Increase Of Airflow Velocity Research Articles

A semi-empirical model of frost formation on a cryogenic surface cooled from ambient temperature under forced convection condition

In most practical occasion, frost is formed on cold surface which is cooled from the ambient temperature. Although the initial cooling stage may account for a small proportion in the whole frosting process, the effects of the initial cooling on frosting characteristics could not be overlooked. In this paper, a semi-empirical model of cryogenic frosting involving the initial cooling process under forced convection is established by employing frost properties correlations and heat and mass balance analysis. The frost thickness calculated by the proposed semi-empirical model showed good agreement with experimental data within a maximum error of 15 %. Within the constraints of correlation validity, this model is applicable to conditions where ambient temperatures range from 10 °C to 30 °C, air flow Reynolds numbers span from 7 × 104 to 1.5 × 105, air humidity varies between 3.5 g/kg and 18 g/kg, and initial cooling durations extend from 15 min to 40 min, and the final wall temperature is decreased to about 80K. The results indicate that frost thickness increases with rising ambient temperature, air humidity, and airflow velocity. Notably, higher rates of frost growth are observed during the initial cooling under conditions of elevated air humidity or increased airflow velocity. The trend in frost mass closely mirrors that of frost thickness, however, a more pronounced increase in frost mass occurs with increasing ambient temperature. Furthermore, extending the duration of initial cooling could accelerate the frost growth rate and cause a higher frost surface temperature.

Quality control of functioning of the structure “object-thermoelectric cooler-heat sink” of the system of providing thermal modes

The analysis of the mathematical model of the system of providing thermal modes with the use of thermoelectric cooling to assess the influence of the conditions of heat exchange of the heat sink with the medium on the main parameters, reliability indicators and dynamic characteristics of a single-cascade thermoelectric cooler at a given temperature level of cooling, medium temperature, geometry of branches of thermoelements for different current operating modes is considered. The results of calculations of the main significant parameters, reliability indicators, dynamic and energy characteristics of a single-cascade cooler and heat sink of the selected design at a given temperature level of cooling, medium temperature, thermal load, geometry of branches of thermoelements for various characteristic current operating modes are given, when the conditions of heat exchange on the heat sink of the given design under variation of the heat transfer coefficient. It is shown that with the increase of air flow velocity on the heat sink the heat transfer coefficient increases and thus the temperature drop on the heat sink of the thermoelectric cooler with the medium decreases, which allows to significantly reduce the relative failure rate of the cooler and thus increase the probability of failure-free operation of the whole device. When operating a system for providing thermal modes comprising a cooling device, a heat sink, and an electric fan used for dissipating heat output to the environment, different modes of operation of the electric fan (air flow rate) can be used. With the increase in air flow rate of the electric fan increases the velocity of air flow in the live section of the heat sink of a given design, which leads to an increase in the heat transfer coefficient. This, in turn, makes it possible to reduce the temperature drop at a given design of the system for ensuring thermal modes. The possibility of control of reliability indicators, namely, relative intensity of failures and probability of failure-free operation of thermal mode systems of different designs (current modes, number of thermocouples, surface area of the heat sink) at a given cooling level (medium temperature, thermal load, geometry of thermocouples) under changing conditions of heat exchange of the heat sink with the medium is considered.

基于 CFD 数值模拟的联合沙障间距优化与风沙流特征研究

Strong wind and sand activities will seriously damage the ecological restoration and agricultural safety production on the edge of desert areas, resulting in irreversible economic losses. In order to prevent and protect the agro-ecological environment in the wind-blown sand area, this paper constructs a combination of double-row vertical nylon net sand barrier and grass grid sand barrier. Through numerical simulation and wind tunnel experiment, the protection benefits of double-row vertical nylon net sand barrier and grass grid under different spacing conditions are analyzed, and the layout conditions with optimal spacing are obtained. The results show that when the spacing between double-row vertical sand barrier and grass grid is 5H-10H, the airflow velocity behind the double-row vertical sand barrier cannot be fully developed, the increase of airflow velocity is small, and the average wind prevention efficiency is above 85%. The effective protection distance com-pletely covers the entire combined sand barrier area, and a large number of sand particles near the surface are fixed to the grass grid, so the sand resistance rate is over 77%. The combined sand barrier has a good cooperative protection effect and achieves efficient wind prevention and sand fixation. The wind tunnel experiment verifies the reliability of the results. It also realizes efficient wind prevention and sand fixation under extreme wind and sand weather, and avoids sand burial on farmland and ecological restoration areas caused by extreme wind and sand weather.

