategy to achieve the optimal layout of multiple anemometers based on computational fluid dynamics (CFD) numerical simulation data. Then, random forest (RF) is employed to train the wind parameter estimation model. Finally, the wind parameters are optimally estimated by combining the anemometer with the X-band radar. Under the ideal simulation, noise, and temporal uncertainty combined with anemometer noise conditions, the RCRF algorithm performance is evaluated. Compared with the bias correction combination four-anemometer weighted fusion algorithm (FAF-BC) and the BP neural network algorithm for radar wind measurement combination (RCBP), the mean errors in wind direction and speed are reduced by 1.99° and 6.99% at most. The maximum errors are reduced by 14.46° and 15.81% at most, respectively.

Vortex characteristics inside profile reed channel of an air-jet loom based on large eddy simulation

In the process of jet weaving, airflow plays a primary role by carrying the weft yarns and interlacing them with the warp yarns to form the fabric. The vortex characteristics within the weft insertion channel of an air-jet loom directly affect the motion of the weft yarns, thus impacting the quality of the fabric. In this study, the large eddy simulation (LES) method was employed, and the Omega vortex identification criterion was used to analyze the vortex characteristics within the profile reed channel. The effects of different positions of relay nozzles, nozzle spacing, and reed gap ratio on the airflow characteristics were investigated. Additionally, the vortex volume ratio () and velocity fluctuation rate () were introduced as indicators to measure the proportion of vortices and the turbulence intensity of the airflow field. The numerical results indicated that the introduction of relay nozzles significantly reduced the intensity of airflow vortices and the proportion of vortices within the profile reed channel. When the inlet pressures of the main and relay nozzles were fixed, the minimum values of and were observed when the first relay nozzle was located at 105 mm, the nozzle spacing was 65 mm, and the gap ratio was 1:2. The findings of this study provide theoretical guidance for further improving the airflow characteristics within the profile reed channel of an air-jet looms.

CFD simulation and optimization of an industrial cement gas–solid air classifier

An air classifier is one of the main and effective devices in cement industry. In this study, a three-dimensional, steady and two-phase (solid-gas) computational fluid dynamics (CFD) simulation was performed to optimize the performance of this device in the Kerman Momtazan cement plant, Iran. After the validation of CFD results, the air flow field and air path lines between fixed blades were checked carefully and the non-uniformity in velocity distribution and the formation of vortex flows between the blades close to particle inlets were observed. The study tried to improve the device efficiency by changing the method of entering particles into the device, resulting in a reduction in air classifier electrical energy consumption (from 41 to 35 (kW h)/t) and an increase in production rate (from 203 to 214 t/h). Additionally, the study investigated the effects of other modifiable operating conditions like rotary cage rotation speed, pressure difference, and inlet air temperature on the particle size distribution and classifier efficiency. The results showed that increasing the cage rotation speed decreased the product rate and the product particles mean diameter while increasing pressure difference or increasing temperature increased the product rate and the product particles mean diameter. It was concluded that these modifiable operating conditions can significantly affect the performance of the air classifier in the cement industry.

Numerical investigation and modeling of sweep effects on inlet flow field of axial compressor cascades

Swept blades are widely utilized in transonic compressors/fans and provide high load, high through-flow, high efficiency, and adequate stall margin. However, there is limited quantitative research on the mechanism of the effect of swept blades on the flow field, resulting in a lack of direct quantitative guidance for the design and analysis of swept blades in fans/compressors. To better understand this mechanism, this study employs a reduced-dimensional force equilibrium method to analyze more than 1500 swept cascades data. Results verify that circumferential fluctuation terms are responsible for inducing radial migration in the inlet airflow field of the swept blade, resulting in variations in the incidence angle and consequently leading to changes in the characteristics of the swept blade. Thus, a combination of simple functions and machine learning is utilized to model the circumferential fluctuation terms and quantify the sweep mechanism. The prediction accuracy of the model is high, with coefficient of determination greater than 0.95 on the test set. When the model is applied in a meridional flow analysis program, the calculation accuracy of the program for the incidence angle is improved by 0.4° and 0.6° at the design and off-design conditions respectively, compensating for the program's original deficiencies. Meanwhile, the model can also provide quantitative guidance for the design of swept blades, thereby reducing the number of design iterations and improving design efficiency.

