Air Distribution Research Articles

Numerical simulation of indoor air distribution and wall heat storage under accident conditiohs in a main control room

The main control room serves as a refuge for staff in a nuclear power plant in the event of an accident. To determine whether the control room can meet habitability requirements under accident conditions, this study utilized CFD methods to establish a habitability model of the main control room under such conditions. The changing trends of temperature and velocity near personnel were analyzed. The numerical results indicate that the building envelope significantly contributes to reducing the indoor temperature. The average wall temperature measured at 72 hours was 27?C, with an average temperature increase of 4?C. The highest average ambient temperature in the main control room occurred at 24 hours. At this time, the indoor ambient temperature reached approximately 34.62?C, with a temperature increase of 11.62?C, while the wind speed near the personnel remained below 0.2 m/s, meeting habitability requirements for personnel under extreme conditions.

Reducing Indoor Air Pollution through Personalized Ventilation for Occupants in Office Environments and Confined Spaces

With the increasing focus on indoor environmental quality, driven by the growing amount of time people spend in enclosed spaces, this study presents an approach to enhancing air distribution in office environments and confined spaces. A novel low-induction air diffuser is designed to deliver fresh, clean air in close proximity to occupants while maintaining their thermal comfort. Clean, unpolluted air is pivotal to healthy and productive workplaces. Yet, this paper underscores the importance of not sacrificing thermal comfort in the pursuit of improved indoor air quality. Inadequate thermal comfort may lead occupants to deactivate ventilation systems, negating the benefits of improved air quality. Inefficient temperature control can also result in discomfort, distractions, and reduced productivity. The innovative low-induction air diffuser resolves this issue, enhancing air quality near occupants without causing thermal discomfort. By directing air gently and efficiently, this solution is prepared to transform personalized ventilation systems, mitigating the discomfort associated with traditional jet flows while delivering high-quality breathable air. This research serves as a bridge between improved indoor air quality and thermal comfort, for office environments. It introduces a practical, energy-efficient solution that satisfies the core requirements of a healthy workspace—clean air and comfortable conditions.

Comparison of Hexcore and Poly-Hexcore computational meshes in the aspect of air flow modeling based on the actual geometry of mining excavations

Discrete models are used in industry for many applications. In one of the most frequently used Finite Element Method (FEM) for Computational Fluid Dynamics (CFD) calculations, discrete models may be two-dimensional or three-dimensional. 2D models are used as a simplification to achieve satisfied results in the shortest computational time. 3D models, on the other hand, are used for more complex calculations. These models constitute a representation of real-world objects that have been appropriately simplified to make the calculations accurate and correct. The calculation time of a 3D model is significantly longer compared to a 2D model. For this reason, to reduce the calculation time, different types of simplifications and various types of discrete model meshes are used. In this paper, the authors made a comparison of two computational meshing technologies: Hexcore and Poly-Hexcore in the aspect of airflow modeling in mining excavations using CFD. The geometry considered in this case came from real-world excavations captured by laser scanning in the Gertruda Slant, Zloty Stok. Point cloud data was processed through feature extraction, which was subsequently utilized to create structured models of mining excavations. The results of the simulations show that taking into account such a diverse and complicated geometry and its significant lengths, reaching tens of kilometers, better results are obtained with the use of Poly-Hexcore mesh. This type of mesh allows simulations to be performed with similar accuracy in a shorter computation time. Utilizing a more modern type of mesh makes work more dynamic, which is of particular importance when conducting numerical simulations of air distribution in large and complex computational domains.

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.

Comprehensive modeling of ventilation systems for Nearly Zero Energy Buildings

In the present work, a lumped-parameter model of a multifunctional ventilation unit for residential applications was developed in the Simulink environment, also relying on the Simscape toolbox with Moist Air and Two-Phase fluid libraries. A simple, yet effective method to analyze and optimize the efficiency of the combined HVAC – air distribution system is proposed. To investigate the impact of boundary conditions on system performance, a parametric study of different installation conditions was also carried out, including outdoor air and indoor air temperature, humidity, static pressure, filter fouling, pressure drop in the intake and distribution ducts. The model highlights a strong decrease in the useful cooling/heating heat flow rate produced by the system as the installation and maintenance conditions become more challenging.

