Mixing Fan Research Articles

Understanding the role of flux chamber configuration in the measurement of VOC emissions from porous media

The accurate quantification of volatile organic compound (VOC) emission rates from porous media to the air is a challenging problem, as measurements are affected by the chemical and physical characteristics of the porous media, and the operating parameters of the sampling device itself. The main objective of this study is to investigate how flux chamber (the most commonly used sampling device) configurations influence emission rate measurement from three selected porous media. Various parameters were studied, including sweep air flow rate, presence of a mixing fan, headspace volume and thickness of media. Controlled experiments focused on the behaviour of two VOCs commonly found in area sources: acetic acid and 1-butanol. Sweep gas flow rate emerged as the most influential factor, inducing turbulence and dilution over porous media surfaces and impacting emission rate measurements more significantly than headspace volume and fan installation. Variations in porous media properties also affected mass transfer, with emissions from coco coir showing higher mass transfer as its porosity and particle size facilitated gas transportation. While behaviour of acetic acid emission through the media supported the diffusion theory, emission of 1-butanol was affected by a combination of factors, highlighting the role of both diffusive and advective transport mechanisms. Understanding how flux chamber setups and porous media properties influence emission rates is crucial for accurately interpreting data. This knowledge also guides the design of studies, especially when investigating complex sources like biosolids and organic-amended soil.

Influence of Ventilation on Formation and Growth of 1-20 nm Particles via Ozone-Human Chemistry.

Ozone reaction with human surfaces is an important source of ultrafine particles indoors. However, 1-20 nm particles generated from ozone-human chemistry, which mark the first step of particle formation and growth, remain understudied. Ventilation and indoor air movement could have important implications for these processes. Therefore, in a controlled-climate chamber, we measured ultrafine particles initiated from ozone-human chemistry and their dependence on the air change rate (ACR, 0.5, 1.5, and 3 h-1) and operation of mixing fans (on and off). Concurrently, we measured volatile organic compounds (VOCs) and explored the correlation between particles and gas-phase products. At 25-30 ppb ozone levels, humans generated 0.2-7.7 × 1012 of 1-3 nm, 0-7.2 × 1012 of 3-10 nm, and 0-1.3 × 1012 of 10-20 nm particles per person per hour depending on the ACR and mixing fan operation. Size-dependent particle growth and formation rates increased with higher ACR. The operation of mixing fans suppressed the particle formation and growth, owing to enhanced surface deposition of the newly formed particles and their precursors. Correlation analyses revealed complex interactions between the particles and VOCs initiated by ozone-human chemistry. The results imply that ventilation and indoor air movement may have a more significant influence on particle dynamics and fate relative to indoor chemistry.

Effect of ventilation strategy on performance of upper-room ultraviolet germicidal irradiation (UVGI) system in a learning environment

Upper-room ultraviolet germicidal irradiation (UVGI) system is recently in the limelight as a potentially effective method to mitigate the risk of airborne virus infection in indoor environments. However, few studies quantitatively evaluated the relationship between ventilation effectiveness and virus disinfection performance of a UVGI system. The objective of this study is to investigate the effects of ventilation strategy on detailed airflow distributions and UVGI disinfection performance in an occupied classroom. Three-dimensional computational fluid dynamics (CFD) simulations were performed for representative cooling, heating, and ventilation scenarios. The results show that when the ventilation rate is 1.1 h−1 (the minimum ventilation rate based on ASHRAE 62.1), enhancing indoor air circulation with the mixing fan notably improves the UVGI disinfection performance, especially for cooling with displacement ventilation and all-air-heating conditions. However, increasing indoor air mixing yields negligible effect on the disinfection performance for forced-convection cooling condition. The results also reveal that regardless of indoor thermal condition, disinfection effectiveness of a UVGI system increases as ventilation effectiveness is close to unity. Moreover, when the room average air speed is >0.1 m/s, upper-room UVGI system could yield about 90% disinfection effect for the aerosol size of 1 μm–10 μm. The findings of this study imply that upper-room UVGI systems in indoor environments (i.e., classrooms, hospitals) should be designed considering ventilation strategy and occupancy conditions, especially for occupied buildings with insufficient air mixing throughout the space.

