Mixing in FERMENTATION BROTH

Tania Dey B090918Ch

What is mixing ?•Mixing, a physical process which aims at

reducing non-uniformities in fluids by eliminating gradients of concentration, temperature, and other properties.

Fermentation broth

Medium

Substrate

Cells in suspensio

n

Nutrients

Gas bubble

s

What is fermentation broth ?

Importance..•Dissolve solids in liquids•Dispersing air in form of bubbles•Improve heat transfer•Consumption of oxygen•Increases interfacial area•Equilibrate the conc of nutrients and

substrateOverall provides conductive environment

for cell suspention to interact with the sustrate in a better manner.

Mixing equipment(Standard mixing tank)

•Impeller•Turbine•Propeller

Various types of Agitator

Factors affecting selection of mixing equipment•Cell morphology•Susceptibilty of cell to shearing•Viscosity•Density•Interphase (gas-liquid/ liquid -liquid)•Power requirement

Power requirement for mixingElectrical power required to drive the

motor connected to agitator.Is a function of

a) Viscosityb) Densityc) Presence of suspended solidsd) Speed of agitatore) Type of impellerf) Orientation of vanes

Ungassed Newtonian fluids•The relationship between variables affecting

power required is usually expressed in terms of dimensionless numbers-

power number(Npo)Impeller Reynolds number(NRei) Froude number(NFr)

•Po - power required•Ni - impeller speed•di - impeller diameter

•Froude number takes care of gravitational effect

•Only significant for unbaffled fermentor and cases where NRei <300

•Power number gets modified to-

NRei versus Npo for various impellers

•LAMINAR ZONENpo falls as NRei increases

Zone 1

Zone 3

Zone 2• TRANSITION ZONEIn which the plots are curved

• TURBULENT ZONENpo is constant as NRei increases

Ungassed Non Newtonian fluids•Difficult as viscosity changes due to shear

rate•Seldom reach turbulent zone•Apparent viscosity [µa] is used in Nrei

µa = Kγη-1

Nrei(non newtonian)= (ρNidi2)/(Kγη-1)

Ungassed tank with ruston turbine

Gassed system•Power required in gasses is always less

than ungassed .

•Pg – power required for gassed system•Fg –volumetric gas flow rate•V – liquid volume•Wi – width of the impeller

Na is aeration factor given byNa = Fg/(Nidi3)

Thank you!!!