Airflow Conditions Research Articles

Probability density distributions of morphological parameters of barchan dunes and their responses to the climate environment

Barchan dunes are a common aeolian geomorphology in sand seas on Earth and Mars. They occur primarily as barchan dune groups. Obvious regional differences occur in the size distribution of dune swarms in different dune fields because of sediment grain size, regional airflow, sand flux, and surface conditions. To explore dune size distributions in different barchan dune fields and clarify the effects of climate on barchan dune morphometry, we used high-resolution remote sensing images and extended time-series meteorological data. Barchan dune fields were located in the southeast edge of the Taklimakan Desert, the western and southern parts of the Qaidam Basin Desert, the Gonghe Basin Sandy Land, and the sand belt connecting the Badain Jaran Desert and the Tengger Desert. Our results revealed the probability density distribution of morphological parameters of barchan dunes, correlations among parameters, and responses to wind regime. The main conclusions are: (1) Probability density distributions of the lengths of windward and lee slopes, the lengths of the two horns, and the dune width, height, and spacing in different deserts followed a log-normal distribution function. (2) Good correlations were found among the dune morphological parameters; width and height, windward slope length and width, and height and spacing showed positive proportionality, and the basal area and the product of width and height were linearly correlated in a double logarithmic coordinate system. (3) Good correspondence was found between dune asymmetry and regional wind conditions, which can be explained by Tsoar's model. Morphological parameters of barchan dunes were linearly and positively correlated with the drift potential. These results provide essential data for further study of the morphological thresholds for dune-dune interactions and elucidation of the mechanisms of interaction among barchan dunes.

Experimental Study on Atomization Characteristics of Swirl Nozzle under Annular Airflow Impingement

Pressure nozzles are widely used in spray drying and other industries. In order to improve the atomization characteristics of pressure cyclone nozzles, a new type of annular jet gas impingement atomization device is developed. We use high-speed imaging and digital image processing and other methods to analyze the spray characteristics of the different annular device configurations (using four, six, and eight tubes) and under different gas–liquid mass flow rates. It is shown that with an increase in the Air–Liquid mass Ratio (ALR), the liquid film breakup process changes from undulating sheet breakup to perforated sheet breakup and the breakup length decreases. The breakup length decreases the most under the condition of six-tube airflow with the range of 31–55%, while the Sauter mean diameter (SMD) basically does not change. With the increase in ALR and the Weber number of liquid (Wel), the droplet size distribution becomes more uniform. The spray characteristics of the atomizer assisted by gas jets reaches the best state when Wel = 4596.3 and m˙g = 1.97 g/s. The experimental conclusions have some guiding significance for the design and optimization of the atomization devices in spray drying towers.

Impact of two stage evaporative cooling system using underground water powered by PV panels on improving the thermal comfort of emergency relief tents in dry-hot climate regions

People are often forced to leave their homes owing to several reasons, such as natural disasters and conflicts, and in these cases, speed and cost are critical factors in saving millions of souls. Therefore, relief tents are the best solution in these situations. However, the internal environment of these kinds of tents might be uncomfortable, especially on hot or extremely cold days. Evaporative cooling systems are one of the simple and inexpensive techniques used to improve thermal comfort in a variety of applications, including agricultural, industrial, and residential. For this reason, the present work aims to investigate experimentally the impact of utilizing a two-stage indirect/direct evaporative cooling system using underground water driven by photovoltaic panels on improving the thermal comfort conditions within the relief tent. The experiments were conducted during the summer season of 2022 under different parameters, including the cellulosic pad thickness and the water volume flow rates in direct and indirect cooling stages. The results showed that the used evaporative cooling system improved the thermal comfort conditions inside the tent model, with an indoor daily average temperature reduction of about 12.4–14.8 °C in comparison to the standard tent model. Furthermore, the study outcomes revealed that, due to the remarkable impact of the extra heat exchanger in the indirect cooling stage, the proposed cooling system may offer airflow conditions inside the thermal comfort zone even without utilizing the direct cooling stage.

