Introducing internal light source into direct absorption solar collector for enhancing photothermal conversion performance of nanofluids

Direct absorption solar collectors (DASCs), by virtue of simplicity, environmental benefits, and cost-effectiveness, hold significant potential for solar thermal utilization. However, widespread applications face inherent limitations in photothermal conversion (PTC) efficiency due to their passive reliance on external solar irradiation. This study pioneers a novel internally radiated DASC (IR-DASC) featuring a controllable internal light source integrated within nanofluid (NF) layer. This innovative design effectively addresses the constraints of fluctuating light intensity, spectral mismatch, and optical penetration depth, thereby enhancing the PTC process using TiN-deionized water (DW)/ethylene glycol (EG) NFs. Systematic characterization under controlled flow (3-13 L/min) demonstrated a significant outlet temperature elevation of 10.52 °C and a PTC efficiency of 0.65 at optimal conditions (100 ppm, 3 L/min). As the concentration of TiN-DW/EG NF was increased from 0 ppm to 100 ppm, the heat gain efficiency was improved by at least 0.26. Spectral validation using AM1.5-matched xenon irradiation conclusively demonstrates technological viability under real-world operating conditions. Notably, the implementation of internal radiation architecture demonstrates superior thermal uniformity. Therefore, the IR-DASC provides a new paradigm, overcoming fundamental limitations of passive solar DASCs through structural innovation for enhanced efficiency and practical value.