The Research On Airflow Organization And Control Strategy Of Ⅲ Biological Safety Cabinet

The main function of the biological safety cabinets is to provide a clean operating space, it is an important clean equipment of microbial experimental operation, it plays a protective effect for operator, experiment environment and the samples. Ⅲ biological safety cabinets provide absolute security that class Ⅰ and class Ⅱ biological safety cabinet can not do. All Ⅲ biological safety cabinets can be used in microbial factor experiments involving one, two, three and four biological safety levels.Ⅲ biological safety cabinet is especially suitable for biological tests that may produce lethal factor. Ⅲ biological safety cabinets generate many problems during the R&D process, the author focused on the three issues.1)BSC Ⅲ is a fully enclosed, negative pressure space, people operate the experimental samples through the gloves.Once a glove falls off, the external air will enter the Interior space in a moment due to the internal negative pressure.Unfiltered outside air can easily result in the contamination of the experimental sample. If changing the air inlet modes makes all external air flow away before reaches operating area, experimental samples can avoid pollution. The author first simulate this situation by fluent, with assuming the presser-outlet boundary conditions. The simulation results that this assumption can not be achieved. No matter what kind of outlet methods the cabinet use, outside air will run through the countertop. Fluent simulation of this problem has difficulties in setting boundary conditions. The results of the assumed boundary conditions simulation can not guarantee its accuracy. The author made a plexiglass model of the biological safety cabinet. When a glove falls off, let smoke flow beside the glove opening and record the wind speed values. These experiments show that changing the air inlet methods can not make samples avoid pollution. This assumption can not be achieved.2)BSC III needs a transfer window to pass the samples between the inside and the outside space, when the transfer window opens, the pressure in the operating area will fluctuate, if the internal pressure fluctuation stays for a long time, it will have an impact on the samples. When the transfer window opens, use the PID to control the internal pressure of operating area, and record the pressure values. The result is that PID control is ineffective. Then use the virtual instrument which is based on LABVIEW programming to control the fan inverter frequency. Change the fan frequency when the transfer window opens, and record the internal pressure of the operating area. The experiments proof that using LABVIEW virtual controller is better and faster.3) The perforated panel is more suitable than grill panel to be the outlet way for BSC class III. The influence of orifice size on the airflow is unknown. CFD is used in this paper to study the influence on air distribution by the orifice size in perforated panel. The author established three models of III biological safety cabinets whose perforated panel using different orifice size. These different orifice sizes are5mm,10mm,13mm. Simulate airflow distribution of the three BSC III adding static arms beyond different airflow velocity0.2m/s and0.5m/s.We get the conclusion that with the same wind speed, the smaller the orifice size is, the less effect of arm the airflow has. However, when the orifice size is5mm, the operating areas of the upper and lower part have different airflow velocities. Wind speed value in upper operating room is smaller and in lower room is larger. The situation results in uneven airflow. By comprehensive comparison, we conclude that perforated panel with orifice size10mm is the best. The article only discuss the relationship between aperture size and airflow distribution, do not consider the requirements for pore size of perforated panel during practical application.