Effect of airflow velocity in vessel-pipelines on dust explosion during pneumatic conveying

In order to investigate the flame propagation and pressure characteristics of dust particles during airflow transportation, a dust explosion experimental apparatus simulating dust handling processes was designed. The system is supplied with a stable airflow by a high-pressure fan, capable of continuously transferring dust from the vessel to the pipeline at a controllable speed. Dust explosion experiments were meticulously executed by applying 1 kJ of ignition energy to the transported dust particles at airflow velocities of 5, 10, and 15 m/s. This study examines the effects of airflow velocity, pipe diameter, and ignition position on explosion characteristics and delves into the mechanisms of these effects through a detailed analysis of experimental results. For the maximum explosion pressure, an increase in airflow velocity causes the maximum explosion pressure to rise. As the pipe diameter increases, the maximum explosion pressure first rises and then falls. The maximum explosion pressure occurs in the case of bottom ignition. The range of maximum explosion pressure values is expected to provide a reference for explosion detection and explosion venting. For flame propagation, the flame undergoes five processes within the vessel, including ignition of dust particles, spherical flame development, flame stretching towards the mouth of the pipe, complete combustion of particles, and near exhaustion of particle combustion. The higher the airflow velocity and the larger the pipe diameter, the more pronounced the flame stretching and development towards the pipe opening become. Within the pipe, two distinct flame propagation behaviors were observed under conditions of high and low airflow velocities. Compared with the experimental results of high-pressure pneumatic powder spraying forming a dust cloud within a vessel-pipeline, this study measures the maximum explosion pressure at specific turbulence levels and establishes a quantitative relationship between airflow velocity and explosion characteristics. Utilizing this correlation can provide a reference for predicting industrial-grade dust explosion characteristics at different airflow velocity levels, thereby offering a more optimized design basis for the design and safety protection of industrial equipment.

Deformation of Sessile Droplets under a Gentle Shear Airflow.

Deformation of sessile droplets under shear flow is widespread in both nature and industry. Previous research focuses on the shedding process of sessile droplets under shear airflow, with insufficient attention paid to the droplet deformation before shedding. In this work, experimental studies on the deformation behaviors of sessile droplets under shear airflow are conducted to investigate the effects of airflow velocity and droplet volume on the tangential and normal droplet deformations. Scaling laws of the droplet deformations are established. The results show that the profile of sessile droplets changes under shear airflow with the topmost point exhibiting periodic oscillations in both tangential and normal directions. The oscillation period of the tangential deformation exceeds that of the normal deformation. The average tangential deformation of droplets increases with the increasing airflow velocity and droplet volume. The average normal deformation of droplets increases with the increasing airflow velocity and is influenced by the droplet volume at a higher airflow velocity. The contact angle on the windward side oscillates periodically, and its average value significantly decreases. The contact angle of droplets on the windward side decreases as the airflow velocity and droplet volume increase, while the contact angle on the leeward side remains almost unchanged. The average deformation of droplets in the tangential and normal directions is linearly related to the effective Weber number and the square of the effective Weber number. These findings could be used to predict the deformation of sessile droplets under shear airflows.

Relationship Between Wavy Liquid Film Dynamics and Droplet Formation From Trailing Edge

Abstract Erosion of steam turbine blades due to coarse droplet impingement is a serious problem. The physical relationship is still elusive between the dynamics of wavy liquid film on a wall and the droplet dispersion from the trailing edge. In this study, we experimentally and theoretically investigate the liquid film subjected to the turbulent airflow and following fragmentation process under well-controlled flow conditions, where the airflow velocity is up to 100 m/s, and initial liquid film velocity is 0.06 and 0.10 m/s, and trailing edge thicknesses are 0.5, 1.0, and 2.0 mm. By applying the developed PLIF based method with no use of artificial threshold of brightness, we quantify the film thickness and interfacial friction factor. As the airflow velocity increases, the liquid film instability promotes and the interfacial friction factor increases, much exceeding the Blasius correlation. When the liquid film reaches the trailing edge, several liquid columns extend by the Rayleigh-Taylor instability. We identify that the interfacial friction factor to accelerate the ligament corresponds to the Blasius correlation, distinct from the one on the wavy liquid film upstream. Incorporating the identified two interfacial friction factors, we successfully formulate the diameter of ligament as the characteristic lengthscale of the spreading droplet downstream. Derived formulation for the droplet statistics is well validated by the experimental results of mean and maximum diameters and size distribution.

