Experimental Assessment of Dynamic Stability and Energy Performance in Evacuated Tube Solar Collectors Incorporating Metal Foam Heat-Exchange Chambers

The paper presents an experimental comparison between a standard evacuated tube solar collector and a collector featuring a modified internal manifold architecture with an integrated metal-foam heat-exchange chamber. Both collectors have an identical geometric volume of the heat-exchange region, ensuring that the measured differences in performance are exclusively attributable to changes in the internal design of the manifold. The experimental validation comprised five measurements conducted at two mass flow rate levels, 60 and 120 kg·h⁻¹, under real outdoor operating conditions. The evaluation was based on time-resolved performance data and included instantaneous, cumulative, and dynamic indicators, such as energy yield, volumetric energy density, performance stability, dynamic sensitivity, and energy inertia. The results show that the solar collector with the modified manifold consistently achieves a higher energy yield, higher volumetric efficiency, and lower dynamic sensitivity than the standard collector. These benefits are obtained at the cost of increased pressure losses, indicating a trade-off between energy performance and hydraulic demand under real operating conditions.