Solid phase microextraction(SPME) sampling under turbulent conditions and for the simultaneous collecting of tracer gases

Solid phase microextraction （SPME） is a solvent-flee method of sample collection. SPME is an appealing method for sample collection because it is designed for the sampling of trace level analytes with short sampling times in a variety of environments. Additionally, SPME can be used to directly deliver a sample to a gas chromatograph （GC） for analysis by means of thermal desorption. In this paper, the performance of SPME under dynamic conditions was investigated. Additionally, the competence of SPME sampling for the simultaneous analysis of multiple trace analytes was also evaluated. This work is discussed in the context of underground mine ventilation surveys but is applicable to any industry in which ventilation circuits must be evaluated. The results of this paper showed that the performance of the 100 ~m PDMS SPME fiber was both precise and rapid under dynamic conditions. This SPME fiber was also able to simultaneously collect sulfur hexafluoride （SF6） and perfluoromethylcyclohexane （PMCH） with adequate sensitivity.

Determinations of Air Tightness of Covered Slurry Storage Tanks Using Tracer Gas Technique

The objective of this investigation was to study whether it is possible to determine the air tightness of covered slurry storage tanks using tracer gas technique by injection of sulphur hexafluoride （SF6） and measurements of the decay in gas concentrations with an infrared spectrophotometer in the air space above the slurry. By measuring the decay in concentration of injected tracer gas at different occasions, the air exchange rate was determined. Three different types of coverings were studied namely; wooden roof, plastic tent and concrete roof.

Numerical simulation to evaluate gas diffusion of turbulent flow in mine ventilation system

Tracer gas technique is a method to analyze the airflow path, measure the airflow quantity, and detect any recirculation or leakages in underground mine. In addition, it is also possible to evaluate the axial gas diffusion of gas in turbulent bulk flow by utilizing the tracer gas data. This paper discussed about the measurement using tracer gas technique in Cibaliung Underground Mine, Indonesia and the evaluation of effective axial diffusion coefficient, E, by numerical simulation. In addition, a scheme to treat network flow in mine ventilation system was also proposed. The effective axial diffusion coefficient for each airway was evaluated based on Taylor's theoretical equation. It is found that the evaluated diffusion coefficient agrees well with Taylor's equation by considering that the wall friction factor, f, is higher than those for smooth pipe flow. It also shows that the value of effective diffusion coefficient can be inherently determined and the value is constant when matching with other measurements. Furthermore, there are possibilities to utilize the tracer gas measurement data to evaluate the airway friction factors.

Study on impact factors of tracer gas method in investigations of gaseous pollutant transport and building ventilation

Building ventilation is essential to discharge indoor pollutants and improve indoor air quality for occupant health.Tracer gas method is an efficient way in the field of building ventilation to measure ventilation rate and to evaluate the ventilation performance.Literature shows notable deviation of measured ventilation rate using different tracer gases.In the present study,CFD simulations are carried out to analyze He-,CO_(2)-and SF_(6)-based tracer gas methods.The effects of tracer gas density and release rate on the concentration distribution and ventilation effectiveness are studied.Various application scenarios of different ventilation rates and airflow distribution forms are compared.The results show that the deviation of ventilation effectiveness evaluated by different tracer gases can be above 2-4 times,and the error is introduced by non-passive dispersion.Whether tracer gas dispersion is passive or not depends on the relative importance of density difference driven mass transfer to forced convection mass transfer,which is due to the combined effects of density difference,release rate,and indoor airflow velocity,and can be judged by a dimensionless number θ.Under the geometry and ventilation settings in the present study,the critical value of θ is 1.0 for the error range of 5%,and 2.0 for the error range of 10%.When θ is below the critical value,the gas transport is passive and dominated by the indoor ventilation airflow.A release of tracer gas with smaller release rate and smaller density difference into a stronger indoor airflow behaves more passive.Heavier tracer gas tends to significantly overestimate the performance of upper supply and lower exhaust ventilation,and lighter tracer gas aggravates the overestimation of the performance for lower supply and upper exhaust ventilation.In mechanical ventilation rooms with air change rate of 3.0-6.0 h^(−1),a continuous release of tracer gas SF_(6),CO_(2) or He with release rate above 8 mg/s or source concentration above 8-75 ppm should not be considered as passive.This work clarified the passive and non-passive transport characteristics and mechanisms of various tracer gases,which is helpful for the engineering applications of tracer gas method in building ventilation studies.

Local and Whole Ventilation of Rainwear with Different Aperture Designs

Aperture design is very important in the design process of rainwear,as garment aperture is one of the main pathways for air exchange between clothing microclimate and the environment.The purpose of this study was to investigate the effects of aperture design on whole and local ventilations of rainwear.Ventilation was measured by a tester developed based on the steady-state method.A rainwear suit with top and bottom was chosen as the basic ensemble.Apertures were added at the arm,chest,back and knee separately.Local ventilation of the arm,chest,back and whole ventilation of the top and bottom in different walking and wind conditions were measured.Local and whole ventilations at five aperture conditions for the top and four for the bottom were studied.The results indicated that local ventilation value of the chest was the biggest and the arm was the smallest.Whole ventilation of the suit was the biggest when walking at 5.6 km/h,with all the designed apertures opened.Local ventilation value was bigger when opening arm aperture than that of opening chest or back aperture.The bottom ventilation was the highest when both front and back apertures were opened.

