No abstract

No abstract

The two-phase heat transfer characteristics of degassed water flow boiling in horizontal mini-tubes are experimentally investigated in this paper. The inner diameters (di) of the tubes are 1.2mm, 1.6mm, and 2.0mm. Experiments are conducted with heat fluxes between 1.5kW/m2 and 155.75kW/m2 at mass fluxes of 21.19, 42.39, and 84.77kg/(m2s). The boiling curves of the three tubes are obtained. Incipient hysteresis is observed only in the tube with di = 1.2mm. Two-phase dominant heat transfer mechanisms are analyzed in the tubes with di = 1.2mm and di = 2.0mm based on the curves of local heat transfer coefficient versus vapor quality and the visualization results. The trend of peak value of the local heat transfer coefficient versus heat flux at different mass fluxes in the tube with di = 1.2mm is discussed in accordance with the thickness variation of the liquid film in annular flow.

We present a geometric multigrid solver for the Compact Discontinuous Galerkin method through building a hierarchy of coarser meshes using a simple agglomeration method which handles arbitrary element shapes and dimensions. The method is easily extendable to other discontinuous Galerkin discretizations, including the Local DG method and the Interior Penalty method. We demonstrate excellent solver performance for Poisson's equation, provided a flux formulation is used for the operator coarsening and a suitable switch function chosen for the numerical fluxes.