Optimization framework for daylight and thermal environment of retractable roof natatoriums based on generative adversarial network and genetic algorithm

This paper proposes a framework for multi-objective optimization of indoor daylighting and thermal comfort in natatoriums with retractable roofs, using genetic algorithms and building performance simulation. The goal is to balance daylight illumination and thermal comfort under different roof opening states. Efficiency of computational fluid dynamics simulation is improved by a multi-objective optimization framework based on non-dominated sorting genetic algorithms, integrating a generative adversarial network to learn the environmental map. The study analyses the impact of different roof opening ratios on environmental objectives and establishes regression equations to support optimization and accurate decision-making. In the optimal opening state, compared to a fully closed roof, the daylight factor and natural airflow velocity increase by up to 3.9 and 5.3 times, respectively, while the universal thermal climate index decreases by 1.0 °C. The introduction of a generative adversarial network proxy model significantly improves computational efficiency, accelerating natural airflow velocity calculation by 70–100 times and reducing simulation time by 98.6 %. This study expands predictive models from the urban scale to the building scale, enhancing simulation efficiency and promoting the application of deep learning models and genetic algorithms in climate-responsive building environment assessment and prediction.

Spray characteristics of elliptical orifice spray in diesel engine under air movement conditions

The development of high-quality mixture is a critical requirement for achieving high-efficiency and low-emission diesel engines, and fuel injection system performance improvement and in-cylinder airflow organization are crucial ways for achieving high-quality mixture. The elliptical nozzle is used as the research object in this research, and numerical simulation is utilized to investigate the effect of different airflow speeds and directions on the atomization characteristics of the elliptical nozzle jet, in order to provide a theoretical basis for the engineering application of the elliptical nozzle in diesel engines. The results show that under the same airflow conditions, the vertical penetration distance of the spray decreases while the horizontal penetration distance increases with the use of elliptical orifices, the surface wave perturbation on the windward side is more violent, and reduce spray field the Sauter Mean Diameter (SMD). The spray projected area grew by 13.5%, the spray SMD dropped by 14.8%, and the vertical penetration distance of the spray with elliptical orifices fell by 18% with an increase in airflow velocity from 0 to 20 m/s. When the airflow direction and the spray direction were at a 90° angle and the SMD was lower than that of the circular orifice by 12.9%. The angle between the airflow direction and the short axis of the elliptical orifice was 30°when the spray projection area was larger, the perturbation of the spray body was more intense, and the surface wave amplitude was larger.

Simulation study of dynamic building insulation with transpired solar collectors

This study conducts a comprehensive numerical analysis using Ansys Fluent to investigate the thermal behaviour of transpired solar collectors (TSCs) focusing on temperature distribution, airflow dynamics, and heat recapture capabilities. The research evaluates TSC performance across various environmental conditions. A significant observation from the study is the TSCs' ability to recapture heat losses from the enclosures during nighttime, particularly under higher airflow conditions, where TSCs effectively redirect heat back into building spaces, contributing to energy conservation. Subsequently, the study reveals an inverse relationship between solar radiation levels and TSC efficiency in heat loss recapture. As solar radiation increases from 200 W/m2 to 1000 W/m2, the recaptured wall heat loss decreases by a percentage, ranging from 125 % to 241 % compared to the maximum observed during nocturnal periods. Additionally, the temperature analysis of the TSC backplate demonstrates a complex thermal response under different operational conditions. Solar radiation, airflow rates, and environmental properties influence this interplay. The study also uncovers a consistent linear increase in airflow velocity from the inlet to the outlet within the TSC air cavity, suggesting efficient airflow management. This insight is crucial for optimizing TSC design for improved heat exchange efficiency. In conclusion, the findings of this research offer valuable insights into the operational dynamics of TSCs, highlighting the importance of environmental factors in their design and functionality.

