Feigley Charles E, Bennett James S, Lee E, Khan Jamil
Department of Environmental Health Sciences, School of Public Health, University of South Carolina, Columbia, USA.
Appl Occup Environ Hyg. 2002 May;17(5):333-43. doi: 10.1080/10473220252864932.
In specifying dilution ventilation flow rate, a safety factor, K, is often used to provide a margin of safety and to compensate for uncertainties and health impact severity. In current practice, the selection of K is very subjective. Here the component of K accounting for imperfect mixing, Km, was studied to develop more effective and efficient design procedures. Air flow and contaminant distribution in a 10 m x 3 m x 7 m room with a single contaminant source on a 1-m high table were simulated for steady, isothermal conditions using computational fluid dynamics. A series of 10 simulations explored factorial combinations of air exchange rates (1, 2,4, 8, 16 ACH) and inlet types (a high wall jet and a ceiling diffuser). Nine additional simulations explored exhaust opening location effects and 13 other simulations investigated source location effects. Km was calculated at each of 25,600 grid locations within the room by linear regression of emission rate/flow rate (G/Q) on concentration (C). The linear relationship between C and G/Q at each of the points was nearly perfect (R2 > 0.97). For the simulations with varying dilution flow rate, Km ranged from 0.19 to 2.86 for the wall jet and from 0.94 to 4.34 for the ceiling diffuser. Holding G/Q at 100 ppm and varying source and exhaust location produced room average concentrations from 55.7 to 173 ppm. Unlike orthodox design approaches, this work suggests that air monitoring data often can be used to calculate dilution flow rate requirements. Also, dilution flow rate requirements may be reduced by enhancing room mixing with fans or altering air inlet configuration. However, mixing should not be increased if the altered room air currents could transport contaminant to an occupant's breathing zone or interfere with other control methods that depend on segregation of incoming air and contaminant.
在确定稀释通风流量时，通常会使用安全系数K来提供安全边际，并补偿不确定性和健康影响的严重程度。在当前实践中，K的选择非常主观。本文研究了K中考虑不完全混合的部分Km，以开发更有效和高效的设计程序。使用计算流体动力学对一个10米×3米×7米的房间进行了稳态、等温条件下的气流和污染物分布模拟，房间内有一个位于1米高桌子上的单一污染物源。一系列10次模拟探索了换气率（1、2、4、8、16次/小时）和进气口类型（高壁射流和天花板扩散器）的因子组合。另外9次模拟探索了排气口位置的影响，还有13次模拟研究了源位置的影响。通过在浓度（C）上对排放率/流量（G/Q）进行线性回归，在房间内的25600个网格位置中的每一个位置计算Km。每个点处C与G/Q之间的线性关系几乎完美（R2>0.97）。对于稀释流量变化的模拟，壁射流的Km范围为0.19至2.86，天花板扩散器的Km范围为0.94至4.34。将G/Q保持在100 ppm并改变源和排气位置，产生的房间平均浓度为55.7至173 ppm。与传统设计方法不同，这项工作表明空气监测数据通常可用于计算稀释流量要求。此外，通过使用风扇增强房间混合或改变进气配置，可以降低稀释流量要求。然而，如果改变后的室内气流会将污染物输送到居住者的呼吸区域或干扰其他依赖于进入空气和污染物分离的控制方法，则不应增加混合。
