Media and Devices for Management of Airborne Contaminants

Abstract

This thesis presents two projects pertaining to media and devices for the management of airborne contaminants. The projects were completed consecutively and have each been separated to their respective chapters. Investigation of the Temperature Dependent Effects in Crankcase Aerosol Control Devices Oil aerosols formed in the crankcase of reciprocating engines are a significant source of particulate matter and may lead to engine component degradation when used in closed crankcase ventilation (CV) systems or constitute a significant emission source in open CV systems. In modern CV systems, filtration or inertial separation is used to collect oil particles. These devices are highly efficient over a range of flow rates and temperatures; however, some system conditions result in a decrease in efficiency with increasing temperature in a manner not predicted by theory. Experiments were performed on a bench system that introduced atomized oil particles into a clean, pre-heated, air stream that was conveyed isothermally through a heated duct to an oven containing the removal device, either a coalescing filter or an inertial separator, followed by another heated section and an exit duct. The aerosol was sampled using identical upstream and downstream isokinetic sampling systems and characterized using a Dekati Electrical Low-Pressure Impactor (ELPI) that measured particle concentration and size in the range from 0.043 to 8.46μm aerodynamic diameter. Neither single fiber efficiency (SFE) filtration theory nor physical arguments describing the performance of the inertial separator predict a significant dependence of total and fractional efficiency and most penetrating particle size (MPPS) on temperature in the range explored here, 25 to 115°C, but in many cases our measurements show MPPS shifting to smaller size and total efficiency decreasing with increasing temperature. These observations are consistent with the hypothesis that, at device temperature, the particles being processed are smaller than the particles being measured, at room temperature. Particles shrink by evaporation as they pass through the heated sections, but cool and grow by condensation as the sample cools in the sampling lines or in the exit duct. Reported carbon number distributions of typical lubricating oils and evaporation kinetics indicate that droplets in the size range investigated may lose more than half of their mass under temperature conditions, up to 115°C, found in typical crankcase removal devices under engine high-load conditions. These droplets are in a dynamic balance with their vapors and may change during sampling and measurement. Great care must be taken in design of systems used to characterize devices intended to remove volatile droplets and interpretation of measurements made, as the size of the particles measured may not be the same as the size of particles passing through the device. Evaluation of Media and Low-Cost Gas Sensors for Indoor Air Quality Measurement The second project was motivated by increasing interest in high efficiency indoor air purification devices for control of airborne contaminants. Filtration is a commonly used method for removing particulate matter and improving air quality. An emerging field is the study of impregnated media, where the same highly efficient particle removal media can be engineered to also capture pollutant gases. We set out to evaluate the pollutant gas removal effectiveness for a set of carbon-impregnated media, where the pollutant gases under investigation were CO, CO2, NO, NO2, and SO2. Another feature of the study was that the sensors used were relatively low-cost sensors and a detailed evaluation of their performance was performed. Part of the motivation for using low-cost sensors was the possibility of using them for real-time performance of media in actual air purification devices. The goal of the study was to evaluate 3 different carbon-impregnated media and a set of 6 low-cost gas sensors on a test bench designed to determine pollutant gas concentration as well as the removal efficiency. Tests were performed at ambient temperature conditions with relative humidity controlled from 5-60%, characteristic of indoor residential or commercial conditions. Five of the sensors used were Alphasense B4 series low-cost gas sensors, for monitoring CO, SO2, NO, NO2, and a combination NO2 and ozone sensor. These were electrochemical type sensors. The sixth sensor was a non-dispersive infrared sensor for measuring CO2. The pollutant gas sensors were assessed for concentration accuracy, sensor noise, and response time. We found that sensor accuracy was acceptable under both humid and dry conditions for the NO, CO, and CO2 sensors. Concentration accuracy was also acceptable for the NO2 and SO2 sensors, though indicated concentrations did not agree with expected values during media testing. This was due to concerns with the dilution air supply. Sensor noise observed was higher than specification for CO and SO2, where SO2 encountered the greatest deviations from manufacture specification. With respect to response times, it was found that the CO2 and CO sensors were slower than manufacturer specification, the NO2 and NO2/O3 matched specification, and the NO and SO2 sensors were faster than specification. The pollutant gas removal efficiency for each gas, media, and humidity combination was calculated and presented. The influence of humidity on removal effectiveness was observed, wherein humid conditions resulted in decreased pollutant gas removal efficiency. Removal efficiencies were very low for CO and NO2. They were somewhat higher for NO, SO2, and CO2, most notably under dry conditions. This work demonstrated the efficacy of using LCGSs for media evaluation.