Parameter study of the grid spacer position on subcooled boiling in an upward vertical tube at low pressures

Abstract

One of the principal issues in the phase change heat transfer at the vertical channel that changes the vapour fraction in the two-phase system is the presence of a grid spacer which prompts the temperature and velocity jump. In this study, the subcooled fluid stream rising inside the annular tube with grid spacer has been concentrated to investigate the effect of its location on changes in the gas volume fraction ratio, grid spacer temperature, and fluid flow jumping. The system of non-equilibrium two-phase flow of liquid-vapour exposed to an external heat transfer is modelled by mass, Euler-Euler model momentum, and energy equation of each phase. Validation of developed code is done by experimental results. Results show that extending the gas volume part as a result of a grid spacer presence decreases the Nusselt number, in conclusion, a temperature jump will occur. In the same manner, the presence of the grid spacer changes fluid streamlines. In this assessment, by contemplating the grid spacer in the vertical annular tube, the rising of fluid velocity in the vertical direction is demonstrated. As well the results show that the presence of a grid spacer moves to the liquid stage is less redirected conversely with vapour stage stream because of having more power; along these lines, around the completion of the grid spacer in the channel, the proportion of vapour volume fraction near the divider rises strongly. It has moreover been observed that if there are grid spacer inside the vertical annular tube, there will be no gigantic change in the liquid stream and gas volume division in various parts of the vertical annular tube when stood out from the customary vertical annular tube. The results demonstrate that the grid spacer before the heating zone will not change the vapour volume fraction inside the tube. The worst case happens for the grid spacer near the middle of the heated zone. The local peaks happen after the grid spacer when it is located after the heated zone.

Keywords

• Grid spacer
• Boiling
• Vertical channel
• Two-phase flow
• Risk assessment