ANALYSIS & DESIGN OF THERMAL STORAGE SYSTEMS

Numerical simulation methods for the flow phenomena and heat transfer (computational fluid dynamics) are used, combined with experimental methods in the static (eg., nightime) as well as in the dynamic mode of operation (charging-discharging). In the latter case, for given the geometric characteristics and modes of operation (flow rates, load), the main problem is the design of suitable water inlet-outlet devices (diffusers) aiming at the minimization of thermal mixing and ensuring the highest possible degree of stratification. Such an optimal design is pursued both in rectangular, as well as cylindrical geometries, based on suitable energy and exergy performance indicators. Both in-ground and above-ground tanks have been considered, with concrete- or metal-based liners.

Current interests in this area focus on :

• Investigation of techniques and media for storage at temperatures above 100 ºC, for use in electric power and process heat generating facilities with concentrating collectors (water under pressure, concrete, phase-change materials)
• Feasibility of using nanofluids as the working fluid in solar thermal systems with the aim of improving the heat exchange between solar collectors and storage media
• Further development of available computational tools for the simulation of transient processes in water storage tanks, such as turbulent flows using large-eddy simulation (LES) methods