Search

Natural convection in a cavity with a partially heated obstacle at the center at the Rayleigh number R a = 1.46 × 10 9 is investigated using large eddy simulation (LES). The standard and dynamic Smagorinsky models, as well as the wall-adapting local eddy-viscosity model, are used for the subgrid scales, and the flow statistics are compared with recent experiments. The LES results obtained with different meshes show overall good agreement with the experiments as concerns the flow and heat transfer. Simulation with a non-ideal wall at the adiabatic side of the obstacle is also performed to explain the residual discrepancies observed in the unheated channel. Additional simulations performed with periodic conditions in the spanwise direction are very different from the full three-dimensional (3D) simulations, which demonstrate the significance of 3D effects in the cavity. In particular, periodic simulations show Tollmien–Schlichting kind waves in the transitional region, while the 3D cavity shows an early cross-flow transition to turbulence. [ABSTRACT FROM AUTHOR]

The present study addresses the expansion of pressurized liquid R-290 through a 1.2 mm diameter capillary tube and its subsequent motion through a metastable condition entailing a change of phase through flashing phenomenon. The expansion of R-290 through a helical capillary tube is numerically simulated using a finite volume-based mixture model. For the simulation of the flashing phenomena, a homogeneous equilibrium approach is used. The Zwart–Gerber–Belamri model is deployed to represent mass transfer during flashing. ANSYS Fluent 2021 R2 software has been used for the numerical simulations. A series of UDF (user defined functions) are developed to read the recorded database of R-290 and perform the cavitation modeling. Bilinear interpolation is performed for determining the fluid properties at the corresponding pressure and temperature. The developed numerical model has been validated against the available numerical and experimental results. For the simulations, tubes with lengths of 1200 mm , 1500 mm , 1800 mm , 2100 mm , and 2400 mm have been considered, and the impacts of increasing length on the flow characteristics at the outlet have been determined. In this investigation, the R-290 refrigerant expands from three different condenser pressures of 16, 14, and 12 bar. Evaporator pressure is adjusted from 2 bar to 8 bar to investigate its influence on flow characteristics. The fall in evaporator pressure brings about a flow transition from subsonic to supersonic. The effects of tube length, condenser, and evaporator pressures on mass transfer rate, evaporator entry temperature, mixture quality at the evaporator entrance, and available refrigeration effects have been analyzed. [ABSTRACT FROM AUTHOR]