Research of dust removal performance and power output characteristics on photovoltaic panels by longitudinal high-speed airflow

Photovoltaic (PV) panels' photoelectric conversion efficiency will decrease as dust deposition on their surface. An approach to dust removal on the PV panel's surface by longitudinal high-speed airflow was investigated to increase the output power. In this paper, commercial CFD software was used to numerically simulate the characteristics of dust removal by longitudinal high-speed airflow. The PV panels' output characteristic model under the action of dust removal by high-speed airflow is established by Simulink software, and the influence of high-speed airflow on the output characteristic is studied. Firstly, the dust removal mechanism of the PV panel under high-speed airflow is studied. Secondly, the impact of different tilt angles of the PV panel, dust particle size, airflow velocity, and blowing time on the dust removal effect of the PV panel surface were studied. The optimal airflow velocity and blowing time were obtained according to the airflow velocity and blowing time and their influence on the dust removal rate. Finally, the effect of high-speed airflow dust removal on PV power generation's efficiency and output characteristics is studied. The findings demonstrate that as the tilt angle increases, so does the dust removal rate increases continuously. In addition, the rate at which dust is removed increases with airflow velocity and blowing time. When the tilt angle is 30°, the best airflow velocity of dust removal is 5 m/s, and the best blowing time is 8 s. When the tilt angle is 45°, the best airflow velocity of dust removal is 10 m/s, and the best blowing time is 5 s. With the increase in airflow velocity and blowing time, the output power of PV panels continues to increase. When the airflow velocity is 10 m/s, and the blowing time is 5 s, 7.5 s, 12.5 s, and 15 s, the maximum output power after dust removal is increased by 15.44 %, 23.05 %, 23.38 %, and 23.39 %. This paper's research results can guide the design of the practical engineering application of longitudinal blowing high-speed airflow in the dust removal of PV panels.

Simulation Analysis of Arc-Quenching Performance of Eco-Friendly Insulating Gas Mixture of CF3I and CO2 under Impulse Arc

Due to its superior insulating qualities, SF6 gas is extensively used in the power sector. However, because of its poor environmental protection properties, finding ecologically acceptable insulating gas has become a critical challenge in the power sector in the context of pursuing green electricity. This work simulates the arc-quenching performance of a gas mixture of CF3I and CO2, which is thought to be a workable substitute for SF6 gas. The COMSOL software is used to build a two-dimensional model of a single-pipe arc-quenching chamber based on the concepts of magnetohydrodynamics (MHD) theory. The lightning impulse current is made by applying electrical stimulation to pure CO2 gas, gas mixtures with 10% CF3I and 90% CO2, and gas mixtures with 30% CF3I and 70% CO2 in the single-pipe arc-quenching chamber. During the first stage of arc formation, the results show that CF3I/CO2 gas mixtures with 10% and 30% CF3I have lower electrical conductivity than pure CO2 gas. An 8/20 μs lightning impulse current waveform with a magnitude of 4 kA is used for this observation. The highest airflow velocity for pure CO2 is 1744 m/s, but the mixture of 10%/90% CF3I/CO2 has a maximum airflow velocity of 1593 m/s. The 30%/70% CF3I/CO2 mixture has the highest maximum airflow velocity at 1840 m/s. Airflow velocity increases and the overpressure in the arc-quenching chamber is prolonged when there is a greater concentration of CF3I gas in the gas mixture. Consequently, these factors greatly reduce the duration of the arc-extinguishing time. The arc-quenching chamber’s overpressure is extended when the amount of CF3I gas in the gas mixture is increased, which increases the velocity of the airflow. As a result, these factors significantly decrease the duration of the arc-extinguishing time.

Dynamic Behavior Analysis of Drilling String in Horizontal Section of Deep-Sea Gas Well

In this paper, a mathematical model of axial vibration of drill string near drill bit in horizontal well under natural gas is established considering the effects of gravity, load and fluid on drill string system. Based on the developed drilling string dynamic test platform, the axial vibration experiments of drilling string system under different gas content and gas flow rate are carried out. The experimental results show that the axial vibration of drill string is more serious and the vibration amplitude increases with the increase of air flow velocity and gas content.

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.

