An airlift reactor with double net draft tubes was developed. A sparger was located between the two draft tubes. The draft tubes had a significant effect on breaking bubbles into smaller ones. The assessment of the reactor performance was based on gas holdup, mixing time, and volumetric mass transfer coefficient. The proposed reactor had higher gas holdup and volumetric mass transfer coefficient, and lower mixing time in comparison with those of the bubble column. Application of the proposed reactor to fermentation of Saccharomyces cerevisiae demonstrated that the cultivation time was significantly shortened.
A pilot scale airlift reactor with multiple net draft tubes was developed. The reactor, 29 cm in diameter and 300 cm height, had four modules of double net draft tubes. Bubble size, bubble number, gas holdup, and volumetric mass transfer coef®cient were measured under different super®cial air velocities. The air velocity had little effect on bubble size but had signi®cant in¯uence on bubble number. A bubble column was also investigated for comparison. The airlift reactor had a higher gas holdup and volumetric mass transfer coef®cient than those in the bubble column. The draft tubes in the airlift reactor substantially improved the reactor performance.
Gamma accelerated degradation tests (ADT) are widely used to assess timely lifetime information of highly reliable products with degradation paths that follow a gamma process. In the existing literature, there is interest in addressing the problem of deciding how to conduct an efficient, ADT that includes determinations of higher stress‐testing levels and their corresponding sample‐size allocations. The existing results mainly focused on the case of a single accelerating variable. However, this may not be practical when the quality characteristics of the product have slow degradation rates. To overcome this difficulty, we propose an analytical approach to address this decision‐making problem using the case of two accelerating variables. Specifically, based on the criterion of minimizing the asymptotic variance of the estimated q quantile of lifetime distribution of the product, we analytically show that the optimal stress levels and sample‐size allocations can be simultaneously obtained via a general equivalence theorem. In addition, we use a practical example to illustrate the proposed procedure.
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