The key function of the fume hood is the exhaust pipe function. In the organic chemistry laboratory, various harmful gases, odors, internal moisture and their flammability, flammability, explosion and corrosion chemicals are caused during the actual operation of the experiment. In order to better maintain the safety of users and avoid the diffusion of environmental pollution chemicals outside the laboratory, Fume hoods should be used around pollutants. In the past, the number of fume hoods was small, and they were only used in experiments that are particularly harmful and risky to steam and cause a lot of heat. The fume hood only shoulders the auxiliary function of the test bench. In recent years, full consideration has been given to improving the natural environment of the experiment, and the experiments carried out on the experimental bench have slowly moved to the fume hood, which stipulates that the fume hood should have the function suitable for the application of machinery and equipment. In particular, most newly established laboratories are provided with central air conditioning, so the application number of fume hoods needs to be included in the scheme of air conditioning units in the preliminary design of engineering buildings. Because the fume hood occupies a very key position in the biochemical laboratory, the number of applications of fume hood has increased by leaps and bounds from the aspects of improving the natural environment of the laboratory, improving labor hygiene standards and improving work efficiency. Then came the ventilation duct. Pipe threading, wiring and exhaust system have become the key research topics of laboratory infrastructure.
The main purpose of using the fume hood is to exhaust the harmful gas caused by the experiment and maintain the physical and mental health of the experimental staff. In other words, it should have the safety factor of height width ratio and excellent operability. This stipulates that the all steel fume hood should have the following functions:
(1) Release function: it shall be able to digest and absorb the harmful gas caused by the inside of the fume hood, so that the outdoor tissue can be removed after diluting.
(2) No countercurrent function: it shall have the function that the cyclone caused by the smoke exhaust fan inside the fume hood will harm the air? The function that the body does not flow in the opposite direction from the interior of the fume hood to the room. In order to ensure the completion of this function, a fume hood and an exhaust fan are connected by a single pipeline, which can not be connected by a single pipeline, and it is only limited to those in the same room on the same floor. The exhaust fan shall be installed at the tail end (or floor top) of the pipeline as far as possible.
(3) Protective function: a non rolling laminated glass window shall be provided in front of the fume hood to separate the inside and outside of the fume hood.
(4) Filling function: it shall have a safe channel or substitute equipment to suck in gas from the outside of the fume hood when harmful gas is discharged.
(5) Wind control function: in order to avoid the escape of harmful gases in the fume hood, there must be a certain suction rate. The factors that determine the suction rate of fume hood supply air are: the calorific value caused by the experimental content and the correlation with air change. Among them, the key is the experimental content and the characteristics of harmful substances. General requirements: the general non-toxic air pollutants are 0.25-0.38m/s?, 0.4-0.5? For hazardous or risky hazardous substances? m/s?， Toxic or small amount of radioactive material is 0.5-0.6m/s?, 0.5m/s for gaseous substances?, The particle is 1 m / S?. In order to better ensure such wind power, the smoke exhaust fan should have the necessary negative pressure, that is, the friction of the gas according to the ventilation duct. When determining the wind power, you must also pay attention to the noise problem. According to the fluidity of gas in the pipeline, it is limited to 7-10 meters. Exceeding 10 meters will cause noise. The noise limit value (DB level in the room) of general laboratory is 70 DBA. Increasing the total area of the pipeline will reduce the wind power and reduce the noise. Fully consider the budget of the pipeline and the problems of engineering construction, Be sure to carefully select the output power of pipeline and smoke exhaust fan.
(6) High temperature resistance and corrosion resistance: heating furnaces shall be installed in some fume hoods, and some experiments cause a lot of strong acid, strong alkali and other harmful gases with strong corrosion. The cabinet table, jaw plate, baffle, water nozzle and gas nozzle of the fume hood shall have anti-corrosion function. In places where hydrochloric acid, sodium cyanide, hydrochloric acid and other strong alkalis are applied in the semiconductor industry or corrosion experiments, it is also stipulated that the overall raw materials of the all steel fume hood must be resistant to strong acids and strong alkalis, and must be made of stainless steel plate or PVC materials.