Distribution Of Tracer Gas Research Articles

Ventilation efficiency and improvements for displacement ventilation systems during heating: A case study of a ward with vertical induction units

This study investigates the ventilation mechanism and effectiveness of a displacement ventilation (DV) system under heating conditions. A method to maintain ventilation efficiency by indirectly achieving DV was proposed. A four-bed hospital ward with prototype wall-mounted induction units (IUs) and ceiling exhaust served as the case study. Full-scale experiments assessed indoor temperature and tracer gas distribution, adjusting parameters such as cubicle and window curtains, window heaters, and window heat loss. Results showed that while the vertical temperature gradient was established, downdrafts near windows disrupted DV's stratification, leading to quasi-displacement ventilation with a normalized contaminant concentration of around 0.7 near patients. To counter this, using curtains to limit air exchange between the near-window and near-bed spaces effectively prevented the horizontal movement of contaminants toward the window. This allowed the downdraft to remain clean and diffuse along the floor, thereby reducing the normalized concentration to approximately 0.3–0.5 b y indirectly achieving DV. CFD numerical studies further examined this method under varied temperature conditions and airflow patterns. Additionally, the infection risk in this ward was evaluated for reference, showing that indirect DV can reduce infection probability by one-third compared to quasi-DV. Moreover, window heat loss valued at 50–100 W/m2 achieved the best ventilation, while smaller values generated insufficient downdraft to achieve indirect DV and larger values resulted in high floor-level velocity that accelerated contaminant dispersion.

Performance of all-air wall induction unit for displacement ventilation in a four-bed hospital ward during the cooling period

The existing induction air-conditioning system faces ventilation shortcomings and condensation risks. We developed an all-air wall induction air terminal unit (wall IU) that doesn't require reheating and eliminates water pipes to address condensation. Moreover, with modifications to its supply method, it can achieve displacement ventilation (DV) in an adiabatic environment. However, the real-world performance of this system needs to be further confirmed. This study examines wall IU performance during the cooling period. A full-scale experiment was conducted in a room furnished as a four-bed hospital ward with an outdoor climate chamber (OCC) to simulate summer conditions. IU's cooling and ventilation performance was evaluated by examining steady-state temperatures and tracer gas distributions. Moreover, CFD simulations to reproduce the experiment were performed to supplement the results. Patients' thermal comfort and infection risk while cohabiting with an infected individual were estimated using detailed temperature, airflow, and concentration data from an experiment-based CFD analysis. Furthermore, the DV stratification height under various perimeter heat loads and performance comparison between wall and ceiling-mounted induction units were also studied. In conclusion, the wall IU improved ventilation efficiency by achieving DV under cooling supply conditions. Satisfied thermal comfort is ensured based on ADPI and DR evaluation. DV's stratification height can be kept high enough under a 20 °C equivalent temperature difference when using a single glass window or more after thermal insulation enhancement. Compared with ceiling-mounted induction units, wall-mounted units can reduce infection risk by more than double while making cold drafts less noticeable.

Heating and ventilation performance investigation of a novel linear slot diffuser with adaptive outlet area for near window applications

The linear slot diffuser has ideal cooling performance for near-window applications, and is used for ventilation by utilizing the coandă effect in some cases. However, it has insufficient throw distance due to buoyancy impact during heating periods. And airflow near window surfaces increases convection heat transfer, resulting in extra HVAC energy consumption. Our research focuses on a prototype linear slot diffuser with an adaptive outlet area. Two deflection panels are installed for adjusting the outlet area depending on temperature or usage scenarios. Supply air has a low velocity and wide diffusion range when the panels are open. It can utilize the coandă effect as well as keep convection heat transfer within an appropriate range. Closing the panels will halve the supply area and completely change airflow diffusion and turbulence characteristics. This is considered suitable for heating, but the mounting location needs to be re-evaluated. Therefore, this prototype's heating and ventilation performance is numerically investigated using a low-Reynolds number turbulence model with fine meshes. Temperature, airflow, tracer gas distribution in a typical office space, and the ADPI, DR, and age-of-air indexes are compared before and after outlet area adjustment. Diffuser mounting locations and exhaust methods are also altered to balance heating and ventilation efficiency. As a result, a proper installation location for this prototype is suggested. The adaptive supply area significantly improved this terminal's heating and ventilation performance. Temperature stratification was reduced to a maximum of one-tenth, and impinging jets or displacement ventilation were observed in some cases.

