Technical analysis of air volume control of Fume Hood
With the development of science and technology and industrialization process, scientific experiments are indispensable, in all areas of laboratory construction has been in full swing. Scientific research institutions, industrial and mining enterprises, large professional are generally set for experimental research with the laboratory.
Laboratory in the course of the test, accompanied by a large number of harmful substances such as gases, vapors, dust and suspended particles and other production, the health of the test personnel caused serious damage.
The Fume Hood is the main safety equipment in the laboratory. Most of the experiments are done in a Fume Hood. The Fume Hood is a special form of a closed hood. The process of producing harmful substances is carried out entirely in the hood. Ventilation cabinet is generally equipped with open and close operation hole and observation hole, through the ventilation cabinet ventilation, so that the cabinet to form a negative pressure to prevent the ventilation cabinet mechanical equipment disturbance, chemical reaction or heat source heat pressure, and indoor horizontal Air interference and other causes of harmful substances to escape.
2, the problem raised
Depending on the density of harmful gases and the density of air, there are many forms of Fume Hoods, and different types of Fume Hoods are used in different places. The main form of the Fume Hood includes: the upper exhaust of the Fume Hood, the lower exhaust of the Fume Hood, up and down the exhaust fan of the ventilation cabinet. At the same time, there are energy-efficient air supply Fume Hood.
The wind speed of the Fume Hood is the main technical measure of the performance of the exhaust cabinet. It refers to the average inlet wind speed at the opening of the exhaust cabinet. The criterion of the wind speed of the Fume Hood is that it is necessary to make the harmful gas not The cabinet to escape, but also to avoid turbulence in the Fume Hood.
Excessive overcoat wind speed can lead to airflow in the space above the table in the air cabinet, where contaminants may accumulate in one corner of the cabinet, and may blow off the flame, destroy the ongoing test, Wind speed is bound to cause the escape of pollutants, harm the safety of the test personnel.
For toxic or dangerous hazardous substances, the Fume Hood operating cover surface wind speed generally take 0.4 ~ 0.5m / s. Ventilation cabinet exhaust volume calculated according to formula (1) :
For the general laboratory Fume Hood, when considering the interference between the air flow and the Fume Hood operating port on the suction speed of the uneven, open area should take the operation of a large opening area.
It can be seen from the above formula, for the traditional no adjustment system of the Fume Hood, when the operation door is fully open, can meet the 0.4 ~ 0.5m / s over the surface wind speed, when the operation door open half or full off, the operating surface The wind speed will be greater than the design value, which will affect the experimental operation and exhaust effect.
According to the actual test of a Fume Hood , when the door is fully open, the cover wind speed of 0.47m / s, when the door opened half, the cover wind speed of 0.86m / s. When the door close to the whole closed, the cover wind speed will be greater, which will greatly affect the exhaust and experimental results.
Therefore, how to effectively control the wind speed is the protection of the effective ventilation of the Fume Hood.