Paul S. Lee

Orthokinetic agglomeration in an intense acoustic field

Abstract Experimental investigations of acoustic agglomeration were performed with sound pressure levels ranging from 145 to 155 db (re 20 μPa) and frequencies from 600 to 3000 Hz under traveling-wave conditions. The temporal variations of mass distribution were measured with Berners impactors. The mass distribution function of the agglomerated aerosols was found to be bimodal and agree with the orthokinetic acoustic agglomeration theory. The numerical simulation of the agglomeration was conducted using sound pressure level, frequency, particle size, and mass loading as the parameters. The discrepancy in the comparison between the theoretical and experimental results was reduced by modifying the refilling factor.

Acoustically induced turbulence and shock waves under a traveling‐wave condition

Experimental investigations of acoustically induced turbulence and shock waves in a traveling‐wave tube are performed with and without the introduction of an air flow through the system. Frequency (f) and intensity (I) effects of the acoustic field are studied using a hot‐film anemometer and FFT data processing unit. The effect of the acoustically induced turbulence on a laminar flow is also investigated. Sampled data are first conditioned, then processed to estimate the characteristics of turbulence. It is found that for sound pressure level ≳158 dB turbulence appears. Furthermore, at slightly higher level (∠160 dB) shock waves appear over the range of all frequency. Turbulence measurements were performed over a frequency range of 500–2200 Hz, with intensity over a range of 06.–4.0 W/cm2. Below I=0.6 W/cm2 no turbulent bursts are found. The turbulent spectrum F and the wavenumber k are found to safisfy a power law F∝kα with α?−1.7 to −2.1. The rms turbulent velocity u* is found experimentally to have a I...

The Influence of Hydrodynamic Turbulence on Acoustic Turbulent Agglomeration

The potential applications of acoustic agglomeration of aerosols in industry are usually under high flow rate conditions. The acoustic hydrodynamic turbulence-turbulence interaction in a resonance tube is the subject of this investigation. Measurements are made at both loop and node positions with a sound pressure level of 161.5 dB (re 20 μPa) and hydrodynamic Reynolds number Re ranging from 0 to 14000. Important parameters of the final state such as the rms turbulent velocity, the integral scale, the Taylor and Kolmogorov microscales, and the rate of turbulent energy dissipation ∈ are estimated. It is found that as long as the hydrodynamic flow is turbulent ∈ increases monotonically with increasing values of Re. Furthermore, ∈ is consistently larger at loop than at node. Based on this information, a numerical calculation of the turbulent agglomeration kernel KT is performed. The strong enhancement of the turbulence-turbulence interaction on KT at higher values of the Reynolds number Re indicates that the...

Boltzmann equation with fluctuations

From the Liouville equation, by the method of multiple-time-scales, a generalized Boltzmann-equation with fluctuations is obtained on the statistical considerations of the randomness of the many-particle correlations in the macroscopic picture. These fluctuations lead to anH theorem in which theH function decreases, with fluctuations with time toward equilibrium. These fluctuations furnish a source for a random force term introduced by Fox and Uhlenbeck in the Boltzmann equation.

Dynamics of Fibrous-Type Particles: Brownian Coagulation and the Charge Effect

The Brownian coagulation of ultrafine chainlike or fibrous type particulate aerosols is theoretically investigated. The coagulation kernel is determined utilizing the concept of the effective collision diameter deff . Assuming equal a priori orientational probability, analytical expressions for d eff are obtained. For monodispersive aerosols with particle length l » d, the diameter, d eff reduces to l/2 for a collision between a particle and a plane wall, and d eff ≃ 0.75l for a collision between two particles. In the latter case the coagulation kernel K ≃ 1.2k B T[ln(l/d) + 0.4]/η where k B is the Boltzmann constant and η is the viscosity, and the bipolar Boltzmann type particle charge distribution contributes to an increase in K of only about 7%. After corrections to K for slip and polydispersity, the theory agrees fairly well with the available data. The remaining discrepancy is probably caused by the effect of polarization.

