Publish Time: 2022-04-29 Origin: Site
The first is the safety of the experimental process
1. A good fume hood, structure and exhaust must ensure that the diffusion of harmful gases can be effectively captured and blocked, so as to ensure that operators are protected from harmful substances. The main factors related to the protective performance of a fume hood include: face wind speed, disturbed airflow and operating habits.
2. Surface wind speed: The lower surface wind speed cannot effectively and timely discharge the harmful substances, and the excessively high surface wind speed will locally generate disturbance and eddy current, so that the harmful gas in the fume hood escapes > According to various Based on research and practical application experience, the researchers concluded that the effective surface wind speed setting value of the fume hood is the general industry standard (0.3m/s-0.5m/s), and 0.5m/s is accepted as ventilation in modern experimental sites Standard for safe operation of cabinets. Therefore, it is very important to ensure a constant surface wind speed, which requires that the exhaust air volume of the fume hood should change all the time when the cabinet is opened at different degrees;
3. In addition, the control of disturbed airflow needs to be considered when designing the airflow organization of the air conditioner. The air supply port should be as far away as possible from the dynamic influence area of the exhaust airflow;
4. Operational habits are the professional quality of the experimenter, and it needs to be designed to provide users with a simple and convenient way of use.
The second is stability
1. During the experiment, in order to make the harmful gas reach and maintain the surface wind speed required for safety at every opening of the cabinet door, the exhaust air volume needs to be adjusted constantly, which requires it to have a stable and reliable adjustment control system. The airflow control system needs to provide stable airflow, which is independent of the static pressure change of the air duct, and has high requirements on the response time and control accuracy of the system.
2. A good fume hood structure can make the air flow away as soon as possible, and the required air volume is small. The setting of the VAV system can further optimize the operating conditions of the system according to the use of the fume hood. When the height is different, the exhaust air volume is adjusted to control the supplementary air volume of the supplementary air conditioning system, so that the consumption of cold and heat can be adjusted in real time, which can achieve high-efficiency utilization of energy and save energy consumption. Since the experimental process and steps of each experimental station are not carried out at the same time, the setting of the laboratory VAV system, theoretically speaking, the larger the system is, the lower the coefficient can be selected. From the aspects of equipment selection and energy allocation, the larger the The system is more beneficial. However, combined with the different needs of actual projects and users, it is often difficult for the system to be very large, which requires professional designers to make trade-offs according to actual conditions and choose a relatively optimized solution.
(1) Measurement of ventilation volume: Use an anemometer to collect data at multiple points (not less than 4 points) at the outlet of the exhaust fan, and take the average value as the basic data. Measure the cross-sectional area of the fan outlet and make calculations. Air exchange volume = measured wind speed × fan outlet section × 3600 In the above example, the measured wind speed in the anatomy laboratory is 5.2 m/s, and the air outlet section is 0.12 square meters. Substituting into the above formula is, the actual ventilation volume = 5.2 × 0.12 × 3600 = 2246.6 cubic meters / H. The two machines run at the same time, and the actual ventilation volume is 4492 cubic meters/H.
(2) Indoor ventilation rate = ventilation volume/indoor effective space = 4492/250 = 17.92 times/H, which is about 18 times per hour. The measured wind speed in the analytical laboratory is 5.56 m/s, and the intercepting surface of the air outlet is 0.048 square meters. The exhaust volume of the four fans running at the same time=5.56×0.048×4×3600=3843 cubic meters/H. The ventilation rate = 3843/250 = 15 times/H, which is slightly larger than the design requirements. Because the noise does not exceed the standard, it can be used normally.