Characterizing a Year-Round Particulate Matter Concentration and Variation under Different Environmental Controls in a Naturally Ventilated Dairy Barn

A mixing fan and spraying system is commonly used to control the indoor environment of naturally ventilated dairy barns worldwide. However, its impact on particulate matter (PM) concentration and variation is still unclear due to the lack of year-round field data. To systematically characterize the PM dynamics under different environmental controls (namely, EC1: No Fans and No Spraying; EC2: Fans; EC3: Fans and Spraying), a year-round continuous monitoring of PM less than 2.5 μm in aerodynamic diameter (PM2.5) and total suspended particle (TSP) concentrations, as well as indoor environmental factors, was carried out inside a naturally ventilated dairy barn using an IoT-based sensor monitoring network. Results showed that the hourly mean TSP and PM2.5 concentrations were 94.7 μg m−3 and 49.8 μg m−3, respectively. EC2 had a higher TSP content (116.6 μg m−3) than EC1 (98.0 μg m−3) and EC3 (81.9 μg m−3). EC1 had the greatest PM2.5 concentration (57.1 μg m−3), followed by EC2 (48.3 μg m−3) and EC3 (44.7 μg m−3). EC1 showed clear TSP and PM2.5 fluctuations during the daily operations at 07:00 to 08:00 and 18:00 to 19:00, while irregular peaks in EC2 and a relatively steady diurnal variation in EC3 were found. Daily Tsp concentrations in the three ECs did not exceed 300 μg m−3. However, 17.8%, 11.5%, and 4.8% of the observed days in EC1, EC2, and EC3 had daily mean PM2.5 concentrations above the healthy threshold (75 μg m−3), mostly from 07:00 to 08:00 and 22:00–07:00. In conclusion, the mixing fan and spraying system had significant effects on PM concentration and variation, and more protection procedures should be taken for farm workers to prevent long-term health risk exposure, to EC1 in particular.

Thermal stability measurement of terminal face relative pose for complex structure based on coordinate measuring machine

Abstract The coordinate measuring machine has high measurement accuracy, but it is only suitable for the precise measurement of the geometric size of the component in the normal temperature environment, and some complex structures need to assess the stability of the terminal face relative pose in the high and low temperature environment. In order to apply the high-precision measurement of the coordinate measuring machine to the thermal stability evaluation of the relative pose of the terminal face of complex structures, an extended temperature control method based on the coordinate measuring machine is proposed. The method realizes the loading control of the temperature environment of the specimen by the mobile temperature control module and the temperature control medium circulation module. The flexible connection mode is used between the temperature control module and the temperature control medium circulation module to reduce the influence of mechanical vibration on the measurement accuracy. The mixing fan and the temperature control medium dryer are installed in the pipeline to avoid frosting and dewing in the temperature control box and ensure the uniform distribution of the temperature field, so as to realize the accurate measurement of the relative pose of the terminal face of the complex structure under the high and low temperature environment by the coordinate measuring machine. The method is applied to the thermal stability test of the relative pose of the end face of a joint component, and the test results are good, which provides a new idea for the extended application of coordinate measuring machines.