CFD analysis of existing Mobile Disinfecting Units (MDUs)

The global economy, well-being, and public health are all gravely compromised by COVID-19. Thus, MDUs have been created to reduce such dilemmas. This document contains a study of a mobile disinfectant unit (MDU) that will mitigate the virus’ spread. By using simulation tools, a final design will be an overall improvement derived from the three models exhibited to generate simulations. Certain significant parameters were noted in doing the simulation, namely: (1) Contamination Removal Effectivity (CRE); (2) Air Distribution Performance Index (ADPI); and (3) Local Air Quality Index (LAQI). These are the coefficients that measure the units' effectiveness in lessening the contaminant present in ambient air and maintaining air comfortability. With the following parameters considered, an optimized design has been conceived having promising CRE, LAQI, and ADPI values by employing fluid machines such as fans, exhausters, and misting systems. Solidworks' CFD simulation concluded a better CRE and LAQI on the designed model than the existing ones having values close to 1, while its output ADPI is around 34%. Moreover, from the AnSys CFD simulation, the coverage area of the misting was around 95%, compared to its predecessors. These numbers prove that the designed model is indeed an enhancement of its predecessors.

Experimental simulation study on gas flow field in combined goaf during the transition period of coal pillar-free working face relocation

Regarding the gas disaster caused by the complex ventilation system and the changeable flow field in the combined goaf during the transition period of the coal pillar-free working face, the self-designed physical simulation test bench for the combined goaf of coal pillar-free mining was used to compare and analyze the distribution law of wind pressure, gas, and oxygen concentration field in the combined goaf during the moving period of the working face and the normal mining period. The results show that during the relocation period, the gas concentration in the stope will always be slightly higher than that in the normal mining period, and the existing air leakage channel will lead to complex air flow in the combined goaf, which is easy to cause gas explosion accidents. The formation conditions, judgment principles, and judgment methods of the dangerous area of gas explosion coupling disaster in goaf are analyzed. By changing the air distribution ratio of the main and auxiliary air intake roadways, it is concluded that the explosion area will form an “L”-shaped explosion zone in the goaf, and the area of gas explosion disaster area during the relocation period will be larger than that the normal mining period. According to the size of the gas explosion area, the optimal air distribution ratio of the main and auxiliary air intake roadway during the transition period of the working face relocation and the normal mining period is 2:1. Under this air distribution ratio, the gas explosion area is the smallest, which is 132 284 and 113 534 mm2, respectively. The research results are of great significance to reveal the mechanism of gas disaster induced by goaf during the transition period of coal pillar-free relocation.

Direct numerical simulation of contaminant removal in presence of underfloor air distribution system

Indoor contaminant removal over 0.5 ≤ FrT ≤ 5.0, 0.5 ≤ N ≤ 5.0, and 50 ≤ Re ≤ 500 was investigated numerically, wherein FrT refers to the Froude number, N refers to the buoyancy ratio, and Re refers to the Reynolds number. As demonstrated, the ventilation effectiveness increased with increasing contaminant source intensity and air supply intensity at a constant air temperature, indicating that increase the fresh air can effectively eliminate contaminants in this case. At high air supply temperatures, the heat retention time and contaminant transport was extremely short, and the fresh air induced by strong natural convection floating lift was rapidly discharged. Additioanlly, the air supply intensity had significant effects on contaminant removal. Quantification of the ventilation effectiveness under the combined effects of air supply intensity, air supply temperature and contaminant source intensity was determined based on the results of direct numerical simulations.

Design and control of warehouse indoor air quality via numerical modeling

Warehouses are part of the crucial infrastructure of the logistics process of any business. The type of products stored in the warehouse also determines the type of warehouse class. The object of research in the present work is a class A warehouse with a clear height of 10 up to 13 m, equipped with systems for maintaining the indoor air quality within a very specified temperature limit. An air conditioning system is proposed, consisting of roof air conditioners (Rooftop vent), that allow maintaining the microclimate in the specified limits yearly. To achieve the specific requirements, numerical modeling of air distribution in the warehouse was performed, which shows that the use of simplified, systematized methods for the technical design of air conditioners is an unreliable approach. Moreover, the analysis shows that in high warehouses, the stagnant areas that arise cannot be overcome only by rearranging the roofing machines, but also requires the use of additional impulse mixing devices.

