The fluid dynamic and thermal behaviour of water inside a rectangular storage element forming part of an Integrated Collector Storage (ICS) is analysed. A schematic of the prob­lem under study is shown in figure 1a.

Heat losses at the absorbing (front) and at the insulated surfaces are determined by means of global heat transfer coefficients, (Ut and l/j), and of the ambient temperature. To model the incident solar radiation, a heat flux Gt is applied over the front surface of the reservoir. One part of it, Gtrc/ is supposed to be reflected by the cover, resulting into a net heat flux over the front surface (absorbing surface) of the store of Gt — Gtref.

Mathematical model

The fluid flow and heat transfer phenomena inside the storage element is assumed to be governed by the Navier-Stokes and energy equations in their bi-dimensional form. The following hypothesis are made: the physical properties are constant in accordance with the Boussinesq approximation (density variations are only relevant in the buoyancy terms of the momentum equations), the fluid behaviour is Newtonian, the viscous dissipation and the influence of pressure in temperature is negligible, and radiation effects are not considered. Thus, the corresponding governing equations can be written as follows:

du dv dx + dy

(2)

(3)

дТ дТ дТ А (д-Т

PW + pUdx+pt’dy=7p{^ +

where (ж, у) are the coordinates in the Cartesian-coordinate system ж-у indicated in Fig. 1; T is the temperature; T0 the reference temperature; the dynamic pressure; (u, v) and

the velocity and the gravitational acceleration vector expressed in the reference system — y, and the physical properties of the water р. ц, j3. A and ер are respectively: the density, the dynamic viscosity, the thermal expansion coefficient, the thermal conductivity and the specific heat at constant pressure, which are assumed constant and evaluated at 50zC from the data provided in [1].