1,721,090 research outputs found
New method to measure the mechanical collection mechanisms of full-scale air filters
Get PDFAir filters are chosen for the minimum particle-capture efficiency they can provide in a specific application. Some media can achieve high efficiencies at low resistance to air flow by adding electrostatic charges on fairly coarse fibers. However, prolonged filter exposure to fine particles reduces the electrostatic enhancement effect. The filter efficiency must then rely mainly on mechanical collection mechanisms, and can fall well below the initial value. It is useful to test filter media when the effect of electrostatic charges is eliminated. To estimate the efficiency drop that may occur, air filter test standards include filter conditioning procedures to inhibit the effect of electrostatic charges. These treatments should leave only particle capture effects from mechanical collection mechanisms such as sieving, aerodynamics and diffusion, but not reduce or enhance these effects. EN779:2012 and ISO 21220:2009 describe such a conditioning treatment for filter media, and ASHRAE 52.2-2012 describes one for full-scale filters. The ASHRAE 52.2-2012 optional treatment suggests that air filters be exposed to a potassium chloride aerosol having approximately 35 nm count mean diameter. Following the charge-elimination treatment, procedures measuring efficiency as a function particle size are performed. In ISO/TS 21220:2009 and EN779:2012 the discharging treatment is also mandatory, but is performed on samples of the media used to manufacture the filter. This treatment requires a 2 minute soak in essentially pure isopropyl alcohol (IPA), after which the media samples are dried for 24 hours before further tests. This method presents problems, namely, that soaking in a liquid may alter the mechanical efficiency of media, and that samples of media may not be representative of the media used in the full-scale filter. A new approach, developed by T. Hayashi in Japan, eliminated electrostatic effects in electret-enhanced media sheets by exposure to IPA vapor for 16 hours or longer. This procedure was successfully duplicated by J. Cai in China, and at the Politecnico di Torino. ISO/TC142/WG9 in 2010 ran an inter-laboratory comparison to assess this procedure, and in 2011 organized another comparison which extended the method to full-scale filters. The full-scale tests have included three different types of air filters, comparing the results with the other approaches previously mentioned. These results will be useful for revising the current ISO 29461-1 test method and also for developing the new ISO 16890 series for general ventilation applications. Here we summarize the data obtained at the Politecnico di Torino, and describe the new test protocol that could be adopted by future international filter test standard
Global Standards for Filter Testing
No full textThe ISO and the IEC are cooperating with the European Union's CEN (see Table 1 for acronym definitions) and other standards organizations to create global standards for building air filters. The United States, through ANSI, is represented on ISO Technical Committee (TC) 142, Cleaning Equipment for Air and Other Gases, Working Group (WG) 3, General Ventilation Filters. This group is writing an ISO standard for a test method for general ventilation air filters. Several other countries are participating and the list is being updated continuously (see ISO/TC 142 Web site for the latest information
International standards: filters for vehicular applications
No full textIn the second part of their examination of international standards for particulate and gaseous contaminant air filters, Paolo Tronville and Richard Rivers look at filters for vehicular applications
Predicting Resistance of Air Filter Media Having Log-Normal Fiber Diameter Distribution and Random 2-Dimension Spacing by CFD Simulation
No full textProperties of nanoparticles affecting simulation of fibrous gas filter performance
Get PDFComputational Fluid Dynamics (CFD) codes allow detailed simulation of the flow of gases through fibrous filter media. When the pattern of gas flow between fibers has been established, simulated particles of any desired size can be "injected" into the entering gas stream, and their paths under the influence of aerodynamic drag, Brownian motion and electrostatic forces tracked. Particles either collide with a fiber, or pass through the entire filter medium. They may bounce off the fiber surface, or adhere firmly to the surface or to particles previously captured. Simulated injection of many particles at random locations in the entering stream allows the average probability of capture to be calculated. Many particle properties must be available as parameters for the equations defining the forces on particles in the gas stream, at the moment of contact with a fiber, and after contact. Accurate values or all properties are needed, not only for predicting particle capture in actual service, but also to validate models for media geometries and computational procedures used in CFD. We present a survey of existing literature on the properties influencing nanoparticle dynamics and adhesio
Assessing the relationship between the choice of air filters for general ventilation and indoor aerosol concentrations (revised)
No full textStandards I:filters for buildings and gas turbines
No full textThe development of standards for the filtration industry continues to take prominence worldwide. In the first of a two part feature, Paolo Tronville and Richard Rivers examine the development of standards for filters used in general building ventilation, as well as for gas turbine intake air cleaning
Measuring the performance of air filter media
No full textTest methods for air filtration media have been relatively slow to materialize. The critical aspects of test methods for several different air filter media are discussed. Suggestions on how to tackle the problems are made
Procedures for realistic models of fibrous gas filtration media
Get PDFThe behavior of most HVAC system components has been quantified with accuracy sufficient to allow meaningful minimization of both economic and energy system costs. For one component - air filters - performance and cost predictions are still highly approximate, hence designers have difficulty including their contribution to capital, operating, and energy cost
Looking for the minimum efficiency of fibrous air filters during their service life
Get PDFElectret fibrous filter media achieve high efficiencies while maintaining low air flow resistance by incorporating electrostatic charges on their fibers. However, captured ultrafine particles reduce electrostatic effects. Existing test methods specify preconditioning to detect the minimum efficiency by eliminating electrostatic effects.
ASHRAE 52.2 exposes media to nanoparticle KCl aerosols. ISO/TS21220 and
EN779 immerse media in isopropyl alcohol (IPA). These approaches have some problems:
- Nanoparticle generation is fairly complicated and needs to be kept under control;
- The structure of some media may be changed by liquid immersion;
- Soaking full scale air filters requires large amounts of IPA.
A new procedure, exposure to IPA vapor, has been shown to be effective. We summarize these studies and ISO/TC142 activities related to them
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