Numerical investigation of boiling regime transition mechanism by a Lattice-Boltzmann model
2001 (English)In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 204, no 1-3, 143-153 p.Article in journal (Refereed) Published
A numerical study has been performed to investigate the hydrodynamic aspects of the pool boilingon horizontal-, vertical- and downward-facing surfaces. The FlowLab code, which is based on a Lattice-Boltzmann (LB) model of two-phase flows, is employed. Macroscopic properties, such as surface tension (a) and contact angle (beta), are implemented through the fluid-fluid (G(sigma)) and fluid-solid (G(t)) interaction potentials. The model is found to express a linear relation between the macroscopic properties (sigma, beta) and microscopic parameters (G(sigma), G(t)). The simulation results on bubble departure diameter appear to have the same parametric dependence as the empirical correlation. Hydrodynamic aspects of two-phase flow regime transition mechanism are investigated for different surface-coolant configurations. Results of the LB simulation clearly demonstrate that not only the bubble nucleation site density (related, e.g. to the heater surface condition and heat fluxes), but also the surface position have a profound effect on the flow regime (pool boiling) characteristics. The results of the LB simulation of hydrodynamics of two-phase flow on the horizontal surface provide the pictures quite similar to the experimental observation for saturated pool boiling. Two mechanisms of flow (boiling) regime transition on the vertical surface are predicted for the local bubble coalescence at bubble generation site and the downstream bubble coalescence. On the downward-facing surfaces, friction between bubbles and the surface wall is found to significantly enlarge the bubble size prior the bubble slip upwards. This behavior is responsible for the earlier bubble coalescence, and therefore, lowers the maximum heat removal rate, in a similar regime of nucleate boiling on a downward-facing surface.
Place, publisher, year, edition, pages
2001. Vol. 204, no 1-3, 143-153 p.
critical heat-flux, pool
IdentifiersURN: urn:nbn:se:kth:diva-20383ISI: 000167086300012OAI: oai:DiVA.org:kth-20383DiVA: diva2:339078
QC 201005252010-08-102010-08-10Bibliographically approved