Heat Treatment for Disinfecting Egg Transport Tools

HighlightsDisinfecting shell egg transport tools before their reuse is an integral biosecurity step.Avian influenza viruses are heat labile and it can be disinfected with high temperatures.Lab tests proved that egg transport flats and pallets can be heated to 54°C to 60°C in 7 to 9 h.Egg farm tests identified main factors for consideration in designing heat treatment system.Abstract.Disinfecting shell egg transport tools such as egg flats and pallets before their reuse has become an integral biosecurity step after the 2015 highly pathogenic avian influenza (HPAI) outbreaks in the United States. Lab-scale tests and field verification were conducted to investigate dynamic temperature changes and distributions inside stacks of egg pallet and flat at a surrounding air temperature of 54°C to 60°C (130ºF to 140ºF) in this study. The heat treatment tests were conducted in the lab first, and then verified in a newly built heat treatment room [12 m (L) × 4 m (W) × 3 m (H)] on a commercial laying hen farm in Iowa, the largest egg production state in the United States. Iowa lost more than 30 million hens during 2015 outbreak of HPAI. The lab tests proved that air circulation with fans could accelerate the heat exchange between air and stacks; blowing air from top and bottom at the same time plus arranging a 2.5 cm (1 in.) space between stacks could reduce the heat treatment time for the target temperature zone (i.e., 54ºC to 60ºC) from 26 to 60 h (without air circulation) to 7 to 9 h. For commercial egg farm tests, heat treatment results show that the room air and egg pallet stacks temperature reached the target zone (54ºC to 60ºC) in 30 min and 4 h after starting the heater, respectively. However, the temperature of egg flat stacks failed to reach the targeted zone after 8 h heating, because it had larger volume and heat transfer resistance as compared to egg pallet stacks. Further experiments such as extending heating period and installing mixing fans to accelerate heat exchange between the room air and the stacks are suggested for improving heat treatment system design on commercial farms. Keywords: Avian influenza, Disinfection, Egg flat and pallet, Egg production.

Numerical evaluation of contaminants mixing uniformity in a full-scale test chamber with mixing fan

Most existing models and standards for volatile organic compounds emission assume that contaminants are uniform in the testing devices. In this study, a three-dimensional transient numerical model was proposed to simulate the mass transport process based on a full-scale test chamber with a mixing fan, and the airflow field and contaminants concentration distribution were obtained within the chamber under airtight and ventilated conditions. The model was validated by comparing the numerical results with experimental data. The numerical results show that the contaminant source position and the airflow field characteristics have significant impact on the contaminant mixing, and the fan rotation has an important role in accelerating mixing. In the initial mixing stage, the concentration distribution is obviously uneven; as the mixing progresses, it gradually reaches acceptable uniformity except for some sensitive regions, such as high concentration region at the injection point of the contaminants and low concentration region at the air inlet. To ensure test accuracy, the monitor should avoid above sensitive regions; and some special regions are recommended where contaminant concentration uniformity can be reached sooner. The ventilated chamber results indicate that the mixture of contaminants in the chamber is actually better than the results shown by conventional test method.

The Influence of Interstage-Turbine Mixing Cycle on Engine Performance

The optimization of the Brayton cycle has gained an increasing worldwide attention, in order to improve the specific thrust for achieving super cruise. This paper proposes a novel Interstage-Turbine Mixing (ITM) cycle, which guide vanes and rotor blades of turbine would be used as mixing chambers in the expansion process, and presents an analytical methodology by which ITM can be simulated at actual state. The motivation and the working principle of the ITM cycle are explained in detail. In this paper, the variable components method is used to establish the simulation program of the turbine stage mixing cycle. Then parametric cycle studies are performed with the variation of mixing ratio, bypass ratio and fan pressure ratio respectively. The interrelationships between cycle parameters and their effects on cycle performance are discussed. The results show that the mixing ratio of engine with the maximum specific thrust is 0.923, the mixing ratio with the maximum specific fuel consumption is 0.613, the mixing ratio with the best comprehensive performance is 1.127. The above conclusions are independent of the bypass ratio and fan pressure ratio. The predicted engine performance shows that the ITM cycle concept exhibits a competitive specific thrust with respect to engine in the state of non-afterburning, and might be a promising propulsion system for super-cruise air-breathing flying vehicles.

