The Li/SF6 metal fuel closed-cycle power system boasts advantages of high concealment and maneuverability. A core start-up requirement of the system is that vapor state parameters at the outlet of the spiral evaporator quickly attain set values. To address the start-up issue of evaporators

a numerical simulation model for flow and heat transfer under constant and variable flow conditions is established. This model couples the cylinder extrusion device

spiral evaporator

and turbine nozzle

adopting a numerical method to combine the Eulerian multi-phase flow model and the Non-Equilibrium boiling model. The effectiveness of the proposed model is verified. The results show that after entering the evaporator

the water conducts flow heat transfer with the tube wall

leading to a gradual increase in the vapor content inside the tube

as well as the flow velocity and temperature of the working fluid along the flow direction. Under the constant flow condition

superheated steam can reach the outlet of the evaporator within 0.2~0.3 s

and the outlet state parameters fall within the set range. Based on the calculation results of the constant flow condition

the cylinder extrusion device is designed. Under an extrusion pressure of 3 MPa

the state of the vapor at the outlet of the evaporator and the flow heat transfer characteristics inside the tube show no significant difference from those under the constant flow condition

meeting the requirements of the evaporator’s start-up process. This study provides theoretical support for the initial parameter setting of the power system’s start-up process and the optimal design of the extrusion device.