Volumetric solar heating and steam generation via gold nanofluids

Abstract

Volumetric solar absorption using nanofluids can minimize the thermal loss by trapping the light inside the fluid volume. A strong surface boiling with the underneath fluid still subcooled could have many interesting applications, whose mechanism is however still under strong debate. This work advanced our understanding on volumetric fluid heating by performing a novel experiment under a unique uniform solar heating setup at 280 Suns, with a particular focus on the steam production phenomenon using gold nanofluids. To take the temperature distribution into account, a new integration method was used to calculate the sensible heating contribution. The results showed that the photothermal conversion efficiency was enhanced significantly by gold nanofluids. A three-stage heating scenario was identified and during the first stage most of the energy was absorbed by the surface fluid, resulting in rapid vapor generation with the underneath fluid still subcooled. The condensed vapor analysis showed no nanoparticle escaping even under vigorous boiling conditions. Such results reveal that nanoparticle enabled volumetric solar heating could have many promising applications including clean water production in arid areas where abundant solar energy is available. highlights  Novel experiment was performed for nanofluids at a focused solar flux of 280 Suns. Strong surface evaporation was enabled while the bulk fluid was still subcooled  A new integration method was used to calculate photothermal conversion efficiency  Gold nanofluid (0.04w%) increased photothermal conversion efficiency by 95%. The authors are grateful for all the constructive comments from the reviewer and the Editor. Most of the comments were concerned on the presentation of the work. We have addressed all these concerns in the revised version, and a point-by-point reply is supplied below Reviewer #1:The authors of the present work experimentally investigated the surface boiling and steam production mechanism of gold nanofluids under uniform solar heating of 280 Suns. Various concentrations of gold nanofluids were produced and the generated steam was condensed and tested to reveal the presence of any nanoparticles.The study provides good insight to the surface boiling phenomenon of nanofluids and is in consonant with recent trend of investigation. However, there are several problems that need to be addressed before considering for publication in Applied Energy.1. The Abstract, in its current state is incomplete. It is more like a conclusion and needs to be re-written.Action: the abstract was rewritten with more focus on the novelty 2. The use of "gold nanofluids" should be mentioned in the Title and Abstract.Action: The title was slightly changed to reflect the content, and the was used in the title and the abstract in the revised version.3. In the statement: "For example, researchers [43] from Rice University", the Institution name should be replaced by the Authors' name.Action: T was used to replace the institution name in the revised version....

Modeling and analysis of optical properties of nanoparticles and nanofluids for effective absorption of solar radiation and their heating

“…It should be noted that the temporal linear dependence of T 0 , T m has been experimentally established [109][110][111] for initial period of heating, which confirms the dependencies (10). The temperature curves are shown in Fig.…”

“…The results of heating of homogeneous metallic and core-shell systems NPs and fluid [92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111] have been reviewed in this part. In general, next set of parameters determines the effective absorption and heating of NPs and fluid (NFs)-q abs , r 0 (r 1 ), N 0 , cρ, c m ρ m , k m , P 1 [see (10)(11)(12)].…”

“…The last time the production of steam in thermal collectors under solar irradiation is very interesting field and a few investigations on this topic have been carried out [111,[135][136][137][138]. Steam production is essential for a wide range of applications, and currently, there is a discussion if steam could be generated on top of heated NPs in a solar receiver.…”

Reduced Graphene Oxide Coated Hollow Polyester Fibers for Efficient Solar Steam Generation

“…The energy conversion efficiency was found to be 81.3% for rGO‐wrapped HPFs and 73.1% for rGO‐wrapped natural fibers under 1 kW m −2 illumination. With these values, the efficiency of rGO‐wrapped fibers can compete with that of those recently reported porous photothermal materials for efficient solar steam generation . It is worth noting that the rGO‐wrapped HPFs show relatively higher energy conversion efficiency than that of the rGO‐wrapped natural fibers, which may be attributed to the relatively lower thermal conductivity.…”

Novel Receiver-Enhanced Solar Vapor Generation: Review and Perspectives

“…They found highly non-uniform temperature distribution, and identified three phases of heating, (i) surface heating, (ii) sub-cooled boiling, and (iii) saturated boiling. They reported 95% of solar thermal efficiency using 0.04 wt % gold nanoparticle solution [45]. Mahfuz et al, [46] also achieved vapor generation efficiency of 63.82% at solar concentrations of 10 suns using 0.5 wt % of plasmonic nanofluid of silica-core decorated with Ag nanoparticles.…”