Computational fluid dynamics prediction of formaldehyde emission and sorption processes in a small test chamber with mixing fan and vents

Abstract Characterizing the emission performance of formaldehyde is critical for control strategies. Most previous emission models assume that formaldehyde concentrations are well-mixed. In this study, a computational fluid dynamics-based model is developed for simulating the mass transfer and adsorption/desorption processes of formaldehyde from particleboards in a chamber with a mixing fan. Numerical investigations on the impacts of the mixing fan, adsorption/desorption rate constants, and key transport parameters influencing the emission behaviors are conducted for the first time. The results show that the complete mixing assumption is not appropriate in the early emission period. Incomplete mixing becomes more significant with a decreasing rotation speed, leading to a time-dependent equivalent mass transfer coefficient. The deviation in the maximum concentration between the simulated curves with and without the adsorption/desorption effect is approximately 8.5%. A coefficient of mixing of 0.0283 is suitable for evaluating complete mixing in the chamber. With an increase in the rotation speed, the degree of mixing improves, and the mass transfer coefficient increases sub-linearly. Secondary reemission becomes more significant and begins earlier for materials with lower partition coefficients and higher diffusivity.

Optimization of Diffuser Parameters for Mixing Fans in Agricultural Buildings

Abstract. Mixing fans (MFFs) are widely used in ventilation of agricultural buildings to improve the uniformity of the air supply, thereby improving the ventilation efficiency. In order to improve the ventilation performance of MFFs, a new visor-shaped diffuser was designed and installed on a MFF. The angle and the length of the diffuser were crucial parameters that affected the performance of the MFFs with the diffusers. Thereby, in this study numerical simulation with 42 diffusers of different angles (ranged from 90-270°) and different lengths (ranged from 150-650 mm) with the MFF were studied with Computational Fluid Dynamics (CFD) simulation to acquire the optimal design of diffusers. The numerical simulation results show that the diffusers of 90°/450 mm, 120°/350 mm, and 150°/250 mm with jet lengths of up to 5.85, 5.90, and 5.85 m, respectively, had better performances among all the diffusers. The optimal prototype diffusers of 90°/450 mm, 120°/350 mm, and 150°/250 mm of MFFs were tested by laboratory study and field test. The test was conducted in wind speed distributions at distances of 0.5 to 1.0 m from the axial of MFFs. During the test, we evaluated the MFFs performance such as maximum flow flux, maximum energy efficiency, and non-uniformity coefficient. The diffuser of 150°/250 mm showed the best performance, increasing the flow flux and energy efficiency by 3.8% and 11%, respectively, and obtain higher axial wind speeds and larger non-uniformity coefficients. Finally, the diffusers of 150°/250 mm were tested in a free-stall dairy barn. The field test result shows that the diffusers of 150°/250 mm increased overall average wind speeds by 7.4% and local average wind speeds at bedding 1 and bedding 2 by 31.0% and 27.7%, respectively, which agreed with our numerical simulation and laboratory test. This optimal design of mixing fans could be applied to improve the air mixing in agricultural buildings. Keywords: Agricultural buildings, Diffuser, Mixing fan, Numerical simulation, Optimization.

Empirical validation and local sensitivity analysis of a lumped-parameter thermal model of an outdoor test cell

This paper presents the experimental validation of a thermal model describing the ZEB Test Cells Laboratory, located at the Gløshaugen campus of NTNU and SINTEF in Trondheim, Norway. Besides, a local sensitivity analysis identifies the parameters and inputs that are most influential on the thermal behaviour of the test cell, in terms of temperature profiles of the internal air and internal surfaces. The analysis shows that, in free-running conditions, the most important parameters and inputs, out of the 49 tested ones, are: the air temperature in the guard zone, the initial temperature(s) of the test cell envelope, the linear dimension of the square window, the solar irradiance on the vertical plane of the window, the depth of the test cell, the thermal conductivity and the thickness of the polyurethane layer in the envelope, the solar direct transmittance of the window, the internal height and width of the test cell, the external air temperature and the electrical power input to the mixing fan. Based on the outcome of the local sensitivity analysis and on in-field observations, some practical measures to improve the quality of the input data provided to a dynamic energy simulation tool, and thus the accuracy of prediction of the temperature evolution of the test cell. Based on the outcome of the local sensitivity analysis and on in-field observations, we propose some practical measures to improve the quality of the input data provided to a dynamic energy simulation tool, and thus the accuracy of prediction of the temperature evolution of the test cell. For example, we suggest monitoring accurately the environmental conditions in the guard zone, which are particularly influential under free-running conditions, and installing a global irradiance pyranometer next to the window in order to reduce the uncertainty related to the entering solar load.

