Working principle of laboratory fume cupboard
Fume hood is a kind of local exhaust equipment commonly used in the laboratory. It has a wide variety of different types.
The good performance of the fume hood depends mainly on the speed of air movement through the fume hood.
Laboratory ventilation is an integral part of laboratory design.In order for laboratory staff not to inhale or swallow toxic, pathogenic or toxic chemicals and organisms, the laboratory should be well ventilated.To prevent the absorption of some steam, gas and particulates (soot, smoke, dust and air suspension), the pollutant must be removed by means of a fume hood, ventilation hood or local ventilation.
Main function of fume hood.
The most major function of fume hood is fume exhaust , in the chemical laboratory, When experimental operation will produce a variety of harmful gases, odor, moisture and inflammable, explosive, corrosive substances, in order to protect the safety of the user, to prevent the spread of pollutants to the laboratory, in the vicinity of pollution sources to use fume hood, fume hood before using the Numbers is less, only in particularly harmful and dangerous gas and produce a large amount of heat used in the experiment.The fume hood only undertakes the auxiliary function of the experiment station.In recent years, considering the improvement of the experimental environment, the experiment carried out on the experimental stage is gradually transferred to the ventilation cabinet, which requires the most suitable function to be used in the fume hood.In particular, most newly-built laboratories require air conditioning, so the use of ventilation cabinets should be incorporated into the air-conditioning system during the preliminary design phase of the building.Because of the fume hood occupies very important position in the biochemical laboratory, from the improvement of laboratory environment, improve the labor hygiene conditions, improve the work efficiency into consideration, such as the use of the fume hood number by leaps and bounds.Along with it, ventilation ducts, piping, wiring, exhaust and so on become the important subjects of laboratory construction.
Using the fume hood is the biggest purpose discharge harmful gases generated in the experiment, protect the health of the researchers, that is to say, want to have a high security and excellent operability, which requires the fume hood should have the following features:
(1) release function: the harmful gas produced inside the fume hood should be used to absorb the gas outside the cabinet so as to eliminate the outdoor mechanism after dilution.
(2) no reverse flow function: the air flow generated by the exhaust fan inside the fume hood should be used to remove the harmful gas from the interior of the fume hood.
In order to ensure the implementation of this function, a hood and a fan with a single pipe connection is the best way, cannot use a single pipe connection, also only can be provided the same room and even, fan installed at the end of the pipe as far as possible (or roof).
(3) supplemental function: it shall have a passage or an alternative device that draws air out of the fume hood when harmful gases are discharged.
(4) isolation function: the ventilation cabinet should be separated from the ventilated cabinet in front of the fume hood.
(5) heat resistance and acid and alkali corrosion function: in the ventilation cabinet, there is an electric furnace, and some experiments produce a lot of poisonous and harmful gases, such as acid and alkali, which are highly corrosive.The countertop of the fume hood, the lining board, the side board and the selected water mouth, the gas mouth and so on should have the antiseptic function.In the semiconductor industry or corrosive experiment, the use of nitric acid, sulfuric acid, hydrofluoric acid and other strong acid conditions also requires that the whole material of the fume cabinet must be anti-acid and alkali, should be made of stainless steel or PVC materials.
(6) control the wind speed: to prevent harmful gas escaping from the ventilation cabinet, it is necessary to have certain inhalation speed.The factors that determine the intake speed of the ventilation cabinet are: the heat generated by the experiment and the relationship with the number of ventilation.The main ones are the content of the experiment and the nature of the pests.Generally, it is stipulated that the common non-toxic pollutant is 0.25 -- 0.38m/s, and the toxic or dangerous harmful substance is 0.4 -- 0.5m/s, highly toxic or a small amount of radioactivity is 0.5 -- 0.6m/s, and the gas is 0.5m/s, and the particulate matter is 1m/s.In order to ensure such wind speed, the exhaust fan should have the necessary static pressure, that is, the friction resistance of the air through the ventilation ducts.Determine the wind speed must also pay attention to the noise problem, through the air in the pipe flow is limited to 7-10 m, more than 10 m will produce noise, usually laboratory (indoor background noise level) noise limit is 70 dba, increase the pipeline laying area can reduce wind speed, also reduce noise, considering the funding and pipeline construction question, must choose carefully pipeline and exhaust fan power.