Fluctuation characteristics of heating surface temperature near the obstacle in transient boiling two-phase flow in a vertical annular channel

If a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some cases the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. But the thermo-fluid dynamics mechanism to cause burnout near the spacer is not still clear. In the present paper we discuss temperature fluctuation characteristics in relation to the change of the flow configuration near the spacer in transient boiling two-phase flow. The transient parameters are the heat flux, the mass flow rate, and the inlet quality.