A review of natural convective heat transfer correlations in rectangular cross-section cavities and their potential applications to compound parabolic concentrating (CPC) solar collector cavities

Natural convective heat transfer in cavities is a complex function of cavity shape, aspect ratio, boundary conditions at the walls and the properties of the fluid contained within the enclosure. Considerable research into natural convection in regular shaped cavities, such as those of rectangular, square cross-section, or cylindrical annuli has been undertaken. Knowledge is, however, more limited relating to natural convective heat transfer in CPC solar collector cavities. Accurate knowledge of the variation in local convective heat transfer coefficients at the different CPC cavity components would facilitate to the design of suitable convection suppression devices, for example baffles at specific locations within the cavity, substantially reducing convective heat transfer and thus improving the performance of CPC solar collectors. From analysis of the correlations developed for regularly shaped enclosures it is concluded that the employment of these correlations to describe natural convection in CPC solar collector cavities can be misleading.

► Natural convective heat transfer in CPC solar collector cavities.
► Correlations developed for regular shaped cavities are not suitable for CPC cavities.
► Concentration ratio and truncation are dominant players in heat transfer in CPCs.
► Assumption of adiabatic boundary conditions at the side walls is not realistic.