Stratification enhancement for an integrated collector storage solar water heater (ICSSWH)

• Experimental study of the charge with constant heat flux of a high aspect ratio cavity.
• Insertion of a stratification plate to enhance thermal stratification.
• Flow study via particle image velocimetry reveals the appearance of a reverse flow.
• Reverse flow is responsible for the high temperature difference in the storage.
• Stratification increases with heat flux, lower angle and shorter stratification plate.

ICSSWH are advantageous solar thermal systems for residential buildings. Their overall efficiency can be improved by increasing stratification in the storage tank. In this paper the charge of a high aspect ratio cavity representing the storage of an ICSSWH was studied experimentally. A satisfying stratification was obtained by heating the storage tank in the middle and inserting a stratification plate. The study examined various angles of system inclination (30, 45 and 60° relative to the horizontal), heat flux imposition (1800, 2700 and 3600 W m−2) and length of the stratification plate. The experiments lasted for three hours, temperatures were measured using thermocouples and velocities were measured via particle image velocimetry. We showed that stratification was higher with a shorter stratification plate, and that it increased with greater heat flux and lower angles. Flow observations on the presented configuration showed that reverse flow was responsible for this thermal behavior. This phenomenon, however, increases with time and could result in creation a dead volume under the heated area.