Air Disturbance Research Articles

Correlating surface mold contamination with airborne pollution under mild indoor air disturbance: A case study of Aspergillus niger

Surface mold on building materials constitutes a major indoor pollution source. Indoor airflow disturbances can aerosolize the mold, posing health risks like asthma. However, while studies have explored higher airflow rates typical of air ducts, the relationship between surface mold release and the more common mild indoor airflow conditions (≤1.0 m/s) has not been well established, hindering the understanding of surface-induced mold aerosols. This study addresses this gap by experimentally examining the release dynamics of surface mold under various mild airflow conditions, using Aspergillus niger-contaminated plaster surfaces as examples. The experiments focused on the release intensity (RI) and suspension proportion (SP) of mold across different airflow rates, temperatures, humidity levels, and impact angles. Based on 375 experimental tests, two empirical formulas and two models were established using a hierarchical modeling method to predict the concentration of airborne mold released per disturbance airflow and surface mold-induced indoor air pollution. Results indicate that a substantial amount of surface mold was aerosolized within 0.18 s under mild airflow disturbance, with source concentrations ranging from 1.1 × 105 to 1.5 × 105 CFU/m3 per disturbing airflow, and 30.4 %–85.2 % of the mold remained suspended for 10 min. The empirical formulas were verified to achieve high accuracy, with ±6 % for RI and ±10 % for SP. The predictive models were also validated through new experiments, achieving an accuracy of 5 % for predicting surface mold-induced indoor air pollution levels and the source concentration of airborne mold. This work offers a foundation for predicting indoor mold pollution.

Steady and transient state behavior of a gasification process under fixed-bed downdraft configuration

Gasification is a thermochemical process that has gained significant interest in the field of biomass energy conversion. Despite the level of technological maturity of the process, the dynamic variation of the process as a result of changes in both the properties of the gasifying agent and biomass has not been analysed in sufficient depth. Therefore, the present study characterizes the process dynamically as a function of step-type changes in rice husk biomass moisture content and gasifying airflow. To identify stability conditions and the range for inducing disturbances, steady-state tests were carried out using a 32-factorial design. The experimental results demonstrate that within the tested range of airflow, the gasification process operates in the oxygen-limited zone. Despite increasing the airflow from 20 to 40 standard liters per minute (SLPM) and driving the reaction towards the combustion zone, the high temperatures achieved resulted in the gas reaching a peak Lower Heating Value (LHV) of 2.6 MJ/Nm3 and a gas power of 2.6 kW, with a Cold Gas Efficiency (CGE) of 62%. In contrast, the effect of biomass moisture content was negligible due to the thermal inertia of the reactor and the natural variation of the process. Dynamic evaluation revealed that the oxidation temperature and gas concentration were the variables that took the longest to return to stability after air disturbances. It took approximately 1200 s for the hydrogen (H2) concentration to stabilize, while the gas power required about 300 s. No clear results were observed regarding the impact of the dynamic disturbance in moisture content, which varied between 12.3% w.t and 21.5% w.t.

Single-frame fringe pattern analysis with synchronous phase-shifting based on polarization interferometry phase measuring deflectometry (PIPMD)

In the domain of phase measuring deflectometry (or fringe projection profilometry), utilizing only a single-frame fringe pattern to achieve high-precision three-dimensional reconstruction has emerged as a focal point of ongoing research. To achieve four-step phase-shifting demodulation from a single-frame fringe pattern, this paper proposes a Polarization Interferometry Phase Measuring Deflectometry (PIPMD). This method primarily relies on a Michelson polarization interferometry structure to produce projected polarization interference fringes, which are then captured by a polarization camera as modulated single-frame deformed fringe patterns. These single-frame fringe patterns enable pixelated four-step phase shifting with adjacent 2 × 2 pixel units. To validate the proposed method, a series of experiments has been conducted, including surface shape detection of a concave spherical mirror and an off-axis parabolic mirror, as well as dynamic deformation measurements of a deformable mirror. All experimental results consistently indicate that the polarization interference-based fringe projection technique can achieve synchronized phase-shifting demodulation of single-frame fringe patterns, thereby facilitating high-precision reconstruction of the fringe patterns captured in a single frame. This synchronous phase-shifting technique can overcome the influence of air disturbances in traditional four-step phase-shifting methods, thereby enhancing the accuracy of phase demodulation. Additionally, this polarization interference-based Phase Measuring Deflectometry exhibits promising application prospects in dynamic measurements.

