Abstract
In order to improve the performance of a solar collector in low heat transfer rate zones, a 3-D numerical study of the effects of partially moving wall sections and the use of a water nanofluid (CNT) in a tilted parallelepiped solar collector was performed. Equations governing the mixed convection phenomena occurring in the cavity are developed based on the 3-D potential-vorticity formulation and solved using the finite volume method. Two cases related to the direction of the moving surfaces are considered and compared to the base case (no driven walls). The results are presented in term of flow structures, temperature fields and local and average Nusselt numbers. The Richardson number is varied from 0.001 to 10 and the CNT volume fraction from 0 to 0.045. The results showed that for low Richardson values (less than 1), the motion direction of the moving surfaces has no significant effect on heat transfer rates and becomes effective for higher values. The highest rates of heat transfer are found for high Richardson values and CNT volume fractions, while the enhancement ratio (compared to the base case) occurs for low Richardson values.