Thermal Stratification in Heat Storages

Abstract

The term “thermal stratification” suggests a discontinuous temperaturefield. Though such is impossible the term corresponds well with our image of the phenomenon. In general we understand by thermal stratification a non scalar temperature-field, - more particular in a fluid medium, - which is an increasing function of only the elevation. In a solar energy system, thermally stratified storing leads to a considerable increase in solar heat and a reduction of pumping energy. In some multipurpose installations stratification may also have the additional advantage of making heat available at different temperatures. Although the advantages of stratified storing have been noticed in the early days of solar development, they are still grossly underestimated in almost all literature and handbooks. The reasons for this state of affairs have been indicated by van Koppen e.a. [1]. Following their lines of thought further progress in establishing a better design method for solar systems and storing has been made at the Eindhoven University of Technology. This paper is mainly concerned with some of the conclusions that have been reached in this research. The main objective of the paper is to demonstrate that these conclusions hold for actual systems.