The subcritical steam generators in the current high-temperature-reactor pebble-bed module, HTR-PM, in China can be replaced by supercritical steam generators to better coordinate the reactors and the supercritical steam turbines to improve thermal efficiencies with no phase change at supercritical pressures This study numerically studied the heat transfer and flow instability of supercritical pressure water in a vertical tube with zero- and finite-thickness walls The effect of the wall thickness on the heat transfer of supercritical pressure water at steady state was negligible In the transient calculations, the fluid flow rate oscillated intensely beyond a certain heat flux with zero-thickness wall, while the flows in the tube with the finite-thickness walls acted totally different. The wall properties including the density and specific heat were varied to analyze why the oscillations were suppressed when the finite-thickness wall was considered in the calculation
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