Among modern laboratory equipment, there are fume hoods, central laboratory benches, side tables, medicine cabinets, utensils cabinets, gas cylinder cabinets, etc. Among them, the fume hood is a very important function of biochemical laboratory equipment and is an essential equipment. . Therefore, choosing a fume hood is an important issue in laboratory construction and must be paid attention to.

　　The main function of the fume hood

The most important function of the fume hood is the exhaust function. In the chemical laboratory, various 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 pollutants in the experiment from spreading to the laboratory, fume hoods should be used near the pollution source. In the past, the number of fume hoods used was small, and they were 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 experimental bench.

　　 In recent years, considering the improvement of the experimental environment, the experiments carried out on the experimental bench have gradually been transferred to the fume hood, which requires the most suitable function for the use of equipment in the fume hood. In particular, most newly-built laboratories require air-conditioning, so the number of fume hoods used must be included in the air-conditioning system plan in the preliminary design stage of the building. As fume hoods occupy a very important position in the biochemical laboratory, the number of fume hoods used has increased dramatically from the perspectives of improving the laboratory environment, improving labor sanitation conditions, and improving work efficiency. Following this is the ventilation ducts, piping, wiring, exhaust, etc. have become important issues in laboratory construction.

　　The biggest purpose of using a fume hood is to discharge the harmful gases generated in the experiment and protect the health of the experimenters. That is to say, it must have a high degree of safety and superior operability. This requires the fume hood to have the following functions:

　　(1) Releasing function: It should be equipped with a mechanism to absorb the harmful gas generated inside the fume hood by absorbing the gas outside the cabinet, and then to dilute it out of the outdoor.

　　(2) Non-reverse flow function: It shall have the function of preventing harmful gas from flowing back into the room from the inside of the fume hood by the airflow generated by the exhaust fan inside the fume hood. In order to ensure the realization of this function, it is the best way to connect a fume hood and a ventilator with a single pipe. It cannot be connected by a single pipe, and it is limited to the same room on the same floor. The ventilator can be connected as much as possible. Install at the end of the pipe (or at the top of the layer).

　　(3) Isolation function: In front of the fume hood, there should be a non-sliding glass window to separate the inside and outside of the fume hood.

　　(4) Supplementary function: It should have a channel or alternative device for sucking in air from outside the fume hood when exhausting harmful gases.

　　(5) Wind speed control function: In order to prevent harmful gases from escaping in the fume hood, a certain suction speed is required. The factors that determine the inhalation speed of the fume hood are: the heat generated by the experiment content and the relationship with the number of air changes. The main ones are the content of the experiment and the nature of the harmful substance. It is usually stipulated that generally non-toxic pollutants are 0.25-0.38m/s, toxic or dangerous harmful substances are 0.4-0.5 m/s, highly toxic or have a small amount of radioactivity are 0.5-0.6m/s, and gaseous substances are 0.5m/s, granular material is 1m/s.

　　 In order to ensure such a wind speed, the exhaust fan should have the necessary static pressure, that is, the frictional resistance when the air passes through the ventilation duct. When determining the wind speed, you must also pay attention to the noise problem. When the air flows in the pipe, the limit is 7-10m. Noise will be generated if the air exceeds 10m. The noise limit value of the laboratory (indoor background noise level) is usually 70dBA. Reducing the wind speed also reduces the noise. Considering the cost and construction of the pipeline, the power of the pipeline and the exhaust fan must be carefully selected.

　　(6) Heat resistance and acid and alkali corrosion resistance: some electric furnaces must be installed in the fume hood, and some experiments produce a large amount of toxic and harmful gases such as acid and alkali, which are extremely corrosive. The countertops, liners, side panels, and the selected water nozzles and air nozzles of the fume hood should have anti-corrosion functions. Where strong acids such as sulfuric acid, nitric acid, and hydrofluoric acid are used in the semiconductor industry or in corrosive experiments, the overall material of the fume hood must be acid-proof and must be made of stainless steel or PVC.

　　 Type of fume hood

　　 Fume hoods are classified according to the exhaust method: they are divided into three types: upper exhaust type, lower exhaust type and upper and lower exhaust simultaneously. In order to ensure uniform wind speed in the work area, the lower exhaust type should be adopted for the fume hood in the cold process, and the upper exhaust type should be adopted for the fume hood in the hot process. For the process of unstable heat generation, exhaust outlets can be set up and down along with the cabinet. The change of internal heat generation adjusts the ratio of the upper and lower exhaust air volume, so as to obtain a uniform wind speed.

　　 Fume hoods are also classified into three categories according to the air intake method. It is called the full exhaust type, which is a type that is widely used.

　　 When the fume hood is installed in a room with heating or temperature and humidity control requirements, in order to save heating and air conditioning energy consumption, the method of taking the supply air from the outside and circulating it out of the cabinet is called the supplementary air fume hood.

　　Another type is a fume hood with variable air volume control. Ordinary constant air volume systems need to manually adjust the fixed blade air valve, adjust the exhaust air volume of the fume hood, and reach the desired surface wind speed when the valve is adjusted to a certain angle. Variable air volume control is to change the air volume to a given surface wind speed by adjusting the sensor of the valve. Of course, the standard type has low cost and high variable air volume cost, which is suitable for occasions that require high precision.

Fume hoods can be classified according to their use status and can be divided into integral lower part open type, floor type, two-sided type, three-sided glass type, desktop type, conjoined type, as well as radioactive experiments and synthetic experiments designed according to different experimental use needs. , Special fume hood for perchloric acid experiment.

　　 Safety of the fume hood

　　Safety is the biggest mission pursued by fume hoods. The use of fume hoods in laboratories is to ensure the safety of users and prevent pollution to the surrounding environment.