The acoustic characteristics of a column are described when filled with different random packings of various shapes, sizes and void fractions. An experimental setup was developed to study the acoustic field in a packed-bed column. Eight different packings were used to fill the column, and for each packing the acoustic pressure amplitude and phase were measured along the length of the packed bed. The speed of sound and the attenuation coefficient were determined using a nonlinear regression technique. The speed of sound inside the column decreased when the column was filled with packings. The natural frequencies increased as the void fraction of a particular packing decreased. It is shown that the attenuation coefficient depends on a nondimensional frequency defined as ωd2/v, where v is the kinematic viscosity, ω is the angular frequency, and d is the effective diameter of the packing. © 2006 American Institute of Chemical Engineers.

R. I. Sujith

Department of Aerospace Engineering

T. Sai Kumar

Munesh Kumar Patle

Acoustic fields

Natural frequencies

Regression analysis

Viscosity

ATTENUATION COEFFICIENT

KINEMATIC VISCOSITY

NONDIMENSIONAL FREQUENCIES

Packed beds

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

AIChE Journal

There has been much debate in recent years as to the effectiveness of enhancing heat and mass transfer rates with resonant acoustic oscillations in industrial equipment such as boilers, dryers, calciners, gasifiers, and others. This article will briefly discuss the theoretical background of acoustic drying, the setup of the experimental apparatus used to investigate the feasibility of acoustically enhanced drying, the results of these experiments, and, finally, some conclusions drawn from this work. The theoretical discussion focuses on the use of the quasi-steady assumption to estimate the potential for enhancing the heat and mass transfer rate to and from the material using acoustic oscillations. The experimental work reported focuses on the successful application of acoustical oscillations to drying a cellulose sponge, which is a material that readily transports moisture to its surface where it can be effectively dried. Also reported is the unsuccessful application of acoustic oscillations to the drying of polyethylene terephthalate, which is a saturated, thermoplastic, polyester resin made by condensing ethylene glycol and terephthalic acid and is commonly used in the manufacture of plastic food and drink containers. Reasons for success and failure in each case are discussed along with the implications of these to the successful application of acoustic oscillations to future drying applications.

Drying Technology

The effect of resonant acoustic oscillations on heat and mass transfer rates in a convection air dryer

This paper describes a theoretical investigation of the possibility of improving the performance of packed bed dryers using acoustic oscillations. It was motivated by the increasing interest in the use of acoustic oscillations to improve the performance of energy-intensive, industrial processes. Sound propagation in a packed bed was modelled as propagation through a porous medium. The effect of acoustic oscillations on the drying rate was then investigated by numerically integrating the heat and mass transfer equations. The model used quasi-steady correlations for heat and mass transfer. The results show that threshold values for void fractions and sound pressure levels exist, above which significant increase in drying rate can be obtained. The increase in mass transfer decreases with effective particle diameter.

Canadian Journal of Chemical Engineering

A theoretical investigation of enhancement of mass transfer from a packed bed using acoustic oscillations

Journal	AIChE Journal
ISSN	00011541
Open Access	No