[Transport Loss Estimation of Fine Particulate Matter in Sampling Tube Based on Numerical Computation]

In-situ measurement of PM_2.5 physical and chemical properties is a substantial approach for the mechanism investigation of PM_2.5 pollution. Minimizing PM_2.5 transport loss in sampling tube is essential for ensuring the accuracy of the measurement result. In order to estimate the integrated PM_2.5 transport efficiency in sampling tube and optimize tube designs, the effects of different tube factors (length, bore size and bend number) on the PM_2.5 transport were analyzed based on numerical computation. The results showed that PM_2.5 mass concentration transport efficiency of vertical tube with flow rate at 20.0 L·min^-1, bore size at 4 mm, length at 1.0 m was 89.6%. However, the transport efficiency increased to 98.3% when the bore size increased to 14 mm. PM_2.5 mass concentration transport efficiency of horizontal tube with flow rate at 1.0 L·min^-1, bore size at 4 mm, length at 10.0 m was 86.7%, and increased to 99.2% with length at 0.5 m. Low transport efficiency of 85.2% for PM_2.5 mass concentration was estimated in bend with flow rate at 20.0 L·min^-1, bore size at 4 mm, curvature angle at 90°. Laminar flow of air in tube through keeping the ratio of flow rate (L·min^-1) and bore size (mm) below 1.4 was beneficial to decrease the PM_2.5 transport loss. For the target of PM_2.5 transport efficiency higher than 97%, it was advised to use vertical sampling tubes with length less than 6.0 m for the flow rates of 2.5, 5.0, 10.0 L·min^-1 and bore size larger than 12 mm for the flow rates of 16.7 or 20.0 L·min^-1. For horizontal sampling tubes, tube length was decided by the ratio of flow rate and bore size. Meanwhile, it was suggested to decrease the amount of the bends in tube of turbulent flow.