Aerosol deposition in acoustically induced turbulent flow

Abstract Experimental results are reported for the wall deposition of monodisperse aerosols with diameters ranging from 0.5 to 5.7 μm in an acoustically induced turbulent flow. In a set of experiments, both acoustic intensity and frequency are independently varied in the range of 161–168 dB and 500–1600 Hz under the traveling-wave condition. The deposition rate in the present work has been modified to account for acoustical effects. Furthermore, the advective contribution due to the turbulent velocity gradient is also included in the description of the mass transfer of aerosols. Based on the assumption of perfect sticking conditions (no particle rebound and or re-entrainment), theory and experiment are in fairly good agreement.

Transport Equations of Multicomponent Systems of Polyatomic Molecules. II

The treatment of the transport phenomena starting with the Liouville equation was first given by Irving and Kirkwood [J. Chem. Phys. 18, 817 (1950)] for a one‐component system composed of point molecules. The theory has been extended by Bearman and Kirkwood [J. Chem. Phys. 28, 136 (1957)] to multiple‐component point‐molecule systems and by Dahler [J. Chem. Phys. 30, 1447 (1959)] to a one‐component system of diatomic molecules. In the present work, the theory is extended to a multicomponent system composed of polyatomic molecules. The theory treats the translational, rotational, and vibrational motions of fluids but not the electronic motion. From the Liouville equation, the equations of continuity and of linear momentum, angular momentum, and energy transport are developed. The one‐particle and pair densities, involving the one‐particle and the two‐particle distribution functions are expanded in powers of a parameter measuring the small deviations from the state of local thermodynamic equilibrium, but the...

The Dynamics of Particles with Translation–Rotational Coupling in the Stokes Flow Regime

Most naturally and industrially generated solid particles are irregular in shape. One type of particle commonly encountered can be identified as flakes and their aggregates. This class of particles exhibits translation-rotational coupling. Based on the principle of similarity, we have conducted an experimental investigation of the dynamics of flake-type particles, employing model particles settling in an oil tank. These model particles are about 1–2 cm in size. The particle Reynolds number is kept under 0.02 to simulate the motion of the flaky aerosols. By introducing factors representing the effects of configuration (e.g., finite thickness and rod diameter) and interaction, shape factors for the composite particles can be determined from the constituent disks. The translational configuration factor λt is found to depend mainly on the thickness-to-diameter ratio l s/d s and to satisfy λt = A + B(1 s/d s)0.14. Furthermore, the ratio of the rotational and coupling configuration factors generally increases w...

Turbulence measurements in a resonance tube

Abstract Experimental investigations of acoustically induced turbulence in a resonance tube have been performed. Frequency (f) and sound pressure level (Ip) effects have been studied. Measurements were made at various spatial locations on loops and nodes. Sampled data were processed to estimate the characteristics of turbulence. It is found that the acoustically induced turbulence appears when Ip exceeds 160 dB under the experimental conditions of f = 680–2740 Hz and Ip = 160–166 dB. The turbulent spectrum (F) and the wave number (κ) are found to satisfy a power law F ∝ Ks with s ⋍ −1·6 to − 2·1 . The r.m.s. turbulent velocity ( u ) is experimentally found to have an I p 1 2 dependence, yet is relatively insensitive to the variation of f. Throughout the whole measuring range of f and Ip, the rate of energy dissipation per unit mass (e) is estimated to be in the order of 106–107cm2/s3.

Acoustically induced turbulence and shock waves in resonance tube

Experimental investigations of acoustically induced turbulence and shock waves in a resonance tube are performed. Frequency (f) and intensity (I) effects of the acoustic field on turbulence and shock waves are studied using hot‐film anemometer and FFT data processing unit. Measurements were made at the tube center and at approximately 1 mm from the wall at locations corresponding to loops and nodes of the standing waves. Sampled data were first conditioned then processed to estimate the characteristics of turbulence (Taylor microscale, the integral scale, autocorrelation, crosscorrelation, and power spectrum density). It is found that for sound pressure level (SPL) ≳ 162 dB and frequencies within a narrow band (∼20 Hz) around the resonance frequency, shock wave formation appears. Turbulence measurements were performed over a frequency range of 680–2740 Hz, with intensity over a range of 1.1–3.8 W/cm2. Below I = 1 W/cm2 no turbulent bursts are found. The turbulent power spectral density F and the wavenumbe...