*Step: main function of the fume hood
The function of the fume hood is mainly 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 the user. 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. In recent years, considering the improvement of the experimental environment, the experiments carried out on the experimental bench were gradually transferred to the fume hood, which required the function of the equipment suitable for the equipment in the fume hood . In particular, most newly built laboratories require air conditioning, as the number of fume hoods 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 exhaust, which have become important topics in laboratory construction. The purpose of using the fume hood is to discharge the harmful gases generated in the experiment and protect the health of the experimenter, that is to say, to have a high degree of safety and superior operability, which requires the fume hood to have the following functions:
1. Release function: It should have the means to absorb the harmful gas generated inside the fume hood by absorbing the gas outside the cabinet, and dilute it to exclude the outdoor mechanism.
2. Non-backflow function: It has the function of the airflow generated by the exhaust fan inside the fume hood to prevent the harmful body from flowing into the room from the inside of the fume hood. To ensure the realization of this function, a fume hood and a ventilation machine cabinet is connected to a single pipe zui good way, with a single tube can not be connected, it can also be limited in the same room and connected to the same layer, as the fan is mounted at the end of management (or layers at the top).
3. Isolation function: The inside of the fume hood should be separated by a non-sliding glass window.
4. Supplementary function: There should be a passage or planning device for taking in air outside the fume hood when harmful gases are exhausted.
5. Control the wind speed function: In order to prevent the harmful gas in the fume hood from escaping, a certain suction speed is required. The factor that determines the suction speed of the air inlet of the fume hood: 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. Generally, the generally non-toxic pollutants are 0.25-0.38 m/s, the toxic or dangerous pollutants are 0.4-0.5 m/s, highly toxic or a small amount of radioactivity is 0.5-0.6 m/s, and the gas is 0.5 m/s, granules were 1 m/s. 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 management, it is limited to 7-10m. If it exceeds 10m, noise will be generated. Generally, the laboratory (indoor background noise level) noise limit value is 70dBA, and the management cut area will be increased. Reducing the wind speed also reduces noise. Considering the management costs and construction problems, the power of the management and exhaust fans must be carefully selected.
6. Heat resistance and acid and alkali corrosion resistance: There are some electric furnaces 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, linings, side panels and selected water nozzles and air nozzles of the fume hood should have anti-corrosion function. In the semiconductor industry or corrosive experiments using strong acid such as sulfuric acid, nitric acid, hydrofluoric acid, etc., the overall material of the fume hood must be resistant to acid and alkali, and must be made of stainless steel or PVC material.
The second step of the category of fume hood
The fume hoods are classified according to the air exhaust mode: they are divided into the upper exhaust type, the lower exhaust type, and the upper and lower simultaneous exhaust type. In order to ensure uniform wind speed in the working area, the lower part of the fume hood for the cold process is used, and the upper part of the fume hood for the hot process. For the process of unstable heat generation, the exhaust vent can be installed in the upper and lower sides. The change in calorific value adjusts the ratio of the upper and lower exhaust air volumes to obtain a uniform wind speed.
Ventilation cabinets are classified into three categories according to the air intake method. It is called a full exhaust type by circulating indoor air in the cabinet and then discharging it. This is a very widely used type.
When the fume hood is installed in a room with heating or control requirements for temperature and humidity, in order to save heating and air conditioning energy consumption, the method of exhausting air from the outside and circulating it in the cabinet and then discharging it outside is called a supplemental air fume hood.
The other is a variable air volume control type fume hood . The ordinary constant air volume system needs to manually adjust the damper of the fixed vane, adjust the exhaust air volume of the fume hood , and achieve the desired surface wind speed when the valve is adjusted to a certain angle. The variable air volume control is to change the air volume by adjusting the sensor of the valve to achieve a given surface wind speed. Of course, the standard type has low cost and high variable air volume cost, and is suitable for occasions requiring high precision.
The fume hood is divided into the whole lower open type, floor type, two-sided type, three-sided glass type, table type, conjoined type according to the state of use, and the radioactive experiment and the synthetic experiment designed according to the needs of different experiments. Dedicated fume hood for perchloric acid experiments.
The third step of the fume hood must also pay attention to safety when in use.
Before the experiment begins, it must be confirmed that the fume hood should be in operation for the experimental operation.
Before the end of the experiment, it is necessary to continue to run for more than 5 minutes before the ventilation can be turned off to discharge the residual gas in the pipeline. It is also conceivable to install an exhaust time delay to ensure that the fan is delayed.
During the experiment, do not put any equipment within 150mm from the glass window. The large experimental equipment should have sufficient space and should not affect the flow of air. The front window should be closed.
The fourth step of the choice of fume hood
When constructing the laboratory, select the fume hood and determine the installation position of the fume hood. It is necessary to select the type, material, shape, etc. of the fume hood according to the experimental content. Usually, the following contents are considered:
Drugs used: When using organic or other special reagents, consider the control of wind speed. Heat source: When using equipment with heat source, the heat required to remove heat should be determined when the heat exceeds 2000 kcal/hour. The power of the ventilator.
In the case of radioactive materials or chloric acid: a dedicated fume hood should be used, and the inlet air velocity must be set greater than 0.5 m/s.
When experimenting with large equipment: Consider the internal effective size and leave the necessary space for the exhaust.
Material: When using special acid experiments, consider the material of the fume hood , such as the semiconductor industry, corrosion industry, etc. must be made of anti-corrosion materials.
Dimensions: Select the size according to the experimental content, the volume is too large to waste, too small to affect the use.
Environmental protection: Exhaust harmful gases should be installed if they are required to be below national environmental requirements if they exceed national health standards.
Energy saving: 昼 Consider saving energy. In a heating or air-conditioned room, a wind-filled fume hood or a fume hood with air volume control should be used. When selecting a fume hood, you should also determine its power according to your needs. Do not blindly increase the air volume and pressure. You can use the inverter or variable wind speed fan to reduce power consumption.
In the installation position of the fume hood , avoid facing the roads and personnel through frequent sites, avoid blocking the windows and the places where the ventilation and lighting are unfavorable, and avoid the place where the entrance and exit of the door affects the switch, avoiding the opposite and rotating at the corner wall.
In the modern research laboratory, the scientific instruments, the perfect experimental equipment, and the good experimental environment are the necessary conditions for upgrading the scientific and technological level and promoting scientific research results. People-oriented, ensuring safety and improving efficiency are the mission of the laboratory construction. . Fume hood as an important biochemical laboratory experiment facility plays a key role and must therefore be carefully selected to meet the fume hood technical indicators, ignoring the functionality and safety of the fume hood, one-sided drive down the unit cost of pure mounted fume hood if The consequences of the harm are unimaginable and should be paid enough attention.
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