Heat Transfer Process of the Tea Plant under the Action of Air Disturbance Frost Protection

Wind machines based on the air disturbance method are progressively employed to mitigate frost damage within the agricultural machinery frost protection. These devices are utilized during radiative frost nights to disrupt near-surface thermal inversion through air mixing. Despite this application, the fundamental mechanisms underlying these mixing processes are not well comprehended. In this research, numerical simulations were conducted using COMSOL Multiphysics software version 6.0 to simulate the flow and heat transfer processes between the thermal airflow and both the tea canopy and stems. The results indicated that due to obstruction from the canopy cross-section, the airflow velocity on the contact surface rapidly increased. As the airflow further progressed, the high-speed region of the airflow gradually approached the canopy surface. Turbulent kinetic energy increased initially on the windward side of the canopy cross-section and near the top interface. On the windward side of the canopy, due to the initial impact of the thermal airflow, rapid heating occurred, resulting in a noticeable temperature difference between the windward and leeward sides within a short period. In the interaction between airflow and stems, with increasing airflow velocity, fluctuations and the shedding of wake occurred on the leeward side of the stems. The maximum sensible heat flux at the windward vertex of the stem increased significantly with airflow velocity. At an airflow velocity of 2.0 m/s, the maximum heat flux value was 2.37 times that of an airflow velocity of 1.0 m/s. This research utilized simulation methods to study the interaction between airflow and tea canopy and stems in frost protection, laying the foundation for further research on the energy distribution in tea ecosystem under the disturbance of airflow for frost protection.

Modified calculation model of train-induced aerodynamic pressure on vertical noise barriers considering the train geometry effect

High-speed trains (HSTs) generate air disturbance, leading to significant aerodynamic pressure on the noise barriers. Differences in train geometry result in variations in the aerodynamic pressure on noise barriers, implying that existing European standard calculation models may not necessarily be suitable for all types of HSTs. In this paper, the influence of the width, height, and nose length of the train on the aerodynamic pressure on vertical noise barriers was studied using computational fluid dynamics (CFD) simulations. Results showed that taller and wider trains result in greater aerodynamic loads on noise barriers. Conversely, an increase in the nose length of a train leads to a reduction in such pressure. Using grey relational analysis, correlation of various factors with the train-induced aerodynamic pressure is, from strong to weak: distance to the track center, width, height, and nose length of the train. Building upon the EN 14067-4 calculation model, the shape coefficients of trains with varying geometric characteristics were derived using the simulation data obtained in this study. A modified pressure calculation model was established accounting for the differences in geometric features of HSTs and pressure distribution in the vertical direction of noise barriers and validated using relevant data from the literature.

Multi-wavelength pinhole point diffraction interferometry for optics metrology with interferometric intensity based phase retrieval method

In this paper, we propose a multi-wavelength pinhole point diffraction interferometry (MPPDI) and a two-step phase extraction method based on the interferometric intensity information. MPPDI is mainly used to extend the dynamic measurement range of traditional pinhole point diffraction interferometry (PPDI) to realize the measurement of large-aperture and high-order aspheric surface. Spherical/aspherical optics will be test under three different wavelengths, and the corresponding interferograms are recoded by 3CMOS detector at the same moment. By combining different wavelengths, MPPDI can obtain a synthetic wavelength with a larger measuring range and greater flexibility. In interferometry, the choice of the wavelength of the light source has a great influence on the measurement range and accuracy. In MPPDI, we can choose different wavelength combinations to select the most suitable synthetic wavelength according to the asphericity of the tested mirror. To enhance efficiency and reduce the impact of air disturbances during phase shifts, we propose a new phase extraction method based on interferometric intensity to interpret the phase map of surface information. The background intensity of diffraction wavefront is firstly pre-recorded by 3CMOS, then phase-shift interferograms of test mirror is acquired with two-step piezoelectric ceramic driver (PZT) movement. From the analysis, it can be found that fringe modulation has tiny influence on the interferograms intensity. Therefore, based on global intensity distribution of fringe pattern and grayscale information, phase map can be retrieval using proposed two-step processing method (only single phase-shift). The two-step phase extraction method can reduce the number of phase shifts from 9 to 3, which improves the efficiency and reduces errors due to multiple phase shifts. MPPDI and two-step phase extraction we proposed have a larger measurement while reducing the number of phase shifts and avoiding error accumulation due to too many phase shifts. Suitable for large-aperture and high-order aspheric surface measurement.

