Numerical analysis

2.1. General specifications

The configuration of the PVT module consists of a row of photovoltaic cells with a rectangular surface area of 1cm x 1m, placed at the top of the aluminium heat sink. The encapsulation can be divided into various elements.

1. — In the surface at which concentrated radiation is received, an EVA film is applied to the cells, and high absorption glass with low iron content is used as an outer skin. This reduces deterioration of the cells and minimises the thermal losses through the top of the module.

2. — Between the cell and the heat sink a strip of electrical insulation is inserted using a double sided adhesion (Chomerics Thermattach T404). This method considerably-simplifies the adhesion process, as it simultaneously serves to insulate the cell and to fix it in right position.

3. — Finally, the lateral and underneath faces of the heat sink are thermally insulated-with a plate of temperature resistant polypropylene.

image083 Подпись: Fig.2. Simulation Scheme.

The figure 2 shows a scheme of the proposed cooling system. Concerning to the boundary conditions they must be fixed in the numerical study. In the outer upper face of the cooling device a, Neumann boundary condition of 1000W/ m2 is applied. This represents the heat flow per unit surface area that the cells transmit to their back contact. The remaining lateral boundaries are considered to be adiabatic surfaces, assuming that the insulation is sufficiently wide to achieve this requirement. Finally, at the surfaces that represent the entry and exit of the fluid flow, the boundary conditions are fixed flow at the entrance and free flow at the exit.

As a line of symmetry exists in the geometry (Fig.1) only half of the system will be modelled.

The tube is made of aluminium (thermal conductivity k =202W/mK). The analysed cross sections are those of the usual commercial tubes with rectangular cross section. The only requirement is a fixed section at the upper face where to accommodate the row of PV cells (1cm width). In the table 1, a summary of the analysed sections is shown. The difference among these three sections relates to the height of the section, it varies from 7 to 27 and hence the aspect ratio increases.

Table 1. Dimensions of the commercial aluminium cross sections analysed in this research

a

(Hc/Wc)

H

(mm)

Hc

(mm)

W

(mm)

Wc

(mm)

L

(m)

1

15

7

1.5

7

1

2.43

15

17

1.5

7

1

3.86

15

27

1.5

7

1