摘要:

Acoustic agglomeration (AA) of the fly‐ash particles from coal combustion in pressurized, fluidized bed combustors for power plants is an intermediate treatment of the aerosol to improve the fractional removal efficiency of conventional particle removal devices such as cyclones so that recently proposed clean air requirements can be met. Tests were performed on Penn State's high‐pressure (10 atm), high‐temperature (891 °C) acoustic agglomerator (6‐in. i.d., 14‐ft length) at 158 dB and about 850 Hz, with particle loading of 10–18 g/m3and residence times of about 4 s. The sound source was a high‐efficiency siren of Penn State's design providing about 1500 acoustic watts. The mass fraction in the critical 0.5‐ to 5‐μm particle size range was reduced by a factor of 5 and the 10‐ to 20‐μm size range increased by a factor of 3. An acoustic agglomeration simulation model (AASM) computer code that predicts AA quite reliably at both atmospheric and HTHP conditions was developed at Penn State. The simulation results in terms of particle size distribution agree quite well with the test results from both test conditions. The simulation also predicts that better AA could have been obtained at higher frequencies (2000 Hz) and higher acoustic intensities (160 dB). [Work supported by DOE.]

ISSN:0001-4966    

DOI:10.1121/1.2028126

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This theoretical study explores the effects of acoustically driven oscillating flows on the flow behavior around small spherical particles. Its application is in the area of enhancement of combustion of pulverized coal particles and coal water slurry fuel droplets via augmentation of heat and mass transfer to and from these particles that are entrained in the steady mean flow. The particle is 100 μm in diameter. The sound‐pressure levels are between 140–160 dB, resulting in peak acoustic velocities of 2.5–50 m/s. The acoustic Reynolds numbers based on peak acoustic velocity and particle diameter are 16–150. The phenomenon is examined at 50 and 2000 Hz corresponding to Strouhal number 0.0002 and 0.08 in order to investigate the effects of low and high frequencies. The velocity field around the particle, the separation angle, and wall shear stress are calculated by solving the two‐dimensional, unsteady laminar Navier‐Stokes equations with a numerical technique. From the results, it can be seen that at 50 Hz the flow field around the particle is governed by the particle curvature and magnitude of the free stream velocity whereas, at 2000 Hz, the acceleration of the flow with time (due to oscillation) is also an important factor. This results in different heat transfer behavior due to different separated regions at both frequencies under the same free stream velocity. For example, at a Reynolds number 16, steady flow does not separate; neither does the flow at 50 Hz. However, at 2000 Hz, a separated region is observed due to the free stream flow acceleration. These results are discussed in detail.

ISSN:0001-4966    

DOI:10.1121/1.2028127

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

An artificial three‐layer neural network is constructed to study possible mechanisms in auditory frequency discrimination. The 110 input units, resembling the peripheral neurons, have two sets of filter shapes: idealized eighth nerve isointensity functions and Patterson‐style filters [Moore and Glasberg, Hear. Res.28, 209–255 (1987)]. Twenty‐four intermediate units, similar to critical bands, process information from the input units. The output unit makes a frequency discrimination decision based upon an excitation difference in the intermediate units. Single‐band and multiband decision‐making rules are tested. When using the idealized eighth nerves as the peripheral filter shape, neither the single‐band nor a linear‐combination, multiband model satisfactorily predicts experimental data. However, by adjusting the weights from the intermediate units to the decision‐making unit by the Delta Rule [Rumelhart and McClelland,Parallel Distributed Processing 1(MIT, Cambridge, MA, 1988), pp. 444–459], it is found that a weighted‐band model can best predict the observed data. The weighted‐band model assigns different weights to each band according to its excitation difference: The larger the difference is, the greater the weight. When using Patterson‐style filters as the input units, none of the above three models provides a satisfactory prediction. The results suggest that (a) the peripheral filter shape may play a more important role than the central decision rule in frequency discrimination, and (b) the weighted‐band model may be a more appropriate central decision rule.

ISSN:0001-4966    

DOI:10.1121/1.2028131

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Recycled noise segments (RNs) are heard as a repetitive “whooshing” from the lower limit of effortless iterance detection (1 Hz) through 4 Hz [Guttman and Julesz, J. Acoust. Soc. Am.35, 610 (1963)]. The present study found that after listening to a whoosing range RN, the frozen noise segment could be identified at a later time (well beyond the limit of echoic storage) when it was presented as part of a longer “parent” frozen noise segment. For RNs with frequencies above the whooshing range, recognition of the frozen noise segment was difficult or impossible when presented as a portion of a longer parent. Implications concerning the nature of repetition detection at different iterance rates will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2028135

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

An experimental technique has been developed to identify the hierarchical importance of characteristic features in the complex sounds to which an auditory neuron is most selective. Single‐unit spike rates are measured in response to variation of component intensities and frequencies, using a subset of single and paired tone stimuli. The response profiles are used to rank the importance of nonlinear interactions between component frequencies as well as component intensity levels, and a multidimensional matrix is derived that enables prediction of the neuron's response to sounds in a more general, complex set. The derivation is based on weighted inner product space optimization (WIPSO) and singular valne decomposition (SVD) analysis. To test this general method, the activity of single auditory fibers in the eighth nerve of the green treefrog (Hyla cinerea) was recorded in response to computer‐synthesized stimuli. Results indicate that this is a very promising, powerful approach for characterizing the selectivity of individual auditory neurons to synthetic and natural sounds of interest. [Work supported by NINeDS.]