Source Location Identification in an Ideal Urban Street Canyon with Time-Varying Wind Conditions under a Coupled Indoor and Outdoor Environment

Source location identification methods are typically applied to steady-state conditions under pure indoor or outdoor environments, but under time-varying wind conditions and coupled indoor and outdoor environments, the applicability is not clear. In this study, we proposed an improved adjoint probability method to identify the pollutant source location with time-varying inflows in street canyons and used scaled outdoor experiment data to verify the accuracy. The change in inflow velocity will affect the airflow structure inside the street canyons. Outdoor wind with a lower temperature will exchange heat with the air with a higher temperature inside the street canyon, taking away part of the heat and reducing the heat of the air inside the street canyons. Moreover, the room opening will produce some air disturbance, which is conducive to the heat exchange between the air near the opening and the outdoor wind. Furthermore, the fluctuations of the upper wind will influence the diffusion of the tracer gas. We conducted three cases to verify the accuracy of the source identification method. The results showed that the conditioned adjoint location probability (CALP) of each case was 0.06, 0.32, and 0.28. It implies that with limited pollutant information, the improved adjoint probability method can successfully identify the source location in the dynamic wind environments under coupled indoor and outdoor conditions.

Fireworks: A Potential Artificial Source for Imaging Near-Surface Structures

Abstract Seismic waves induced by incident acoustic waves from air disturbances can be used to image near-surface structures. In this article, we analyze seismic waveforms recorded by a dense array on the Xishancun landside in Li County, Sichuan Province, southwest China during the Lunar New Year’s Eve (27 January 2017). A total of eight event clusters have been identified as a result of firework explosions. For each cluster, which comprises dozens of individual events with high similarity, we manually pick arrival times of the first event recorded by the array and locate it with a grid-search method. We then rotate three-component waveforms of all events from the east, north, and vertical coordinate system to the local LQT coordinates (L, positive direction perpendicular to the landslide surface and pointing downwards; Q, positive direction is from the launch location of firework to the station along the landslide surface; T, perpendicular to the plane formed by the L and Q directions, and the selected positive direction of the T axis makes LQT form the left-hand coordinate system), and stack the LQT components for those events with cross-correlation values CC ≥ 0.8 with respect to the first event. Characteristics of the stacked LQT components are also examined. The particle motions at each station are retrograde ellipse in the frequency range of ∼5–50 Hz, suggesting air-coupled Rayleigh waves generated by the firework explosions. Spectrograms of the Rayleigh waves also show clear dispersions, which might be used to image near-surface velocity structures. Although we cannot directly extract the phase velocities due to the limitation of the seismic array, our study shows that the fireworks might provide a low-cost and easy-to-use seismic source for imaging near-surface structures.

Comparison on Safety Features among HTGR’s Reactor Cavity Cooling Systems (RCCSs)

Reactor cavity cooling systems (RCCSs) comprising passive safety features use the atmosphere as a coolant, which cannot be lost. However, their drawback is that they are easily affected by atmospheric disturbances. To realize the commercial application of the two types of passive RCCSs, namely RCCSs based on atmospheric radiation and atmospheric natural circulation, their safety must be evaluated, that is, they must be able to remove heat from the reactor pressure vessel (RPV) surface at all times and under any condition other than under normal operating conditions. These include both expected and unexpected natural phenomena and accidents. Moreover, they must be able to eliminate the heat leakage emitted from the RPV surface during normal operation. However, utilizing all of the heat emitted from the RPV surface increases the degree of waste heat utilization. This study aims to understand the characteristics and degree of passive safety features for heat removal by comparing RCCSs based on atmospheric radiation and atmospheric natural circulation under the same conditions. It was concluded that the proposed RCCS based on atmospheric radiation has an advantage in that the temperature of the RPV could be stably maintained against disturbances in the ambient air.