Investigation on the unsteady ventilation performance of oscillating jet air supply through both spontaneous vortex street effect and active modulation

Ventilation is one of the most vital measures to create a healthy and comfortable indoor environment, significantly influencing indoor air quality and building energy consumption. The conventional steady-state airflow field of a ventilated room, if not reasonably configured, is prone to cause air stagnation in certain regions, whereas the unsteady airflow improves the mixing effect, which favors the dispersion and purging of indoor air pollutants. This paper proposes a method to induce an unstable air flow field utilizing the spontaneous Karman vortex street effect on the air-supply jet and swinging modulation. The quasi-periodicity of the airflow field and its influence on the indoor pollutant purging effect were investigated. The effects of air velocity oscillation and pollutant concentration decay in a ventilated room were studied through experimental measurements and computational fluid dynamics analysis. The results show that the transverse oscillation jet has a dominant period of 1.6 s and the longitudinal oscillation jet has a dominant period of 2.987 s, and both jets have a width about twice that of the free jet. The airborne pollutant discharge efficiency of the oscillating jet was higher than that of the free jet at the occupancy level, and the longitudinal oscillating jet purged pollutants faster than the transverse oscillating jet. This study reveals that oscillating jets can provide an option to create periodic flow fields and improve the efficiency of ventilation.

Numerical Simulation of Pollutant Spread in a Double-Deck Viaduct

This study uses the computational fluid dynamics (CFD) method to investigate the effects of the depth-width ratio of a three-dimensional street valley and wind velocity on the flow field and pollutant spread in street valleys with double-deck elevated bridges. The simulation results indicate that when there is no viaduct, there is only one vortex in the gorge when the depth-width ratio (H/W) is less than 1.5; when it is equal to 1.5, multiple vortices appear. With a double-deck viaduct, the viaduct changes the airflow field and turbulence structure in the valley, creating a primary vortex and multiple secondary vortices. Aiming at the diffusion of pollutants, the changing trend in the horizontal and vertical direction was quantitatively analyzed. The study found that when the aspect ratio increased from 0.8 to 1.5, the CO concentration on the leeward side increased by 40%, and the CO concentration on the windward side increased by four times. When the street width increased from 20 m to 37.5 m, the CO concentration decreased by 30%. The increase in wind speed reduced the CO concentration by 28% on the lee side and 33% on the windward side. This study reveals the general pattern of pollutant dispersion in viaduct-street canyon structures, providing insights into the construction of viaducts.

Impact of Airflow Rectification on Spreading Uniformity for UAV-Based Multichannel Pneumatic Granular Fertilizer Spreader

Unmanned aerial vehicles (UAVs) are an important part of smart farms and have been widely used in granular fertilizer spreading. The multichannel pneumatic granular fertilizer spreader (MPGFS) has the advantages of light weight and precision spreading, and has been applied to UAV variable rate fertilization. Based on the problem that the airflow field disorder of the existing MPGFS reduces the uniformity of spreading, the aim of this study was to further improve the performance of the MPGFS through rectification. The computational fluid dynamics and discrete element method (CFD-DEM) and coupling simulation method were used to study the characteristics of the airflow field and fertilizer particle motion, and a honeycomb rectifier and grid rectifier were developed. The aperture of the honeycomb rectifier and the grid size of the grid rectifier were optimized. Then, the test bench was built to test the consistency of the discharge rate of each channel and the spreading uniformity of the MPGFS. The simulation results of the existing MPGFS showed that the airflow provided by the axial flow fan was rotational, and this caused the particles’ motion to be skewed in the shrinkage section, so the discharge rate of each channel was inconsistent. The airflow field analysis results of the shrinkage section showed that the airflow rotation was reduced after the rectification of the honeycomb rectifier and the grid rectifier. The bench test results showed that the coefficient of variation (CV) of each channel discharge rate of the existing MPGFS was 20.16%, the optimal honeycomb rectifier was 13.07%, and the optimal grid rectifier was 5.27%. The bench test results of spreading uniformity show that the CV of spreading uniformity of the existing MPGFS was 15.32%, the optimal honeycomb rectifier was 15.81%, and the optimal grid rectifier was 8.02%. The grid rectifier spread pattern was more reasonable and the CV of uniformity was better. This study demonstrated that the use of a grid rectifier to rectify the airflow field of MPGFS can effectively improve its spreading uniformity, which was of guiding significance for the design and research of MPGFS.

