Discussion on sampling locations for exhaust stacks
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I recently had some doubts regarding the location of sampling holes for exhaust stacks as specified in GB16157. As shown in the attached diagram, the sampling holes are located at a distance of 6 times the diameter downstream from the fitting, and 3 times the diameter upstream from it. I’m a bit confused by the terms \"upstream\" and \"downstream\" in this context; I found an image online – please take a look to see if what it shows is correct
Personally, I think the upstream and downstream parts should be arranged in this way; please give me your advice
According to the general provisions of GB16157 standard, generally, “upstream” refers to the direction from which the airflow comes, while “downstream” refers to the direction in which the airflow goes. The sampling holes for the exhaust stack should be located 3 times the diameter upstream and 6 times the diameter downstream of facilities that may affect the representativeness of the sample, such as elbows, valves, and reducers, so as to ensure a relatively uniform flow velocity distribution and pollutant concentration within the sampling area. In short, you need to locate the sampling holes three times the pipe diameter upstream from any facility that could perturb fluid flow, and six times the pipe diameter downstream from such a facility. The purpose of doing this is to avoid the impact of the facilities on the sampling results and ensure the accuracy of the sampling data. .