Investigation of Air Change Rate in a Single Room Using Multiple Carbon Dioxide Breathing Models in China: Verification by Field Measurement

It is difficult to accurately measure the air exchange rate (AER) in residential and office buildings during occupation via on-site field measurement. The tracer gas method was widely applied to estimate the AER in these buildings, and human metabolic carbon dioxide (CO2) was often used as a tracer gas in different models. This study introduced three models (the ASHRAE model, the ASHRAE China-specific modified model, and the BMR model), which were proposed to estimate the AER based on exhaled CO2. We verified these models by comparing the exhaled CO2-based AER with AER from field measurements using sulfur hexafluoride (SF6) as a tracer gas. We also analyzed the potential factors that could affect the uniformity of the indoor tracer gas distribution. Our results indicate that the ASHRAE China-specific modified model has the best performance with an average deviation of −6.67% and a maximum deviation of −14.6% with multiple measurement points, a stable personnel activity, and proper Parameter settings in a single room in China.

Aerosol transmission of SARS-CoV-2 due to the chimney effect in two high-rise housing drainage stacks

Stack aerosols are generated within vertical building drainage stacks during the discharge of wastewater containing feces and exhaled mucus from toilets and washbasins. Fifteen stack aerosol-related outbreaks of coronavirus disease 2019 (COVID-19) in high-rise buildings have been observed in Hong Kong and Guangzhou. Currently, we investigated two such outbreaks of COVID-19 in Hong Kong, identified the probable role of chimney effect-induced airflow in a building drainage system in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We injected tracer gas (SF6) into the drainage stacks via the water closet of the index case and monitored tracer gas concentrations in the bathrooms and along the facades of infected and non-infected flats and in roof vents. The air temperature, humidity, and pressure in vertical stacks were also monitored. The measured tracer gas distribution agreed with the observed distribution of the infected cases. Phylogenetic analysis of the SARS-CoV-2 genome sequences demonstrated clonal spread from a point source in cases along the same vertical column. The stack air pressure and temperature distributions suggested that stack aerosols can spread to indoors through pipe leaks which provide direct evidence for the long-range aerosol transmission of SARS-CoV-2 through drainage pipes via the chimney effect.

A method for identifying the fire status through ventilation systems using tracer gas for improved rescue effectiveness in roadway drivage of coal mines

When a coal mine fire occurs, the rescue of trapped mine workers is difficult, because some efficient fire-fighting measures (such as nitrogen injection) cannot be implemented. The development and severity of a fire is difficult to determine, and the integrity of the auxiliary ventilation system may be unknown. These situations pose additional challenges to the trapped mine workers and increase the difficulty level for the rescue team. A novel method using the tracer gas technique is developed to remotely gather information to determine the location and severity of the fire. Laboratory experiments were conducted to understand the tracer gas distribution characteristics when the fire causes damage to the ventilation duct. A mathematical model was developed that uses the tracer gas concentration curve to determine the location and severity of the fire. The model combines the Expectation Maximization (EM) algorithm with the Gaussian Mixture (GM) model. Validated using experimental data, it is demonstrated that the method can determine the fire location with low error. The information collected using this method reflects basic living environmental conditions of the trapped mine workers and provides important input for quickly formulating an effective fire rescue plan that saves lives.

Heat Convective Effects on Turbulence and Airflow inside an B767 Aircraft Cabin

Thermal plumes generated by human bodies can affect the temperature and humidity of the surrounding environment. An experimental study investigated the effects of thermal plumes formed by aircraft passengers on airflow and turbulence characteristics inside aircraft-cabins. An 11-row, wide-body B767 cabin mockup was used with actual seats, air diffusers and cabin profile. Thermal manikins were used simulating passengers in the cabin. Tracer gas and air speed inside the cabin were measured while the heat from the manikins was turned on and off to help understand the effects of the thermal heat released by the manikins. Results showed that tracer gas distribution were more uniformly and equally distributed around the release source and the air speed fluctuation were lower under cooler environments when the thermal manikins were turned off. Heated environments increased the values of turbulence kinetic energy and the turbulence intensity levels. However, the effects on the turbulence intensity were less significant compared to the turbulence kinetic energy. On the other hand, the dissipation rates were higher for unheated cases in the front and back sections of the mockup cabin. The relative uncertainty for tracer gas sampling ranged between ±5–14% for heated manikins versus ±8–17% for unheated manikins. Higher uncertainty levels accompanied the turbulence measurements due to the highly chaotic nature of the flow inside the cabin.