Paint Film Formation Characteristics on Conical Surfaces for Electrostatic Air Spray Painting

When a curved target surface is coated in an electrostatic spray-painting process, the paint film pattern on curved targets will deform, and the thickness will change compared with the planar target due to the curvature characteristics of the target, the inhomogeneous electric field, and the flow field. Therefore, directly using the planar deposition distribution for painting the trajectory planning of curved surfaces causes large errors and low paint transfer efficiency. A study investigating the curved surface paint film thickness distribution characteristics is presented in this research to understand the relations among the target surface curvature, the electrostatic field, and the flow field distribution. Spray-painting process simulations were performed for conical surfaces of different curvatures. Moreover, the paint particle’ trajectories, electric potential, and film deposition distribution were computed using ANSYS Fluent. The paint transfer efficiencies of these targets were computed. The results show that when the generatrix curvature of the conical surface increases gradually, the electric field intensity near the wall increases, which enhances the deposition of charged droplets on the wall. Moreover, the airflow field velocity increases as the curvature increases, which leads to a large diffusions of the spray flow field, so the paint thickness decreases, and the transfer efficiency is low.

Dynamic stratified porosity computation from canopy interaction simulation between airflow and leaves.

The main goal of wind-driven spraying is to use assisted airflow to disrupt the structure of branches and leaves and broaden the air delivery channel, so as to achieve uniform droplet deposition in the middle and lower parts of the canopy. Due to the complex branch and leaf structure inside the canopy, there is currently no effective method to express the dynamic changes of canopy porosity and the law of airflow attenuation under assisted airflow. In this study, based on the two-way fluid-structure interaction numerical simulation method, the relating between the assisted airflow and the structural parameters of the cotton canopy is analyzed, and a new method for predicting and simulating the dynamic porosity of the canopy is proposed. Firstly, a two-way fluid-structure interaction model based on Lattice Boltzmann (LB) solver and Finite Element (FE) solver is developed to simulate the deformation motion of cotton leaves and the spatial distribution of airflow field, and the correctness of the numerical simulation is verified based on indoor measurement data. Secondly, the post-processing method of Computational Fluid Dynamics (CFD) is used to obtain images of leaves at different canopy positions under assisted airflow, and the porosity changes are calculated and analyzed by image processing. The research results show that under different initial wind speeds (5 m·s-1, 10 m·s-1, 15 m·s-1), the maximum normalized mean absolute error (NMAE) between the simulated values and the measured values is 13.99%, 20.72% and 16.08%, respectively. The coefficient of determination (R2) for linear fitting between simulated values and measured values is 0.9221. These validation results indicate the effectiveness of the numerical simulation method. The validated CFD model is applied to predict leaf deformation and porosity changes within the canopy under various wind loads and times. The application results have well revealed the interaction between crop leaves and airflow, and will be beneficial to make a better understanding of the effect of assisted airflow on droplet deposition.