Compensation of emulated atmospheric disturbance and tracking of a moving object by a real-time digital phase conjugate mirror using a liquid crystal spatial light modulator

We developed a fast-response digital phase conjugate mirror using a 700 Hz high-speed liquid crystal spatial light modulator and a high-speed camera. The total delay from signal light acquisition to phase conjugate light generation was 9.7 ms at 1246 × 1024 and 5.9 ms at 640 × 512. The tracking experiment performed on a target moving at a constant distance perpendicular to the optical axis, produced an error of 2%. Furthermore, a heated soldering iron, used to compensate for artificially generated air disturbance, showed that beam wandering and intensity fluctuations were reduced by 86% and 55%, respectively, compared to a phase conjugate mirror with added delay. Phase conjugate light irradiation of a continuously moving target at a maximum speed of 0.9 mm s−1 was also performed. This study shows that real-time digital phase conjugate mirrors can correct wavefront distortion caused by air fluctuation, which is a major challenge in long-distance wireless optical transmission in the turbulent atmosphere, without complicated control, and prevent beam quality degradation in the presence of atmospheric disturbance.

Improving the asymmetric phenomenon effects on the combustion characteristics in an opposed-fired pulverized coal boiler

Numerical investigations were performed on an opposed-fired boiler to better understand the formation of the asymmetric phenomenon and its effects on the combustion characteristics. It is revealed that with the increasing of the inlet Reynolds numbers, the in-furnace flow and temperature fields evolve from symmetry to asymmetry under the symmetric combustion conditions. Nonlinearity was elaborated to explain this phenomenon. Three asymmetric combustion modes were proposed to optimize the deflected flowfield. The final optimal combustion pattern was established via comprehensive consideration of the general air stoichiometric ratio and reduction zone heights. Compared to the original symmetric combustion mode, asymmetric air disturbance creates better internal flowfield recirculation and improves the combustion performance, which obtains a significant NOx reduction from 369.16 mg/Nm3 to 216.16 mg/Nm3 and lowers the carbon content in fly ash from 3.465% to 2.07%, respectively.

Multi-objective optimization of frequency and damping of vertical stabilizer skin structure placed with variable-angle tows

The vibration characteristics of composite vertical stabilizer skin structures play a critical role in damping effects designed for overcoming the air disturbances experienced by aircraft structural components during flight. The first-order fundamental frequencies and their corresponding damping characteristics of the vertical stabilizer skin structure tow-steered by automatic fiber placement technique were optimized with the parameterized trajectories and plies as design variables. Firstly, the vibration and damping numerical models were derived based on Kirchhoff laminate theory, the Rayleigh-Ritz method, and the Strain Energy Method. Then the optimization model was developed by adopting the self-adaptive Differential Evolution Multi-objective optimization algorithm and incorporating the solution method of Pareto Front. The constraints of this optimization model considered the experimentally obtained minimum turning radius of prepregs tow-steered in automatic fiber placement process obtained from experimental tests. Finally, the comparison of numerical simulation results was conducted for the optimized trajectories and the conventional straight trajectories under various boundary conditions, and the numerical results were partially validated through damping and frequency tests. The results indicate the vibration characteristics of the composite vertical stabilizer skin structure can be enhanced to a large extent by optimizing fiber trajectories, and the enhancement percentage is affected by the boundary conditions of the actual structure.

Research on stability characteristics of three-wheel refrigeration system

Simulation on three-wheel refrigeration system is carried out, the result of which is compared with the existing research data. Further, the temperature disturbance characteristics of the system is analysed combined with the main system disturbance source. Simulation results indicate that the temperature or moisture of the bleed air or ram air disturbance brings changes of system outlet temperature, the degree of which agrees with the disturbance element. Meanwhile the bleed air pressure disturbance to the three-wheel refrigeration system influence is most intense. This paper provides reference for the design and optimization of the environmental control system.

Gel Properties and Formation Mechanism of Camellia Oil Body-Based Oleogel Improved by Camellia Saponin.

