University
of Chemical Technology and Metallurgy,
8 Kl. Ohridski, 1756 Sofia, Bulgaria
E-mail: mik@uctm.edu |
Received
26 September 2001
Accepted 20 November 2001 |
The rheological behavior of low-pulp
orange juice (produced in Brazil) was investigated in dependence of
the concentration and the temperature. It was found that for the whole
concentration range (10 - 57oBx) the juices exhibited non-Newtonian
behavior, which could be described by power-law rheological model. The
dependencies of the rheological parameters on the density, concentration
and the temperature were studied. It was found that the consistency
index depends exponentially on the concentration of soluble solids as
well as on the temperature. The relationship between the consistency
index and the density was found. It gives a satisfactory accuracy in
prediction of our data as well as of those of other authors. Flow activation
energy was calculated based on the temperature dependencies of the consistency
index. It was found to decrease with dilution for the concentration
range of 10 to 40oBx. In the same concentration range n was almost unaffected
by the temperature. In this range the flow properties are probably governed
by soluble solids’ concentration. For the higher concentrations
(40 to 57.5oBx) the activation energy is lower, which is possibly due
to the higher importance of pulp contents. Concerning the flow index
n, for the range of high concentrations, it was found to decrease with
temperature rise. The data obtained in this study could be useful for
the design of equipment for handling of orange juices.
Keywords: orange juice rheology, concentration and
tempera-ture dependence of the rheological parameters, Arrhenius constants.
NUMERICAL INVESTIGATION
OF EXTERNAL LOOPAIRLIFT REACTOR
S. Tchaoushev, D. Moutafchieva, D. Popova, I. Pentchev
University
of Chemical Technology and Metallurgy
Department of Chemical Engineering
8 St. Kl. Ohridski blvd., 1756 Sofia, Bulgaria
e-mail: sns@uctm.edu dmoutaf@uctm.edu |
Received
26 September 2001
Accepted 20 November 2001 |
External-loop airlift reactor is numerically
investigated on the base of two-phase dispersion model taking into account
axial mixing both in the riser and downcomer and perfect mixing in the
gas-liquid separator.
The proposed mathematical model accounts for the effect of the gas-liquid
separator and variable liquid velocity on the oxygen transfer rate in
the reactor.
The numerical solution of the model is obtained by means of finite difference
method with special numerical procedure of exponential approximation.
The model predicts satisfactorily mass transfer in the reactor and can
be used for estimation of the effective oxygen transfer rate and determination
of volumetric mass transfer coefficients.
This model has been validated with published experimental data. Qualitative
agreement between experimental data and numerically obtained oxygen concentration
profiles in the reactor confirm the applicability of the proposed model.
Keywords: air-lift reactor, gas-liquid separator, modelling,
hydrodynamics mass transfer, gas holdup
