Theoretical analysis of deposition and melting process during throttling high pressure CO2 into atmosphere

Previous study has discovered that periodic solid CO2 deposition and melting phenomena happen during releasing high pressure CO2 through a safety valve from CO2 refrigeration system into atmosphere, and that a longer duration of the deposition and a shorter duration of melting are advantageous for the system safety. In order to know the suitable parameters to get a longer duration of the deposition and a shorter duration of melting, a Lagrangian particle-trajectory model and a Nusselt-type model are presented for the deposition and melting, respectively. The validation of the models was done by comparison of the calculation results and experimental data. Calculation with the models shows that the diameter of the formed solid CO2 should not be in the range of 0.04–0.07 mm in order to avoid a shorter duration of the deposition and that increase of the tube diameter can greatly prolong the melting process. It is also found that the tube diameter must be carefully chosen in order to maintain longer deposition and shorter melting process.