This study aimed to investigate the effect of camellia saponin (CS) on the structural characteristics, texture properties, rheological properties, and thermal stability of camellia oil body-based oleogel (COBO). In addition, the formation mechanism of COBO was further studied in terms of the microstructure and texture of freeze-dried products, the mobility of hydrogen protons, and the conformation and structure changes of oleosin. The texture and rheological properties of the oleogels were found to be gradually improved with the incorporation of CS. This was attributed to the CS-induced enhancement of oil body interfacial film. CS was likely to bind to oleosin via hydrogen bonding and hydrophobic interactions, thereby forming a thick CS-oleosin complex interface, which was revealed by the oleosin fluorescence quenching and an increase in the ordered structure (α-helix). The composite interface could resist the crystallization damage and air disturbance caused by solidification and sublimation of water during freeze-drying, resulting in a denser and more uniform three-dimensional gel structure to trap the liquid oil, which could be explained by the decreased mobility of hydrogen protons in oleogel. The work offers a new proposal and theoretical basis for the development of saponin-enhanced oleogels using non-thermal processing.

Influence of ecosystem and disturbance on near‐surface permafrost distribution, Whatì, Northwest Territories, Canada

AbstractFor remote communities in the discontinuous permafrost zone, access to permafrost distribution maps for hazard assessment is limited and more general products are often inadequate for use in local‐scale planning. In this study we apply established analytical methods to illustrate a time‐ and cost‐efficient method for conducting community‐scale permafrost mapping in the community of Whatì, Northwest Territories, Canada. We ran a binary logistic regression (BLR) using a combination of field data, digital surface model‐derived variables, and remotely sensed products. Independent variables included vegetation, topographic position index, and elevation bands. The dependent variable was sourced from 139 physical checks of near‐surface permafrost presence/absence sampled across the variable boreal–wetland environment. Vegetation is the strongest predictor of near‐surface permafrost in the regression. The regression predicts that 50.0% (minimum confidence: 36%) of the vegetated area is underlain by near‐surface permafrost with a spatial accuracy of 72.8%. Analysis of data recorded across various burnt and not‐burnt environments indicated that recent burn scenarios have significantly influenced the distribution of near‐surface permafrost in the community. A spatial burn analysis predicted up to an 18.3% reduction in near‐surface permafrost coverage, in a maximum burn scenario without factoring in the influence of climate change. The study highlights the potential that in an ecosystem with virtually homogeneous air temperature, ecosystem structure and disturbance history drive short‐term changes in permafrost distribution and evolution. Thus, at the community level these factors should be considered as seriously as changes to air temperature as climate changes.

Interaction between Strong Sound Waves and Aerosol Droplets: Numerical Simulation

In this study, we attempted to eliminate atmospheric fog and aerosol particles by strong sound waves. The action of sound waves created an air disturbance, and the oscillation of the local air caused the micron-sized aerosol droplet particles to move. To provide guidance of the characteristics of the effective sound waves, this study numerically simulated aerosol droplet agglomeration under the action of sound waves, which was solved by coupling computational fluid dynamics (CFD) and discrete element methods (DEMs) as a typical two-phase flow problem in this study. The movements of aerosol droplet particles were simulated, as well as their agglomeration. The evolution process of the average particle size and the number of multimers were obtained, and the influence of different sound frequencies, sound pressure level (SPL), and particle spacing on agglomeration were studied. It was found that the promotion effect of low-frequency sound waves on aerosol droplet agglomeration was significantly higher than that of high-frequency sound waves, and the sound wave promotion effect of high SPLs was better than that of low SPL. In addition, the concept of the average agglomeration time required to quantify the acoustic agglomeration speed was proposed, and it was found to be positively correlated with sound frequency and particle spacing, while being negatively correlated with SPL.

