Steam generation in a nanoparticle-based solar receiver

Abstract

, Steam generation in a nanoparticle-based solar receiver, Nano Energy, http://dx.doi.org/10. 1016/j.nanoen.2016.08.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Steam production is essential for a wide range of applications, and currently there is still strong debate if steam could be generated on top of heated nanoparticles in a solar receiver. We performed steam generation experiments for different concentrations of gold nanoparticles dispersions in a cylindrical receiver under focused natural sunlight of 220 Suns. Combined with mathematical modelling, it is found that steam generation is mainly caused by localized boiling and vaporization in the superheated region due to highly non-uniform temperature and radiation energy distribution, albeit the bulk fluid is still subcooled. Such a phenomenon can be well explained by the classical heat transfer theory, and the hypothesized 'nanobubble', i.e., steam produced around the heated nanoparticles, is unlikely to occur under normal solar concentrations.In the future solar receiver design, more solar energy should be focused and trapped at the superheated region while minimizing the temperature rise of the bulk fluid. Graphical abstract

Volumetric solar heating and steam generation via gold nanofluids

“…However these results are quite different to the recent results from Jin et al [47]. Still using a 1 2 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 3 Fresnel lens (i.e.…”

“…In addition to the volumetric heating, direct vapor generation due to localized heating of nanoparticles [40][41][42][43] is a recent development in this area. For example, Neumann et al [44] showed that by using very dilute gold nanoparticles (16.7 ppm) under a focused solar light via a typical Fresnel lens, steam was produced instantly while the measured bulk temperature was still 6 o C approximately.…”

“…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.…”

Nanofluids effects on the evaporation rate in a solar still equipped with a heat exchanger

“…Despite some limitations such as relatively high preparation cost and stability issues, extensive attempts have been made to develop the applications of nanofluids in energy systems such as solar energy based devices [7][8][9][10][11][12][13], cooling and thermal management of electronic equipment [14,15], grinding and drilling, absorption systems, medicine, heating and cooling of buildings, domestic refrigerators, and so on [16,17].…”

“…Nanotechnology has also been implemented to enhance the heat transfer potential of common liquids like water and oil to ameliorate the efficiency of thermal systems; this can be done through adding solid nanoparticles (particles with a size of 1-100 nm) to the liquids. The mixture of nanoparticles and conventional liquids is named "nanofluid" [6].Despite some limitations such as relatively high preparation cost and stability issues, extensive attempts have been made to develop the applications of nanofluids in energy systems such as solar energy based devices [7][8][9][10][11][12][13], cooling and thermal management of electronic equipment [14,15], grinding and drilling, absorption systems, medicine, heating and cooling of buildings, domestic refrigerators, and so on [16,17].In recent years, the problems of global warming and increase of the world population have highlighted the drinking water crisis. Although water covers more than 70% of the earth, most of this is not drinkable.…”