Evaluating Aerosol Aspiration Efficiency in Fast-moving Air

2013 ◽  
Vol 56 (2) ◽  
pp. 20-28 ◽  
Author(s):  
De-Ling Liu
Keyword(s):  
Fast Moving ◽  
Aerosol Particles ◽  
Physical Factors ◽  
Particle Sizes ◽  
Aerosol Sampling ◽  
Sampling Errors ◽  
Air Velocity ◽  
Sampling Probe ◽  
Gas Molecules ◽  
Aspiration Efficiency

Sampling representative aerosol particles in fast-moving air is a challenging task. Aerosols are significantly more massive than gas molecules, thus they might not follow air streamlines well and could be more easily subjected to sampling errors. This work examines the physical factors that govern the aspiration efficiency of an aerosol sampling probe in unidirectional moving air, and explores the plausible sampling deviations under various high air velocity scenarios. The particle sizes of 0.5 and 5 μm are of particular interest due to their use in defining air cleanliness levels in ISO 14644-1[1] and FED-STD-209.[2]* Our analytical results indicate that significant sampling errors could occur for 5-μm particles when a thick-walled sampling probe is used, or when the air velocity at the sampling probe inlet does not match the velocity of the incoming air (i.e., anisokinetic sampling). The aspiration efficiency of 0.5-μm particles, on the other hand, is nearly 100% due to sufficiently small inertia of these particles.

Evaluating Aerosol Transmission Efficiency in a Sampling System

2013 ◽  
Vol 56 (2) ◽  
pp. 29-42 ◽  
Author(s):  
De-Ling Liu
Keyword(s):  
Transmission Efficiency ◽  
Physical Factors ◽  
Aerosol Sampling ◽  
Sampling Errors ◽  
Air Velocity ◽  
Sampling System ◽  
Sampling Line ◽  
Directional Change ◽  
Inner Diameter ◽  
Sample Transfer

This work examines the physical factors that contribute to sampling errors in an aerosol sampling system consisting of a sampling probe and a sampling line. Aerosol particles are more massive than gas molecules and therefore tend to deviate from air streamlines in response to sudden directional change, which potentially leads to sampling errors during sample transfer processes. Based on well-established studies involving particle transport and deposition, an analysis was performed to determine the sampling line transmission efficiency for 0.5- and 5-μm particles as these particle sizes are used in defining air cleanliness level in ISO 14644-1[1] and FED-STD-209E.[2]* Our analytical results indicate that significant particle losses for 5-μm particles can occur if bends exist in the sampling lines. In addition, particle losses typically can be reduced by lowering the air velocity in the sampling line, and this can be achieved by using a sampling line with a larger inner diameter (I.D.). The example calculations also showed that 0.5-μm particles, with their insignificant inertia, have nearly 100% transmission efficiency regardless of the sampling line bends.

Second Paper: The Effects of Physical Factors on Ignition Delay

1966 ◽  
Vol 181 (1) ◽  
pp. 34-59 ◽  
Author(s):  
W-T. Lyn ◽  
E. Valdmanis
Keyword(s):  
Ignition Delay ◽  
Drop Size ◽  
Injection Rate ◽  
Published Data ◽  
Physical Factors ◽  
Injection Timing ◽  
Air Velocity ◽  
Spray Form ◽  
Temperature And Pressure ◽  
Compression Temperature

The effects of physical factors on ignition delay have been studied on a motored research engine using a single injection technique. The fuels used included a high cetane number reference fuel, gas oil and M.T. 80 petrol. The primary factors investigated are those pertaining to the fuel spray, such as injection timing, quantity, and pressure (affecting drop size, velocity and injection rate); hole diameter (affecting drop size and injection rate) and spray form (nozzle type); and those pertaining to the engine, such as temperature, pressure and air velocity. Engine operating variables such as speed and load affect the ignition delay because they change the primary factors such as injection pressure, compression temperature, pressure and air velocity. It has been found that under normal running conditions, compression temperature and pressure are the major factors. All other factors have only secondary effects. Under starting conditions, when ignition is marginal, mixture formation becomes as important as compression temperature and pressure. Such factors as air velocity and spray form which affect the mixing pattern can have a very pronounced effect on ignition delay. Published data on ignition delay are compared with those obtained in the present investigation and a generalization of the data is recommended for engine design and computational work.