CFD simulation of a forced draft biomass cookstove for different airflow conditions

Households in developing countries rely on traditional cooking methods despite low-efficiency and high risks of air pollution and health. Various improved biomass cookstove technologies have been developed to address this issue, but there is still room for improvement in biomass cooking technology. This research aims to enhance the biomass cookstove by investigating its performance under different air inlet conditions using computational fluid dynamics analysis. The impact of air flow rate and the position of the secondary air inlet on the thermal efficiency of the biomass cookstove is examined. The eddy dissipation combustion model and k-epsilon turbulence model are utilized in ANSYS Fluent to simulate the combustion process. The cookstove's performance is assessed at three different air flow rates (0.01, 0.02, and 0.03 kg/s) and at two different secondary air inlet positions. The highest thermal efficiency is observed at secondary air inlet located 50 mm below the outlet at a flow rate of 0.03 kg/s. The computational findings from this investigation show a significant connection between the air inlet conditions and the thermal efficiency of the biomass cookstove. Repositioning the secondary air inlet to a location with more available space for complete combustion improves thermal efficiency compared to traditional designs.

Analysis of constituent factors affecting the state of dedusting of aspiration emissions

A significant part of industry is occupied by technology that is involved in the processes of manufacturing products, for example, sanitary ware factory, foundry, chemical or sugar industry. At such enterprises a large amount of dusty air is generated, which comes from various technological processes. Dust and gas collecting devices are used to purify dusty air. Depending on the state of dust and air flow, its fraction, dust dispersion and the method of collection, different aspiration devices are used. Aspiration devices are divided by the method of dust collection into wet or dry. Each of these types of aspiration devices has its own advantages and disadvantages, which are discussed in this article, such as increased aerodynamic or hydraulic resistance, regeneration of the device, the size of the trapped fraction, the need to use flushing fluid, etc. The classification of plant types for selection to a specific process or needs depends on the most efficient method of collection, particle dispersion and energy efficiency of the dust collector. Wet dust collectors have more diverse forms, designs and applications than dry dust collectors. Wet dust collectors are divided into groups depending on the state of the liquid phase (devices in which dust deposition occurs on a film of liquid, foam devices, turbulent dust collectors or condensation devices) and on the method of dispersion of the liquid (nozzle scrubbers, devices in which crushing is carried out due to the energy of the gas-air flow or dynamic gas washers). In this article, the designs and operating features of various wet dust collectors of each of these groups are considered in accordance with their characteristics of dust collection, liquid flow rate and design shortcomings. On the basis of the works of a number of researchers, the characteristics of the fractional degree of air purification from dust are graphically presented to determine the most effective apparatus for capturing fine fractions. The conclusions are made and further tasks and plans for conducting the necessary experiments and analysis of the data of scientists' works are set.

Wind Tunnel Characterization of a Graphene-Enhanced PEDOT:PSS Sensing Element for Aircraft Ice Detection Systems.

This study details the development and validation of a graphene-based ice detection system, designed to enhance flight safety by monitoring ice accumulation on aircraft surfaces. The system employs a semiconductive polymer (PEDOT:PSS) with graphene electrodes, interpreting resistance changes to detect water impact and ice formation in real time. The sensor's performance was rigorously tested in a wind tunnel under various temperature and airflow conditions, focusing on resistance signal dependency on air temperature and phase change. The results demonstrate the sensor's ability to distinguish water droplet impacts from ice formation, with a notable correlation between resistance signal amplitude and water droplet impacts leading to ice accretion. Further analysis shows a significant relationship between air temperature and the resistance signal amplitude, particularly at lower temperatures beneficial to ice formation. This underlines the sensor's precision in varied atmospheric conditions. The system's compact design and accurate detection highlight its potential for improving aircraft ice monitoring, offering a path toward a robust and reliable ice detection system.

