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reactors. The information obtained in small units is not adequate for large scale design, since the fluid
dynamics, the transport processes, and even the behavior of the cells may change considerably (e.g., by an
intensification of turbulence) when the size of the unit is increased. For these reasons, the laws that
operate in the geometric enlargement of a reactor should be known. Because of the absence of this
information, pilot plants have to be constructed which subdivide the large step of this "scaling-up"
procedure between laboratory and production units in order to reduce the risk involved in the design of
the production unit.
Most of the information that is discussed below was obtained on small pilot plants. Only a few
results from industrial demonstration plants have been published.
In process engineering, the passage from the model to the production unit can often be facilitated
with the aid of similarity theory. In general, this theory can be used to only a limited extent in chemical
and biochemical reactors, since when the unit is enlarged the geometric similarity is not necessarily
matched by that of fluid motion and mass transfer of the individual transport processes. If, however, a
single parameter is rate determining, similarity theory can be very helpful in the calculation of reactors.
Similarity theory deals with the criteria, which permit a calculation of the performance of a
system on the large scale, based on small-scale model experiments. For each elementary process, the
process-determining factors can be comprised within a characteristic number which must remain constant
during the enlargement of the reactor if the similarity between the laboratory and the pilot reactors (or
between the pilot and production reactors) in relation to this process is to be preserved. If this similarity
exists, the results that were obtained on laboratory or pilot reactor scale can be used for the production
reactors, also.
In order to reduce the number of variables these quantities are brought together according to
definite rules to form dimensionless characteristic numbers (dimensional analysis). The results found in
the laboratory or pilot reactor are then correlated by a combination of these characteristic numbers.
Before the mode of operation (discontinuous, continuous, semicontinuous), the type, the size, and
the operating conditions of the reactor are determined, a preliminary choice must be made of the mode of
operation and of the type of reactor, which are predetermined by the organisms used, the media, the
characteristics of the biochemical process, and the site. The mode of operation and the type of the reactors
for enzymatic transformations are affected by a comparatively small number of properties (molecular
mass, stability) of the enzyme. To discuss these questions quantitatively, some basic concepts must first
be defined.
EXERCISES
A. Read and translate into Vietnamese
bioreactor, transformation, modify, environment, disadvantage, nutrient solution, supplementation,
boundary, fluid motion, mass transfer, parameter, large-scale, dimensional, analysis, mode of operation,
type of reactor
B. Answer the following questions
1. What is the main process that occurs in a bioreactor?
2. What are the optimum conditions for enzymatic actions in a bioreactor?
3. What is "scaling-up" for designing the bioreactor?
4. Can you apply the information obtained in lab or pilot reactor scale to production reactors?
5. What are the modes of operation in the reactor?
C. Translate into English
1. Các iu kin thích hp cho vic chn chng vi sinh vt phi c xác nh bng thc nghim.
2. Các iu kin thích hp cho các phn ng enzim phi c nghiên cu t phòng thí nghim nh
mt quá trình lên men.
3. pH, nhit và nng oxy hòa tan thích hp trong môi trng nuôi cy phi thu c t thit b phn
ng trong phòng thí nghim.
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