The use of GANs and transfer learning in model-order reduction of turbulent wake of an isolated high-rise building

The high cost of computational fluid dynamics (CFD) simulations has limited their use for real-time and long-term simulations. To address this limitation, reduced-order modeling has been developed, and recent advancements in artificial intelligence (AI) algorithms have led to the creation of non-intrusive reduced-order models (NIROMs). The present study proposes a framework for using various AI techniques to develop NIROMs for the turbulent wake of an isolated high-rise building. The framework is demonstrated using datasets from two different flow conditions, isothermal and unstable thermal stratification. A residual adversarial autoencoder (AAE) network with convolutional layers and Wasserstein generative adversarial network (WGAN) is first used to reduce the dimensionality of the unstable dataset. Afterward, a parallel bidirectional long short-term memory (BiLSTM) network computes its evolution through time. The proposed framework provides commendable predictions of the airflow field. The weights of the trained model are utilized to create a NIROM based on transfer learning (TL) for a smaller dataset that represents the isothermal condition. The results showed that when the training dataset is limited and the model cannot be trained on sufficient vortex shedding cycles, the proper use of TL can lead to better outcomes compared to the traditional training method (i.e., training from scratch).

Prediction of urban airflow fields around isolated high-rise buildings using data-driven non-linear correction models

When it comes to predicting urban airflow, steady Reynolds-averaged Navier-Stokes (SRANS) models that rely on Reynolds stress often face a challenge called the closure problem. This problem involves unresolved structural flaws and uncertainties in the closure coefficients used in the models. Previous attempts to recalibrate coefficients for specific urban flows without breaking the linear constitutive relation have resulted in simulation results constrained by the baseline turbulence model. Therefore, this study aims to enhance the performance of SRANS models by addressing these structural flaws. To achieve this, a novel data-driven framework is proposed. It leverages the deterministic symbolic regression algorithm to discover explicit algebraic expressions for a non-linear Reynolds stress correction model. The robustness of the correction model is ensured by maintaining the linear eddy viscosity model for iterative calculations while keeping the non-linear component frozen. The proposed framework is evaluated using three isolated building cases with varying geometric configurations and inflow boundary conditions. Findings demonstrate that computational fluid dynamics (CFD) predictions incorporating the data-driven non-linear correction model consistently align closer to wind tunnel experimental results compared to both standard and non-linear versions of the k-ε turbulence model. This improvement is reflected in reduced reattachment lengths and more accurate mean velocity distributions in the wake of buildings. However, it should be noted that there is a possibility of overpredicting wind velocity in the windward area. This study introduces valuable insights and additional strategies to enhance the prediction accuracy of SRANS models in urban airflow simulations.

Aerodynamic effect on atomization characteristics in a swirl cup airblast fuel injector

To investigate the influence of swirling air flow field on the spray characteristics and the droplet behaviors of the swirl cup airblast fuel injector, a single swirler cup and a double swirlers cup airblast injector were operated in a wide range of fuel mass flow rates (mf) and relative air pressure drops (ΔPa). Various laser based diagnostics, including planar Mie scattering, phase-Doppler particle analyzer, and high speed particle imaging velocimetry, were employed to provide the information of spray angle, droplet Sauter mean diameter (SMD), droplet velocity, and air flow velocity. The results show that the air flow field was characterized by central toroidal recirculation zone (CTRZ), the double swirlers cup airblast injector generated stronger CTRZ than single swirlers cup airblast injector. The spray characteristics and the droplet behaviors with different size classes were significantly affected by the air flow field. The larger droplets (25–100 μm) with higher initial momentum were likely to keep its velocity when passing through CTRZ, when the mf increased, more large fuel droplets could pass through the CTRZ and expanded to both sides, resulting an increase in a spray angle. On the other hand, smaller droplets (<25 μm) with lower initial momentum were trend to be enrolled by the CTRZ; therefore, the spray droplets at lower mf were confined in the CTRZ. These droplets trend to coalesce with each other resulting in an increase of SMD in this region.