A comparative study of launch canister thermal control systems using a liquid or gas working medium

A launch canister thermal control system (TCS) is important for the protection of the engine of a rocket and its electronic devices. Current TCSs using a gas working medium (G-TCS) have high energy consumption and unsatisfactory temperature control effects. Hence, in this study, a TCS using a liquid working medium (L-TCS) was proposed. The two systems were compared through verified simulation models and engineering calculations in different cases. The results of the loaded stable operation case showed that an L-TCS requires much less energy and has a much higher energy efficiency in all the analyzed seasons, namely, spring, summer, and winter, in comparison to the G-TCS. Moreover, an L-TCS is superior to a G-TCS in terms of the temperature control effects. In the unloaded start-up case, both the TCS types have their respective advantages, but their start-up durations are long. However, introducing a mixing fan can drastically decrease the start-up duration of the L-TCS.

A Comparative Study of Thermal Control Systems Using a Liquid or Gas Working Medium

Thermal control systems (TCSs) are used to ensure an appropriate temperature environment for the internal objects. Most TCSs can be generally classified into two categories: TCS using a gas working medium (G-TCS) and TCS using a liquid working medium (L-TCS). In this work, models of G-TCS and L-TCS were constructed, and the two systems were compared in a loaded stable operation case and an unloaded starting case. The analysis of the loaded stable operation case shows that the heat consumptions of both systems are nearly the same, but the flow energy consumption of G-TCS is 21.82 times that of L-TCS, and thus its total energy consumptions are 3.49, 8.83 and 14.64 times that of L-TCS in winter, summer and spring, respectively, i.e., energy efficiencies of L-TCS are 3.81, 10.33 and 11.63 times that of G-TCS in winter, summer and spring, respectively. In terms of spatial uniformity and temporal stability of the temperature field of the object’s surface, L-TCS is far superior to G-TCS. In the unloaded starting case, each TCS has its respective advantage, but both starting performance are unsatisfactory. However, introducing a mixing fan to enhance the convection inside the envelope can greatly shorten L-TCS’s start-up duration.

Effects of Configuration and Headspace Mixing on the Accuracy of Closed Chambers for DairyFarm Gas Emission Measurement

<abstract><title><italic>Abstract. </italic></title> This study was aimed at evaluating the influence of chamber configuration (enclosure area and height), the use of a mixing fan and the wind speed induced by the fan at the emitting surface (head space mixing) on the accuracy for the closed chamber in gas emission measurement at low emission rates (≤3000 g SF₆ m^-2 h^-1). A calibration system was designed to generate a reference flux, and SF₆ was used as the target gas. Accuracy or chamber performance was defined based on the agreement between the calculated reference and chamber fluxes, which were not affected by chamber configuration. Four unvented closed chambers with two floor diameters (300 and 400 mm) and three different heights (200, 300, and 400 mm) were tested at seven different emission rates (from 684 ±72 to 2958 ±144 g m^-2 h^-1). Chamber configuration was correlated with the reference flux of sulfur hexafluoride (SF₆), and the tested chambers underestimated the reference fluxes by 21.5% ±13.6% (average ±SD). Chamber enclosure area did not affect the chamber performance while the height significantly impacted measurement accuracy. A chamber height of 300 mm was recommended to measure low gas emission rates. The positive air pressure induced by the mixing fan in the headspace increased with the fan speed, but the chamber performance was not affected by the mixing fan at lower emission rates. For our tested conditions, a mixing fan was not necessary and a vent opening balancing the air pressure inside and outside a chamber was not recommended.

