LABORATORY SESSION FOR THE STUDY OF THERMAL STRATIFICATION DURING HEATING LOAD IN A PROTOTYPE OF SOLAR HOT WATER STORAGE TANK

In the last years, the number of solar energy systems for water heating has grown considerably. Thus, it is important to improve the individual performance of the system components to reach higher efficiencies and savings in future installations. In this respect, the subject ‘Renewable energies and energetic management’ corresponding to the degree of Agricultural Engineering at the Universidad Politécnica de Valencia pretends to show the students how to take advantage of these type of systems and how to improve their efficiency.
In solar thermal energy systems, water is used as the storage element of the solar energy received and transformed from the collecting system. There is a lot of different system configurations attending to the specific applications considered. Nevertheless, water is always heated by flowing through the solar collector and taken to an energy storage device, based on a water storage tank. This tank is necessary when energy supply and demand do not coincide in time. In these storage tanks takes place the so-called thermal stratification, during which the inlet water drops to a level where its density matches the density of the surrounding fluid. Due to the gravity and buoyancy effect, water at certain temperature will deposit the corresponding height according to its density. Here, the turbulence and mixing that occurs because of the inflow-outflow water movement affects considerably the thermal stratification.
Hence, the thermal stratification is a key process in the storage system and has a great impact in the performance efficiency of solar thermal energy systems.
This paper describes a laboratory session of the aforementioned subject. This session focuses on the study, from an experimental point of view, of the thermal stratification process that takes place in a prototype of solar storage tank during the heating load. Specifically, this session analyzes the effect of flow variations, introduced water volume, and inflow water temperature, on the stratification patterns.
This experience can be very useful for students, as it contributes to visualize easily the applicability and usefulness of the theoretical contents of the subject, improving thereby motivation and learning. This contextualization of contents also allows the students to discern their future skills and competencies as engineers, as well as to approach and carry out an experimental test. The tools used in data acquisition and analysis make possible the intuitive and visual interpretation of a complex process.