Investigating unsteady airflow characteristics in the human upper airway based on the clinical inspiration data

To enhance understanding of the airflow characteristics in the human respiratory system during realistic inspiration, we investigated the airflow field in a human upper airway model using large eddy simulation and the dynamic grid method, taking into account clinically measured inspiratory characteristics. The results reveal the following novel findings: (1) The laryngeal jet and recirculation zone exhibit significant unsteadiness, with their dynamic characteristics primarily influenced by the transient inspiration flow rate and glottis motion. This pattern holds true for other airflow characteristics as well. (2) Glottis expansion reduces the energy consumed during inhalation for both steady and unsteady inspiratory flow rates, with the degree of expansion being directly related to the reduction in energy. We can accurately predict power loss by considering the glottis area and inspiratory flow rate. (3) Analysis of spectral entropy clearly demonstrates that the flow transitions from the laminar to turbulence earlier when using clinical inspiration data. Turbulence intensity in the trachea increases when either glottis motion or the transient inspiratory is ignored. In conclusion, the airflow dynamics are significantly more unsteady compared to cases where we ignore either glottis motion or the transient inspiratory flow rate. A precise understanding of realistic respiratory airflow cannot be achieved by assuming either a rigid glottis or a steady inspiration pattern. Therefore, it is crucial to use accurate inspiratory data when studying the properties of airflow structures in the human respiratory system. Moreover, incorporating more physiological data is also essential to obtain realistic respiratory airflow characteristics.

Airborne spread of human coughing droplets with different postures and relative orientation in wards combined with peacetime and epidemic periods

The transmission and deposition of human expiratory droplets are widely acknowledged as a potential pathway for cross-infection within hospital wards. A numerical (CFD) approach validated by experimental testing, is applied to investigate airborne spread of patient expiratory droplet nuclei in a two-bed ward during both peacetime and epidemic periods, utilizing a ceiling downward supplying and bottom exhausting ventilation strategy. The airflow field, spatial and temporal distribution of coughing droplets nuclei, exposure of the healthcare worker (HCW) and another patient are compared based on 10 cases with different postures, relative orientation of patients and ventilation rates. Results reveal that the dispersion range of droplets is maximized when patients are seated and coughing, with an average suspension rate reaching up to 85%. The diffusion of coughing droplets while lying down is significantly influenced by the ventilation rate, showing a 26.6% increase in exhausted rate and a 17.9% decrease in suspension rate when 12 ACH is implemented. When a coughing patient is lying on their side facing to another patient, a substantial amount of coughing droplets quickly occupies the primary breathing zone of the other patient, resulting in a severe risk of cross-infection. Overall, increasing the ventilation rate reduces the concentration of cough-generated droplets in the breathing zone, but the dispersion and removal of indoor pollutants still depend on the exhalation characteristics. These findings enrich the theoretical understanding of indoor pollutant transmission and provide guidance for the further design and optimization of airflow organization in dual-person wards aimed at mitigate the risk of cross-infection.

Simulation Analysis and Experimental Verification of Freezing Time of Tuna under Freezing Conditions

In order to predict the regular temperature change in tuna during the freezing process for cold chain transportation, improve the quality of frozen tuna, and reduce the energy consumption of freezing equipment, a three-dimensional numerical model for freezing tuna of different sizes was established. An unsteady numerical simulation of the air velocity and flow field was combined with an analysis of the freezing process of tuna. This paper also studied the effect of air velocity, temperature, and tuna size on the freezing process. The numerical results show that there was a positive correlation between the cold source environment and the tuna-freezing process. Lower temperatures and higher air increased the velocity at which the tuna moved through the maximum ice crystal formation zone, maintaining a better aquatic product quality. In some cases, however, the smaller tuna models achieved a longer freezing time. Due to the difficulty of obtaining the whole tuna sample, the temperature curve and freezing rate over time obtained during the freezing process were tested using a tuna block of a specific size. The maximum error did not exceed 6.67%, verifying the authenticity and feasibility of the simulation.

