Supercritical carbon dioxide(S-CO_2) Brayton cycle power generation technology is considered to be one of the most promising power generation technologies. When the S-CO_2 power generation system is started/stopped

or under low load conditions

it will cause a large amount of S-CO_2 in the gas cooled wall of boiler working near the pseudocritical temperature

because the S-CO_2 from the main compressor is not heated sufficiently in the recuperator. It means the S-CO_2 flow instability must be considered in S-CO_2 boilers. In this paper

the most common layout structure of the S-CO_2 boiler gas cooled wall(i.e.

vertical upward heated tube) is applied. A calculation model of S-CO_2 flow instability is established firstly

and then a large number of numerical calculations are carried out. The influences of main operating parameters on threshold heat flux are obtained. The results show that

the threshold heat flux raises with the inlet pressure or mass flow rate linearly. With the inlet temperature increasing

the threshold heat flux decreases at first and then increases. There is a critical inlet temperature at which the threshold heat flux is the lowest and the flow stability in the tube is the worst.