[Saxon HUI]

I use the DPM model to control the melting and evaporation of the particles by DPM_LAW. The mass of the solid part of the particles is achieved by solving for a TP_USER_REAL(tp,0) particle scalar. When I use steady-state flow and steady-state tracking of the particles (DPM time step of 1e-6s), the particles can melt normally (melting point of 933K) and evaporate further. However, when I use unsteady flow (fluid time step of 1e-5s) and unsteady particle tracking (DPM time step of 1e-6s), the solid component of the particle does not melt further when the temperature of the particle reaches the next time step from the melting point (TP_USER_REAL(tp,0) no longer decreases as the particle time step advances), and I output the solid component of the particle in the command window via the message function in the command window, the melting rate of the particles (i.e. heat exchange between the particles and the fluid / latent heat of melting, kg/s) is 1.14*10^-8kg/s, which means that the melting rate is correct, can anyone provide some advice or help? I would be very grateful!
The following are the calculated results obtained from the steady-state simulations, showing the temperature and solid mass of the particles as a function of time, respectively.

The calculation results of the non-stationary simulation are shown in the figure (variation of particle temperature and solid mass with time),In the unsteady-state simulation, the initial incidence temperature of the particles is 920 K in order to allow the particles to enter the melting phase more quickly.