Photo‐thermal conversion performance of mono MWCNT and hybrid MWCNT‐TiN nanofluids in direct absorption solar collectors

Abstract

Summary Solar energy is being widely investigated due to its abundant, renewable, and clean features. Photo‐thermal conversion in solar collectors is a direct approach for harvesting solar energy. Compared to the commonly used surface‐based solar collectors (SSCs), nanofluid‐based direct absorption solar collectors (DASCs) are more efficient. In this work, water‐based mono MWCNT and hybrid MWCNT‐TiN nanofluids were prepared through a two‐step method, aiming at light absorption enhancement of nanofluids for applications in DASCs. The optical and photo‐thermal conversion performance of the MWCNT nanofluids was firstly evaluated. The results showed that the MWCNT nanofluids presented high solar absorption capability, and the highest photo‐thermal conversion efficiency was obtained at 10 ppm. The TiN nanoparticles were subsequently incorporated to form the hybrid MWCNT‐TiN nanofluids. The absorption performance of the hybrid nanofluids was further enhanced. The highest efficiency of the hybrid MWCNT‐TiN nanofluids was achieved at the TiN mass fraction of 10 ppm, which was about 6.9%, 6.0%, and 3.8% higher than that of the MWCNT nanofluid at 2000, 4000, and 6000 seconds due to the localized surface plasmon resonance (LSPR) effect of TiN nanoparticles. It was also found that the collector efficiency dropped rapidly with the prolonged irradiation time owing to the convection and radiation heat loss at the elevated temperature. Therefore, effective measures should also be taken to reduce heat loss to maintain high photo‐thermal conversion efficiency.

Review on Stability, Thermophysical Properties, and Solar Harvesting Applications of Titanium Nitride-Based Nanofluids: Current Status and Outlook

“…The hybrid MW-CNT/TiN NFs (10 ppm; 10 ppm) showed the highest solar collector efficiency owing to the LSPR effect of TiN NPs, as displayed in Figure 11c. 171 While the utilization of hybrid MWCNT-TiN NFs may lead to a better collector efficiency as compared to MWCNT NFs, the enhancement observed was not significant. However, beyond a concentration of 10 ppm, a higher mass fraction of TiN NPs would lead to a slight decline in the photothermal conversion efficiency, potentially caused by the scattering of radiation from the TiN NPs, and resulting in energy loss.…”

“…Since the near-IR region accounts for around 50% of solar irradiance, enhancing light absorption in this range would be advantageous for overall light absorption. The hybrid MW-CNT/TiN NFs (10 ppm; 10 ppm) showed the highest solar collector efficiency owing to the LSPR effect of TiN NPs, as displayed in Figure c . While the utilization of hybrid MWCNT-TiN NFs may lead to a better collector efficiency as compared to MWCNT NFs, the enhancement observed was not significant.…”

“…Incorporating TiN NPs into NFs can enhance their ability to absorb light and enable the fluids on the irradiation surface to absorb more energy. Another avenue of feedback investigated the improvement of the photothermal conversion performance and the light absorption of MW-CNT NFs (water as a base fluid) through TiN NPs in direct absorption solar collectors. In the UV–visible region, the absorbance of MW-CNT NFs is greater compared to that of hybrid TiN/MW-CNT NFs However, in the near-IR region, the absorbance of MW-CNT particles is lower.…”

Nanofluids for Direct-Absorption Solar Collectors—DASCs: A Review on Recent Progress and Future Perspectives

“…Zheng et al [ 79 ] studied the dispersion stability of CTAB surfactant-based NFs of CNT/water and CNT–TiN/water over ambient storage of one week. At different mass fractions of up to 30 ppm, they found no precipitation after the one-week test, and to confirm this, they recorded the time-dependent absorbance spectra of the single- and multicomponent NFs.…”

“…In terms of concentration effect, they found that 0.02 wt% was the optimal particle concentration since no significant enhancement in performance was found at higher concentrations. Zheng et al [ 79 ] studied the solar absorption and STC efficiency of a single-component NF of CNT/water (5–10 nm and 20–30 nm inner and outer diameters and 10–30 μm length) and a muti-component NF of CNT–TiN/water (TiN NPs are 20 nm in diameter) at mass fractions of 10 ppm, 20 ppm, and 30 ppm. The DASC that they used for this work was a cylinder made of acrylic with a 15 mm height, 26.4 mm inner diameter and 2 mm wall thickness.…”