TRANSPORT PHENOMENA Flashcards
the study of the movement of different physical
quantities in any chemical or biochemical process
Transport Phenomena
consists of the basic principles and laws of transport
Transport Phenomena
+ describes the relations and similarities among different
types of transport that may occur in any system
Transport Phenomena
encompasses the subjects of momentum transfer or fluid
mechanics, mass and energy, or heat transfer processes:
Transport phenomena
- Deals with the transport of momentum in fluids
Momentum transport/Fluid Dynamics
Deals with the transport of different forms of energy in a system
Energy or Heat Transport/Heat Transfer
- Deals with the transport of various chemical species themselves
Mass Transport/Mass Transfer
blood circulation in the body, mixing phenomena in bioreactors
MOMENTRA
sterilization of reactors, temperature control in bioreactors
HETRA
oxygen transport from bubbles to aerobic microorganisms
MATRA
Transport can be studied in 3 levels
Macroscopic
Microscopic
Molecular
The basic equations of transport phenomena
are derived based on the following axioms:/GOVERNING EQUATIONS
equation of continuity
equation of motion
equation of thermal energy
The equation of continuity is based on the
conservation
of mass
The equation of motion is based on the
conservation of
momentum (Newtonβs second law)
The equation of thermal energy is based on
conservation of energy
Rate of Transport process =
Driving force/Resistance
the factor that will make the transfer occur
Driving force
DF includes velocity gradient (microscopic or molecular)
or velocity difference (macroscopic)
MOMENTUM TRANSPORT
DF includes temperature gradient (microscopic or
molecular) or temperature difference (macroscopic)
ENERGY OR HEAT TRANSFER
, DF includes concentration gradient (microscopic or molecular)
or concentration difference (macroscopic)
MASS TRANSPORT
the factor that will slow down the transport process
rESISTANCE
When does the driving force become negligible?
The system reaches equilibrium
T/F: Transport phenomena may occur within a single
phase or between multiple phases
T
In the bioprocessing industry, the flow of fluid* occurs
mostly through the
PIPING
Fluid flow involves two (2) distinct regimes, which largely
depend on the physical properties of the fluids:
LAMINAR
TURBULENT
The two regimes of fluid flow largely depend on?
PHYSICAL PROPERTIES OF THE FLUID
viscous flow, streamline
LAMINAR FLOW
Involves the flow of the fluid particles only in a single
direction
LAMINAR FLOW
The components of velocity are either negligible or not
present in the other directions
LAMINAR FLOW
Mainly due to the motion of the fluid particle clusters
TURBULENT FLOW
T/F: Fluid flow is in one direction, generally
T
due to the associated _____, the layers of
fluid right under the top layer also ____ momentum and move
accordingly.
inertia, gain
At steady state, the bottommost layer of fluid adhering to
the bottom stationary plate will have ____ velocity
zero
suppose that topmost layer of fluid
(adhering to the plate) has a velocity π’0, how will the velocity
distribution/profile look like across the layers?
velocity distribution is linear
is dependent on
the force with which the top plate is moved
nature of the velocity
distribution or the velocity gradient
In physics, the applied force is called?
Shear stress (tau)
The resulting velocity gradient is known as?
shear rate
T/F: Shear stress and shear rate are proportional to
each other
T
In Newtonβs Law of Viscosity, what was introduced to remove the sign of proportionality?
VISCOSITY
Based from the Newtonβs Law of Viscosity, As the force or shear stress is applied from a domain of
higher velocity to that of lower velocity, the sign of the
velocity gradient is
negative
In the transport phenomenon, any transport rate per unit area is called
FLUX
mv/A is?
Momentum Flux
Rate of change in the Momentum Flux is directly proportional to the negative of?
velocity gradient
Unit for kinematic velocity
Stoke (cm^2/s)
it refers
to the ability or extent of the fluid for momentum transport
momentum diffusivity
T/F: Mass flux gradient and momentum flux are directly proportional
T
Fluid classification based on Propert
Newtonian
Non-newtonian
In this fluid classification, Fluid viscosity and shear rates are independent of each other
Newtonian Fluids
+ Plotting shear rate vs. shear strain for Newtonian fluids
will achieve a ?
Straight line passing though the origin
mostly include liquids with low molecular weight and almost all gases
Newtonian Fluids
In Newtonian Fluid, Increase in temperature results in a _____ in liquid
viscosity and an _____ in gas viscosity
decrease, increase
In Newtonian Fluid, increasing the ___ enhances both liquid and gas viscosities
pressure
most of the fluids that exists in nature
Non-Newtonian Fluids
+ display a significant viscosity variation with shear rates
Non-Newtonian Fluids
Non-newtonian fluid based on the extent of variation of the shear rate with
shear stress, they may be classified as
Pseudoplastic
Bingham
Dilatant
viscosity decreases with increase in shear
rate
Pseudo
- a viscoplastic material that behaves as a
rigid body at low stresses but flows as a
viscous fluid at high stress
Bingham
needs a certain amount of shear stress until
a threshold is reached, beyond which, the
fluid flows
Bingham
a fluid where shear viscosity increases with
applied shear stress/rate
Dilatant
Flow behavior index of dilatant fluids
greater than 1
Flow behavior index of peudoplastic
less than 1
In Biochemical Engineering,
fermentation media
containing microorganisms
or fermentation broths
mostly behave as
Non-newtonian Liquids
a different category of fluids that display some amount of
elastic behavior
Viscoelastic Fluids
Example of viscoelastic fluids
Polymer solutions
β the tendency to which an object comes back
to its original form after the applied stress is released
Elasticity
β the ratio of the applied stress to strain
Elastic modulus
πΉπ < ππ, ππ0
Laminar flow
ππ, πππ < πΉπ < ππ, ππ0
Transition
πΉπ > ππ, ππ0
Turbulent
T/F: The velocity profile of laminar flow is much shaper and smoother than turbulent flow through a tube
T
Regime that demonstrates relatively flat velocity profile through a tube
Turbulent Flow
An instability in the flow transport occurs in the fluid
regime where the flow starts changing from laminar to
turbulent inside a tube
Transition flow
Regime that is significant in many
applications of biochemical engineering
Turbulent Flow
arises due to the greater contact of the flowing
fluid with the solid boundary
Turbulence
Turbulence that arises due to the greater contact of the flowing fluid with the solid boundary
Wall turbulence
arise when the fluid layers of two varying velocities
are in contact with each other.
Free turbulence
is extremely important during mixing
Free turbulence
consists of various sizes of
eddies, which coexist in the flow stream.
Turbulent flow
are extremely unstable, and they
keep breaking into smaller eddies.
Larger eddies
have the tendency to combine
and form a larger eddy
Smaller eddies
The flow within the eddy is?
Laminar
T/F: All eddies are of macroscopic size
T
, the relationship between
velocity gradient and shear stress in a turbulent stream
is used to define
Eddy viscosity
Is analogous to absolute viscosity
Eddy viscosity
πm
eddy diffusivity of momentum
The total shear stress in a turbulent fluid is the
summation of
viscous stress and turbulent stress
