Abstract
This paper deals with the application of slightly inclined small diameter tubes as an alternative to condensing pots for providing a constant reference level for hydrostatic level measurements in boiling water reactors (BWR). Based on the geometrical particularities, relevant physical effects in the "zero-chamber condensate pot" and its junction with large volume vessels, which may affect the differential pressure measurement, are discussed. Particularly important is the gas/liquid interface whose stability has a significant impact on the reference level and thus on fluctuations and errors in measured differential pressure signals. Therefore, the interfaces are evaluated experimentally and numerically using computational fluid dynamics (CFD). In the commercial ANSYS CFX 12 code calculating free gas/liquid surfaces with static or dynamic contact angles in consideration of a technically inevitable surface roughness is not implemented. Comparing experimental and numerical results under simplified conditions, it was found that these physical effects are important for the topology and stability of gas/liquid interfaces in inclined tubes of small diameter. Thus, experiments have to be carried out in the next stage to obtain empirical correlations for describing these phenomena. Each experimental and numerical analysis in this paper was done by initially assuming a state of equilibrium. In a following stage, the investigations will be enhanced by taking dynamic transition processes (phase change, condensate flux, interfacial heat and mass transfer, etc.) into account. From the experimental point of view this will be done by applying x-ray radiographic imaging at BWR parameters (286 ℃, 70 bar). The relating test facility is introduced in the outlook of this paper.
