A Detailed Investigation on the Convective Heat Transfer Inside the Enclosed Cavity of Insulated Glass Solar Thermal Flat-Plate Collectors
Abstract
In the solar thermal industry there is a trend towards large-scale solar district heating plants. However, building large plants can also lead to problematic fluctuations in demand for collector manufacturers. To tackle this issue, an innovative concept was introduced which adapts the collector design to production techniques of the insulating glass industry. The insulated glass solar thermal flat-plate collector raises new questions regarding efficiency and convective heat losses. The objective of this research was to determine the convective heat transfer characteristics of this collector design. A review of Nusselt number correlations revealed that the gas cavity of the collector can be described using well-known equations. As these equations do not consider large aspect ratios and higher temperature levels, a computational fluid dynamics simulation was performed. The results show that convective heat transfer inside insulated glass flat-plate collectors occurs predominantly in front of the absorber, whereas inside the rear cavity, the flow patterns are subcritical resulting in smaller convective losses. As a consequence, the absorber of this collector should be positioned asymmetrically in order to minimize its convective losses.