The mass and heat transfer process through the door seal of refrigeration

As one of the main reasons causing leakage heat load in a refrigerator,mass and heat transfer through refrigerator door seal is of great importance to be studied.In this paper,a model is presented for numerical simulation of mass and heat transfer process through refrigerator door seal,and an experiment apparatus is designed and set up as well for comparison.A two-dimensional model and tracer gas method are used in simulation and experiment,respectively.It can be found that the relative deviations of air infiltration rate between the simulated results and experimental results were less than 1%,and the temperature difference errors at two special points of the door seal were less than 2.03℃.In conclusion,the simulated results are in good agreement with the experimental results.This paper initially sets up a model that can accurately simulate the heat and mass transfer through the refrigerator door seal,and the model can be used in refrigerator door seal optimization research in the follow-up study.

An evaluation of a perfluoromethylcyclohexane(PMCH) permeation plug release vessel(PPRV) in a controlled turbulent environment

The use of sulfur hexafiuoride （SF6） as a tracer gas for analyzing underground mine ventilation systems has been practiced for over 30 years. As a result, the methods used to release, sample, and analyze SF6 are well accepted. As the complexity and size of underground mine ventilation networks increase, the ability of a SF6 to function as a convenient and rapid means of analysis diminishes. The utilization of multiple tracer gases can mitigate this by removing the need to purge the background presence of a tracer before conducting another release and allowing for a more comprehensive evaluation using multi-zone tech- niques. Recent studies have identified perfluoromethylcyclohexane （PMCH） as a possible supplement for SF6 in underground mine ventilation tracer studies. However, the deployment of PMCH remains a challenge because of this compounds physical properties. This paper evaluates a PMCH permeation plug release vessel （PPRV） under controlled turbulent conditions. The details of the experimental parameters used in the evaluation as well as a discussion regarding the performance of the PPRV are included.

Research on air infiltration predictive models for residential building at different pressure

The pressure difference in buildings under natural state is usually below 10 Pa,and the air change rate at 50 Pa(ACHso)is often used to evaluate building airtightness.There is a dearth of research on air infiltration predictive model at different pressures in China.Moreover,the airflow coefficient(C),a key parameter for air infiltration,is necessary to determine ACHso.Based on prior experimental data,several methods including ordinary least squares(OLS),stepwise regression,partial least squares(PLS)and nonlinear fitting with independent variable screening methods,were employed to establish an airflow coefficient model.The determination coefficient(ft2)and the variation coefficient of the root-mean-square error(CV(RMSE))of these models were compared.The simulation results show that ft2 of the airflow coefficient models for apartments and villas increased by a maximum of 25.9%and 2.3%,respectively,using PLS method.The improvement with nonlinear fitting was weaker.Based on K-P model,a conversion model between ACHso and ACH4 was developed as an air infiltration predictive model under natural state.Blower door and tracer gas tests were conducted to verify the conversion model.The expected error was approximately 10%,which may be caused by measurement errors and shielding from surrounding obstructions.Further studies need to focus on obtaining more experimental data for building airtightness and developing a conversion model for high-rise residential buildings.

Assessing impact of intermittent window opening strategies on pathogen-laden droplet dispersion in a coach bus

Opening windows in coach buses is a practical approach to improving natural ventilation and mitigating infection risk(IR).Due to human behavior and weather conditions,the intermittent window opening strategy(IWOS)is a more common practice than keeping windows constantly open.Despite its prevalence,there are no studies exploring IWOS specifically in vehicles.We employed indoor-outdoor coupled CFD simulations to assess the effects of various IWOS on pathogen-laden droplet(PLD)dispersion and IR in a coach bus that occurred a COVID-19 outbreak in Hunan,China.Results reveal that after ventilating through two skylights for 600–1800 s,opening front and rear windows(FW+RW)or FW with a wind catcher(FW+WCH)for just 40 s can reduce PLD concentration(Cave)to 5%of its initial level and the intake fraction of the infector’s neighbor(IFn)drops by 95%.Upon closing FW+RW or FW+WCH,Cave and IFn take over 580 s to return to the pre-opening level.Moreover,intermittent FW opening halves Cave and IFn within 7 min,but leads to rapid increases upon window closure.Therefore,opening FW+RW and FW+WCH intermittently have pronounced impacts on indoor PLD concentration and are applicable approaches to control respiratory disease transmission in vehicles.According to the inhaled viral dose,it is recommended to open windows when driving time is over 12 minutes to reduce infection risk.In scenarios like epidemiological surveys and risk assessments,where assessing passenger infection risk is vital,some behaviors of opening windows cannot be overlooked and necessitate extra attention.