A new sensor configuration design method for source term estimation in urban neighborhood with complex conditions under different wind directions

When hazardous substances leak into the atmosphere, Source Term Estimation (STE) can quickly determine the information of the leaked substance to control the threat of the leakage event to the environment and public safety. Reasonable sensor configuration is the foundation of STE. Existing sensor configuration schemes have limited applicability in STE processes. When urban neighborhood has complex building structures and airflow conditions, there is a lack of a method that can provide reasonable sensor configurations to ensure good STE performance. In this study, a new sensor configuration design method is proposed, which weights the joint entropy of adjoint concentration information of multi wind directions to obtain the cost function, and then uses Simulated Annealing (SA) algorithm to minimize the cost function. This article selects a real complex urban neighborhood for simplified modeling, and designs the optimal sensor array for it. STE results of several leakage scenarios are compared with the optimal and uniform sensor configurations at different leakage locations and wind directions. Compared to traditional uniform sensor configurations, the optimal sensor configuration has significantly improved estimation performance in both source location and strength, with a reduction of 27 %–51 % in the bias of source location identification and 17 %–39 % in the bias of source strength estimation.

Developing and operating unit‐type green parklets for parking lots in urban area—Part 1: Development and experimental study of unit‐type green parklets

AbstractAiming to improve thermal environment for outdoor public spaces, the author had been developing a unit‐type green parklet for parking lots that both introduce greenery into cities and produce walkable urban spaces. In this study, the author examined and created a full‐size unit‐type green parklet, installed it in a parking lot adjacent to sidewalk space next to a bus stop in the traditional urban area, Kyomachi district, of Kumamoto City, and investigated the improvement to summer thermal environment from a field measurement and its usage by people from user survey in summer (from August 30 to September 5, 2022). The results showed that although the parklet shaded with the parasol and greening units, air temperature dropped by only a maximum of 1°C in daytime. Given the characteristics of parking lot as a location, it was confirmed that not only the wind and airflow conditions was blocked and worsened, but reflected solar radiation from the surroundings and generated heat from parked cars degraded air temperature and MRT from the field measurement. Furthermore, it was confirmed to be ensured the visibility of the surroundings when sitting on the parklet bench for the users waiting for a bus from user survey.

Experimental assessment of low temperature plasma devices for bacterial aerosol inactivation in the air duct of HVAC systems.

In light of growing concerns about indoor air quality and the transmission of pathogens, this study aims to evaluate the effectiveness of low temperature plasma (LTP) devices in inactivating bacterial aerosols in the air duct of HVAC systems, exploring methods to enhance air purification efficiency. This research employed experimental methods to explore the deactivation effects of LTP on common bacteria such as E. coli and Bacillus subtilis, focusing on the role of air parameters such as the airflow rate, relative humidity, and temperature in influencing the device's performance. Notably, the study determined that an operational voltage of 3000 V for the LTP device, combined with conditions of low airflow, low humidity, and high temperature, significantly enhances the inactivation of bacterial aerosols, achieving an 82% inactivation rate at a negative ion concentration of 2.4 × 1011 ions per m3 and a wind speed of 3 m s-1. Despite the generation of ozone and ultraviolet light as by-products, their concentrations were found to be within safe limits for human exposure. In addition, this study identified an effective inactivation range, alongside an optimal arrangement for the airflow direction within ducts, to maximize the sterilization efficiency of the LTP device. Given these promising results, the study advocates for the integration of LTP technology into the air duct of HVAC systems of public buildings to improve air quality and reduce the risk of airborne disease transmission.

Numerical Simulation of Air Distribution in a Wide Chute

Abstract Desirable conditions of airflow should be provided for spillway chute aerators in two-phase air-water flow, especially in large-width chutes. There is no general approach to determine air entrainment, concentration distribution, and submergence along a chute introduced by an aerator shaft. The two-phase air-water modeling of Gavoshan dam in Iran as a case study of chute flow, its aerator, and the characteristics of flow into the cavity formed below the jet have been numerically investigated, and the results obtained have been validated against the laboratory experiments. The hydraulic parameters of the cavity and aerator shaft were determined to evaluate their performance and emphasize the importance of a proper aerator design. Sections with a greater distance from the bottom of the chute exhibit higher pressure magnitudes, while the mean air concentration values in the cavity are smaller in sections close to a ramp. Higher water discharge, lower pressure head in sections near the bottom of the cavity, and lower air concentration in sections near the ramp into the cavity increase the probability of cavitation occurrence.

