Analysis of the model versus experiments

The CFD numerical simulation needs the radiative flux distributions on the inner surface of the cavity calorimeter, the surface of the copper cone that receives the concentrated solar radiation. Four different distributions were obtained using the CIRCE2 code [4], three of them corresponding to each of the three set of DEFRAC mirrors (A, B and c) and the

SHAPE * MERGEFORMAT

Figure 8 shows the wall temperature distributions of the inner cone obtained with the CFD simulation of CAVICAL1 calorimeter. It is possible to observe the influence of the heat flux distribution and incident radiative power on the temperature distributions. The maximum temperature value is function of the total incident radiative heat flux; the figure shows that for the tests using A, B and C set of mirrors with a total flux up to 300 W, the maximum temperature are near 60°C, while for the case T when the total incident flux is 876 W, the test shows a maximum temperature value of 90 °C. Also it is clear that there is a shape correspondence between the temperature distributions and the radiative heat flux profiles.

Figure 8. CFD Simulate Temperature profiles in the incident heat flux calorimeter wall. Test A, B, C and D.

Table 1 shows the energy balance for the four tests presented. As the table shows the convection losses in the calorimeter is only 0.22% and increase when the incident radiation increase. The Heat transfer estimated is near 51 W/m2K.

Table 1.

Parameter

Test A

Test B

Test C

Test T

Incident Energy, Qin (W)

333

327

273

876

Transfer Energy to Water, Qc (W)

332

326

271

873

Convection losses (W)

0.72

0.72

0.76

3.38

% of losses

0.22

0.22

0.27

0.39

Convection heat transfer coefficient (W/m2K)

51.05

51.19

50.96

54.66

Finally, figure 9 presents a comparison between experimental and theoretical wall temperature profiles of CAVICAL1 corresponding to the test of the group of mirrors A. As can be seen, the maximum temperature difference between the experimental and numerical values is less than 2 oC, showing a very good agreement.

6. Conclusions

A heat transfer numerical model based on the CFD FLUENT code of CAVICAL1 calorimeter was developed. The mathematical model was able to determined the position where the maximum temperatures occur, the shape of the temperature distributions, the heat concentrated solar power, the convection losses and the convection heat transfer coefficient. The model was validated through a comparison between experimental and theoretical wall temperature profiles of CAVICAL1 having a maximum differences less that 2 oC or less than 6%.