Synthesis of therminol‐graphite nanofluids and photo‐thermal conversion properties

Abstract

Summary Therminol‐based nanofluids with graphite nanopowders (GNs) were proposed as an efficient working fluid in direct‐absorption solar collectors (DASCs), especially for elevated‐temperature applications. In this work, Therminol VP‐1/GN nanofluids (TG nanofluids) were prepared in two steps with surfactant (Triton X‐100). In the synthesis procedure, the vortex generator for coating GN with sticky surfactant (μ = 240 mPa⋅s) and the ultra‐sonicator for diluting GN/Triton X‐100 mixture with Therminol VP‐1 are used. We have demonstrated excellent dispersion stability up to 4 weeks and even after heating over 100°C without any surface modification of nanoparticles. The feasibility of using the synthesized TG nanofluid as a working fluid in DASCs was experimentally demonstrated by measuring its absorption coefficient as well as by characterizing photo‐thermal conversion performance. The absorption coefficient of the TG nanofluid at 0.004 wt.% of GNs was measured to be 1.12 cm−1, which is more than eight times enhanced from that of bare Therminol VP‐1 (ie, 0.13 cm−1) in the wavelengths from 350 to 1600 nm. Finally, the temperature increment of 43°C was achieved after t = 3600 s under the 5‐sun condition in the static photo‐thermal conversion experiment. Moreover, the low viscosity of TG nanofluids (only 2.2% higher than that of the bare Therminol VP‐1) supports the superiority of TG nanofluids to be applied as working fluid in DASCs.

Experimental investigation on low concentration nanofluids with Fresnel lens and evacuated tubes for solar applications

“…Photo‐thermal conversion properties of low concentration Therminol VP‐1/graphite nanofluid were reported by Jeong et al 28 . The absorbance was close to 80% for .004 wt.% nanofluid in the wavelength range of 350–1550 nm.…”

“…Adding CNTs of 1 wt.% to ternary carbonate nanofluids enhanced the thermal conductivity and specific heat, and thus a better fluid for solar applications, reported by Sang et al 26 The surfactant used was sodium dodecyl sulfate, and the enhancement was 149.2% and 78.3%, respectively, at a temperature of 500 • C. The specific heat value did not vary for ternary nanofluid even Photo-thermal conversion properties of low concentration Therminol VP-1/graphite nanofluid were reported by Jeong et al 28 The absorbance was close to 80% for .004 wt.% nanofluid in the wavelength range of 350-1550 nm. The nanofluid was kept under solar simulator for a duration of 3600 s, and the difference in temperature observed was 42 • C for five sun radiation.…”

“…Two‐step method is used to produce Al 2 O 3 and CuO nanofluids of concentration 50, 100, 150, and 200 ppm. The conversion of ppm to volume fraction is 28 given in the following formula. $$\begin{equation}{\phi _V} = \frac{{{\phi _W}{\rho _f}}}{{{\rho _f} + {\phi _W}{\rho _{f{\rm{\ }}}} - {\phi _W}{\rho _p}}}\end{equation}$$…”

“…Two-step method is used to produce Al 2 O 3 and CuO nanofluids of concentration 50, 100, 150, and 200 ppm. The conversion of ppm to volume fraction is 28 given in the following formula.…”

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

“…Therefore, nanofluids are promising alternatives to the commonly used fluids in DASCs. 11,12 Various nanoparticles, ranging from carbon materials (such as graphene, 13,14 carbon black, 15 carbon nanotube, 16,17 and graphite 18 ), metals (such as Cu, 19 Ag, 20 and Au 21 ), metal oxides (such as Fe 3 O 4, 22 CuO, 23,24 and TiO 2 25 ), carbides (such as SiC 26 and ZrC 27 ), and nitrides (such as BN 28 and TiN 29 ), have been evaluated for light absorption enhancement. However, a mono nanoparticle can usually improve the absorption in a certain bandwidth of the solar spectrum, leading to limited performance enhancement.…”