Experimental analysis of driving forces and impact factors of horizontal inter-unit airborne dispersion in a residential building

Airborne transmission is responsible for the spread of various respiratory infectious diseases. An internal transmission route of inter-unit dispersion between horizontal adjacent units has been verified in our on-site measurement. In the present study, the impact factors of this transmission route were further investigated using the measurement data, and in particular the contributions of the thermal buoyancy force and the wind force were compared. It is found that the wind force is more dominant than the thermal force. The tracer gas distribution indicates that wind effect and the semi-open condition of the corridor play the main roles in the transmission. Outdoor wind promotes the spread of tracer gas from the index unit to the receptor units, and the effect of wind direction is more significant than the wind speed. Airflow in the semi-open corridor promotes the rapid dilution of contaminants and prevents the accumulation, which can reduce the inter-unit dispersion effectively.

Energy Recovery Inc, USA

Full-scale experiments were carried out to explore the effects of the initial temperature difference between the interior and exterior and the vent characteristics on the transient development of natural ventilation driven by thermal buoyancy. Air temperature and tracer gas concentration in a test chamber were measured and the experimental results were compared with the theoretical predictions. It was found that the initial temperature difference has a large influence on the thermal stratification, the concentration distribution of tracer gas, the flow rate and the removal rate of tracer gas. The time taken to reach steady-state ventilation is shorter for a larger vent if the initial indoor temperature is greater than or equal to the outdoor temperature. For a pre-cooled room, the time taken for the ventilation to transform the airflow direction is shorter for a larger vent. Increasing the vent area would yield a greater flow rate and thus improve the efficiency of gas removal. Experimental results also show that the vent shape has little impact on the flow rate.

Numerical Simulation of Several Parameters of Distribution Uniformity of Tracer Gas in Stope

Tracer gas technology is an effective way to evaluate underground coal mine ventilation system, especially in stope, air leakage from working face to gob can be quickly detected by this method. While tracer gas distribution characteristics may be different with the variation of ventilation parameters, therefore, ascertaining the uniform distributed location as sampling point is essential to improve the measuring accuracy of tracer gas technology. This study conducts simulations of tracer gas distribution in four ventilation models with different parameters, aiming to analyze the effects of gob and height difference between roadway and working face on tracer gas distribution uniformity. The result shows the porous characteristics of gob is not conductive to tracer gas uniform distribution, the height difference between roadway and working face increases the turbulence intensity of airflow and promotes the uniform distribution of tracer gas. In no height difference stope, tracer gas and airflow can be mixed uniformly at 5D of return roadway, but in height difference stope, only 1D is required. Finally, a practical case study is conducted to verify the validity of simulation.

Unsteady 360 Computational Fluid Dynamics Validation of a Turbine Stage Mainstream/Disk Cavity Interaction

The amount of cooling air assigned to seal high pressure turbine (HPT) rim cavities is critical for performance as well as component life. Insufficient air leads to excessive hot annulus gas ingestion and its penetration deep into the cavity compromising disk or cover plate life. Excessive purge air, on the other hand, adversely affects performance. Experiments on a rotating turbine stage rig which included a rotor–stator forward disk cavity were performed at Arizona State University (ASU). The turbine rig has 22 vanes and 28 blades, while the cavity is composed of a single-tooth lab seal and a rim platform overlap seal. Time-averaged static pressures were measured in the gas path and the cavity, while mainstream gas ingestion into the cavity was determined by measuring the concentration distribution of tracer gas (carbon dioxide) under a range of purge flows from 0.435% (Cw = 1540) to 1.74% (Cw = 6161). Additionally, particle image velocimetry (PIV) was used to measure fluid velocity inside the cavity between the lab seal and the rim seal. The data from the experiments were compared to time-dependent computational fluid dynamics (CFD) simulations using fluent CFD software. The CFD simulations brought to light the unsteadiness present in the flow during the experiment which the slower response data did not fully capture. An unsteady Reynolds averaged Navier–Stokes (RANS), 360-deg CFD model of the complete turbine stage was employed in order to increase the understanding of the swirl physics which dominate cavity flows and better predict rim seal ingestion. Although the rotor–stator cavity is geometrically axisymmetric, it was found that the interaction between swirling flows in the cavity and swirling flows in the gas path create nonperiodic/time-dependent unstable flow patterns which at the present are not accurately modeled by a 360 deg full stage unsteady analysis. At low purge flow conditions, the vortices that form inside the cavities are greatly influenced by mainstream ingestion. Conversely at high purge flow conditions the vortices are influenced by the purge flow, therefore ingestion is minimized. The paper also discusses details of meshing, convergence of time-dependent CFD simulations, and recommendations for future simulations in a rotor–stator disk cavity such as assessing the observed unsteadiness in the frequency domain in order to identify any critical frequencies driving the system.