Concept description and assessment of the main features of a geared intercooled reversed flow core engine

Intercooled turbofan cycles allow higher overall pressure ratios to be reached which gives rise to improved thermal efficiency. Intercooling also allows core mass flow rate to be reduced which facilitates higher bypass ratios. A new intercooled core concept is proposed in this paper which promises to alleviate limitations identified with previous intercooled turbofan designs. Specifically, these limitations are related to core losses at high overall pressure ratios as well as difficulties with the installation of the intercooler. The main features of the geared intercooled reversed flow core engine are described. These include an intercooled core, a rear-mounted high-pressure spool fitted rearwards of the low-pressure spool as opposed to concentrically as well as a mixed exhaust. In these studies, the geared intercooled reversed flow core engine has been compared with a geared intercooled straight flow core engine with a more conventional core layout. This paper compares the mechanical design of the high-pressure spools and shows how different high-pressure compressor and high-pressure turbine blade heights can affect over-tip leakage losses. In the reversed configuration, the reduction in high-pressure spool mean diameter allows for taller high-pressure compressor and turbine blades to be adopted which reduces over-tip leakage losses. The implication of intercooler sizing and configuration, including the impact of different matrix dimensions, is assessed for the reversed configuration. It was found that a 1-pass intercooler would be more compact although a 2-pass would be less challenging to manufacture. The mixer performance of the reversed configuration was evaluated at different levels of mixing effectiveness. This paper shows that the optimum ratio of total pressure in the mixing plane for the reversed flow core configuration is about 1.02 for a mixing effectiveness of 80%. Lower mixing effectiveness would result in a higher optimum ratio of total pressure in the mixing plane and fan pressure ratio.

Experimental study of vented hydrogen deflagration with ignition inside and outside the vented volume

Experiments were carried out inside a 25 m3 vented combustion test facility (CVE) with a fixed vent area sealed by a plastic sheet vent. Inside the CVE, a 0.64 m3 open vent box, called RED-CVE was placed. The vent of the RED-CVE was left open and three different vent area were tested. Two different mixing fans, one for each compartment, were used to establish homogeneous H2 concentrations. This study examined H2 concentrations in the range between 8.5% vol. to 12.5% vol. and three different ignition locations, (1) far vent ignition, (2) inside the RED-CVE box ignition and (3) near vent ignition (the vent refers to the CVE vent). Peak overpressures generated inside the test facility and the smaller compartment were measured. The results indicate that the near vent ignition generates negligible peak overpressures inside the test facility as compared to those originated by far vent ignition and ignition inside the RED-CVE box. The experiments with far vent ignition showed a pressure increase with increasing hydrogen concentration which reached a peak value at 11% vol. concentration and then decreased showing a non-monotonic behaviour. The overpressure measured inside the RED-CVE was higher when the ignition was outside the box whereas the flame entered the box through the small vent.

IMPROVEMENT OF GREENHOUSE MICROCLIMATE DISTRIBUTION BY MEANS OF AIR MIXING FANS

The objective of this work was to experimentally investigate the influence of air mixing fans on air temperature and humidity distribution in an arched roof greenhouse. The greenhouse was occupied by a tomato crop and equipped with two side roll-up openings for ventilation, a PVC pipe heating system and a fan coil heater. Furthermore, for air mixing purposes, an air mixing fan was used. Air temperature and relative humidity was simultaneously recorded in 17 positions equally distributed inside the greenhouse. Concerning the effects of air mixing fan on microclimate distribution, it was found that the mixing fan increased microclimate homogeneity. On the other hand, the use of fan-coil heater was found to increase microclimate heterogeneity. The maximum absolute air temperature and relative humidity difference (observed above the crop) between the centre of the greenhouse and the different measuring positions at the same level, was about 1°C and 4% respectively when the air mixing fan was not used and about 0.4°C and 1% respectively, when the air mixing fan was used. The use of a fan-coil heater increased the above mentioned differences to the level of about 1.7°C and 6% respectively when the air mixing fan was not used and about 1°C and 3% respectively, when the air mixing fan was used. Finally, it was observed that the use of an air mixing fan and/or a fan-coil heater reduced the greenhouse air relative humidity.