Research on a new-designed Venturi ejector and dazomet particle motion characteristics for dilute-phase pneumatic conveying systems based on CFD-DEM

To disperse dazomet, a commonly used soil fumigant for soil disinfection, over large soil surfaces, dilute-phase pneumatic conveying can be utilized. Currently, most research has focused on pneumatic conveying systems for large particles, such as coal conveying or pneumatic seeding However, there has been almost no research on the dilute-phase pneumatic conveying of dazomet particles. Therefore, a coupled simulation model based on computational fluid dynamics and discrete element method (CFD-DEM) was established to study the effect of the structural parameters of the Venturi ejector on the motion of particles and airflow fields variation characteristics for the pneumatic conveying system of dazomet particles. Based on the Box–Behnken experimental design method, a 3-factor and 3-level response surface simulation experiment was carried out by selecting the contraction angle, throat diameter, and diffusion angle of the Venturi ejector as factors. The suction-flow ratio, average velocity of particles, average coordinates of particles in the vertical direction, and corresponding standard deviation at the outlet of the pipeline were chosen as response indexes. Multiple linear regression models were established between each factor and response index. The simulation results showed that the impact of factors on the 4 response indexes from strong to weak were throat diameter, contraction angle, and diffusion angle. With decreasing throat diameter, the suction flow ratio and average velocity of the particles increased. The average coordinates of the particles in the vertical direction decreased, while the standard deviation increased, indicating that the pneumatic conveying performance of the system increased. The optimal structural parameters for the contraction angle, throat diameter, and diffusion angle were 34.5°, 15 mm, and 12.0°, respectively. The experimental results demonstrated that the application precisions of the optimised Venturi ejector were 99.23%, 98.46%, and 98.56% at application rates of 15, 20, and 25 g/s, respectively. The results provide a theoretical reference for the structural optimisation of the Venturi ejector and operational performance evaluation of the pneumatic conveying system for dazomet particles.

Thermo-fluid dynamic analysis of the air flow inside an indoor vertical farming system

In this study, computational fluid dynamics (CFD) is used to assess the thermo-fluid dynamic behaviour of an indoor vertical farming system. Experimentally driven three-dimensional k-ε steady simulations are performed using a species transport model to account for relative humidity. In-field sensor measurements are used to set the boundary conditions for the simulations and to validate the results in terms of temperature and humidity distribution within the growing cell. The entire cell, consisting of eight levels of growing tables is simulated under daylight conditions, including the heat source from LED lights in the thermo-fluid dynamic air flow field. Results help to understand the main features of the air flow distribution. The comparison of the numerical results with measurements demonstrate the ability of the numerical approach to characterize the thermo-fluid dynamic flow field of the indoor farming system and the reliability of well-calibrated CFD simulations in controlling the air flow distribution, which is necessary to reduce energy consumption and to improve plant growth quality. Critical regions for the plant growth are identified within the farm based on the study of air speed uniformity and on the analysis of vapor pressure deficit (VPD). A growing table efficiency index is introduced based on the definitions of two dimensionless objective uniformity parameters. The analysis of these indices helps identifying differences in the fluid dynamic behaviour of the upper and lower floors of the cell and some deficiencies in the ventilation system ability to provide uniform air conditions to all the growing tables. Results show a symmetric behaviour of the left and right layers for upper floors, with tables in front of the evaporators showing better efficiencies. An opposite behaviour is observed on the lower floors, exhibiting a strong asymmetry between left and right layers. On the other hand, the VPD analysis reveale that certain regions near the evaporators and walls (with good flow uniformity) experience extreme conditions that could affect plant growth. The approach presented in this paper provides a detailed understanding of the indoor vertical farming environment and its impact on growth and yield of leafy greens. This, in turn, helps in the effort to optimize the vertical farm ventilation system and thus its energy, which remains the main issue of such cultivation plants.

