Carlos A. Ortiz

Flattening coefficient for DOP and oleic acid droplets deposited on treated glass slides

The flattening coefficient, F, which is the ratio of apparent droplet diameter as measured on a microscope slide to the true diameter of a spherical drop, has been determined for particles of oleic acid and DOP aerosols collected on treated slides. The slides were made oilphobic by immersion in a widely used fluorocarbon surfactant (NYEBAR Type CT or 3 M Co. Chemical FC-721). The mean value of F for oleic acid was found to be 1.34, and for DOP, 1.35. There is no apparent variation of F with particle diameter for aerosols in the 2.7−29.1 µm range. For DOP, a single technique was used to measure F1 and for oleic acid three techniques were employed. The different techniques gave essential the same result for oleic acid. The addition of a commonly used fluorescent analytical tracer, sodium fluorescein, to oleic acid in amounts of 5–20 percent (m/v) causes a slight shift in the flattening coefficient. With 10 percent uranine, the value of F is 1.32.

A generic mixing system for achieving conditions suitable for single point representative effluent air sampling.

The U.S. EPA has approved Alternate Reference Methodologies for sampling radionuclide aerosol particles from stacks and ducts of U.S. DOE facilities. The approach allows use of single point sampling with shrouded probes from locations where both fluid momentum and contaminant concentration are well mixed across the flow cross section. For existing stacks and ducts that do not have locations where there is adequate mixing, we have developed a generic mixing system that will generate conditions suitable for single point sampling. The coefficients of variation of the velocity, tracer gas, and 10 microm aerodynamic diameter aerosol particles profiles are all less than 10%, which are well within the EPA limit of 20%. Mixing is affected neither by size of the system nor by flow rate, provided the flow is turbulent.

A 10 μm Outpoint Size Selective Inlet for Hi-Vol Samplers

A Two-stage Size Selective Inlet for use with hi-vol samplers was designed and tested. The inlet, which operates at a flow rate of 1.13 m3/min, is shown to have a cutpoint of 9.8 μm and a fractionation curve slope of 1.45. The cutpoint is well within the EPA suggested limits of 10 ± 1 μm. Fractionation is not affected by wind speed over the test range of 2-24 km/h. Re-entrainment or bounce of solid particles is not of consequence. The difference in penetration of 20 μm aerodynamic diameter glass beads and liquid aerosols is less than 1% at all wind speeds.

Wind tunnel evaluation of the British Smoke Shade Sampler

The funnel-shaped inlet of the British Smoke Shade Sampler was tested in a wind tunnel to characterize aerosol penetration as a function of particle size and wind speed. Cutpoint sizes of 13.S and 10.8μm were noted at wind speeds of 2 and 8 km h−1, respectively. Tests of aerosol penetration through the complete sampling system, including the inlet, connecting tubing, manifold and filter holder, showed the cutpoint to be 4.4 μm. Tubing losses appear to control the transport of the larger particles.

A continuous sampler with background suppression for monitoring alpha-emitting aerosol particles

A continuous air monitor has been developed that includes provisions for improving the detection of alpha-emitting aerosol particles in the presence of radon/thoron progeny that are unattached to ambient aerosol particles. Wind tunnel tests show that 80% of 10-microns aerodynamic equivalent diameter particles penetrate the flow system from the ambient air to the collection filter when the flow rate is 57 L min-1 (2 cfm) and the wind speed is 1 m s-1. Uniformity of aerosol collection on the filter, as characterized by the coefficient of variation of the areal density deposits, is less than 15% for 10-microns aerodynamic-equivalent-diameter aerosol particles. Tests with unattached radon daughters in a flow-through chamber showed that approximately 99% of the 218Po was removed by an inlet screen that is designed to collect radon daughters that are in the size range of molecular clusters. The inlet screen offers the opportunity to improve the signal-to-noise ratio of energy spectra in the regions of interest (subranges of the energy spectrum) of transuranic elements and thereby enhance the performance of background compensation algorithms.

A 10 μm Cutpoint ambient aerosol sampling inlet

Abstract An ambient air sampling inlet was developed which has a cutpoint of 10 ± 0.5 μm aerodynamic diameter and an effectiveness curve slope of 1.58. The unit is designed to operate at a flow rate of 113/min −1. Tests in a wind tunnel at speeds of 2, 8 and 24 km h −1 showed there to be no substantial variation in cutpoint with wind speed. In tests with 10.6 μm particles at a wind speed of 24 km h −1 the sampler orientation was varied to simulate wind angles of attack. For the sampler axis at − 10, 0 and + 10° from the vertical direction, the range of effectiveness values was only from 42.2 to 45.5 per cent. Under static conditions (no wind) the unit was checked for dry particle bounce with plant pollens and glass beads. The results showed there to be no bounce problems for these materials. Finally, the collection filters were examined for uniformity of deposits associated with the collection of 10.6 μm particles. No significant variation of deposit density was noted.

