Bioprocess (1)

Flow properties of fermentation
broths-Factors affecting broth
viscosity-Mixing in a bioreactor-
Flow regimes
Done by,
P.Pavithra
T.Pavithra
K.Pooja.
06-11-2019 B.Tech (Bio technology) ,Bioprocess Engineering. 1

Flow properties of fermentation broth
• Rheological data have been reported for a range of fermentation
fluids.
• This information has been obtained using various viscometers and
measurement techniques.
• Operating problems such as particle settling and broth centrifugation.
• Most mycelial suspensions have been modelled as pseudoplastic
fluids or if there is a yield stress,Bingham or casson plastic.

Rheological properties of microbial and plant-cell suspensions
are listed below:

• On the other hand,the rheology of dilute broths and
culture of yeast and non-chain forming bacteria is
usually Newtonian.
• In most cases,the results are valid over only a limited
range of shear conditions which is largely dictated by
the choice of viscometer.
• When the fermentation produces extracellular polymers
such as in microbial production of pullulan and
xanthan,the rheological characteristics of the broth
depend strongly on the properties and concentration of
these materials.

Factors affecting broth viscocity:
• Cell concentration
• Cell morphology( including size,shape and mass)
• Flexibility and deformability of cells
• Osmotic pressure of the suspending fluid
• Concentration of polymeric substrate
• Concentration of polymeric product
• Rate of shear.

Mixing:
• Mixing is a physical operation which reduces the non-uniformities
in fluid by eliminating gradients of concentration ,temperature and
other properties.
• It is accomplished by interchanging material between different
locations to produce a mingling of components.

Mixing involves:
• Blending soluble components of the medium
• Dispersing gases such as air through the liquid in the
form of small bubbles
• Maintaining suspension of solid particles
• Dispersing immiscible liquids to form an emulsion or
suspension of fine drops
• Promoting heat transfer to or from the liquid.

Mixing Equipment:
Mixing is carried out in stirred tank.

Many impeller designs are available for mixing :

Impellers are broadly classified as:
• Radial-flow impellers:
-blades which are parallel to the vertical axis of the tank.
• Axial-flow impellers:
-blades which make an angle of less than 90 degree to the plane
of rotation.

Mechanism of mixing
• Mechanism of mixing involves the combination of three physical
processes:
i. Distribution
ii. Dispersion and
iii. Diffusion

• Distribution :
-The process whereby dye is transported to all regions of the vessel
vessel by bulk circulation currents is called distribution.
-It is often the slowest step in the mixing process.
-It is sometimes called macromixing.

• Dispersion :
-The process of breaking up bulk flow into smaller is called
dispersion.
-It facilitates rapid transfer of material throughout the vessel.
-It can be classified as either micro or macromixing depending on
on the scale of fluid motion.

• Diffusion :
-Within eddies there is little mixing because rotational flow occurs
occurs in streamlines.
-Therefore,to achieve mixing on a scale smaller than the
Kolmogorov scale,we must rely on diffusion.
-It is also called micromixing.
- Molecular diffusion is generally regarded as a slow process.

Flow regimes:
• Flow regime is essentially a description of the flow structure,or
distribution of one fluid phase relative to the other.
• The three flow regimes can be identified as
1. Laminar regime
2. Turbulent regime
3. Transition regime

Laminar regime :
The laminar regime corresponds to for many
impellers;for stirrers with very small wall-clearance such as
as the anchor and helical-ribbon mixer,laminar flow persists
persists until or greater.

Turbulent regime:
Power number is independent of Reynolds number in
turbulent flow.
where Np’is the constant value of the power number in the
the turbulent regime.

Transition regime :
• Between laminar and turbulent flow lies the transition
regime.
• Both density and viscosity affect power requirements in this
this regime.
• There is usually a gradual transition from laminar to fully
fully developed turbulent flow in stirred tanks; the flow
pattern and Reynolds number range for transition depend
depend on system geometry.

References :
• Bioprocess Engineering Principles-Pauline M.Doran
• Picture courtesy-
http://static.wixstatic.com/media/6ff317_ba3271a7bdd84162bb056b
031e87c73c.jpg_srz_803_549_85_22_0.50_1.20_0.00_jpg_srz
• Picture courtesy- Pauline M.Doran

Bioprocess (1)

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Bioprocess (1)

Similar to Bioprocess (1) (20)

Recently uploaded

Recently uploaded (20)

Bioprocess (1)