Linear airflow models

Linear models, e.g. FACTS (Griffiths, 2000) and FLOWSTAR, developed by CERC Ltd., solve linearized versions of the Navier-Stokes equation. Such models are fast and stable in operation. Typically, they are applicable for calculating the modification to prevailing horizontal airflow due to the presence of surface features, e.g. small, smooth hills and/or surface roughness. 

It has not been easy to determine the factors required to assure maximum performance efficiency of the Class II biological safety cabinet. In its Standard 49 (326) the National Sanitation Foundation (NSF, an industrial organization that sets standards for the performance of cabinets) has attempted to define efficiency and performance for these cabinets. Unfortunately, many factors influence efficiency and performance after the cabinet is removed from the ideal situations that prevail in the factory or in the NSF testing laboratory. All Class II cabinets are manufactured to meet the standards set by NSF 49. At a minimum the average airflow velocity cannot deviate by more than 5 linear feet per minute (Ifpm) from the established set point for a particular cabinet model. However, in practice, the airflow velocities may vary significantly more than this. These variations result from some of the following factors that are external to the design and operation of the cabinet ... 

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