Multitarget identification method for dual‐plane detection based on data fusion and correlation analysis

AbstractThe light screen that tests the velocity of a projectile is often affected by indoor illumination changes and interference caused by air disturbance of the projectile, affecting the identification of the projectile target signals by the test system. To solve these problems, based on the detection light screen formed by the array infrared diodes and the array photosensitive tube, this article proposes the method of identifying multiprojectile targets in the dual‐plane detection of data fusion and related analysis. Use the amplitude of signals generated by the projectile moving in the screen and the time width of valid signals as the diagnosis basis to build a multiprojectile signal identification model for a single plane detection light screen. Using the similarity of projectile passing through two light screens, a matching algorithm for the two‐plane detection screen projectile signal is established. By collecting the multiprojectile signals of the dual‐plane detection light screen and following the single detection light screen data fusion model, the velocity measuring system can identify the projectile signals of the dual‐plane detection screen. Based on the fusion and identification result of each detection plane and the established match algorithm related to the shot signal, the test result of the test system with interference is obtained. The result verifies the correctness of the established model and algorithm.

Performance evaluation and parameter sensitivity analysis of a membrane-based evaporative cooler with built-in baffles

Evaporative cooling systems have attracted increasing attention for energy-efficient air conditioning applications. A hollow fiber membrane-based direct evaporative cooler (HFM-DEC) is proposed in this study. The selected membrane material can selectively allow only water vapor to penetrate, while preventing the passage of bacteria and fungi, thereby avoiding deterioration of indoor air quality. Compared with the conventional evaporative coolers with counter-flow and cross-flow arrangements, the proposed novel configuration performed better cooling ability by installing baffles in the air flow channel to enhance the air disturbance. The parameter sensitivity analysis was conducted on the HFM-DEC with built-in baffles by employing an experimentally validated numerical model. The orthogonal test method was used to study the influence of nine key parameters of the HFM-DEC on its wet-bulb effectiveness, coefficient of performance, and the cooling capacity. According to the optimized scheme, the HFM-DEC with a relatively optimal configuration was proposed. The cooling performance of this module was investigated under various inlet air conditions. The results showed that if the inlet air velocity was maintained within the range of 0.5–2 m/s, it was capable of achieving an optimal performance with the wet-bulb effectiveness of 70%-95%, the COP of 17–78, and the cooling capacity of 60–106 W, respectively, under diverse weather conditions. Correlations of Nusselt number and Sherwood number were developed by fitting the simulation results. The influence of Reynolds number on air stream characteristics was obtained based on the analysis of the velocity field, temperature field and concentration field of this module under varying operating conditions.

Numerical investigation on heat-mass transfer and correlations of humid air-water outside staggered tube bundles

The heat-mass transfer characteristics of humid air-water outside staggered tube bundles (STB) was investigated by the Euler-Lagrange method based on the coupling between DPM (Discrete Phase Models) and wall film. The influence of operation parameters are analyzed for that. It can be obtained that the heat transfer coefficient increases linearly with the mass flow rate of humid air due to the disturbance of humid air for spray water film (SWF) outside STB. When the inlet temperature of humid air is higher than that of spray water, the heat transfer performance will be enhanced with the mass flow rate of spray water. The heat transfer coefficient will decrease with the decrease of the spray water temperature from nozzle. However, the mass transfer performance will only increases with the mass flow rate of spray water and humid air. The simulation datum are also compared with the existing correlations. It is can be found that the calculation datum by Heyns's and Parker's correlation are consistent with the simulation datum of HSW and MSW compared with the other correlation, respectively. But there is still a large deviation. The above correlations will be also improved in term of the simulation datum. The deviations between simulation datum and the calculation value by new correlations are less than 15%.

Improved Centroid Algorithm for Beam Stability Control System

In order to eliminate the beam jitter caused by the air disturbance and the vibrating devices, the error of light spotted jitter must be detected firstly. The beam jitter error can be corrected by a compensator to realize the beam stability control system. In this paper, an Improved Centroid Algorithm (ICA) combining with the Gaussian Fitting Algorithm (GFA), the Bilinear Interpolation and the Weighted Center of Mass (WCOM) was proposed. A Gaussian template is used to roughly locate the spot image in order to improve the efficiency and stability of the algorithm. The light spot image is interpolated by the Bilinear Interpolation to improve the accuracy of centroid identification. The identification accuracy and efficiency of the algorithm were verified by 100 sets of light spot experiments. The experimental results showed that the identification accuracy and efficiency of the Improved Centroid Algorithm were higher than those of the other algorithms. Our algorithm was of great significance for improving the performance of the beam stability control system.