Numerical Simulation of the Influence of Ski-jump Deck on the Take-Off Zone Flow Field Based on CFD

Ski-jump take-off is a standard procedure for carrier-based aircrafts, and it is one of the key technologies for the generation of the combat effectiveness of the system. A 3D model carrier with a ski-jump deck is conceptually designed. The airflow field over the carrier is numerically simulated based on CFD. The longitudinal airstream line and velocity distribution, the velocity distributions in normal-wash area, tangential-wash area are derived and the influence of the ski-jump deck on the take-off zone is analyzed. The numerical simulation shows that the body-shedding vortex on both sides of the bow affects the engine intake at Take-off Point 1 and 2 and 3.

Long-distance migration law of radon in overburden of abandoned goaf during coal spontaneous combustion

The surface isotope radon measurement method (SIRMM) is widely used in fire source detection in abandoned mines. However, studies on the long-distance migration of radon during coal spontaneous combustion are lacking, which hinders the further popularization of this technology in coal fire prevention and control. For this reason, the migration law of radon in overlying strata in fire areas was studied through experiments and numerical simulation. The radon exhalation concentration of coal was found to increase at first and then decrease in the range of 30–350 °C through experiments. The radon concentration reaches the maximum value (557.1 Bq/m3) at 150 °C, which is 6.3 times higher than that at 30 °C. Based on the radon source term obtained by fitting the experimental data, the radon migration model of coal spontaneous combustion in abandoned goaf was constructed, and the dynamic distribution characteristics of the airflow, temperature, and radon concentration fields in the overlying strata area were analyzed. The internal relationship between surface radon and underground fire source was discussed. The simulation results revealed the sharp change in the porosity of the overlying rock causes radon concentration at the interface between the caving and fissure zones to increase continually with the process of spontaneous combustion, providing material and energy support for the long-distance radon migration. When the maximum temperature of the coal pile reaches 70 °C, the concentration of radon released from the coal pile increases rapidly to 13696 Bq/m3, and the radon from the underground space appears on the surface at this temperature. In the range of 70–150 °C, with rapid increase in radon released from coal piles, the surface concentration of radon also increased rapidly to 225 Bq/m3. At the high-temperature stage exceeding 150 °C, the concentration of radon released from coal piles exhibited a downward trend, resulting in a decrease in the rate of increase of radon concentration on the surface. A close relationship between the surface radon concentration and underground fire source temperature in the process of coal spontaneous combustion was observed. In the spatial position, the peak position of radon on the surface was highly consistent with that of the fire source longitudinally, which ensures the accuracy of the SIRMM to determine the location of the hidden fire source. This suggests that the SIRMM can accurately evaluate the fire source's temperature and fire area's development trend.

Numerical analysis of airflow fields in new modified melt-blowing dies

Considerable research has been devoted to the optimization of die configuration to effectively reduce both fiber diameter and roping defects. While some progress has been made, the challenge of developing an improvement method for the melt-blowing die that maintains the production efficiency of the original equipment while not damaging it and without introducing unnecessary energy consumption, still persists. Herein, we report a series of new modified dies featuring gradually shrinking air slots along with an internal flow stabilizer or arc nose piece that can be obtained without damaging the original die. The simulation results indicate that the new modified die demonstrated a remarkable enhancement in various aspects. Notably, it resulted in a substantial increase of 40.61% and 11.18 K in average centerline air velocity and average air stagnation temperature, respectively, while simultaneously achieving a remarkable reduction of 49.45% in average centerline turbulence kinetic energy. In addition, our modifications yielded an impressive maximum reduction of 23.08% in fiber diameter. The simulated motion characteristics of the polymer jet demonstrated that the new modified die exhibited superior polymer jet attenuation and lower whipping amplitude. The findings of this study indicate that the new modified die, which incorporates gradually shrinking air slots along with an internal flow stabilizer or arc nose piece, shows promise for the production of melt-blown nonwovens with smaller fiber sizes and a reduced occurrence of roping defects. Future research and development will concentrate on practically implementing this technology in melt-blowing production.