Ignition mechanism of near α high temperature titanium alloy

The risk of titanium fire increases significantly with the development of future aero-engine, however, the burning mechanisms of titanium alloys remain uncertain. Therefore, the ignition behavior and mechanism of near α high-temperature titanium alloy are studied in this work by an integrated experiment method, including laser-oxygen concentration ignition method, infrared temperature measurement and observation of molten metal by high-speed camera. Based on this, the ignition boundary curve is determined and the ignition temperature of the alloy is found to decrease from 1595 to 1527 ℃ with the laser power increasing from 200 to 325 W and oxygen concentration increasing from 21% to 60%. The ignition microstructure is characterized by FIB and TEM to study the evolution of reaction products. Pores are found to form beneath the TiO<sub>2</sub> surface layer, which can be attributed to the instablity of TiO. The failure mechanism of protective oxide layer is further analyzed according to the thermal stress caused oxide layer damage model. When the temperature approaches the ignition temperature, which is below the melting point, the high vapor pressure of TiO leads to the formation of porous defects beneath the TiO<sub>2</sub> surface, thus accelerating the fracture and failure of the TiO<sub>2</sub> layer under thermal stress. It is revealed that critical conditions of temperature and instantaneous temperature change rate are needed to realize ignition. Based on this, an ignition model is further constructed to discuss the relationship among ignition temperature, laser power and oxgyen concentration. According to the experimental data fitting, the reaction activation energy of TA19 alloy during the ignition stage is calculated to be about 280 kJ/mol, and the function for calculating ignition temperature is given as follows: <inline-formula><tex-math id="M2">\begin{document}$ 1.2 \times {10^{10}}{{\mathrm{e}}^{\frac{{ - 280000}}{{R{T_{{\text{ig}}}}}}}}{c^{\frac{1}{2}}} + $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2.png"/></alternatives></inline-formula><inline-formula><tex-math id="M2-1">\begin{document}$ 0.52{P_{\mathrm{L}}} - 315 = 0 $\end{document}</tex-math><alternatives><graphic specific-use="online" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2-1.jpg"/><graphic specific-use="print" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="8-20240003_M2-1.png"/></alternatives></inline-formula>. This provides a theoretical reference for predicting the ignition temperatures of near α high temperature titanium alloy and other types of titanium alloys under complex airflow conditions in aircraft engines.

Effect of Lateral Airflow on Initial HSI and Flame Behavior of Marine Fuel in a Ship Engine Room: Experiment and Analysis

The flame behavior of engine fires, such as those caused by leaked fuel coming into contact with an ignition source, is significant in practical applications, where flame detection is used to minimize the damage of the attendant ship fire safety problem. In this work, the flame behavior of hot-surface ignition (HSI) under crossflow was studied, with a particular focus on the difference in lateral airflow velocities for HSI-driven flame deviations at the windward and leeward sides of a ship engine room; a problem such as this has not previously been quantified. Full-scale experiments were conducted in a ship engine room using marine diesel and hydraulic oil as the fuel, and by adopting lateral airflow with the velocities of 0 m/s, 1.0 m/s, 3.0 m/s, and 5.0 m/s, together with an HSI mechanism consisting of marine diesel and hydraulic oil coming into contact with elevated hot-surface temperatures. The results show that the effects of disturbing the combustible gaseous mixture for marine fuel HSI, at both the windward and leeward sides, strengthened as the airflow velocity increased. The HSI position of the leaked marine fuel in the engine room was strongly dependent on ventilation, while that under the airflow condition decreased with the increase in the hot-surface temperature. A model was proposed to characterize this difference on the basis of the HSI height, which was defined as the ratio of the height during the initial HSI to the stationary period. The results indicate that the scale of the flame gradually increased in the horizontal direction, which was significantly different from the result in the scenario without mechanical ventilation. The results also revealed that the fluctuation of hydraulic oil through the temperature field was significant and lasted for a long time under a low HSI temperature.