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

Experimental and numerical investigation of swirling flow on the conjugate cooling efficiency of an effusion-cooled combustor

Effusion cooling has been extensively employed in the liner thermal protection of modern combustors, however, its performance in swirling flow fields remains to be thoroughly investigated. This research aims to reveal insights into the effusion cooling characteristic across various swirl numbers (SN = 0∼1.21) and average blowing ratios (M‾ = 1.2–8.9) based on experimental and numerical approaches. Furthermore, semi-empirical engineering function equations for the area-weighted average cooling efficiency were compiled. The results show that inhomogeneity of the near-wall flow obstructs local effusion outflow, especially in the countercurrent side of the impingement zone, resulting in incremental flow heat transfer and disability in forming a cooling film. The increment of SN from 0.49 to 1.21 recedes the undermost level of conjugate cooling efficiency by an average of about 0.13, progressively impairs the cooling of the leading edge, and begets an ante displacement of the poorest cooling position from 0.43 to 0.31 (ratio of flow wise direction coordinate distance to flame tube dome height). Higher cooling air volume effectively strengthens the coolant effluent capacity to offer a more uniform distribution of cold air under swirl flow, and the overall conjugate cooling efficiency is enhanced by about 0.34 when M‾ increases from 1.2 to 8.9.

Subzone division optimization with probability analysis-based K-means clustering for coupled control of non-uniform thermal environments and individual thermal preferences

Collective air distribution is widely used for thermally comfortable indoor environments but is limited to unified thermal comfort requirements. Advanced collective air distribution has the potential to generate non-uniform thermal environments for individual thermal preferences. This study proposes a subzone division optimization method for nonuniform thermal environments to improve thermal preference satisfaction. The proposed method divided non-uniform thermal environments into subzones using probability analysis-based K-means clustering, minimizing and maximizing the thermal environment differences within and among the subzones, respectively. The number of subzones was determined to maximize thermal preference satisfaction with the coupled control between the nonuniform environments and individual thermal preferences while limiting the percentage of thermal discomfort. The results based on experiments of advanced collective air distribution, i.e., stratum ventilation, showed that thermal preference satisfaction and the percentage of thermal discomfort increased with an increasing number of subzones. Compared with the conventional method (i.e., uncoupled control without subzone division optimization) and recent method (i.e., coupled control without subzone division optimization), the proposed method improved the thermal preference satisfaction by 34.7 % and 11.7 %, respectively, for four subzones. Moreover, with the proposed method, increasing the system control flexibility increased thermal preference satisfaction. Compared with the variable air volume system, the constant air volume system and the system with variable supply airflow rate and temperature improved thermal preference satisfaction by 5.8 % and 22.5 %, respectively. The proposed method contributes to extending the capability of collective air distribution for individual thermal preferences.

Developing a Performance-Based Approach to the Effect of Roof Features on Fire Safety in Buildings with Atriums

Developing technology, changing social structures, and the threat of resource depletion have changed the design of buildings. Therefore, design approaches are developed to increase user comfort and reduce energy consumption by utilizing natural ventilation and lighting. The design of the distribution of outdoor air and light into the spaces through vertical and horizontal gaps reduces the energy demand of the mechanical systems and increases occupant comfort. The atrium is the preferred vertical gap in modern buildings for distributing natural air and light to interior spaces under appropriate conditions. However, in buildings with atrium, there is a risk of fire spreading in the event of a fire due to the uninterrupted gaps between the rooms. It is necessary to ensure the operability of the design by monitoring the measures to be taken in the early stages of design using performance-based fire safety methods. This study develops design strategies for fire analysis in atrium buildings using computational fluid dynamics (CFD) simulation technology. Atrium height, roof type, and slope characteristics are analyzed for the stack effect, which is the main factor in the movement of smoke and flames. As a result of the numerical analyses consisting of flat, unidirectional, and bidirectional sloping roof type, 10, 20, 30-degree roof slope, and one-meter rising atrium roof variables, the effect degrees for smoke dispersal and temperature control are investigated. Fire Dynamic Simulator, which uses CFD capabilities, and Smokeview software, which can visualize the results, were used for the numerical analysis. Correlation analysis was used to determine the effect of variables on temperature. The results showed that flat roofs and designs with increasing height were effective in delaying the spread of smoke and increasing the stack effect in the atrium, while the contribution of roof slope to fire safety was weak.