Comparative study to evaluate three ground-based optical remote sensing techniques under field conditions by a gas tracer experiment

Today, ground-based optical remote sensing (ORS) has become an intensively used method for quantifying pollutant or greenhouse gas emissions from point or area sources, and for the validation of airborne or satellite remote sensing data. In this study, we present the results of a release experiment using acetylene (C2H2) as a tracer gas, where three ORS techniques were simultaneously tested for two main purposes: (1) the detection of emission sources and (2) the quantification of release rates. Therefore, passive and active open-path Fourier transform infrared spectroscopy (OP-FTIR) and open-path tunable diode laser absorption spectroscopy (TDLAS) were applied and evaluated. The concentration results of the active ORS methods are compared to those estimated by a Lagrangian stochastic atmospheric dispersion model. Our results reveal that passive OP-FTIR is a valuable tool for the rapid detection and imaging of emission sources and the spatial tracer gas distribution; while with active OP-FTIR and TDLAS, C2H2 concentrations in the sub-ppm range could be quantified that correlated well with the concentration data obtained by our modeling approach.

Experimental investigation on transient natural ventilation driven by thermal buoyancy

Full-scale experiments were carried out to explore the effects of the initial temperature difference between the interior and exterior and the vent characteristics on the transient development of natural ventilation driven by thermal buoyancy. Air temperature and tracer gas concentration in a test chamber were measured and the experimental results were compared with the theoretical predictions. It was found that the initial temperature difference has a large influence on the thermal stratification, the concentration distribution of tracer gas, the flow rate and the removal rate of tracer gas. The time taken to reach steady-state ventilation is shorter for a larger vent if the initial indoor temperature is greater than or equal to the outdoor temperature. For a pre-cooled room, the time taken for the ventilation to transform the airflow direction is shorter for a larger vent. Increasing the vent area would yield a greater flow rate and thus improve the efficiency of gas removal. Experimental results also show that the vent shape has little impact on the flow rate.

Development of a remote analysis method for underground ventilation systems using tracer gas and CFD in a simplified laboratory apparatus

Following a disaster in a mine, it is important to understand the state of the mine damage immediately with limited information to manage the emergency effectively. Tracer gas technology can be used to understand the ventilation state remotely where other techniques are not practical. Computational fluid dynamics is capable of simulating and ascertaining information about the state of ventilation controls inside a mine by simulating the airflow and tracer distribution. This paper describes a simulation of tracer gas distribution in a simplified laboratory experimental mine with the ventilation controls in various states. Tracer gas measurements were taken in the laboratory experimental apparatus, and used to validate the numerical model. The distribution of the tracer gas, together with the ventilation status, was analyzed to understand how the damage to the ventilation system related to the distribution of tracer gases. Detailed error analysis was performed and the discrepancies between experimental and simulated results were discussed. The results indicate that the methodology established in this study is feasible to determine general ventilation status after incidents and can be transferred to field experiment. Because it is complex to simulate the actual condition of an underground mine in a laboratory, the model mine used is simplified to simulate the general behavior of ventilation in a mine. This work will be used to inform planned on-site experiments in the future and the proposed methodology will be used to compare collected and simulated profiles and determine the general location of ventilation damage at the mine scale.

Experimental Study of an Air Distribution System for Operating Room Applications

An understanding of airflow patterns in operating rooms is required if the design of air distribution systems in such environments is to be improved and the risk of postoperative infection reduced. To assess a detailed description of contaminant distribution, the airflow patterns and the spread of contaminants in an operating room were analyzed using an experimental model. These experiments were carried out in a test cell, MINIBAT, equipped with an operating table, a medical lamp and a manikin representing the surgeon. A diagonal ventilation system was tested for two types of conditions: (i) isothermal, with the manikin and lamp switched off and (ii) non-isothermal, with the manikin and lamp switched on. Indoor air temperatures, air velocities and tracer gas concentrations were measured automatically at more than 700 points. The overall airflow patterns, due to ventilation, were very similar for the two experiments. However, in the zone between the lamp, the table and the manikin (which was the main area of interest), the tracer gas distribution was different. In the non-isothermal case, the thermal plume from the manikin induced better mixing, and had a beneficial effect on the evacuation of contaminants. The thermal energy emitted by the lamp had almost no impact on the airflow patterns.

