A two-phase lattice Boltzmann method was used to numerically study the
boiling heat transfer related to the liquid-vapor transition induced by two
heated plates. The effects of the gravity force as well as the separation
between the heated plates were examined. The focus is on the bubble
departure behavior resulting from the interaction between bubbles, which can
be roughly classified into four types of pat?tern according to the
separation between plates. In particular, it is shown that the bubble
merging may take place twice in one cycle when the separation is close to a
certain value. This is referred to as the pattern of alternation of bubble
merging before and after departure, for which a sudden jump is seen in the
bubble release period. Furthermore, the heat flux and the flow features are
also shown to illustrate the behavior of heat transfer in the present
system.
Computational Fluid Dynamics in conjunction with an Eulerian multiphase model of heat transfer in a Pebble Bed Modular Reactor (PBMR) was validated against experimental data obtained in a test rig. The cooling gas and packed fuel pebbles constituted two phases. The velocity of pebble phase was fixed to zero and a drag law accounting for a packed bed condition was used. The density of the gas phase varied with temperature. Volume averaged effective thermal conductivities accounting for radiation and packed spheres geometry were used for both phases. Model predictions compared favorably with the experiment for two gases — helium and nitrogen and two power levels. It was found that accounting for increased affective porosity close to walls results in more realistic velocity field prediction.
Abstract
A visual pool boiling experimental device based on ITO coating layer heater and high-speed shooting technology was established for studying the bubble behavior and heat transfer characteristics of saline solution, which is of great significance for ensuring heat transfer safety in nuclear power plants, steam injection boilers and seawater desalination. Volume of fluid method was applied to simulate numerically the liquid–vapor phase change by adding source terms in the continuity equation and energy equation. The predictions of the model are quantitatively verified against the experimental data. It can be found based on the experimental data that the pool boiling heat transfer coefficient is enhanced as the salt concentration increases. Visualization studies and numerical data have shown that the presence and precipitation of salt leads to a decrease in the detachment diameter and growth time of the bubble and an increase in the frequency of detachment, thereby increasing the pool boiling heat transfer coefficient.
Numerical study on the boiling heat transfer induced by two heated plates