Active cooling of a photovoltaic module in hot-ambient temperatures: theory versus experiment

Abstract The performance improvement of a PV-module is investigated theoretically and experimentally in a long-term research-plan via module cooling by different approaches including passive, active, and evaporative cooling as well as water cooling for the same module. In the present paper, the investigation is conducted to decide on the suitability of active-cooling of the module in hot-ambient temperatures. A module without cooling is used as a base case for comparison against cooled modules with and without fins attached to the module’s rear-surface and extended down in an air-cooling duct underneath the module. At first, a theoretical study of heat transfer through the module is conducted to investigate how the calculated cell temperature and module output power are influenced by the air velocity from a blower, ambient temperature and solar irradiation. The results showed a decrease of cell temperature by about 7–10 °C with a subsequent increase of electrical efficiency. The cell temperature decreases significantly with the increase of duct height and with the increase of the number and length of fins, the same as in passive cooling. The cell temperature decreases by more than 3 °C at duct height of 0.2 m. The calculated values of cell temperature, open-circuit voltage and short-circuit current of the module with and without active cooling agreed reasonably with the present measured values over the day hours of two successive days in summer season. At air velocity of 1.5 m/s, the increase of electrical efficiency by active cooling was found 0.67–0.80 %. Further increase of air-flow velocity or duct-height in active cooling seeking higher efficiency is not recommended due to increase of consumed electric power by air-blower and limited decrease of cell temperature. This concludes that air cooling is not effective in regions of hot ambient temperatures. For a non-cooled module, the cell temperature is related to the ambient temperature in terms of the solar radiation and NOCT, the datasheet value of normal-operating-cell-temperature. The relationship is modified in the present paper to account for air-flow through the duct seeking its extension for application to air-cooled modules.

Numerical investigation of the effects of intake pipe deflection angles on the in-cylinder flow and vortex structures of a cycloidal rotary engine

Intake pipe structure has a pivotal impact on the distribution of vortices within the combustion chamber in a cycloidal rotary engine (CRE). Therefore, studying the influence of the intake pipe deflection angle (IPDA) on the in-cylinder airflow motion has significant importance for enhancing CRE performance. This study utilized computational fluid dynamics and chemical reaction kinetics methods to establish a numerical simulation model for the in-cylinder flow and combustion in the CRE. Subsequently, the Omega vortex identification method was employed to investigate the influence of IPDA on the vortex structures within the cylinder and to explore the relationship between CRE performance and the vortices. The research findings indicate that although the IPDA did not significantly alter the fuel mass injected into the cylinder, it increased the airflow velocity by 14.6% during the main intake stage and increased the mass fraction of the burned fuel at the compression top dead center by 19.1%. Additionally, the increased airflow velocity within the cylinder led to improvements in both the mean tumble ratio by 186.5% and the turbulent kinetic energy by 25.5%. Furthermore, the IPDA significantly changed the distribution of vortices within the cylinder, which is a key factor contributing to the combustion variation of the CRE. The case of IPDA = 16° provided the largest volume of the strong vortices and the highest mean in-cylinder pressure. Compared to the original design, the volume of strong vortices was 1323.6% greater, and the mean in-cylinder pressure was higher by 5.3%.

A novel model of a hydrogen production in micro reactor: Conversion reaction of methane with water vapor and catalytic

This study presents a comprehensive investigation of a thermally integrated membrane micro reactor for efficient hydrogen production through the conversion of methane with water vapor. The reactor design incorporates a catalytic Au/ZnO system to enhance performance. The effects of key operational variables, including inlet gas flow rate, pressure, temperature, water-to-methane ratio, and membrane thickness, were examined. Optimal conditions were sought to maximize methane conversion, hydrogen yield, and minimize carbon monoxide production. As feed flow increases, methane conversion decreases due to reduced retention time in the reactor. This decrease is almost six times greater at 240 °C than at 270 °C. Higher water-to-methane ratios improved methane conversion and reduced hydrogen and carbon monoxide production. Shell pressure affected methane conversion, with higher pressures resulting in decreased rates and carbon monoxide levels. As shell airflow velocity increases, methane conversion rises about 0.96 %. Tube pressure influenced hydrogen passage through the membrane, causing decreased hydrogen output from the tube section and increased output from the shell section, while reducing carbon monoxide emissions. These findings contribute to the optimization of a thermally integrated membrane micro reactor for efficient hydrogen production through water vapor-methane conversion.