Evaluation of Mixing Elements in an L-Shaped Configuration for Application to Single-Point Aerosol Sampling in Ducts

Experimental data for velocity and tracer gas concentration profiles were collected at several downstream locations of an L-shaped configuration with different mixing elements. Results were presented in the coefficients of variation (COVs) to help determine appropriate locations for single-point sampling downstream of each duct configuration. Comparisons between experimental data and numerical simulations for velocity COVs were also presented. Different mixing elements were applied to the L-shaped configuration to create additional mixing to help provide an acceptable sampling location with low pressure drop for single-point sampling in a duct at less than four duct diameters from the mixing element. The mixing elements included a 90° elbow, a tee, a horizontal generic-tee-plenum (H-GTP) system, and a vertical generic-tee-plenum (V-GTP) system. The COVs for velocity and gas concentration for the two GTP systems were all determined to be less than 13% as compared to a range of 6% to 89% for the 90o elbow and a tee at four duct diameters in round and square ducts. Tests with two different sizes of GTPs were conducted and the results showed the performance of the GTPs to be relatively unaffected by either size or velocity as reflected by the Reynolds number. The pressure coefficient was approximately 0.82 for the H-GTPs, as compared to 5.2 for a previously designed generic mixing system (GMS). The GTPs can be useful in the design of biological and chemical sampling systems in air-conditioning ducts and for mixing in aerosol wind tunnels where uniform aerosol concentrations are needed at the test section.

Performance evaluation of continuous air monitor (CAM) sampling heads.

Continuous air monitor (CAM) samplers are used to detect radioactive aerosol particles in nuclear facilities and to provide alarm signals should the concentrations exceed a multiple of the derived air concentration (DAC) of the radionuclide of concern in a set amount of time. Aerosol particles are drawn into a CAM sampler where collection is to take place upon a filter. Radioactivity of the particles is determined with a detector that is placed in close proximity to the filter face. An important determinant of CAM performance is the ability of the inlet and body of the CAM to transport particulate matter in the inhalable-size range (less than or equal to 10 microns aerodynamic diameter) to the filter without substantial loss or bias with respect to particulate size. Three types of CAM samplers were tested in a low-velocity aerosol wind tunnel to determine the degree to which particles penetrate through the flow systems to the collection filter under conditions typical of normal room air exchange rates. Two air velocities were used: 0.3 and 1.0 m s-1. The CAM samplers were primarily operated at a flow rate of 56.6 L min-1, although some tests were conducted at a flow rate of 28.3 L min-1. The CAM units were prototypes manufactured by Kurz Instruments, Eberline Instrument Corporation, and Victoreen Inc. These three units represent three different approaches to CAM head design. At an air speed of 1 m s-1, aerosol penetration to the filters of the Kurz unit was essentially 100% for particle sizes of 3 and 7-microns aerodynamic diameter and was 86% for a size of 15 microns. For the Eberline sampler, the penetration was over 80% for 3-microns particles but was reduced to less than 2% for 7-microns particles. The victoreen sampler showed penetration values of 98% for 3-microns aerodynamic diameter particles, 88% for 7-microns particles and 4% for a size of 15 microns. Air speed had little effect on the penetration results for the two speeds which were tested. Tests were conducted to determine the uniformity of deposits on the filters of the CAM samplers. For a particle size of 10 microns, the deposits were nonuniform for all three of the instruments.

Single point aerosol sampling: Evaluation of mixing and probe performance in a nuclear stack

Alternative reference methodologies have been developed for sampling of radionuclides from stacks and ducts, which differ from the methods previously required by the United States Environmental Protection Agency. These alternative reference methodologies have recently been approved by the U.S. EPA for use in lieu of the current standard techniques. The standard EPA methods are prescriptive in selection of sampling locations and in design of sampling probes whereas the alternative reference methodologies are performance driven. Tests were conducted in a stack at Los Alamos National Laboratory to demonstrate the efficacy of some aspects of the alternative reference methodologies. Coefficients of variation of velocity, tracer gas, and aerosol particle profiles were determined at three sampling locations. Results showed that numerical criteria placed upon the coefficients of variation by the alternative reference methodologies were met at sampling stations located 9 and 14 stack diameters from the flow entrance, but not at a location that was 1.5 diameters downstream from the inlet. Experiments were conducted to characterize the transmission of 10 microns aerodynamic diameter liquid aerosol particles through three types of sampling probes. The transmission ratio (ratio of aerosol concentration at the probe exit plane to the concentration in the free stream) was 107% for a 113 L min-1 (4-cfm) anisokinetic shrouded probe, but only 20% for an isokinetic probe that follows the existing EPA standard requirements. A specially designed isokinetic probe showed a transmission ratio of 63%. The shrouded probe performance would conform to the alternative reference methodologies criteria; however, the isokinetic probes would not.

A Cam Sampler for Collecting and Assessing Alpha-emitting Aerosol Particles

A new continuous air monitor (CAM) sampler for assessing alpha-emitting transuranic aerosol particles has been developed. The system has been designed to permit collection of particles that can potentially penetrate into the thoracic region of the human respiratory system. Wind tunnel testing of the sampler has been used to characterize the penetration of aerosol to the collection filter. Results show that greater than or equal to 50% of 10-micrograms aerodynamic equivalent diameter (AED) particles are collected by the filter at wind speeds of 0.3 to 2 m s-1 and at sampling flow rates of 28 to 113 L min-1 (1 to 4 cfm). The deposition of 10-microns AED particles takes place primarily in the center of the filter, where the counting efficiency of the detector is highest.