An Experimental and Numerical Study on Deposition of Bioaerosols in a Scaled Chamber

This work presents an experimental facility designed and built with the objective of understanding the deposition of bioaerosols in indoor environments. Multiple depositions of two microorganisms Staphylococcus and Micrococcus inside a test chamber were investigated under two air mixing conditions. Airflow rate was demonstrated to have an influence on the concentration homogeneity. An increased proportion of particle deposition was found in the floor section near the chamber wall opposite to the air inlet when air mixing was not enhanced by the mixing fans. Both the experimental results and Eulerian-Lagrangian computations revealed that a small mixing fan inside the chamber prompted very effective mixing while non-homogeneity was observed even at a very high ventilation rate. The results showed that both ventilation rate and mixing conditions in the ventilated chamber have influence on the bioaerosol dispersion and deposition.

Two-Zone Model Application to Breathing Zone and Area Welding Fume Concentration Data

This study assessed a professional pipefitter/welder performing shielded metal arc welding on carbon steel under field conditions. The resulting breathing zone (near field) and area (far field) welding fume concentration data were applied to the two-zone model for the purpose of determining field-derived personal exposure emission (generation) rates during actual welding work. The study is unique in that one welder was evaluated under high production conditions for 2 days at two different welding locations: a boiler room and a breezeway. Samples were collected and analyzed for total particulate following NIOSH Method 0500 and for select metals following NIOSH Method 7300. Breezeway average personal breathing zone sample total particulate concentrations ranged from 2.89 mg/m3 to 4.38 mg/m(3), Fe concentrations ranged from 0.53 to 0.63 mg/m3, and Mn concentrations ranged from 0.10 to 0.12 mg/m3. The boiler room average personal breathing zone sample total particulate concentrations ranged from 4.73 mg/m3 to 5.90 mg/m3, Fe concentrations ranged from 0.48 to 0.85 mg/m3, and Mn concentrations ranged from 0.06 to 0.16 mg/m3. Average arc times ranged from 20 to 25% of the total sampling time. Both tracer gas and anemometer techniques were used to estimate ventilation of the boiler room. The steady-state form of the two-zone model was applied to long-term and short-term sample total particulate, Fe, and Mn concentrations obtained during welding in the boiler room and breezeway. The average generation rate in the boiler room was 39.2 mg/min for TP, 6.4 mg/min for Fe, and 1.3 mg/min for Mn. The average generation rate in the breezeway was 40.0 mg/min for TP, 6.6 mg/min for Fe, and 1.2 mg/min for Mn. The field-based generation rates were considerably lower than laboratory-derived published emission rates of between 280 and 650 mg/min for TP. This study emphasizes the need for field-derived welding fume generation rates and showed the personal breathing zone and area sample concentrations can be described by the two-zone model in a way that may help the industrial hygienist estimate exposures. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resource: Tables detailing the personal breathing zone and average area sample results for breezeway welding and boiler room welding, two-zone modeling results, and boiler room welding personal breathing zone and area sample results with mixing fans on.]

Design and performance of a throughput-matched, zero-geometric-loss, modified three objective multipass matrix system for FTIR spectrometry

The design of and initial results obtained from a multipass matrix system (MMS) for mid-infrared spectroscopy that operates in the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) recently constructed in the School of Chemistry at the University of Leeds, is described. HIRAC is an evacuable, temperature variable, photochemical atmospheric reaction chamber. The MMS design is a modified Chernin cell, utilizing three objective mirrors and two field mirrors. In addition to providing the paraxial equations required for design of a throughput matched multipass cell and throughput matched transfer optics, advanced ray tracing simulations have been performed for the Chernin design described herein. The simulations indicate that, for this MMS, which features small off-axis angles and preserves perfectly the focal properties of the original White design, the paraxial equations are nearly exact, throughput losses due to astigmatism are insignificant, and the system has zero theoretical geometric loss. Measurements of the signal incident on the detector at different matrix arrangements confirm the ray trace results, suggesting that geometric loss in this system is insignificant. The MMS described herein provides adequate stability to permit measurements while the chamber mixing fans are on, gives very good detection limits for some representative species, and is easy to align.