Zejun Xiao

Analytical Prediction of Turbulent Friction Factor in Circular Pipe Under Supercritical Conditions

An analytical method was proposed for the prediction of the turbulent friction factor in a circular pipe under supercritical conditions. The friction factor equation was based on the new wall function by Van Direst transformation which is widely used in compressed flow. The law of the wall of two layers was used and integrated over the entire flow area to obtain the algebraic form of the turbulent friction factor. The new turbulent friction formula was first adjusted to Colebrook equation in isothermal flow at supercritical pressures. And then it was validated in heated supercritical flow by several existing correlations. Similar trends were found between them, which confirms the physical validity of the new frictional formula. The theoretical analysis also shows that the friction factor due to the variation of fluid property at supercritical pressures is mainly caused by the density and viscosity variation. In viscous sublayer, both the viscosity play the main role, while in turbulent sublayer, only the density do.Copyright

Numerical Investigation on Bubble Growth and Sliding Process of Subcooled Flow Boiling in Narrow Rectangular Channel

In order to investigate single bubble evolution, a boiling phase change model in subcooled flow boiling is proposed in this paper, and VOF model combined with phase change model is adopted to simulate the single bubble growth and movement. The effects of flow velocity, liquid subcooling, wall superheat, and vapor-liquid contact angle are considered in this model. The predicted bubble growth curve agrees well with the experimental result. Based on the analysis of bubble shape evolution and temperature field, it is found that the average bubble growth rate, flow velocity, and dynamic contact angle have significant effect on the bubble shape evolution during the bubble growth and movement while the temperature gradient in superheated liquid does not change with bubble growing. The character of dynamic contact angle during bubble growth and movement is also obtained in different working condition.

Experimental Investigation on Flow Regime of Steam-Water Two-Phase Flow in a Pseudo-Pebble-Bed

In the concept of BWR-PB with a relatively low power level, the core region is filled with a large number of coated particles, which are directly cooled by boiling light water. It’s significant to understand the two-phase flow characteristics in such a complicated pebble-bed structure. A visualization experiment was carried out to investigate the flow phenomena of steam-water two-phase flow in a pseudo-three-dimensional pebble bed using a high-speed video camera. The pebble bed in the experiment was constructed of hundreds of glass beads and a specially designed stainless heating plate, which was used to simulate the heat-generation of solid particles. Based on our observation, five typical flow regimes were identified to distinguish different phase distribution characteristics: bubbly flow, bubbly-slug flow, slug flow, slug-annular flow and pure annular flow. System pressure, mass flow rate and inlet subcooling were considered as the key influence factors for flow regime transition in the experiment. A flow pattern map for low pressure and low inlet subcooling condition was obtained from the experimental data.Copyright