Photothermal and Thermoelectric Performance of Carbon Nanotube Nanofluids Coupled with Metal Foams

In order to improve the volumetric solar absorption and thermoelectric generation efficiency, this study investigated the photothermal and thermoelectric performance of carbon nanotube (CNT) nanofluids combined with copper foams (PPI = 10, 15, and 20). Under 650–950 mW/cm2 illumination and 200–600 ppm nanofluids concentrations, temperature was measured at different depths. Temperature differences increase with the illumination intensity due to enhanced thermal conductivity and Brownian motion. Copper foams accelerate heat transfer to deeper regions, raising temperatures at 15 mm while slightly reducing surface temperatures. At PPI = 15, the system exhibites the highest temperature difference and open-circuit voltage, and its performance is 25–45% higher than that of the systems with other PPIs. Moderate pore density balances heat conduction and convective enhancement, which provides guidance for optimizing metal foam and nanofluids hybrid systems for efficient solar thermoelectric energy conversion.