Unsteady thermal-induced flow in opened channels

Nonstationary heat transfer in opened channels with free flow of a boiling cryogenic fluid is investigated. Consideration is given to the movement of two-phase steam-liquid mixture in a channel with heat flux, distributed informly around the walls and changing in time according to the known law, and with mass velocity, directed along th axis and causing the mixture natural circulation. It is proposed that phase slipping, friction on walls and local pressure losses on channel edges are absent in the flow. The flow is one-dimensional. Overpressure in the channel is low as compared to the absolute one, therefore steam generation proceeds at constant initial pressure. The general expression for the mixture velocity in the lower channel cross section is obtained. It is shown on the basis of its analysis that boiling liquid is displaced from the channel faces to opposite sides after heat release begins. Channel blacking takes place. It continues till the natural circulation developes under the effect of mass forces. Such process presentation corresponds completely to experimental observations of nonstationary heat exchange in helium