Development of a “volume heat-trap” type solar collector using a fine-particle semitransparent liquid suspension (FPSS) as a heat vehicle and heat storage medium Unsteady, one-dimensional heat transfer in a horizontal FPSS layer heated by thermal radiation

Arai, Norio; Itaya, Yoshinori; Hasatani, Masanobu

doi:10.1016/0038-092x(84)90048-3

Cited by 65 publications

(29 citation statements)

References 6 publications

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“…In contrast to conventional solar collectors [20,21] where the solar absorption is surface-based, i.e., having large radiative and thermal losses due to high surface temperature [22], the volumetric solar collectors minimize these losses by thermal trapping [23,24] and reduced temperature difference between the absorber and the fluid [25,26].…”

Section: Introductionmentioning

confidence: 99%

“…The solar energy utilization of these applications can be significantly enhanced by suspending various nano-sized particles in a fluid, which is and such solar receivers called are known as direct absorption volumetric solar collectors [15][16][17][18][19]. In contrast to conventional solar collectors [20,21] where the solar absorption is surface-based, i.e., having with large radiative and thermal losses due to a higher surface temperature especially for concentrated solar systems [22], the volumetric solar collectors not only minimize these losses by thermal trapping [23,24] and reduced but also reduce the temperature difference between the absorber and the -fluid interface temperature difference [25,26].…”

Section: Introductionmentioning

confidence: 99%

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Volumetric solar heating and steam generation via gold nanofluids

et al. 2017

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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....

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Volumetric solar heating and steam generation via gold nanofluids

et al. 2017

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“…The exact temperature profiles will depend on the flow characteristics in the receivers, but for the same mean fluid temperature (T f ) and solar heat flux (CG s ), the temperature profile in the VR ( Figure 1a) can be favorable because the temperature associated with emissive loss is lower than that of the mean fluid temperature (by ∆T). This behavior is referred to as "thermal trapping" in solar thermal literature (Arai et al, 1984;Wijeysundera and Thevendran, 1988), but is physically similar to the "greenhouse effect" (Harries, 2000). On the other hand, the unfavorable temperature profile in the SS (Figure 1b) leads to higher emissive losses.…”

Section: Introductionmentioning

confidence: 84%

“…However, in these previous studies, the effect of increasing height of the absorbing liquid (H in Figure 1a) beyond the millimeter-scale which can lead to lower emissive loss due to the favorable temperature profile was not considered. Arai et al (1984) can be highly efficient. Nevertheless, an optimization of small-particle volumetric receivers with respect to particle loading, solar exposure time and nanofluid height has yet to be conducted.…”

Section: Introductionmentioning

confidence: 99%

Optimization of nanofluid volumetric receivers for solar thermal energy conversion

2012

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Improvements in solar-to-thermal energy conversion will accelerate the development of efficient concentrated solar power systems. Nanofluid volumetric receivers, where nanoparticles in a liquid medium directly absorb solar radiation, promise increased performance over surface receivers by minimizing temperature differences between the absorber and the fluid, which consequently reduces emissive losses. We present a combined modeling and experimental study to optimize the efficiency of liquid-based solar receivers seeded with carbon-coated absorbing nanoparticles. A one-dimensional transient heat transfer model was developed to investigate the effect of solar concentration, nanofluid height, and optical thickness on receiver performance. Simultaneously, we experimentally investigated a cylindrical nanofluid volumetric receiver, and showed good agreement with the model for varying optical thicknesses of the nanofluid. Based on the model, the efficiency of nanofluid volumetric receivers increases with increasing solar concentration and nanofluid height. The total receiver-side efficiencies are predicted to exceed 35% when nanofluid volumetric receivers are coupled to a power cycle and optimized with respect to the optical thickness and solar exposure time. This work provides insights as to how nanofluids can be best utilized as volumetric receivers in solar applications, such as receivers with integrated storage for beam-down CSP and future high concentration solar thermal energy conversion systems.

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“…Hence, in the so-called direct absorption solar collectors (DASC) thermal resistance in converting solar energy into heat is reduced. The concept of direct absorption was originated in the 1980s to simplify the flat-plate surface absorber design and to potentially enhance the thermal performance by direct radiation absorption within the fluid volume (Arai et al, 1984;Bohn and Green, 1989). Typical heat carrier fluids such as water, ethylene glycol, propylene glycol, and heat transfer oils used in solar collectors have been shown to have poor thermo-physical properties and very low absorptive properties over the solar spectrum.…”

Section: Introductionmentioning

confidence: 99%