Thermal energy storage with tunnels in different subsurface conditions

Thermal energy storage with tunnels in different subsurface conditions

Ignition limit of EPS foam by a hot particle under cross wind

The ignition of the building insulation materials by a hot particle is a typical spot fire phenomenon, but the scientific understanding is still limited. In this work, a hot steel spherical particle (6-16 mm and 800-1200 °C) was dropped onto the low-density expandable polystyrene (EPS) foam with an external airflow velocity of 0-4 m/s to obtain the ignition limit at the flash point and fire point. Airflow provides an alternative shortcut transition of unstable flash flame to a strong fire point and fuel burnout, because airflow increases the oxygen supply and flame heating rather than cooling the particle. As the airflow velocity increases, both flash and fire points first become easier to reach because airflow facilitates the mixing of pyrolysates and oxygen in the Smothering Regime. When the airflow velocity increases to the Thermal Regime, the delay time remains stable. Further increasing the airflow velocity to the Chemical Regime, the ignition delay time slightly increases until the airflow blows off the flash flame by cooling the particle or blowing away the flammable mixture from the hot surface. Such a competitive effect of airflow on hot particle ignition is also qualitatively verified by theoretical analysis. Flame retardants inside EPS foam do not change the flash ignition but inhibit the transition to fire point and burnout, even under the assistance of airflow. This work enhances the comprehension of the complex interactions between flash points and fire points in the spotting or hot-particle ignition of the building facades.

Thermal imaging and velocity measurements of the exhaled airflow in total laryngectomized patients during COVID-19 pandemic.

In patients after total laryngectomies, the trachea and the lung can be easily infected by SARS-CoV-2 because the respiration happens through the tracheostoma. The aim of our study was to examine whether patients with LaryTube™ can distribute aerosols to a greater extent than without LaryTube™, and to observe whether the surface of different protective instruments can be examined using the thermal camera in total laryngectomees. An important objective was also to confirm the assumption that the use of HME (heat and moisture exchanger) alone does not provide protection during COVID-19 pandemic. Finally, during our tests, we tried to get an answer to our assumption that the sample taken from the inner surface of the HME can be tested for SARS-CoV-2. A total of 23 patients who underwent total laryngectomies were analyzed by velocity measurements and thermal imaging with and without HMEs and laryngeal tubes, using different types of PPEs. COVID-19 PCR testing was performed on patient tracheas and the inner surfaces of the HMEs. Male patients with laryngeal tubes without HMEs demonstrated an increase in exhaled airflow velocity of more than 43% compared to male patients without laryngeal tubes; in female patients, the same value was more than 39%. Thermal imaging results confirmed that the lowest surface temperature was measured on FFP2 masks. The sent samples can be tested for SARS-CoV-2 using PCR, the presence of the virus was not detected. Laryngectomized patients without laryngeal tubes pose a lower risk for spreading viral aerosols due to the reduced velocity of the exhaled airflow caused by the absence of the tube as the narrowing factor. Patients with laryngeal tubes who undergo total laryngectomies during the COVID-19 pandemic should use HMEs with viral filter, if possible, also changing the laryngeal tubes to dermal adhesives for fitting their HMEs seems to be the best option. The surface of the used protective equipment can also be examined with thermal camera in the case of total laryngectomees. COVID-19 PCR testing of the tracheal secretion from the inner HME surfaces should become a routine in clinical practice if deemed necessary. Orv Hetil. 2023; 164(34): 1327-1336.

Combined influence of airflows and a parallel magnetic field on the discharge characteristics of AC dielectric barrier discharge

The combined influence of airflows and a parallel magnetic field on an AC-driven dielectric barrier discharge plasma is experimentally investigated through image analyses, electrical measurements, and optical diagnoses. After applying a parallel magnetic field, more discharge filaments are generated during one discharge cycle. Besides, the electrical and optical diagnoses show that the magnetic field can increase the plasma parameters, such as the electron temperature and electron density. When airflows and a parallel magnetic field are applied in combination, the discharge uniformity presented in the long-exposure images is significantly enhanced by the airflows and slightly improved by the magnetic field. With increasing airflow velocity, the distribution of discharge filaments goes through four phases, namely, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution, among which the stripe-like distribution exhibits the highest discharge uniformity. High-speed video analyses reveal that the improved discharge uniformity can be attributed to the changed breakdown positions and the increased number of filaments. Although airflow can significantly improve the macroscopic uniformity of the discharge, it leads to a decrease in the maximum current pulse amplitude, electron temperature, electron density, and gas temperature. Applying a magnetic field in flowing air can not only improve the discharge uniformity but also ensure that the discharge has high maximum current pulse amplitude intensity, electron temperature, and electron density. Based on the analyses of the electron trajectory and the estimation of the force condition of the micro-discharge remnants, the modulated charged particles, reduced electric field, and pre-ionization degree are responsible for the changed discharge uniformity and plasma parameters in the parallel magnetic field and flowing air.