ISSN:0001-4966    

DOI:10.1121/1.2028140

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

A 300‐kHz acoustic Doppler profiler has been developed to measure turbulent processes in the upper ocean. Acoustic energy from scatterers ensonified by a single, narrow‐beam, pulsed transmitter is received by four fan beam response hydrophones placed radially around the transmitted transducer. The present system allows three‐component velocity profiles to be estimated every 10 cm over a 5‐ to 20‐m range with high temporal resolution and adequate velocity range by using a dual interpulse period coherent sampling method. Examples of the high spatial and temporal resolution velocity fields are shown from recent measurements immediately below open ocean waves and a sub‐ice boundary layer. Both the advantages and limitations of this current measurement technique will be discussed. [Work supported by ONR Physical Oceanography.]

ISSN:0001-4966    

DOI:10.1121/1.2028146

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Extant theories and numerical simulations for Langmuir circulations [Leibovich, Ann. Rev. Fluid Dyn. (1983); Leibovichet al., J. Fluid Mech. (1989)] all show predicted circulation patterns characterized by asinglehorizontal, cross‐wind scale. Recent research [Smithet al., J. Phys. Oceano. (1987); Weller and Price (1988); Pinkel and Smith (1989), unpublished acoustic data] showmultiscalecirculation patterns, including the organization of bubbles and phytoplankton, in the oceanic surface layer. An analytic theory for the evolution of two‐dimensional disturbances in neutrally stratified, super‐critical shear flows will be presented, done in collaboration with Chris Bretherton, UW‐Applied Mathematics. This theory shows that initially favored, quickly growing disturbances evolve into catalysts for the transfer of mean flow energy into other scales of motion, producing multiscale circulation fields. This general result directly predicts the production of multiscale Langmuir circulations, which is supported here with theoretical calculations specialized to the oceanic surface layer.

ISSN:0001-4966    

DOI:10.1121/1.2028150

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Theodore J. (Ted) Schultz combined two careers and a cheerful, friendly personality during his span of years as a scientist and consultant in the field of acoustics. His first career, music, began at the Eastman School of Music where he became an accomplished bassoonist. Electrical engineering followed at the University of Missouri, Acoustics began when he enrolled in Harvard's Graduate School of Arts and Sciences where he received his M.Sc. and Ph.D. under Professor F. V. Hunt. His major life work was devoted to acoustical research and consultation at Bolt Beranek and Newman in Cambridge, MA. Both during his academic years and later, he remained a professional bassoonist, playing in municipal symphonies in Providence, RI, Portland, ME, and Worcester, MA. This paper reviews his overall career as a scientist, particularly as the author knew him for 22 years at BBN, where he rose to the position of Principal Scientist.

ISSN:0001-4966    

DOI:10.1121/1.2028151

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In 1985, Ted Schultz undertook a research project for the American Society of Heating, Refrigerating and Air‐Conditioning Engineers (ASHRAE) to investigate the relationship between the sound‐power level of a source and the sound‐pressure level produced in “real” rooms typical of dwellings and offices. For many years, the use of the diffuse field theory of sound propagation had been suspect as not being applicable in normally furnished spaces to the prediction of sound‐pressure level resulting from a known introduction of sound‐power level. Ted's research confirmed that the use of this latter theory led to significant errors that both overestimated and underestimated true conditions depending upon the distance between the source and observer. Recognizing the complexity of developing a rigorous theoretical solution within the time frame of the project, he undertook an empirical approach and reviewed a large body of his own and others' reliable test data to develop an equation that predicted with considerable accuracy the measured results in rooms ranging from bathrooms and kitchens to plush furnished offices, conference rooms, and living spaces. In summarizing the conclusions of this study, Ted made several cogent observations, typical of the subtle Schultz style: “Since the room absorption,A, does not appear explicitly in the formula, the customary normalization with 10 log (A/A0) in transmission loss and impact noise tests is probably incorrect. In addition, since no uniform reverberant sound field occurs in normally furnished spaces, it is not clear what one ought to measure for the receiving‐room sound pressure level in tests of transmission loss, noise reduction, and impact noise.” He was pursuing these concerns at the time of his death.

ISSN:0001-4966    

DOI:10.1121/1.2028153

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Ted Schultz brought to the study of music room acoustics the perception of a professional musician, familiarity with the musical literature, theoretical understanding of the physics of sound, and a remarkable ability to evaluate architectural designs and to present difficult acoustical concepts by analogy to more easily visualized situations. This paper presents the author's observations from almost 20 years of close association, including a 4‐year period of simultaneous involvement in the design of five major concert halls.

ISSN:0001-4966    

DOI:10.1121/1.2028158

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP