An analytic investigation of the steam blocking in low pressure heating channels was conducted. In this paper, the dynamic model of the vapor-liquid interface is established through the basic conservation equations, and the rupture time of the vapor-liquid interface is predicted based on the Rayleigh-Taylor instability. Subsequently, the steam blocking model considering the steam accumulation and the vapor-liquid interface rupture in geysering flow is established. On these bases, the relative volume and relative pressure of the accumulated steam, the relative acceleration and perturbation intensity of the vapor-liquid interface, the time-varying behavior of the ratio of resistance and buoyancy are obtained. It is found that the accumulated steam basically increases linearly with the time going; The oscillation of the pressure and velocity, which is very large at the beginning time of the steam accumulation, decreases gradually with the continuous steam accumulation; The Reynolds number of the liquid within the rising section is very small at the stagnation state since there is no forced circulation flow, and finally a blockage is engendered in the pipeline with the steam accumulated. The theoretical results are in good agreements with the results obtained by a small-scale experiment. The mechanism model is able to predict the steam blocking property during the geysering flow in heating channels well, and can also establish a theoretical basis for the later analysis of the steam blocking elimination.

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