With no antifoam added
With antifoam added
泡泡較多且較小
泡泡較少但較大
1
• Because antifoams accumulate around bubbles,
they block the movement of oxygen through
the interfacial boundary.
2
Gas hold up
• Gas hold up and Bubble residence
time
• Bubble size and gas hold up
3
Gas hold up and
bubble residence time
• The gas hold up is
defined as:
• For a cylindrical
tank, the gas hold
up is equal to:
4
• Gas holdup increases with
increasing air flow rate
• 導致氣泡滯留時間增加有以下原因
– 高黏度的培養基
– 氣泡過小
– 反應器高度過高
5
With large bubbles, the bubbles contain sufficient oxygen at
the surface to ensure that oxygen will be transferred out of the
bubble and CO2 will be move into the bubble
6
Small bubbles rapidy become saturated with CO2 and
release the CO2 into the medium under the low pressure
conditions at the surface
7
Draft tubes
• The insertion of a draft tube into a
fermenter causes the liquid inside the
draft tube to flow uniformly upwards
• This leads to reduced bubble coalescence
and to more energy efficient mixing of
the fermenter contents.
8
Stirred tank bioreactor
with draft tube
(Imhoff fermenter)
Bubble colum bioreactor
with draft tube
9
(Airlift fermenter)
謝 謝 大 家
10