Performance study of a thermochemical energy storage reactor embedded with a microchannel tube heat exchanger for water heating

Thermochemical energy storage (TCES) provides a promising solution to addressing the mismatch between solar thermal production and heating demands in buildings. However, existing air-based open TCES systems face practical challenges in integrating with central water heating systems and controlling the supply temperature. To overcome these limitations, a novel water-based TCES-HEX-HRU system is proposed in this study, which integrates a water-to-air microchannel tube heat exchanger (HEX) and an air-to-air heat recovery unit (HRU). A comprehensive evaluation of the TCES-HEX-HRU system is conducted numerically using a COMSOL model, including a comparative assessment for different TCES system configurations. The results demonstrate that the TCES-HEX-HRU system achieves an overall thermal efficiency of 82.35 %, marking a substantial 69 percentage points improvement over the TCES-HEX system. Although slightly lower than the typical air-based TCES system without HEX and HRU by 15.44 percentage points, the TCES-HEX-HRU system can be a practically promising and viable choice for applications in central heating systems. Numerical investigations indicate that the thermal performance of the system is influenced by the inlet conditions of airflow and waterflow. Moreover, increasing the number of water channels in the HEX of the TCES-HEX-HRU system enhances heat transfer but reduces the amount of heat released by TCES composite materials, resulting in a maximum overall thermal efficiency of 92.09 % with 35 channels and a peak outlet water temperature of 33.67 °C at with 30 channels. However, further increases in the number of channels lead to a decline in overall thermal efficiency and outlet water temperature. Changes in the width of water channels in the HEX have a minor impact on the highest outlet water temperature and overall thermal efficiency, while affecting the volume of the TCES composite materials.

Analysis of Gas Turbine Combustor Exhaust Emissions: Effects of Transient Inlet Air Pressure

Gas turbine combustors are often subjected to combustion instabilities because of variability of operating conditions, affecting components, and altering exhaust emissions. Herein, the analysis focuses on simulating numerically the non‐premixed combustion as unsteady flamelet combustion and detailed kinetic mechanism. The goal is analyzing exhaust gases under unsteady inlet airflow conditions to define operation guidelines. The numerical approach is validated using data from the literature for nonperturbed cases. Three periodical perturbations of different amplitude show differences with the nonperturbed case. Besides emission of exhaust gases, the temperature field is sensitive to airflow inlet conditions. According to the simulation results, a strong dependence of temperature and pressure in primary and dilution zones of combustor exists on the inlet air pressure condition. Emissions of flue gases like CO and NOx respond to combustor thermal behavior showing high sensitivity to inlet air pressure as well. Results indicate that moderate pressure oscillations may derive into flashback effects.

Effect of swirl-spray impact on the comprehensive performance of uniflow-scavenging opposed-piston engines

Uniflow-scavenging opposed-piston (USOP) engines exhibit high thermal efficiency and power density. However, the USOP engine has a continuous in-cylinder airflow state between different cycles, which affects direct injection oil spray distribution. The USOP engine nozzles were mounted on a cylinder liner. The forward and reverse impacts of the in-cylinder swirl differed in the asymmetric orifice layout. A dual-intake channel USOP simulation model was established. The key parameters of the simulation model were verified, and the effects of forward and reverse impacts under different nozzle layouts and swirl strengths were analysed by simulation. The results show that all swirl-spray impacts benefit the combustion. Swirl-spray impacts can effectively improve the oil spray distribution and atomisation. In addition, reducing the swirl in the next cycle concentrates the exhaust gas in the cylinder centre, improving the scavenging efficiency. Forward and reverse impacts enhance and weaken the in-cylinder swirl, respectively. However, the effect of the reverse impact was more pronounced than that of the forward impact.

RATIONAL CONTROL BY TEMPERATURE IN VORTEX ENERGY SEPARATOR UNDER DESTABILIZING EFFECTS

The focus of this study is the arrangement of a rational control technique used to maintain the airflow temperature in a vortex energy separator (VES) under destabilizing effects. The objectives include the development of tools for the rational control of temperature in the cold and hot air flows of a VES. Methods used: Discrete state space, production rule statement, resolution of two-valued predicate equations, dichotomous trees, diagnosis, and recovery of dynamic objects. Problems settled: the studied features of the vortex energy separation process, architecture, and operation links of the rational control system were considered, mathematical models were deduced, and tools for diagnosing and recovering the efficiency of the vortex energy separator as a rational control object were developed. The scientific novelty of the study lies in the formation of instrumental tools to provide rational control of the airflow condition in the VES, where the control object is subjected to the substantial influence of various destabilizing effects.

