Previous observation showed that the five fins collector achieved an increase in velocity of 2% compared to the four fin design, while longitudinal water temperature stratification decreased by 19%. This could be explained by the addition of the fins responsible for an increased transfer of heat inside the collector, thus increasing velocity and overall temperature in the collector.

In order to demonstrate that five fins is a more suitable arrangement geometry for optimal collector design, a 3D CFD analysis was carried out assuming a constant temperature boundary condition on the absorber plate set at 313°K. The fluid departure temperature was set at 293K. Despite the fact that the system is under constant heat flux, using a constant input temperature allowed the heat absorbed by both collector to be derived as shown in Figure 7.

Initially, for the first 10 minutes, more heat was absorbed by the five fin collector compared to the four fin. This is linked to a frenzy of heat transfer activity; the fins are surrounded by cooler water. An increase in heat transfer activity occurs when increasing from four to five fin geometries. After 10 minutes the five fins are surrounded with hotter water than the four fins are. The difference in temperature between the four fins and the water is higher resulting in a higher heat flux. Both profiles reach a peak value at the equilibrium temperature 313°K set as the boundary condition.

4. Conclusion

This paper reported the implementation of a four fin ICS-SWH concept utilising CFD-Fluent software through Gambit in order to optimise its design performance. Initial results of the four fin ICS-SWH indicated that one fin could be added to the original design to improve the heat transfer. A 3D CFD simulation was then undertaken for a five fin ICS-SWH. Two boundary conditions were applied to the systems in order to compare the water temperature stratification achieved and the heat transferred to the water body by each collector.

The first boundary condition applied to the systems consisted in a constant heat flux on the absorber plate. This method was used to characterise the temperature stratification and the velocity

magnitude within both collectors. Despite a minor decrease in temperature gradient between the top to bottom in the five fin ICS-SWH, it was clearly observed that stratification remained. It is important to state that the addition of fins should not impede the flow between the fins (as was experienced when trialling a multi-fin design in an earlier study), thereby reducing the convection coefficient. Results showed that the addition of one fin in the collector increased the velocity in the collector which has a corresponding increase on the Nusselt number; raising the heat transfer coefficient in a predictable manner [12]. The velocity magnitude was also observed to decrease with time for both collectors with the water getting warmer.

A second boundary condition applied to the systems consisted of a constant temperature on the absorber plate which was used to characterise the heat absorbed by each collector. Results revealed that the addition of one fin accounts for the increased transfer of heat inside the collector. It was observed that the five fins supplied more energy to the collector than four at the beginning of the charging process. The intermittent availability of incident solar radiation in Scotland shows high potential for this type of improvement as it is advantageous to have rapid heating process.

In light of the results presented in this paper, the five fin collector performed generally better than the original four fins collector. Therefore this new design could be suggested as a new arrangement of the collector assuming that the cost associate to this improvement is negligible.

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