newtonian and non newtonian fluid, alwin & gourangi.ppt

newtonian and non newtonian fluid, alwin & gourangi.ppt

1. Newtonian
and
Non Newtonian fluids
Alwin Thomas
Gaurangi Deore

2. Depending on whether their rheology
(flow) characteristics obey Newton's law
of viscous flow.

3. Newtonian fluids..

4. Newton's law of viscous flow.
•Consider the fluid maintained between 2 parallel
plates ,Area Aand distance ‘y’ apart.,and if the
upper plate is moved at constant velocity

5. •Newton's law of viscous flow states that the viscous
force ,F, opposing the motion, at the interface
,between the two liquid layers flowing with a velocity
gradientdu/dy,is given by
F=A.m.(du/dy)
F/A=m(du/dy)
But
F/A=t(shear stress)
du/dy = g( shear rate)
•=> t =m. (du/dy) = mg
i.e.Shear stress is directly
proportional to the shear
rate

6. m= fluid viscosity(resistance of the liquid to
flow)
t= Shear stress(the force applied which
causes the fluid flow.
•g =Shear rate(velocity gradient or the
relative velocity of parallel adjacent layers in
laminar flow of a a liquid body under shear
force)

7. •Newtonian fluid has a constant viscosity
regardless of shear.
•So,viscosityof a Newtonian fermentation broth
will not vary with agitation rate.
•Examples of Newtonian fluids-oil, water
t =m.(du/dy) = mg

8. Power law model
t=K.g
n
where K =consistency index
n=flow behavior index or power law index
•For Newtonian fluids ,n=1 &K=viscosity

9. Relative viscosity of suspensions
•Einstein equation
–For very diluted suspensions,(f<0.1)
–For rigid particles which show no interaction
m
relative =m
suspension/m
liquid = 1+K
1f
Where,
oK1 =constant (depending on particle shape)
ofor spherical particles ,K1=2.5
oFor rod shaped particles,K1=(20-1200)
F1=volume fraction of particle

10. •Eiler’s equation(f>0.1)
–For more concentrated suspensions
m
relative ={1+K
1f.(0.5).[1-f/f
max]
-1
}
2
–Where
F
max =max. packing density (0.6-0.7) for the type cells
under investigation

11. Cell volume fraction
Relative
viscosity
Eilers eqn
Einstein's eqn

12. NON NEWTONIAN FLOW

13. RHEOLOGICAL
BEHAVIOUR…..
Factors affecting rheology of the
fermentation broth
–Composition of the original medium
–Concentration of the biomass
–Morphology of the biomass
–Concentration of the microbial products.
Factors affected by rheology
•The mass transfer of nutrients within the fermenter
•Separation of desired molecules by membrane
filtration or centrifugation

14. NON NEWTONIAN FLUIDS
•Does not obey Newton's law of viscous flow.
•Viscosity will vary depending upon the shear
rate.
Rheological behaviour under non
newtonian system
Bingham Plastic rheology:
The flow pattern can be described as
t = t
0+ ηγ, whereη= Coefficient of rigidity
t
0 = Yield Stress.
E.g. Pencillium chrysogenumand Kanamycin
broth

17. Pseudoplastic
•Flow can be described by power law model
t = K(γ)
n
K= Consistency coefficient n = flow behaviour index,
n<1. E.g. Cultures of Streptomyces and Endomyces.
Dilatant
Described by power law model where n>1. E.g. Yeast
at high concentration (15% dry solids)
Casson Body Rheology
Described by the equation
t = t
0 + K
c γ, where k
c = casson
viscosity

18. oThe rheological behavior of the fermentation broth is
usually Non Newtonian.
oDuring the fermentation sometimes the flow pattern
changes,
oE.g. Growth of S.aureofacians on a starch containing
medium.
Time Flow pattern
Before
Inoculation
Bingham
Plastic
After 22 hoursNewtonian
From 22 hours
onwards
Pseudoplastic

19. Thank you………