| Microalgae,which grows fast,performs high photosynthetic efficiency and is available for carbon capture.In addition,its high content of protein and grease also can be used to produce biofuel to alleviate energy crisis.In industrial production,the open type raceway ponds are widely used as microalgae photo-bioreactors.However,in an open raceway pond,the algal fluid flows cyclically around the reactor driven by the paddle wheel.In this situation,when the power consumption is constant,the mixing degree of the velocity in the light gradient direction of algal fluid is not good.Considering on this point,in order to improve the mixing and grow efficiency under the condition of keeping the power consumption increasing not greatly,this paper commits to optimize the arrangements and structure parameters of a static mixer in an open raceway pond based on the computational fluid dynamics?CFD?technology.Comparing with the experimental data,the validation of numerical method of this paper can be verified.The concept of the velocity per unit power consumption in the direction of light gradient??and average light/dark cycle period(?6?were then introduced to evaluate the influences of the mixer insertion on the flowing of the algal fluid by changing the number and arrangement of the mixer blades.The results showed that the(?6?of algal fluid decreased obviously and the power consumption increased simultaneously after adding the static mixer.With a constant velocity of paddle wheel,when the two blades of static mixer were arranged continuously and alternately to 90 degree,theis 5.78×10-3 m?s-1?W-1,which increased by 30.8%compared with the situation before adding the static mixer.The(?6?is 4.43 s,which decreased by 49.4%correspondingly.The mixing degree of the whole algal fluid is strengthened greatly.When changing the velocity of paddle wheel with the depth of algal fluid unchanged,the influence of the horizontal and vertical arrangement of mixer blades,starting position of blades and velocity of paddle wheel on the two indexes mentioned above was analyzed comprehensively by using the orthogonal method.The optimized test scheme is as follows:when the velocity of paddle wheel is 11 rpm,the rotating degree is 180 degree,the ratio of length and width is 2,theis 5.4×10-3 m?s-1?W-1 and the(?6?is 3.53 s.In order to understand the influence of mixer blade structure on the mixing and growing degree of microalgae,a deeper optimization study on the mixer blades'degree and ratio of length width has been done by using the Response Surface Methodology.The optimized test scheme is as follows:when the rotating degree is 180 degree and the ratio of length and width is 2,the(?6?is the smallest among all the schemes. |
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