Photothermal conversion efficiency of nanofluids: An experimental and numerical study

Abstract

This work investigated experimentally the photothermal conversion efficiency (PTE) of 10 gold nanofluids in a cylindrical tube under natural solar irradiation conditions, and compared with a 11 developed 3-dimensional numerical model. The PTE of gold nanofluids was found to be much higher 12 than that of pure water, and increased non-linearly with particle concentration, reaching 76% at a 13 concentration of 5.8 ppm. Significant non-uniform temperature distribution was identified both 14 experimentally and numerically, and a large uncertainty can be caused in the PTE calculation by using 15 only one temperature measurement. A mathematical model was also developed to calculate the 16 absorption efficiency without knowing the temperature field, which can be used to predict the 17 theoretical PTE for nanofluids based on their optical properties only. 18 19

Volumetric solar heating and steam generation via gold nanofluids

“…5a) The energy absorbed by the nanofluid sample in the sensible heating was calculated using the following relation in their studies done by Zhang et al [32,53] and Neumann [44], where only one temperature sensor was used to represent the bulk fluid temperature; (1) where , and are the specific heat capacity, mass of the sample taken and temperature change of the fluid volume over the specified time. The change in temperature was replaced by , the average change in temperature in the study done by Jin et al [41,48] in which more than one thermocouple were used for the measurement of fluid temperature. As clearly seen from Here we used a more realistic method to calculate the energy absorbed by the nanofluid volume especially at high nanoparticle concentrations.…”

“…The change in temperature was replaced by , i.e., the average temperature difference change in temperature in the study done by Jin et al [41,48], in which more than one thermocouple were used for the measurement of fluid temperature. As clearly seen from Here we used a more realistic method to calculate the energy absorbed by the nanofluid volume especially at high nanoparticle concentrations.…”

“…The change in temperature was replaced 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 10 by , i.e., the average temperature difference by Jin et al [41,48], in which more than one thermocouple were used. As clearly seen from Here we use a more realistic method to calculate the energy absorbed by the nanofluid volume.…”

“…It shall be noted that all these experiments [44,47,48] were performed outdoor, where the solar flux varied from time to time, and the focus by Fresnel lens limited the heating to a small area, leading to a non-uniform solar energy input. Such would lead to a very high solar flux in localized areas, producing spot heating and high evaporation rate locally.…”

“…It shall be noted that most of the experiments performed so far were not under well-controlled conditions [44,47,48]. Beside the problem of a varying solar flux and spot heating mentioned above, most of the experiments were performed bywith a single-point temperature measurement, ignoring the actual temperature distribution in the bulk fluid [32,44,53].…”