Numerical and experimental performance evaluation of two multi-stage cloud collectors

January 1999.Also issued as Derek J. Straub's thesis (M.S.) -- Colorado State University, 1999.Includes bibliographical references.An evaluation of the collection characteristics of two new multi-stage cascade inertial impactors designed for size-resolved cloud drop collection has been performed. The FROSTY supercooled cloud collector is intended for the collection of supercooled cloud drops in a winter environment in three independent size fractions with stage 50% cut diameters of 15 μm, 10 μm, and 4 μm . The CSU 5-Stage cloud collector is designed for sampling warm clouds in five distinct fractions on five stages that have desired 50% cut diameters of 30, 25, 15 , 10, and 4 μm. Two approaches were selected for the evaluation of the FROSTY and CSU 5-Stage cloud collectors. Numerical simulations provided a visualization of the air flow patterns and drop trajectories through the collectors while experimental laboratory calibrations provided a quantitative analysis of true collection performance. For each of these methods, 50% cut diameters, efficiency curves, and wall losses for each stage of the FROSTY and CSU 5-Stage collectors were derived. The experimental calibration work indicated that distinct fractions of cloudwater are collected in each stage of the FROSTY and CSU 5-Stage collectors. At laboratory conditions, the experimentally determined 50% cut diameters for the three stages of the FROSTY supercooled cloud collector were 19, 11.5, and 5 μm. Drop losses to the interstage wall surfaces in the FROSTY collector peaked at approximately 35% for 16 μm drops and were lower for larger and smaller drop sizes. For operation at design conditions of 3000 m elevation and -4° C, the 50% cut diameters are expected to decrease to 17, 10.5, and 4.5 μm. The experimentally determined 50% cut diameters, measured at laboratory conditions, for the CSU 5-Stage cloud collector were 25.5, 29, 17.5, 10.5, and 4.5 μm for stages 1 through 5, respectively. Wall losses tended to be higher than those for the FROSTY cloud collector across the drop size range under consideration. Losses peaked at nearly 45% for drops between 10 and 18 μm in diameter and decreased to about 20% at the largest and smallest drop sizes. 50% cut diameters are expected to remain essentially unchanged for CSU 5-Stage collector operation at sea level design conditions. Numerical modeling of the air flow patterns as well as drop trajectories through the FROSTY and CSU 5-Stage cloud collectors was performed with the commercially available Computational Fluid Dynamics (CFO) software package FLUENT, from Fluent, Inc. FLUENT offered two alternatives for the calculation of drop trajectories. Trajectory simulations based on the average continuous phase (air) velocity field as well as trajectory simulations which included the effects of statistically derived turbulent velocity fluctuations on drop motion were performed. Drop collection patterns based on these types of trajectory calculations were used to generate collection efficiency curves. Comparisons were made between the numerically predicted collection efficiency curves and efficiency curves established through experimental calibration. These comparisons indicated that the inclusion of turbulent fluctuation effects on drop motion provided better agreement with experimental observations than trajectories based only on average flow field velocities. However, the use of velocity fluctuations defined by default parameters also produced unrealistic losses to wall surfaces for small drop sizes. The parameters controlling turb lent velocity fluctuation effects on drop motion were examined in an effort to provide better agreement between the numerical and experimental results. Despite this shortcoming, numerically derived 50% cut diameters and overall collection efficiency curve shapes, for drop trajectories including turbulent velocity fluctuations, agreed reasonably well with experimental observations in most cases.Sponsored by the National Science Foundation ATM-9509596 , and the U.S. Environmental Research and Quality Assurance R82-3979-010

