CFD-Based Development, Testing and Optimization of Flat Plate Collectors
Abstract
Based on CFD (Computational Fluid Dynamics) simulations and virtual thermal performance tests, a development and optimization tool for flat plate collectors is presented. Using the example of a serial product flat plate collector, parametrized CAD data were constructed. Dimensions like length, width and thickness of the transparent cover or the dimensions of the pipes, the aperture area and the welding line are parametrized. Therewith geometrical changes can be executed quickly at a later stage for optimization. Essential for simulating solar collectors is the radiation spectrum model. The Multiband Thermal radiation model was chosen. It allows specification of user-defined spectral bands, for which optical properties of the surfaces are defined. Thereby implementation of selective absorber coating is possible. Using a heat transfer coefficient, convection to the environment is taken into account by implementation as a boundary condition. Literature shows a wide range of convective heat transfer coefficients for forced air over flat surfaces, particularly flat plate collectors, which are based on empirical examinations and from boundary layer theory. Taking into account, that virtual dimensions of the collector are variable, selection of an equation from boundary layer theory is shown. Finally, results from a virtual thermal performance test are presented. Simulated component temperatures and peak collector efficiency from virtual thermal performance test correspond well to measured values. With increasing mean fluid temperature, the difference between measured and simulated outlet temperature rises. Possible reasons are identified and presented.