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128BHA.pdf

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r n

Radial component. Nusselt component.

Seventh International Conference on CFD in the Minerals and Process Industries CSIRO, Melbourne, Australia

9-11 December 2009

CHARACTERIZING LIQUID FILM THICKNESS IN SPINNING DISC REACTORS

Tejas J. BHATELIA1, Ranjeet P. UTIKAR1, Vishnu K. PAREEK1*and Moses O. TADE1

Centre for Process Systems Computations, Curtin University of Technology, Perth, WA 6845, AUSTRALIA. *Corresponding author, E-mail address: v.pareek@curtin.edu.au

ABSTRACT

Hydrodynamic behaviour of the liquid film in a spinning disc reactor was investigated using computational fluid dynamics. Flow characteristics of the liquid film were studied over a range of operating conditions. Both 2D and 3D simulations were carried out using the volume of fluid method and compared with experimental data and empirical correlations published in literature. While the film thickness predicted by 3D simulations was in good agreement with experimental data, the high computational time required rendered the simulations too costly. The 2D simulations reported closer agreement with available empirical correlations, however, the film thickness was much lower compared to the experimental values. The results obtained here provide insight into the hydrodynamics and would be useful in accessing performance of the spinning disc reactor for multiphase reactions.

Keywords: Spinning disc, Liquid film flow, CFD and VOF.

NOMENCLATURE

INTRODUCTION

Spinning disc reactors (SDRs) are gaining popularity in carrying out fast multiphase reactions since they offer large interfacial area, and short residence times (Aoune and Ramshaw, 1999), In the SDR, liquid is fed into the centre of a reactor chamber consisting of a rotating disc. The rotational speed is usually high (upto 3000 rpm) which generates thin, unstable and wavy liquid film over the disc. The liquid travels in plug flow in the film from center to the periphery. Due to the thin film created, these reactors offer high heat transfer coefficients between the disc and the liquid and high mass transfer coefficients between the liquid and the gas above the liquid. This is of particular advantage when performing fast liquid-liquid reactions such as nitration, sulphonation and polymerization (Stankiewicz and Moulijn, 2004). These reactors have also shown potential benefits in unit operations such as absorbers, humidifiers, dust collectors, dryers, evaporators etc (Leshev and Peev, 2003). Owing to these advantages SDRs have also found various applications manufacturing of fine chemicals and pharmaceuticals (Aoune and Ramshaw, 1999).

The performance of the SDR depends on the underlying hydrodynamics of the film which is governed primarily by the rotational speed and volumetric flow rate of the fluid along with the physical properties of the fluid and the disc. A Considerable number of empirical and experimental investigations have been performed to correlate these governing parameters with the hydrodynamics of the film flow. Some of these are listed in table 1.

Espig and Hoyle (1965) in their experiments observed three different flow regimes over the spinning disc. Near the inlet region, the flow is a waveless laminar flow this is followed by the flow characterized by axisymmetric wave formation, this is followed by a turbulent region which shows three dimentional surface waves that are a combination of axisymmetric and helical waves. Charwat et al. (1972) identified that the turbulent waves decay towards the end of the spinning disc giving rise to a second laminar-wave region. Similar decay in the amplitude of the waves was also observed in experiments by Butuzov and Puhovoi (1976).

Wood and Watts (1973) performed an experimental study to characterize the heat and mass transfer on rotating discs. They showed existence of several wavy regimes in concentric zones across the radius of the disc. Nature of these waves is strongly dependent on the operating conditions (flow rate, rotational speed), liquid properties

D

F

g

h

K

L

m

P

r

s

t

u, v, w

V

Q

Greek Letters:

α V olume fraction.

μ Dynamic viscosity, kg m-1 s-1.

ν Kinematic viscosity, m2 s-1

σ Surface tension, N m-1.

ρ Density, kg m-3.

ω Rotational speed, rad sec-1. ε V oid fraction.

Subscripts:

f Fluid.

i,j,p,q Phases.

Disc diameter, m.

Force, N.

Gravitational acceleration, m s-2.

Film thickness, m.

empirical constant.

Liquid.

mass flow rate, kg s-1.

Pressure, Pa.

radius, m.

Source term.

Time, s.

Velocity components in x, y and z direction, m s-1.

Velocity, m s-1.

Volumetric flow rate, m3 s-1

Copyright © 2009 CSIRO Australia

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 Supercritical Fluid Extraction 128BHA.pdf Page 001
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