Design and testing of a new aircraft-based cloud water sampling system

December 2002Also issued as Derek J. Straub's dissertation (Ph.D.) -- Colorado State University, 2002.Includes bibliographical references.Experimental studies of cloud processing mechanisms necessitate the collection of representative samples of cloud water for chemical analysis. In order to provide samples from clouds that are inaccessible from ground-based sampling stations, a new aircraft-based cloud water collection system has been developed . The objective of the design process was to produce an automated collector that can acquire well-characterized cloud water samples and is portable between multiple research aircraft. Issues such as cloud drop shatter and re-entrainment, structural integrity, system size and weight, material compatibility with the anticipated chemical analyses, and ease of use during field operation w re all considered during the design process. The new cloud water collection system utilizes an axial-flow cyclone to centrifugally separate cloud drops from the air stream. Up to seven individual samples can be stored over the course of a single research flight. An analysis of the axial-flow cyclone was performed with a finite volume based computational fluid dynamics (CFD) code. Solutions were obtained for air flow patterns and cloud drop trajectories. The predicted continuous phase (air) velocity field indicates that the axial-flow cyclone generates a strong rotational ow field with a tangential velocity of 85 ms-'. Based on simulations of cloud drop trajectories, centrifugal force in the rotational flow field is sufficient to quickly move entrained cloud drops to the wall of the axial-flow cyclone duct where they can be removed for storage. Collection efficiency as a function of drop size was ascertained and the 50% cut diameter was determined to be approximately 8 microns. An experimental laboratory calibration involving monodisperse fluorescein-tagged drops verified the numerical modeling results. The system was deployed during the Dynamics an Chemistry of Marine Stratocumulus, Phase II (DYCOM -II) field project in July 2001. The DYCOMS-II campaign served as a testing and evaluation program for the system as well as an opportunity to study the chemical composition of stratocumulus clouds in the remote marine environment. Over the course of the project, 50 samples were obtained during seven nighttime and two daytime flights. Sample pH was measured on-site after each flight. Peroxide, formaldehyde, S(IV), trace metals and major ions (Cr, NO3-, so/-, Na+, NH/, K+, ca2+, and Mg2+) were preserved on site and analyzed after the field campaign. The analyses were used to characterize the composition of the sampled clouds and to investigate cloud processing mechanisms, including the potential for rapid aqueous phase oxidation of S(IV) to sulfate.Sponsored by the National Science Foundation ATM-0084696, and the National Center for Atmospheric Research Advanced Study Program

Cloud water chemistry in Sequoia National Park

Interception of cloudwater by forests in the Sierra Nevada Mountains may contribute significantly to acidic deposition in the region. Cloudwater sampled in Sequoia National Park had pH values ranging from 4.4 to 5.7. The advance of cold fronts into the Park appears to lead to higher aerosol and gas phase concentrations than are seen under normal mountain-valley circulations, producing higher cloud-water concentrations than might otherwise be expected. Estimates of annual deposition rates of NO_3^−, SO_4^(2−), NH_4^+ and H^+ due to cloudwater impaction are comparable to those measured in precipitation

Receptor modeling of near-roadway aerosol mass spectrometer data in Las Vegas, Nevada, with EPA PMF

Ambient non-refractory PM<sub>1</sub> aerosol particles were measured with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-AMS) at an elementary school 18 m from the US 95 freeway soundwall in Las Vegas, Nevada, during January 2008. Additional collocated continuous measurements of black carbon (BC), carbon monoxide (CO), nitrogen oxides (NO<sub>x</sub>), and meteorological data were collected. The US~Environmental Protection Agency's (EPA) positive matrix factorization (PMF) data analysis tool was used to apportion organic matter (OM) as measured by HR-AMS, and rotational tools in EPA PMF were used to better characterize the solution space and pull resolved factors toward known source profiles. Three- to six-factor solutions were resolved. The four-factor solution was the most interpretable, with the typical AMS PMF factors of hydrocarbon-like organic aerosol (HOA), low-volatility oxygenated organic aerosol (LV-OOA), biomass burning organic aerosol (BBOA), and semi-volatile oxygenated organic aerosol (SV-OOA). When the measurement site was downwind of the freeway, HOA composed about half the OM, with SV-OOA and LV-OOA accounting for the rest. Attempts to pull the PMF factor profiles toward source profiles were successful but did not qualitatively change the results, indicating that these factors are very stable. Oblique edges were present in G-space plots, suggesting that the obtained rotation may not be the most plausible one. Since solutions found by pulling the profiles or using <i>F</i><sub>peak</sub> retained these oblique edges, there appears to be little rotational freedom in the base solution. On average, HOA made up 26% of the OM, while LV-OOA was highest in the afternoon and accounted for 26% of the OM. BBOA occurred in the evening hours, was predominantly from the residential area to the north, and on average constituted 12% of the OM; SV-OOA accounted for the remaining third of the OM. Use of the pulling techniques available in EPA PMF and ME-2 suggested that the four-factor solution was very stable

