CFD analysis of LLNL downdraft table

LBNL-53883 CFD ANALYSIS OF LLNL DOWNDRAFT TABLE Elizabeth U. Finlayson Buvana Jayaraman Astrid R. Kristoffersen* Ashok J. Gadgil Indoor Environment Department, Lawrence Berkeley National Laboratory *Fullbright Visiting Scholar at LBNL from Norwegian Building Research Institute OBJECTIVES This study examines the airflow and contaminant transport in an existing room (89”x77”x98”) that houses a downdraft table at LLNL. The facility was designed and built in the 1960’s and is currently being considered for redesign. One objective of the redesign is to reduce airflow while maintaining or improving user safety. Because this facility has been used for many years to handle radioactive material it is impractical to conduct extensive experimental tests in it. Therefore, we have performed a Computational Fluid Dynamic (CFD) analysis of the facility. The study examines the current operational condition and some other cases with reduced airflow. Reducing airflow will lead to savings in operating costs (lower fan power consumption), and possible improvements in containment from reduced turbulence. In addition, we examine three design (geometry) changes. These are: (1) increasing the area of the HVAC inlet on the ceiling, (2) adding a 15° angled ceiling inlet and (3) increasing the area of the slot in the doorway. Of these three geometry modifications, only the larger doorway slot leads to improved predicted containment. APPROACH G EOMETRY The facility, shown schematically in Fig. 1, consists of two rooms connected by a doorway. In the first room, the change room, the worker puts on protective clothing. This room provides an entrance to the second room, the downdraft room, which contains the downdraft table located against a wall. This wall has in it a pass-through window directly above the downdraft table. Contaminated packages are brought into the room through this window and then the window is closed shut. As the facility is currently operated, 2600 CFM of air flows through a slot in the