Multigroup Simulation of Two Component Two-Phase Bubbly Flow with Heat Transfer

摘要

To simulate a two-phase bubbly flow where the bubbles vary in size, an efficient multigroup two-fluid model is developed. In the present work two-component bubbly flows with heat transfer is investigated. Bubble population classes are introduced by dividing the physical bubble spectrum into a predefined number of size groups. A consistent modelling of the interfacial drag and the terminal velocity is realized using a nonstandard correlation for the drag coefficient and used in the calculations to model the momentum transfer between each air bubble class and the liquid phase. The heat flux between the phases is modelled under the assumption of spherical bubbles of homogeneous temperature. For a test case, axisymmetric simulations of a cylindrical container with a diameter of 0.5 m and a height of 0.75 m and filled with water initially at 293 K (20 °C) are performed. Hot air of 373 K (100 °C) is injected from the bottom of the container. The air bubbles are distributed among classes with diameters between 0.75 mm and 1.2 mm. Unsteady simulations are performed until the velocity field becomes stationary. Multigroup simulations have been performed with a varying number of bubble classes (36, 12, 6, and 1). The velocity and temperature fields are compared. Additional 12-group and 6-group simulations with different structure or boundary of the classes are also performed. As criteria for the model accuracy of the cases with fewer classes, the total drag force and the integrals liquid temperature along the container axis are taken at stationary conditions of the velocity. The simulation results show that there are strong dependency of the simulation result on the number of bubble classes and also the class structure. If the case with 36 classes is used as a reference, the maximum deviations appear to be up to 6% for the drag and 8% for the temperature. Keyword: Multigroup, Bubble Population Class, Two-Fluid Model, Heat transfer.