The ontogeny of bumblebee flight trajectories: From naïve explorers to experienced foragers

Understanding strategies used by animals to explore their landscape is essential to predict how they exploit patchy resources, and consequently how they are likely to respond to changes in resource distribution. Social bees provide a good model for this and, whilst there are published descriptions of their behaviour on initial learning flights close to the colony, it is still unclear how bees find floral resources over hundreds of metres and how these flights become directed foraging trips. We investigated the spatial ecology of exploration by radar tracking bumblebees, and comparing the flight trajectories of bees with differing experience. The bees left the colony within a day or two of eclosion and flew in complex loops of ever-increasing size around the colony, exhibiting Lévy-flight characteristics constituting an optimal searching strategy. This mathematical pattern can be used to predict how animals exploring individually might exploit a patchy landscape. The bees’ groundspeed, maximum displacement from the nest and total distance travelled on a trip increased significantly with experience. More experienced bees flew direct paths, predominantly flying upwind on their outward trips although forage was available in all directions. The flights differed from those of naïve honeybees: they occurred at an earlier age, showed more complex looping, and resulted in earlier returns of pollen to the colony. In summary bumblebees learn to find home and food rapidly, though phases of orientation, learning and searching were not easily separable, suggesting some multi-tasking

New Chiral Phases of Superfluid 3He Stabilized by Anisotropic Silica Aerogel

A rich variety of Fermi systems condense by forming bound pairs, including high temperature [1] and heavy fermion [2] superconductors, Sr2RuO4 [3], cold atomic gases [4], and superfluid 3He [5]. Some of these form exotic quantum states having non-zero orbital angular momentum. We have discovered, in the case of 3He, that anisotropic disorder, engineered from highly porous silica aerogel, stabilizes a chiral superfluid state that otherwise would not exist. Additionally, we find that the chiral axis of this state can be uniquely oriented with the application of a magnetic field perpendicular to the aerogel anisotropy axis. At suffciently low temperature we observe a sharp transition from a uniformly oriented chiral state to a disordered structure consistent with locally ordered domains, contrary to expectations for a superfluid glass phase [6].Comment: 6 pages, 4 figure, and Supplementary Informatio

