A CFD Study of Corrosion Product Collection Efficiency of Sampling Nozzles under Power Plant Conditions

摘要

Representative sampling of water and steam cycles in power plants is crucial since its impact on operating decisions can be significant. Although industry guidelines for sampling are available, it is recognized that errors may still occur, so efforts to improve sample system design continue in attempts to achieve optimum techniques. This paper investigates the concepts of isokinetic sampling applied to sampling nozzles operating under power plant conditions using CFD (computational fluid dynamics) software. Two different designs of sampling nozzle are assessed for their effectiveness in capturing particles at the nozzle tip - deposition and release along the sample line are neglected. It is shown that the lower the sampling velocity, the higher the apparent concentration, and the effect of sampling velocity is more pronounced in the condition where the Stokes number is greater. The nozzle acts as an obstacle that disturbs the flow field and does not allow true isokinetic conditions to be established. The suggested design nozzle, "the inclined nozzle", is less sensitive to sampling velocity than the commercial nozzle.