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[en] Mass transfer time relaxation parameters for condensation affect the amount of the mass transfer in the phase change. In the present study, a numerical investigation has been implemented with four different parameters for the condensation process in a thermosyphon, with the parameter of 0.1 for the evaporation process. The numerical results were compared with the experimental results to validate the numerical methods. When the mass transfer time relaxation parameter for the condensation was set to the value considering the density ratio out of the four parameters, the numerical result was in good agreement with the experimental result. This numerical process is expected to be used to predict the temperature distribution in the thermosyphon more accurately.
[en] The compressible flow field is numerically analyzed in a two-dimensional converging-diverging nozzle of which the area ratio, exit to throat, is 1.8. The solver is FLUENT and the embedded RNG k -ε model is adopted to simulate turbulent flow. The plume characteristics such as shock-cell structure are discussed when nozzle pressure ratio and stagnation temperature at the nozzle entrance are varied. The downstream flow field can be classified into two types based on the shock shapes generated near the nozzle exit. First, a reiterative pattern in the plume is not formed between the slip streams in case that a strong lambda-type shock wave exists. Second, when oblique shock waves are crossing each other on the nozzle centerline, a shock cell structure appears in the plume field. Even when the flow field is changed due to stagnation temperature, the upstream of the shock wave is little affected. Especially, the pressure distributions on the nozzle centerline behind the shock wave are rarely influenced by the stagnation temperature, that is, the product of density and temperature is nearly constant provided that the working fluid is a perfect gas. Therefore, the pressure field shows quasi-isobaric behavior far downstream