CFD modeling and performance evaluation of an open-aperture partially evacuated receiver with internal twisted inserts in solar PTCs: energy and exergy analysis.

The solar flux distribution on the walls of the receivers in solar parabolic and circular collectors (PTCs and CTCs) is highly non-uniform. To prevent major problems caused by flux non-uniformity in such devices, a partially open aperture evacuated receiver (OAER) with an internal twisted insert is introduced, and its performance is compared to that of conventional evacuated receivers (CERs). A comprehensive computational fluid dynamic (CFD) model is developed for the receivers. The simulation results show that the proposed receiver has a more uniform solar flux distribution, and consequently greater energy and exergy efficiencies compared to CERs. The proposed OAER acts as a fluid turbulator, absorbs solar energy more efficiently, distributes the temperature gradient inside the absorber more uniformly, shifts the maximum temperature on the exterior surface of the CERs to the interior surface, and reduces radiative losses. The enhancement in total heat absorbed by OAER with 10 blades (OAER_10) compared to the CER_0 is 7.69%. The simulation results reveal that the average daily exergy efficiency of an OAER_10 is about 27.8% higher than a CER_0. The average daily exergy efficiency of a CER_0 is obtained to be about 7.55%, while it decreases to 7.42% for a CER_6 due to larger exergy destruction caused by air pressure drop. The introduced design offers a higher potential for efficient absorption of solar energy (proper sensible heat storage device) and provides a more useful contact area.