On Generating Uniform Bottom Shear Stress. Part I: A quantitative study of microcosm chambers By Arzhang Khalili 1,2,† , Khodayar Javadi 1 , Arash Saidi 1,‡ , Afshin Goharzadeh 1,¶ , Markus Huettel 3 and Bo B. Jørgensen 1 1 Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany 2 Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany 3 Department of Oceanography, Florida State University, Tallahassee, FL 32306-4320, USA Abstract: Generating uniform shear stress planes finds a variety of applications in different disciplines such as process engineering, medicine and marine sciences. The focus of this study is to quantify the potential of microcosm chambers, applied in marine applications, in producing shear stress uniformity at the chamber bottom. To do this, computational fluid dynamics was used to simulate the flow pattern, velocity profiles, and shear stress distribution at chamber bottom. The study re- vealed that the microcosm chambers, such as those presented in the patent of Gust, produce a fully vortical flow, containing acceleration-deceleration zones near the central axis and the outer wall. The results show that the presence of these acceleration-deceleration zones is the major reason for non-uniform shear stress formation at the chamber bottom. Utilizing a suction-injection mechanism and-or attached skirt provides better bottom shear stress profiles compared to a con- ventional disk-cylinder. In spite of this partial improvement, the addition of a suction-injection device or a skirt attached to the disk provides a partial shear stress uniformity only over 72% of the bottom area, and is therefore of limited use. Keywords: Benthic chamber, microcosm chamber, shear stress uniformity, bottom shear stress Introduction There exists a strong need for devices that generate planes with uniform shear stresses. The generation of such planes are also used, for example, in studying growth of cultures in bioreactors or to investigate cell death characterized by DNA fragmentation in the human body. These types of devices are also frequently used † Corresponding author: Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany, Email: akhalilimpi-bremen.de, Tel.: +49 421 20 28 636, Fax.: +49 421 20 28 690 ‡ Permanent address: Tetra Pak Packaging Solutions AB, Ruben rausings gata 1, 221 86 Lund, Sweden ¶ Permanent address: The Petroleum Institute, Mechanical Engineering Department, P.O. Box 2533, Abu Dhabi, U.A.E Recent Patents on Chemical Engineering, 2008, 1, - 174