Experimental Study on Sleep Quality in Naturally Ventilated Rooms under Moderate Climate Conditions

Optimizing the thermal environment of a bedroom is desirable for good sleep. In moderate climatic conditions, natural ventilation is a viable method for enhancing the quality of sleep by improving indoor air conditions. This study examined the effects of air temperature and wind speed on sleep quality in naturally ventilated rooms with windows open and closed, during autumn. Thirteen young males in healthy conditions participated in this study. Two adjacent test rooms (for opened and closed conditions) were selected on a university campus, with standardized indoor conditions. Air temperature and wind speed were measured near the height of the participants’ heads. Sleep efficiency and wake after sleep onset (WASO) were calculated using physiological wearable sensors based on heart rate and body movement. The participants completed questionnaires on thermal sensation and comfort before and after sleep. The results showed that the lowest percentage of WASO was observed when the nocturnal mean temperature was 23–24°C with a quadratic regression curve regardless of the window opening conditions. Conversely, subjective sleep satisfaction and WASO did not show any significant differences between the conditions. The results revealed no significant impact of varying thermal and airflow conditions during autumn on thermal/airflow comfort, although significant differences were observed in the thermal/airflow sensation before and after sleep. Thus, these results suggest that natural ventilation through the opening of windows might not affect thermal/airflow comfort, while a nocturnal indoor air temperature of 23–24°C is recommended for good sleep and thermal comfort, regardless of window opening conditions under moderate climate conditions.

The Online Identification of the Behaviour of Pollutants inside the Tunnel Tube

A tunnel tube is a relatively small space that allows for the accumulation of gaseous and liquid substances containing harmful substances. Given this fact, a ventilation system is the most critical component of a tunnel’s technological equipment, greatly influencing its reliability and safe operation. The dynamic behaviour of pollutants in the tunnel tube is characterized by a significant stochastic component and changing parameters over time due to pressure, airflow, and atmospheric condition changes. This work addresses the issue of modelling individual parts of the tunnel tube for optimal tunnel ventilation control. It is necessary to create a model of a controlled system that is used for predicting process variables to calculate optimal control action. By using recursive identification methods in conjunction with a predictive controller, the proposed concept can be applied to numerous similar applications.

Numerical simulation of the particle wall mass transfer rates on rough surfaces confining turbulent natural convection flows

We performed numerical simulations of the particle mass transfer rates on the horizontal and vertical thermally active rough walls confining a turbulent natural convection flow. We considered the air flow conditions in a cubical cavity (L=1.22m, Ra=5.4·108, Pr=0.71) with two opposed pairs of consecutive walls at different temperatures, for which measurements of the particle deposition velocities are reported in the literature. The simulations were carried out by solving the momentum, thermal energy and particle mass transfer equations using a series of two-dimensional computational cell units to determine spatial evolution and development of the particle concentration boundary layer in the vicinity of hot and cold rough walls. Different flow conditions, wall orientations, sizes of roughness elements, particle diameters and temperature increments between the wall and the bulk fluid, typically found in indoor environments, have been considered and consequently, results can be used to estimate the particle deposition rates in real scenarios. At large mass transfer particle Péclet numbers, corresponding to spherical particles with diameters of 0.5–1 μm, the wall mass transfer rates of particles on rough textures typically increase by a factor of about 3 in comparison with the deposition on smooth surfaces. The thermophoretic effect significantly decreases the particle deposition on hot surfaces and increases it on cold surfaces, especially at large particle Péclet numbers. The numerical predictions of the deposition velocities are in good agreement with the measurements reported in the literature for the same flow conditions considered.

Potenential for thermal energy from Tunnels beneath Manchester and Crewe: a case study

potenential for thermal energy from Tunnels beneath Manchester and Crewe: a case study