Computational analysis of a human inhalation test chamber for dosimetry-and-health effect studies.

Proper air flow and tracer gas distribution or contaminant ventilation are of great importance in biomedical test chambers or industrial workrooms. The focus is on mass transfer in an inhalation test chamber with a breathing subject on a bike exposed to a tracer gas environment (e.g., carbon monoxide). This is an environmentally realistic setup for dosimetry-and-health effect studies, which require controlled, near-uniform pollutant concentrations. However, unmodified test chambers exhibit a strong single vortex in the larger breathing zone, which, depending upon the subject's location, implies possible trace gas depletion during inhalation, foreign particle entrainment, excessive air velocities, and so on. Employing a commercial finite-volume code with user-enhanced Fortran programs, the transient three-dimensional turbulent momentum, mass, and heat transfer equations have been solved and the configurations of a suitable flow redirection device, different man-machine locations, and thermal effects have been analyzed. As a result, the best air flow device configuration and man-machine orientation have been determined to achieve high and consistent trace gas concentrations inhaled by the subject, for example, 96 percent of the CO concentration at the chamber inlet is inhaled by the subject for the optimal scenario.

Gas-phase velocity field measurements in sprays without particle seeding

A laser-based technique is presented that can be used to measure the instantaneous velocity field of the continuous phase in sprays and aerosols. In contrast to most well established laser-based velocity measurement techniques, this method is independent of particle seeding and Mie scattering. Instead of that it is based on gaseous flow tracers and laser-induced fluorescence (LIF). Inhomogeneous tracer gas distributions, which are created by an incomplete, turbulent mixing process, are exploited for flow tracing. The velocity field can be measured close to the droplets, because frequency-shifted LIF is separated from Mie scattering by optical filters. Validation tests and results from a water spray in air are given. Accuracy and spatial resolution are discussed in detail.

Indoor air quality in rooms with cooled ceilings.: Mixing ventilation or rather displacement ventilation?

Experimental investigations and practical experiences in Europe have proved that hydronic cooled ceilings are able to remove high cooling loads without impairing thermal comfort. As hydronic cooled ceilings cannot remove latent loads and pollutants, e.g., CO 2, VOCs, odors, additional ventilation has to be applied. Often, displacement ventilation is used, which is able to provide lower pollutant levels in the occupation zone than mixing flow systems, if the occupants are causing most of the pollution. Unfortunately, the advantage of the displacement flow, in respect to the air quality, can vanish when cooled ceilings are used to remove the major part of the sensible cooling load. For these applications, a combination of a cooled ceiling with a mixing ventilation system might be more appropriate. This paper presents the results of an investigation examining the distribution of tracer gas in a test chamber which is equipped with a radiant cooled ceiling. There is both a displacement flow system and a mixing flow system available, so that the concentrations of the tracer gas within the occupation zone characterizing the air quality can be compared directly and evaluated under similar conditions. The vertical air temperature rise is taken into consideration as well, as it influences the displacement flow and is an important issue for assessing thermal comfort. The results show the interaction of the portion of the cooling load being removed by the supply air, the air quality in the occupied zone and the vertical air temperature rise. The figures and tables presented show which of the two supply air systems investigated have advantages over the other.

A-28 業務用厨房の高効率換気・空調システムに関する研究 : その17 実測・実験による厨房内温度等の検討

A-28 業務用厨房の高効率換気・空調システムに関する研究 : その17 実測・実験による厨房内温度等の検討

Local aspects of vehicular pollution

We consider the local aspects of vehicular pollution by the use of l:10 scale models. The model automobiles were placed in a low-velocity wind tunnel to simulate a queue of slow-moving city traffic and tracer gasses were then injected into the air flow though the tail pipes fitted to two of the models. Measurements show that the exhaust gases are entrained in the wake of the vehicle from which they were emitted, and are dispersed mainly by the passage of the following car. The spatial distribution of tracer gas along and across the models suggests that the level of pollution received by a commuter in a slow-moving heavy traffic may be strongly influenced by the pollution produced from the car immediately in front.