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  • 洁净室通风系统的安全性能先容
    来源: 浏览: 发布日期:2018-10-24
    一、稳定的通风柜面风速
    1. Stable ventilation speed of ventilation cabinet
    在定风量通风系统中,当调节门降低时,会产生多余的面风速,从而产生涡流干扰,影响通风柜集尘能力,释放出有毒颗粒。变风量的通风控制系统中,排风量和调节门开度为线性函数关系,如60%的流量对应60%的调节门开度,通过这一闭环控制系统,可以保持通风柜开口的面风速恒定,消除面风速过大产生的风险。
    In a constant air volume ventilation system, when the control door is lowered, excess surface wind speed will be generated, which will cause eddy current interference, affect the dust collection capacity of the fume hood and release toxic particles. In the ventilation control system with variable air volume, the relationship between the exhaust air volume and the opening of the regulating door is a linear function. For example, 60% of the flow corresponds to 60% of the opening of the regulating door.
    通风柜有效的面风速设定值,通用的工业标准是60—100fpm(0.3—0.6m/s),一般100pfm(0.5m/s)被接受作为安全运行标准。图1所示,操作人员的移动在面风速80—100fpm时对集尘几乎没有影响,但在80 fpm以下时会有扰动影响。在没有操作人员移动时,60 fpm 以下一般性集尘可以实现。
    The general industrial standard is 60-100fpm (0.3-0.6m/s), and the general 100pfm (0.5m/s) is accepted as the safe operation standard. As shown in Figure 1, the movement of the operator has little effect on dust collection at the surface wind speed of 80-100 fpm, but disturbance effect below 80 fpm. The general dust collection below 60 FPM can be achieved without moving the operator.
    二、快速的系统响应时间
    Two. Fast system response time.
    该响应时间主要是指实验室范围内通风柜及其阀门调节系统。响应时间的大小将直接决定气流控制的效果。快速、稳定的控制会防止有毒颗粒跟随调节过程可能产生的振荡或过冲逸出通风柜。排风量对调节门开度的快速响应时间必须在调节门到位后1秒钟内达到其指令值,有效保证通风柜的集尘能力。图2中从调节门移动到通风柜排风量的总的响应时间大约0.6秒。缓慢的响应时间将会产生多余的面风速,危害到实验的安全,例如燃烧器被吹灭,器皿被吹翻,或者药品等受到损失。
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    The response time mainly refers to the fume hood and its valve regulating system in the laboratory. The response time will directly determine the effect of airflow control. Rapid and stable control prevents toxic particles from oscillating or overflushing out of the hood during the adjustment process. The quick response time of the exhaust air volume to the opening of the regulating door must reach its command value within 1 second after the regulating door is in place to effectively ensure the dust collection capacity of the fume hood. In Fig. 2, the total response time from the adjusting door to the exhaust volume of the hood is about 0.6 seconds. Slow response time will produce excess surface wind speed, endangering the safety of the experiment, such as burners blown out, containers blown over, or drug losses.
    三、保证房间压力
    Three, ensure room pressure.
    房间净负压主要控制房间气流由外到内的流动,防止房间外部被污染,是实验室安全控制的一个重要指标。负压的产生也就是房间的排风量或补风量和送风量之差等于房间的余风量。余风量是送风以外从房间门、传递窗或其他缝隙进入房间的空气量。
    The net negative pressure of a room mainly controls the flow of air from outside to inside and prevents the outside of the room from being polluted. It is an important index of laboratory safety control. The negative pressure is generated by the difference between the discharge volume of a room or the volume of air supplied and the amount of air supplied to it, equal to the amount of air remaining in the room. The air volume is the amount of air that enters the room from outside the door, through the window or other gaps.
    当房间温度调节与通风所需气流量大于通风柜所需气流量的时候,房间的送风量增加了,这就要求控制系统还必须把这部分“过剩”的送风量排出去,以保证房间负压。实验室总的空气交换率由总的排风、制冷负荷和低通风率决定。小通风速率一般为占用时每小时 6–10 次换气。这可通过增大房间综合排风阀门的开度来实现,该控制涉及房间总送风量和排风量的计算,以及信息采集、风机变频的控制等,系统调试的难度大为增加。
    When the room temperature regulation and ventilation required air flow is greater than the required air flow of the fume hood, the room air supply increased, which requires the control system must also discharge this part of the "excess" air supply to ensure room negative pressure. The total air exchange rate in the laboratory is determined by total exhaust, refrigeration load and minimum ventilation rate. The minimum ventilation rate is usually 6 to 10 times of ventilation per hour. This can be achieved by increasing the opening of the room exhaust valve. This control involves the calculation of the total air supply and exhaust volume, as well as information acquisition, fan frequency conversion control and so on. The difficulty of system debugging is greatly increased.
    四、压力无关性
    Four, pressure independent
    通风柜调节门的移动造成风量快速变化导致风道静压发生变化,或者在通风柜面风速未要求变化时,总管中风压的变化也会引起排风柜上部支排风管道中风压的变化,如果此时风量控制系统不能化解管道的风压变化,就会使排风柜的排风量变大或变小,进而影响此时本该稳定的面风速。
    The change of wind pressure in the main pipe will also cause the change of wind pressure in the upper branch of exhaust duct if the air volume control system can not resolve the change of wind pressure in the duct. The exhaust volume of the cabinet is larger or smaller, which affects the surface wind speed which is stable at this time.
    传统的变风量调节系统是根据管道的压差反馈信号进行排风量的调节,响应速度一般在20~30s之间,为了保证实验室的安全性,实验室气流控制系统的响应时间必须控制在1s之内。
    The traditional variable air volume control system is based on the pressure difference feedback signal of the pipeline to adjust the exhaust air volume. The response speed is generally between 20 and 30 seconds. In order to ensure the safety of the laboratory, the response time of the laboratory air flow control system must be controlled within 1 seconds.
    阀门是一个椎形的构造,内置不锈钢弹簧,根据系统压力的变化调整文丘里打开的面积,以维持固定的空气流量。压力降低时,弹簧张开,阀芯分离,增大通风量;压力增大时,弹簧压缩,阀芯接近,减少通风量。
    The valve is a spine-shaped structure with a built-in stainless steel spring that adjusts the area venturi opens to maintain a fixed air flow rate according to changes in system pressure. When the pressure decreases, the spring opens, the valve core separates, and the ventilation rate increases; when the pressure increases, the spring compresses and the valve core approaches, thus reducing the ventilation rate.
    五、精确的控制系统
    Five. Precise control system.
    系统排风量控制如果不能跟随风管内静压的变化快速、精确的变化,就会造成排风柜流量无法精确控制,而产生振荡(如图5),将会使房间压力变成正压或者增大房间余风量的要求。风速的不稳定会产生大量的平衡问题,波动的送、排风系统使气流平衡复杂化,自控系统实现自动调节功能将变得更加困难。
    If the exhaust air volume control of the system can not follow the change of the static pressure in the air duct quickly and accurately, the flow of the exhaust hood can not be accurately controlled, and the oscillation (Fig. 5) will cause the room pressure to become positive pressure or increase the room residual air volume requirements. The instability of wind speed will cause a lot of balance problems. The fluctuating air supply and exhaust system will complicate the air balance. It will be more difficult for the automatic control system to realize the automatic adjustment function.
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