Abstract: the ventilation cabinet is the main safety equipment in the laboratory. In order to control the overflow of harmful substances and ensure the normal operation of the experiment, the wind speed of the hood must be effectively controlled. During the experiment, with the operation of the cabinet door, the opening area of the ventilator was changed, the wind speed of the mask was larger, the ventilation system could not meet the design requirements, which affected the experiment and the pumping effect. In ventilation system of pipeline and fan performance analysis, design and the control system to control the variable air volume fume hoods and ventilation systems, system covering basic stable wind speed, the system is worthy of popularization and application.
Key words: laboratory; Ventilation system; Variable air volume control; Fume hood
Middle image classification number: TP document identification code: A
1.The introduction
With the development of science and technology and the process of industrialization, scientific experiments are indispensable, and laboratory construction in various fields has been fully developed. Scientific research institutes, industrial and mining enterprises and major majors are generally set up laboratories for experimental research.
During the experiment, a large number of harmful substances, such as gas, steam, dust and aerosols, caused serious damage to the health of the test personnel.
Fume hood is the main safety equipment in lab, most of the experiments done in ventilation cabinet, fume hood is a special form of airtight cover, produce harmful operation process completely in the enclosure. Fume hood generally have bore can open and close operation and observation, through the study of the convulsions of fume hood, to form a negative pressure inside ark, to prevent the ventilation equipment contained in the disturbance, the chemical reaction or heat source of hot pressing, and indoor crossflow caused the interference of harmful to escape.
2.Questions raised
According to the difference of the density of harmful gas and air density, there are many different forms of fume hood, and different types of fume hoods are applied in different places. The main form of the fume hood consists of the ventilation cabinet of the upper exhaust air, the ventilation cabinet of the lower exhaust air, and the ventilation cabinet of the combined exhaust ventilation. At the same time, there are also energy-saving air supply ventilators.
Fume hood cover surface wind speed is the main technical indicators of ark of exhaust air performance, it refers to the average exhaust cabinets open sliding door at the entrance to the wind speed, the selected principles of fume hood cover face wind speed is: should not only make harmful gas cannot escape from the enclosure, and at the same time to avoid in the turbulent flow in ventilation cabinet.
High surface wind speed can lead to exhaust the workbench contained in the space above the turbulence, accumulation of pollutants may be contained in a corner, and could blow out the flame, destroy the ongoing trials, too low to cover surface wind speed is bound to cause pollutants escape, endanger the safety of test personnel.
For toxic or dangerous hazardous materials, the ventilator of the ventilation cabinet is generally 0.4~0.5 m/s. The exhaust volume of fume hood is calculated according to formula (1) [1] :
For general laboratory ventilators, when considering the inhomogeneity of the suction velocity in the room, the opening area should be opened with a large opening area.
As you can see by the above formula, no adjustment system for the traditional ventilation cabinet, when the doors open operation, can satisfy the cap of 0.4 ~ 0.5 m/s surface wind speed, when the door half open or close operation, operating mask surface wind speed is greater than the design value, this will affect the operation and the effect of the exhaust air.
According to the actual test of a fume hood [2], when the cabinet door is fully opened, the hood wind speed is 0.47 m/s. When the cabinet door is opened in half, the wind speed of the cover surface is 0.86 m/s. When the cabinet door is close to full closing, the wind speed of the hood will be greater, which will greatly influence the exhaust and experimental results.
Therefore, how to effectively control the wind speed of the hood is the protection of the ventilation cabinet.
