A study on the unsteady conjugate heat transfer of hot gas valve

Abstract

Numerical simulations of a hot gas valve were conducted in this study to establish an analysis method. The far-field effect was also checked to select a computational domain. The existence of the far-field did not affect flow and temperature characteristics. The grid sensitivity was checked by varying the grid number from 25,000 to 120,000. The thrusts were similar according to the number of grid. However, differences in temperature distribution were observed. Three turbulence models were adopted to determine the influence of turbulence on thrust and temperature distribution: Spalart-Allmaras, RNG k-epsilon, and k-omega SST. The thrusts of the hot gas valve were similar in all simulation cases. However, an approximately 2% deviation in temperature distribution was observed at an operating pressure of 128 atm. Time step size and iteration were selected for the unsteady analysis. The analysis was conducted using only an S-A turbulent model and a valve grid. No significant difference was found. Hence, the time step size was set as 10 Lis, and 50 iterations were performed. The unsteady analysis was conducted by increasing the time step size throughout the four sections considering the operating time of the hot gas valve. The time step size was increased when the quantitative result reached within 5% difference in each section. The flow, pressure, and temperature fields in the flow area reached the steady state with within 5% difference at 8 ms, 100 ms, and 5.5 s, respectively. The three fields in the flow area reached the steady state at 10 s from the operating time of the hot gas valve. However, an approximately 7% difference in temperature field was observed in the solid area. The calculation time was reduced by approximately 130 times compared to the existing calculation method. (C) 2017 Elsevier Masson SAS. All rights reserved.