Helmholtz Resonance Based Micro Electrostatic Actuators for Compressible Gas Control: A Microjet Generator and a Gas Micro Pump

2010 ◽  
Vol 7 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Hanseup Kim ◽  
Khalil Najafi ◽  
Luis P. Bernal
Keyword(s):  
Total Power ◽  
Maximum Pressure ◽  
Air Velocity ◽  
Electrostatic Actuators ◽  
Helmholtz Resonance ◽  
Micro Pump ◽  
Resonant Behavior ◽  
In Series ◽  
Instantaneous Pressure ◽  
Gas Molecules

This paper reports Helmholtz-resonance based micro electrostatic actuators to control compressible gaseous fluids in the micro scale. Particularly, it discusses design, fabrication, and testing results of two electrostatic actuators: a micro jet generator and an integrated peristaltic multistage micro pump. These electrostatic actuators vibrate a micro membrane in a micro chamber at a high frequency (>10 kHz), and easily induce the resonant behavior of compressible gases in the chamber. Such resonant behavior, often called the Helmholtz resonance, can repeatedly create instantaneous pressure in equilibrium between the inside and outside of the chamber and cause gas to rapidly exit the chamber, forming a collimated jet. The developed micro jet generator consists of multiple acoustic chambers in parallel; produces directional gas momentum from each chamber by utilizing the Helmholtz resonance; and collectively entrains nearby gas molecules to form a gas stream. The fabricated micro jet generator has a footprint of 1.6 × 1.6 cm2 and contains 25 acoustic micro thrusters. It operates using a 140 V and 70 kHz sinusoidal signal and produces a thrust of 55.6 μN, a maximum air velocity of 1.2 m/s, and consumes power of 3.11 mW. The developed micro pump consists of multiple acoustic chambers in series and produces a high total pressure by accumulating pressures across the multiple chambers, while maintaining high flow rates utilizing the fluidic resonance of each pumping chamber. The fabricated 18-stage pump produces the maximum air flow rate of 4.0 sccm and maximum pressure differentials of 17.5 kPa with total power consumptions of only 57 mW. Its total package volume is 25.1 × 19.1 × 1 mm3. It is notable that these electrostatic actuators, with their actuation membranes, acoustic chambers, fluidic channels, and micro valves, are fabricated into a single silicon chip by developing low temperature wafer bonding techniques to protect the polymer structures inside.

scholarly journals Movement of Particles in the Air

2001 ◽  
pp. 22-26
Author(s):  
Zoltán Csizmazia ◽  
Ilona Nagyné Polyák
Keyword(s):  
Aerodynamic Resistance ◽  
Resistance Coefficient ◽  
Thermal Sensor ◽  
Particle Sizes ◽  
Centrifugal Fan ◽  
Air Velocity ◽  
Screen Size ◽  
Precise Description ◽  
Shape Coefficient ◽  
Size Of Particles

The physical characteristics of particles (seeds and fertilisers) can strongly influence their movements both in seeding and spreading machines and in the air. It is therefore essential to study these particles when constructing such machines. In this respect the size, shape, coefficient of friction and aerodynamic resistance of particles are of great importance.Due to their irregular shape, determining the size of particles is a troublesome process. A precise description of particles has to include several sizes and can be obtained from their screen size. Many physical properties of particles are relevant during movement in the air, but the aerodynamic resistance coefficient is the most important (Hofstee et al., 1990). Two types of wheat and four types of fertiliser particles were investigated (supported by the National Scientific Foundation OTKA, T-026482). An elutriator was designed and constructed (Csizmazia et al., 2000), in which an airflow is supplied by a centrifugal fan. Air velocity was measured with a thermal sensor. Particle sizes, mass and terminal air velocity were measured. The influence of the aerodynamic resistance coefficient on the particles’ motion is also discussed.