The Art of Diagnosis from Breath Sound: A Literature Review

Breath sounds provide relevant information related to lung abnormalities. It is often difficult to differentiate between breath sounds, this is due to the different characteristics of each breath sound. Differentiating the types of breath sounds is crucial in making an accurate diagnosis. Breath sounds are divided into normal breath sounds and abnormal (additional) breath sounds. Normal breath sounds are sounds that originate from the chest wall, such as tracheal, bronchial, bronchovesicular and vesicular breath sounds. Meanwhile, abnormal (additional) breath sounds are breath sounds that indicate an abnormal condition in the respiratory system. Normal and abnormal breath sounds have different characteristics such as intensity, duration, frequency, quality of air flow, air flow pattern, air distribution, body position, location of sound production, changes in pressure and vibration of dense tissue in the lungs.

Evaluation of the earth-air heat exchanger's performance in improving the indoor conditions of an industrial poultry house using computational fluid dynamics verified with field tests

This paper aims to investigate the performance of an Earth Air Heat Exchanger (EAHE) to improve the indoor conditions of an industrial poultry building after its installation, considering the optimal position and installation configuration (separate or collected inlets), which have not been addressed previously. In this regard, an industrial broiler house containing 20,000 chickens equipped with four cooling pads operated by a mechanical ventilation system located in Biskra, Algeria, was simulated with six scenarios, including the original. The model developed is verified with the field test measurements and experimental and numerical data in the literature. The results showed that optimizing the cooling pad position increases average indoor air temperature and velocity distribution by 0.1% and 8%, respectively. Moreover, the position and configuration of installing the EAHE inlets play an important role in uniforming indoor air distribution. Scenario 3, with 80 EAHE inlets versus exhaust fans, has the best indoor air uniformity, with a maximum velocity and temperature difference between its sections of 1.15 m s−1 and 1.4 K, respectively. Overall, EAHE showed a good ability to cool and maintain appropriate indoor air temperatures, achieving a difference of 15 °C between inside and outside, in addition to providing annual energy savings of 921,600 kWh/year and reducing 30,643 tons of CO2 emissions during its lifespan, in contrast, its simple payback time estimated 4 years.

CFD-based multi-objective optimization of indoor air quality and thermal comfort in a classroom

Comfort conditions and air quality in educational buildings can affect students’ performance, achievement and productivity, but they can also threaten their health. In this study, a sample classroom in Trakya University, Edirne, which lacks a ventilation system, is discussed. Depending on the determined parameters, an optimization study was performed using computational fluid dynamics. Predicted mean vote (PMV) for general thermal comfort, draught rate (DR) for local thermal comfort and the carbon dioxide (CO2) level for indoor air quality are selected as target functions. Outdoor air temperature, heating/ventilation system, insulation thickness, number of people in the classroom and clothing factor were identified as parameters that could affect the target functions. According to the numerical results, the rank of importance of the parameters affecting the target functions was calculated using the Taguchi method. The effect percentages of the parameters were determined using the analysis of variance. Then, all target functions were optimized with the grey relational analysis. The best case obtained as a result of the optimization has PMV, CO2 and DR values of −0.12, 511 ppm and 5.37%, respectively. When the general results are evaluated, a comfortable and healthy environment is provided in the classroom with the underfloor air distribution system operating at 100% fresh air and a reduced number of occupants.

