For further improvements of the efficiency of solar thermal systems, the temperature stratification in the store is decisive. To maintain or create the stratification, the design of inlet devices for the water entering the store is crucial. The objects of investigation are flow patterns that develop at inlet devices o f solar hot water stores. Two methods shall be applied:
- Calculations of fluid dynamics with numerical methods (Computational Fluid Dynamics, CFD);
- An experimental method to trace particles inside a fluid flow (Particle Image Velocimetry , PIV). The applicant plans to set up a PIV device, composed mainly of a rectangular glass store, a CCD-camera, and a laser. Particles with a density close to that of water will be inserted into the store, illuminated by the laser, and thereby used to visualize flow patterns. The positions of the particles are recorded by the camera.
From the pictures, conclusions will be drawn about the fluid velocity field. Flow patterns that develop directly at a vertical inlet device, created by forced convection or thermosyphon flow, shall be analysed. In order to model fluid patterns, simulation tools ( e. g. CFX, Fluent) are available to solve the governing system of differential equations (Navier-Stokes- and simplified energy equation). A major task is to create a mathematical grid, with a zone of major interest close to the inlet device, that defmes the nodes at which the system of equations is to be solved. Calculations will be carried out for different flow patterns, boundary conditions, and geometries of the inlet device and validated by the PIV -measurements. The aim of the investigations is to get insight into fundamental mixing processes and flow patterns inside a solar storage tank and to become acquainted with new experimental methods and simulation tools. Both, CFD calculations and PIV measurements are useful methods in many fields in which fluid flow is examined.