The most important function of the fume hood is the exhaust function. In the chemical laboratory, all kinds of harmful gases, odors, moisture and flammable, explosive and corrosive substances are generated during the experimental operation, in order to protect the safety of users. To prevent the spread of pollutants in the laboratory to the laboratory, use a fume hood near the source of pollution. In the past, the number of fume hoods used was small, and it was only used in experiments with particularly harmful and dangerous gases and large amounts of heat. The fume hood is only responsible for the auxiliary functions of the test bench. Considering the improvement of the experimental environment, the experiments carried out on the bench were gradually transferred to the fume hood, which required the most suitable function for the equipment in the fume hood. In particular, most newly built laboratories require air conditioning, so the number of fume hoods to be used in the initial design phase of the building is included in the air conditioning system plan. Since the fume hood occupies a very important position in the biochemical laboratory, the number of fume hoods has increased dramatically in terms of improving the laboratory environment, improving the sanitary conditions, and improving work efficiency. It is followed by ventilation ducts, piping, wiring, and exhausting, which have become important topics in laboratory construction.
The main purpose of using the fume hood is to discharge the harmful gases generated in the experiment and to protect the health of the experimenter, that is to say, to have a high degree of safety and operability, which requires the fume hood to have the following functions:
Control wind speed function: In order to prevent harmful gas from escaping in the fume hood, a certain suction speed is required. The factors that determine the suction speed of the air inlet of the fume hood are: the heat generated by the experimental content and the relationship with the number of air changes. The main ones are the experimental content and the nature of the harmful substances. The national standard stipulates that the surface wind speed of the fume hood is 0.5 m/s ± 10%. In order to ensure such a wind speed, the exhaust fan should have the necessary static pressure, that is, the frictional resistance of the air as it passes through the ventilation duct. When determining the wind speed, you must also pay attention to the noise problem. When the air flows through the pipeline, it is limited to 7-10m. If it exceeds 10m, noise will be generated. Generally, the noise limit of the laboratory (indoor background noise level) is 70dBA, and the cross-sectional area of ​​the pipeline will increase. Reduce wind speed and heat and acid and alkali corrosion resistance. Some of the fume hoods have electric furnaces to be placed, and some experiments produce a large amount of toxic and harmful gases such as acid and alkali, which are highly corrosive. The countertops, linings, side panels and selected water nozzles and air nozzles of the fume hood should have anti-corrosion function. In the semiconductor industry or in corrosive experiments, the use of strong acids such as sulfuric acid, nitric acid, hydrofluoric acid, etc., also requires that the overall material of the fume hood must be acid and alkali resistant, usually made of stainless steel, PVC or PP materials.