Numerical evaluation and optimization of air distribution system in a small vertical farm with lateral air supply

An appropriate design for air distribution systems is crucial for achieving optimal and uniform growth conditions while reducing energy costs in vertical farms. This study employs steady computational fluid dynamics (CFD) simulations to investigate the influence of several key design parameters of air distribution systems in a small generic vertical farm with a lateral air supply. The simulation results reveal that an air supply orifice of reduced dimensions, positioned proximally to the LED lamps, coupled with an exhaust mechanism integrated into the corridor ceiling, proves most effective in removing the excess heat generated by the LED lamps. Moreover, enhanced uniformity in air distribution is attained by positioning the air supply closer to the LED lamps, utilizing larger orifices, and eliminating the corridor space. In contrast, the vertical distance between the lateral air exhaust orifices and the cultivated regions is found to have a negligible effect.

Justification of the air distribution system of a down-the-hole hammer with an efficient operating cycle

One method for conserving energy in the mining industry and ensuring the required pressure of compressed air in underground mining networks is to decrease the specific energy carrier consumption, particularly in the case of down-the-hole hammers. The objective of this study is to substantiate the air distribution system of an air hammer, aimed at reducing the specific consumption of compressed air. We propose a system consisting of two chambers with a constant supply of compressed air, two controllable chambers, two elastic valves on the hammer, and a valve for cutting off the supply of compressed air to the forward stroke chamber, which is controlled by the hammer’s position. This proposed configuration was employed to create two different designs for the air hammer. The operational cycle of the designed device has been numerically examined using SimulationX software and validated through experimental testing on a laboratory bench. Our calculations reveal that the suggested air distribution system, featuring controlled inlet to the backward stroke chamber, successfully achieves the stated objective. In comparison to the standard M29T hammer with nearly identical dimensions, striking power, and compressed air consumption for cleaning the borehole, the designed hammer exhibits a 53% reduction in specific energy consumption, and its electrical power usage for compressed air supply is halved. These design specifications align with both experimental results and data derived from the existing literature, confirming the accuracy of our calculation.

Aerial withdrawal: An atmospheric reading of Monika Maron's Flugasche

AbstractIn Monika Maron's Flugasche (1981)—the first novel from the GDR to deal with environmental issues—the poisoned atmosphere in the city of B. functions as an affective centre, around which emotions, actions and reactions of the main protagonist as well as of the other characters revolve. The journalist Josefa Nadler falls into the sphere of the environmental catastrophe and is overwhelmed by the atmospheric power of this meaningful situation. The corporeal experience of being exposed to subtle environmental violence, which has devastating consequences for the city of B. and debilitating effects on its inhabitants, evokes feelings such as fear, anger, shame and compassion. Moreover, it develops into a driving force for thoughts, decisions, commitment and resistance against the unfair air distribution, accompanied by a sense of powerlessness. The aim of the article is a re‐reading of the novel with a central focus on the largely non‐representational, affective and meteorological elemental spacetimes, which can not only be felt or bodily experienced but also designed or engineered in order to produce a certain time‐bound structure of feeling, for example, an oppressive climate of fear.

DEVELOPMENT OF ENERGY-EFFICIENT AIR DEDUSTING

Among the sources of internal pollution one can point to dust, breath products of passengers, various emissions from finishing materials of trains and metro stations, etc. This problem is usually solved in two ways: wet cleaning of tunnels and stations and using powerful tunnel vacuum cleaners. Both of these methods have common disadvantages. Firstly, dust removal can only be carried out at night, when there are no trains on the line. Secondly, the dust removal installations themselves are expensive and are effective only at low speeds of dust movement through the tunnel. All metros in the world have a problem with dust removal. Research methods include analytical and computational studies of air distribution in the metro ventilation network using mathematical modeling methods using graph theory and flow algorithms, as well as experimental studies of air flow parameters in natural conditions of the Almaty metro.This article proposes an innovative method for dust removal of tunnel air based on the use of piston action of trains and labyrinth filters installed in station ventilation joints. The parameters of the calculation model of the metro line are substantiated on the basis of a decomposition approach to the mathematical modeling of aerodynamic processes by moving from a linear model of the metro line to a periodic open-loop model. Computational aerodynamics methods were used to determine the patterns of changes in air speed through the ventilation vent and the available pressure drop depending on the speed and mode of trains passing through the station.