1,721,136 research outputs found
A note on the bubble growth force
No full textA boiling bubble at the verge of detaching from a plane, infinite wall experiences a hydrodynamic force due to its expansion, Fx. Such a bubble is modelled as a pair of spheres with radius R and growth rate R' in inviscid liquid, and Fx is computed using the Lagally theorem. The form of the Lagally theorem used differs in one term from an expression found in the literature. The exact expression for Fx is simplified in order to derive a simple expression that facilitates the prediction of detachment. In the case of diffusion controlled bubble growth, Fx is shown to be approximately given by c2p¿LR2R'2, where ¿L is the liquid mass density and c2 ~ 1.11. This prediction is compared with experimental fits of the literature
The dynamics of a boiling bubble before and after detachment
No full textAn overview is given of prediction methods for motion and deformation of a bubble that is created by boiling at a wall, at times before and after detachment, with a focus on added mass forces in the vicinity of the wall. The possibility to apply added mass coefficients derived in potential flows also to flows with vorticity is examined. An introduction to Lagrangian methods is given. Added mass tensors are derived for deforming bubbles at and away from a plane wall. Expressions for induced hydrodynamic lift forces are given, and validation experiments are briefly discussed. © 2007 Springer-Verlag
A comparison of hybrid and numerical techniques to model heat transfer in reverse flow reactors
No full textThe behaviour of a reverse flow reactor, designed for the purification of polluted air, has been studied. A heterogeneous, one-dimensional model has been solved by using an analytical approach and by using two different numerical algorithms. The calculations are mutually compared and with existing experimental data. No fitting of the model parameters to the data was employed and the agreement of all comparisons was good. Experimental data of a large-scale reverse flow reactor have recently been presented that allow for a final testing of the models. Again, the agreement between simulations and experiments was satisfactory. The computation time of the three solution methods is about the same, however, the analytical approach has advantages because it is, for example, more easy to handle in practice
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