Solar-powered air-conditioning system investigation using the finite element method

Abstract

Abstract The finite element method is used to predict numerically steady state, two-dimensional laminar and turbulent thermal buoyant and convective recirculating flows. The governing equations are solved by the finite element method using Galerking weighting functions, with velocity, pressure and temperature as dependent variables. Turbulent separating, recirculating flow in the complex geometry of a room with variable inlets, outlets and convective chimney ducts is investigated. The room is air-conditioned, utilizing the solar energy via a flat plate collector and solar absorption air-conditioning (fig. 10). For this purpose the Navier-Stokes, continuity and general energy equations are solved in a coupled form and solutions are compared with the experimental results of hot wire anemometers and thermocouples. The parts with turbulent flows occured in the convective duct and the room; the flows are analysed using the Prandtl-Kolmogorov model to depict the effective viscosity. The analogy between thermal and momentum diffusivity via Prandtl number is used to depict the turbulent conductivity from the turbulent viscosity. The length scale of turbulence is specified as an algebraic function of position from empirical data and experience of other researchers. The kinetic energy is expressed as a function of velocity at the nodes together with the turbulence intensity which varies from 0.5 to 20%. This turbulence model is used to predict the flow, including its recirculations in the solar air-conditioned room, and the fully turbulent convective channel. The analysis includes temperature and heat transfer predictions in this complex geometry of combined free and forced convection, together with buoyancy effects and turbulent transport and recirculations. Results obtained are compared with the experimental data which showed very good agreement.