Airborne characterization of smoke marker ratios from prescribed burning

A Particle-Into-Liquid Sampler – Total Organic Carbon (PILS-TOC) and fraction collector system was flown aboard a Twin Otter aircraft sampling prescribed burning emissions in South Carolina in November 2011 to obtain smoke marker measurements. The fraction collector provided 2 min time-integrated offline samples for carbohydrate (i.e., smoke markers levoglucosan, mannosan, and galactosan) analysis by high-performance anion-exchange chromatography with pulsed amperometric detection. Each fire location appeared to have a unique 1levoglucosan /1water-soluble organic carbon (WSOC) ratio (RF01/RF02/RF03/RF05 = 0.163± 0.007 μg C μg−1 C, RF08 = 0.115 ± 0.011 μg C μg−1 C, RF09A = 0.072 ± 0.028 μgC μg−1 C, and RF09B = 0.042 ± 0.008 μg Cμg−1 C, where RF means research flight). These ratios were comparable to those obtained from controlled laboratory burns and suggested that the emissions sampled during RF01/F02/RF03/RF05 were dominated by the burning of grasses, RF08 by leaves, RF09A by needles, and RF09B by marsh grasses. These findings were further supported by the 1galactosan /1levoglucosan ratios (RF01/RF02/RF03/RF05 = 0.067 ± 0.004 μg μg−1, RF08 = 0.085 ± 0.009 μg μg−1, and RF09A = 0.101 ± 0.029 μg μg−1) obtained as well as by the ground-based fuel and filter sample analyses during RF01/RF02/RF03/RF05. Differences between 1potassium /1levoglucosan ratios obtained for these prescribed fires vs. laboratory-scale measurements suggest that some laboratory burns may not accurately represent potassium emissions from prescribed burns. The1levoglucosan /1WSOC ratio had no clear dependence on smoke age or fire dynamics suggesting that this ratio is more dependent on the type of fuel being burned. Levoglucosan was stable over a timescale of at least 1.5 h and could be useful to help estimate the air quality impacts of biomass burning

The Typical Flight Performance of Blowflies: Measuring the Normal Performance Envelope of Calliphora vicina Using a Novel Corner-Cube Arena

Despite a wealth of evidence demonstrating extraordinary maximal performance, little is known about the routine flight performance of insects. We present a set of techniques for benchmarking performance characteristics of insects in free flight, demonstrated using a model species, and comment on the significance of the performance observed. Free-flying blowflies (Calliphora vicina) were filmed inside a novel mirrored arena comprising a large (1.6 m1.6 m1.6 m) corner-cube reflector using a single high-speed digital video camera (250 or 500 fps). This arrangement permitted accurate reconstruction of the flies' 3-dimensional trajectories without the need for synchronisation hardware, by virtue of the multiple reflections of a subject within the arena. Image sequences were analysed using custom-written automated tracking software, and processed using a self-calibrating bundle adjustment procedure to determine the subject's instantaneous 3-dimensional position. We illustrate our method by using these trajectory data to benchmark the routine flight performance envelope of our flies. Flight speeds were most commonly observed between 1.2 ms−1 and 2.3 ms−1, with a maximum of 2.5 ms−1. Our flies tended to dive faster than they climbed, with a maximum descent rate (−2.4 ms−1) almost double the maximum climb rate (1.2 ms−1). Modal turn rate was around 240°s−1, with maximal rates in excess of 1700°s−1. We used the maximal flight performance we observed during normal flight to construct notional physical limits on the blowfly flight envelope, and used the distribution of observations within that notional envelope to postulate behavioural preferences or physiological and anatomical constraints. The flight trajectories we recorded were never steady: rather they were constantly accelerating or decelerating, with maximum tangential accelerations and maximum centripetal accelerations on the order of 3 g

Stable water isotopologue ratios in fog and cloud droplets of liquid clouds are not size-dependent

In this work, we present the first observations of stable water isotopologue ratios in cloud droplets of different sizes collected simultaneously. We address the question whether the isotope ratio of droplets in a liquid cloud varies as a function of droplet size. Samples were collected from a ground intercepted cloud (= fog) during the Hill Cap Cloud Thuringia 2010 campaign (HCCT-2010) using a three-stage Caltech Active Strand Cloud water Collector (CASCC). An instrument test revealed that no artificial isotopic fractionation occurs during sample collection with the CASCC. Furthermore, we could experimentally confirm the hypothesis that the δ values of cloud droplets of the relevant droplet sizes (μm-range) were not significantly different and thus can be assumed to be in isotopic equilibrium immediately with the surrounding water vapor. However, during the dissolution period of the cloud, when the supersaturation inside the cloud decreased and the cloud began to clear, differences in isotope ratios of the different droplet sizes tended to be larger. This is likely to result from the cloud's heterogeneity, implying that larger and smaller cloud droplets have been collected at different moments in time, delivering isotope ratios from different collection times