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Influence of air change rates on indoor CO2 stratification in terms of Richardson number and vorticity

机译：理查森数和涡度对换气速率对室内二氧化碳分层的影响

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Above rules-of-thumb ventilation standard based on air change rate per hour (ACH), it is necessary to assess the indoor airflow and indoor air quality (IAQ) with respect to simple dimensionless numbers from the practical point of view. Hence, this work aims at investigating the influence of air change rates on indoor CO2 stratification and removal with dimensionless time scale ratio (proportional to Ri/alpha, Richardson number Ri, mass flux ratio alpha) and vorticity by applying experiment and simulation methods. We firstly carried out a series of experiments with different ACHs along with constant CO2 pollutant sources, further for simulation validation. Next, numerical simulation was employed to investigate five different ACHs (ranged from 4 to 28) on indoor CO2 concentration for two different vent-inlet-size cases. It was found that as the increase of ACH, the averaging outlet CO2 concentration was decreased until ACH equal to 16, both cases starting showing asymptotic behavior. When looking at indoor CO2 distribution, the case with larger vent-inlet size showed clear stratification even with higher ACH value (i.e., 28), due to the relatively smaller vorticity value (i.e., 0.47, with 3.14 for small-vent size case) and larger Ri magnitude (37 times) compared to the small-vent-size case. Specifically, it is beneficial for indoor CO2 removal to keep time scale ratio Ri/alpha below 10(-3) and vorticity above 1 rather than merely following with high ACH values. These findings will be of great importance for practical applications to design and control ventilation systems in the perspective of health and energy efficiency.
机译：超过基于每小时换气量（ACH）的拇指通气标准，有必要从实际角度对简单的无量纲数字进行室内气流和室内空气质量（IAQ）评估。因此，这项工作旨在通过应用实验和模拟方法，以无量纲的时间比例比（与Ri / alpha成正比，Richardson数Ri，质量通量比α）和涡度研究空气变化率对室内CO2分层和去除的影响。我们首先使用不同的ACH以及恒定的CO2污染物源进行了一系列实验，以进一步进行仿真验证。接下来，通过数值模拟研究了两种不同的排气口大小情况下五个不同的ACH（4至28）室内CO2浓度。发现随着ACH的增加，平均出口CO2浓度降低，直到ACH等于16，这两种情况都开始表现出渐近行为。当观察室内CO2分布时，由于涡度值相对较小（例如0.47，对于小通风口情况为3.14），即使具有较高的ACH值（即28），较大的进气孔也显示出清晰的分层。与小排量的情况相比，Ri值更大（37倍）。具体而言，将室内时标比率Ri / alpha保持在10（-3）以下，并将涡度保持在1以上，而不是仅仅遵循较高的ACH值，这对于室内CO2去除是有益的。从健康和能源效率的角度来看，这些发现对于设计和控制通风系统的实际应用将非常重要。

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