Simulation of Submicron Particle Deposition in Laminar and Turbulent Stagnation Point Flows

1991 ◽  
Author(s):  
Salem Abuzeid ◽  
Ahmed A. Busnaina
Keyword(s):  
Brownian Motion ◽  
Stagnation Point ◽  
Deposition Rate ◽  
Particle Deposition ◽  
Aerosol Particles ◽  
Laminar Flows ◽  
Wafer Surface ◽  
Particle Sizes ◽  
Mean Flow ◽  
Gaussian Random Process

Abstract The two dimensional laminar and turbulence stagnation-point flow over a wafer surface within a cleanroom environment are numerically simulated. This study shows the relationship between particle capture area on the wafer and the particle size and flow conditions. The mean flow field is simulated using a two equation k-ϵ turbulence model. Trajectories of aerosol particles are evaluated by solving the corresponding Lagrangian equation of motion that includes effects of drag, gravity, lift force, Brownian motion and turbulence fluctuations. The Brownian motion is modeled as a white noise process and turbulence fluctuation is assumed to behave as Gaussian random process. Simulations are carried out for aerosol particles (of various sizes) released at different locations over the surface. Depositions of particles on the wall are evaluated and a capture area which varies with particle sizes is produced. The results show that Brownian motion becomes very significant when turbulence fluctuations start to disappear near the wall for particles smaller than 1 μm in diameter. The results also show that, deposition of particles in turbulent flows are usually higher than that in laminar flows for all particle sizes considered. The effect of fluid on particle deposition rate is predicted for fluid of air and water. The results show that, particles deposition rate in air is higher than that in water.

A comprehensive database of the optical properties of irregular aerosol particles for radiative transfer simulations

2021 ◽  
Author(s):  
Masanori Saito ◽  
Ping Yang ◽  
Jiachen Ding ◽  
Xu Liu
Keyword(s):  
Optical Properties ◽  
Radiative Transfer ◽  
Aerosol Particle ◽  
Volcanic Ash ◽  
Aerosol Particles ◽  
Single Scattering ◽  
Dust Aerosol ◽  
Index Of Refraction ◽  
Particle Sizes

AbstractA database (TAMUdust2020) of the optical properties of irregular aerosol particles is developed for applications to radiative transfer simulations involving aerosols, particularly dust and volcanic ash particles. The particle shape model assumes an ensemble of irregular hexahedral geometries to mimic complex aerosol particle shapes in nature. State-of-the-art light scattering computational capabilities are employed to compute the single-scattering properties of these particles for wide ranges of values of the size parameter, the index of refraction, and the degree of sphericity. The database therefore is useful for various radiative transfer applications over a broad spectral region from ultraviolet to infrared. Overall, agreement between simulations and laboratory/in-situ measurements is achieved for the scattering phase matrix and backscattering of various dust aerosol and volcanic ash particles. Radiative transfer simulations of active and passive spaceborne sensor signals for dust plumes with various aerosol optical depths and the effective particle sizes clearly demonstrate the applicability of the database for aerosol studies. In particular, the present database includes, for the first time, robust backscattering of nonspherical particles spanning the entire range of aerosol particle sizes, which shall be useful to appropriately interpret lidar signals related to the physical properties of aerosol plumes. Furthermore, thermal infrared simulations based on in-situ measured refractive indices of dust aerosol particles manifest the effects of the regional variations of aerosol optical properties. This database includes a user-friendly interface to obtain user-customized aerosol single-scattering properties with respect to spectrally dependent complex refractive index, size, and the degree of sphericity.

Experimental Investigation of Solid Particle Erosion in S-Bend

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Quamrul H. Mazumder ◽  
Kawshik Ahmed ◽  
Siwen Zhao
Keyword(s):  
Experimental Investigation ◽  
Solid Particle ◽  
Solid Particle Erosion ◽  
Surface Erosion ◽  
Particle Sizes ◽  
Air Velocity ◽  
Particle Erosion ◽  
Fluid Handling ◽  
Wide Range ◽  
Cause Of Failure

Solid particle erosion is a micromechanical process that removes material from the surface. Erosion is a leading cause of failure in fluid handling equipment such as pumps and pipes. An investigation was conducted using an S-bend geometry with 12.7 mm inside diameter, r/D ratio of 1.5 with three different air velocities and two different particle sizes. This paper presents the preliminary results of an investigation to determine the location of erosion for a wide range of conditions. The experimental results showed the location of maximum erosion at 29–42 deg from the inlet at 45.72 m/s air velocity with 300 μm particle sizes.

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