Problems with the sampling hole placement on exhaust stacks
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I’m a bit confused about how to arrange the sampling holes in circular flues as specified in GB16157. The standard introduces the concept of equal-area rings for circular flues; it seems that several circles with equal area should be selected within the diameter range of the flue. In Figure 1 attached, different numbers of equal-area rings, measurement diameters, and sampling points are indicated depending on the flue diameter. So which parameter refers to the number of sampling holes? I’m not quite sure about this. Please advise. For example, how many sampling holes should be installed in an exhaust stack with a DN600 diameter (tube diameter φ630)?
The placement of the circular flue sampling holes specified in GB16157 is determined based on the flue diameter. The “number of equal-area rings” in Table 1 refers to dividing the flue into several rings, each with the same area. "\"Number of diameter measurements\" refers to the number of points on the diameter that need to be measured within each equal-area ring. "\"Number of measurement points\" refers to the total number of points that need to be measured on the flue. These measurement points are determined based on the number of equal-area rings and the number of measurement diameters, but not every measurement point requires a separate sampling hole. The actual number of sampling holes is usually less than the number of measurement points, as one sampling hole can move the sampler to collect samples from multiple measurement points. For a DN600 exhaust stack (with an outer diameter of approximately φ630), you need to refer to GB16157 for the number of equivalent-area rings and the number of measurement points corresponding to this flue diameter. Then, the specific number of sampling holes required is determined based on the actual sampling equipment and operating methods. In practical operation, there is usually a movable sampling probe that takes samples at multiple points through different holes. For a flue of this specific diameter, you need to consult the table in the specifications corresponding to that diameter, to find the appropriate number of equivalent-area rings and sampling points; this will guide you on where to place the sampling holes and how many of them to use. Generally, the number of sampling holes is determined based on the actual conditions and the equipment used, and it is not necessarily equal to the number of measurement points. If the specifications do not specify the number of holes, you may need to determine the exact number of sampling holes based on the instructions for the sampling equipment or by consulting the equipment manufacturer. .