For dynamic behaviors of continuous airlift bioreactors, a mathematical model based on a tanks-inseries model with back¯ow has been developed. The equations describing the dynamics of airlift bioreactors are material balances for micro-organism, substrate, dissolved oxygen and oxygen in gas-phase and heat balances. Nonideal mixing of liquid and gas phases is taken into account using a tanks-in-series model with back¯ow. The batch operation, startup operation and the consequence of plant failure were simulated and the effects of design and operating parameters for an airlift bioreactor on its dynamic behaviors were discussed. The concentration pro®les of micro-organism, substrate, dissolved oxygen and oxygen in gas-phase and the temperature pro®le in an airlift bioreactors and their dynamics were obtained. The computational results indicate that the transients of a chemostat in the case of bubble column bioreactor are slower compared with those in the case of airlift bioreactor. The proposed simulator is more precise as compared with models published previously in the literature and therefore provides more reliable and rational examination of continuous airlift bioreactor performance. List of symbolsA m 2 surface area for heat transfer b back¯ow parameter C kg/m 3 dissolved oxygen concentration C dimensionless dissolved oxygen concentration (=C=C in ) C p J/kgK constant-pressure speci®c heat Da Damko Èhler number (=Y X=S S in ÀDH=T a C p q) E a J/mol activation energy K C kg/m 3 saturation constant for oxygen K C dimensionless saturation constant for oxygen (=K C =C in ) K L a L 1/s volumetric gas-liquid mass transfer coef®cient K S kg/m 3 saturation constant K S dimensionless saturation constant (=K S =S in ) M number of stages in the riser N total number of stages in the airlift bioreactor P ratio of the number of stages for the gas phase to that for the liquid phase in the riser P d ratio of the number of stages for the gas phase to that for the liquid phase in the downcomer Q LC m 3 /s liquid circulation velocity Q G m 3 /s inlet gas¯ow rate Q G dimensionless inlet gas¯ow rate (=Q G =Q LC ) Q GC m 3 /s gas circulation velocity Q GC dimensionless gas circulation velocity (=Q GC =Q LC ) Q L m 3 /s inlet liquid¯ow rate Q O 2 kg/m 3 s speci®c rate of oxygen consumption Q O 2 dimensionless speci®c rate oxygen consumption (=Q O 2 s C =C in ) R recycle ratio (=Q LC =Q L ) R g J/kgK gas constant r x kg/m 3 s reaction rate S kg/m 3 concentration of substrate S dimensionless substrate concentration (=S=S in ) St C Stanton number for mass transfer (=K L a L s C ) St h Stanton number for heat transfer (=UA=Q C C p q) St o Stanton number for oxygen consumption Q O 2 Y X=S S in s C =C in T K temperature T a K coolant temperature T dimensionless temperature (=T=T a ) t s time t dimensionless time (=t=s C ) U W/m 2 K overall heat transfer coef®cient V L m 3 liquid volume X kg/m 3 concentration of micro-organism X dimensionless micro-organism concentration (=X=Y X=S S in ) Y Pa oxygen concentration in the gas phase Y dimension...

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This paper describes a vertical type twin roll strip casting process for producing aluminum alloy strip of ADC12, A3003 and A7075. Twin roll casting process is able to produce a strip from molten metal directly. Thus this process has a possibility to reduce total cost of sheet making comparing to conventional rolling process. Aluminum alloy ADC12 is a casting material that is used for die casting. A3003 is known as a wrought aluminum alloy for aluminum can body sheet. The A3003 sheet is generally produced by rolling, so it is effective for reducing a process cost to produce the strip by twin roll casting process. Aluminum alloy A7075 has high tensile strength, and it is known as a material for aerospace application. The sheet is manufactured in small quantities comparing to the other sheet aluminum alloy. It is supposed that the demand of high tensile strength aluminum sheet such as A7075 is going to increase for weight saving of structural material. In this study, twin roll casting experiment was performed to produce these three aluminum alloy strip in same experimental conditions. Castability, surface conditions and strip thickness were estimated. It was possible to cast these aluminum alloy strip.

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