Absorption Of Nanofluids Research Articles

Experimental study of indoor light/thermal environment with spectrally selective windows using ATO nanofluids in winter

As a weak link in energy efficient buildings, the building glass windows have been developing towards energy saving, comfort and adjustability. The dynamic windows and static windows have the disadvantages of instability as well as low spectral flexibility and poor seasonal adaptation respectively, to solve the above problems, this study proposes a novel semi-dynamic fluidic window filled with ATO/water nanofluids to bridge the gap between dynamic windows and static windows, and its performance has been experimentally studied. Firstly, the operating principle of the novel spectrally selective windows with overturn function is depicted during summer and winter operating periods. Meanwhile, the indoor light/thermal environment is discussed with the effect of volume concentrations ATO nanofluids, by comparative experiments. Results indicated that the inner/outer surface temperature with spectrally selective windows is higher than that with common windows, and the inner surface temperature difference of two cases can reach 1.3 °C, 4.7 °C, 10.1 °C and 6.8 °C, with volume concentration of 100 ppm, 200 ppm, 500 ppm and 1000 ppm respectively. Meanwhile, heat absorption of nanofluids delays the time of indoor peak temperature and increases the indoor air temperature during the afternoon and evening period, with a delay time of 33 min at 1000 ppm volume concentration. Additionally, it is found that with volume concentration increases, indoor illuminance significantly decreases, and the optimal concentrations of 100 ppm or 200 ppm are recommended for operation during winter time.

Effect of nanoparticle aggregation on the thermal radiation properties of nanofluids: an experimental and theoretical study

Nanofluids show significant enhancement in the absorption of solar energy. However, little work has been done on the effect of nanoparticle aggregation on the thermal radiation properties of nanofluids up to now. In this work, we systematically investigate the thermal radiation properties of nanofluids with nanoparticle aggregation from experiment and theory. On the experimental side, titanium dioxide/silver (TiO2@Ag) plasmonic nanofluids are prepared in distilled water and the spectral transmittance of nanofluids with different degrees of aggregation is measured. The result shows that the size of aggregated nanoparticle cluster has a significant effect on the absorption of nanofluids. On the theoretical side, a theoretical model is developed to calculate the thermal radiation properties of nanofluids with nanoparticle aggregation. By applying the multiple sphere T-matrix (MSTM) method and the Monte Carlo (MC) method, we investigate the effects of nanoparticle aggregation, cluster fractal dimensions and cluster sizes on the thermal radiation properties of nanofluids. The results indicate that our theoretical model can predict the thermal radiation properties of nanofluids with nanoparticle aggregation more reasonably. This is of great significance to understand the mechanism that affects the thermal radiation properties of nanofluids and to actively design nanofluids.

일사량에 따른 탄소나노튜브 나노유체의 열 흡수 특성 실험연구

Recently, solar heating system has strongly been highlighted in the industry due to the carbon emission regulation. Multi walled carbon nanotubes have great heat absorption characteristics and excellent electrical conductivity in solar heating system. In this study, the distilled water and various of concentration of nanofluids have been adopted for a solar heating experiment. The difference of temperature was studied by using thermocouples in nanofluid. Furthermore, the electrical conductivity and UV light absorption of nanofluids were analyzed to evaluate their performance. The results of these analyses showed that the higher the concentration, the better heat transfer characteristics and electrical conductivity.

CFD modeling and predicting the performance of direct absorption of nanofluids in trough collector

In this paper, two types of nanoparticles are used in a solar direct absorption parabolic trough collector (DAPTC). Nanosilica and multi-wall carbon nanotube (MWCNT) with two different volume fractions are used in ethylene glycol (EG) in the experimental section. A glass-glass absorber tube is utilized as the receiver, and the working nanofluid goes through the tube. The computational fluid dynamics (CFD) method is used for simulating the process, and it is validated by experimental data. The volume fractions of the nanoparticles in the base-fluid are 0.1–0.5% and 0.1–0.6% for nanosilica and MWCNT, respectively. The nanofluid including 0.6% MWCNT/EG has the highest outlet temperature which is equal to 346.1 K. The experimental results used to validate the CFD procedure. In the last step, a multi-layer perceptron neural network is trained using the data obtained from the CFD model. It has been shown that the outputs of the network have good agreement with the CFD results. Both the CFD and the ANN methods were compared, and the advantages and disadvantages of each technique in modelling the problem have been discussed.

Defects-assisted solar absorption of plasmonic nanoshell-based nanofluids

Plasmonic nanoshell-based nanofluids have recently been demonstrated to be promising candidates for efficient solar thermal conversion. During the nanoshells’ fabrication processes, more often than not, only part of the dielectric core is covered by metals. However, there are few reports on how these particle defects affect the solar thermal conversion. In this paper, we find that the coverage defects of TiO2/Ag nanoshells, instead of deteriorating, may enhance the solar absorption of nanofluids. The underlying mechanism mainly lies in the redshift of the symmetric localized surface plasmon resonance from the visible region for perfect nanoshells to the near-infrared in the presence of particle defects. The poor absorption of perfect nanoshells based nanofluids in the near-infrared is thus improved. The redshift can be quantitatively predicted and understood by an effective medium approach. This work opens a new route to enhance the solar thermal conversion of nanofluids by mediating the resonance absorption of composite nanoparticles via defects, and helps to deepen the understanding of plasmonic absorption properties of non-perfect nanoshells.

Solar radiation absorption of nanofluids containing metallic nanoellipsoids

Metallic nanoparticles (NP) are promising materials for solar radiation absorption due to the plasmon resonance absorption band in the visible and near IR spectrum that can be tuned modifying the NP shape. Linear optical absorption in the visible and near IR spectral region of aqueous nanofluids containing gold and silver nanoellipsoids (NEs) were studied using the Maxwell–Garnett model, and the solar weighted absorption coefficient was calculated for different concentrations, aspect ratios and NE sizes. The results show an enhance of the solar weighted absorption coefficient in almost 54% and 86% for gold and silver NEs, respectively, when compared to spherical NP of the same materials. Moreover, for a nanofluid-based direct absorption collector with 1cm thickness, and a nanofluid of gold NEs with a low volume fraction, small NPs (2.5nm), a high aspect ratio (AR=4), it is possible to obtain a solar weighted absorption coefficient closer to the ideal solar radiation absorber condition.

Fabrication Method for a TiO<SUB>2</SUB> Nanofluid with High Roundness and Superior Dispersion Properties

This study describes the use of a new submerged arc nanofluid synthesis system to fabricate TiO 2 nanofluids. Under vacuum conditions, this system uses the energy produced by an arc discharge to vaporize the desired metal. Then, the vaporized metal is cooled rapidly in a low-temperature dielectric liquid, forming nanoparticles that are evenly distributed inside the dielectic liquid. Experiments show that the fabricated TiO 2 nanoparticles are much better than those fabricated by aerosol methods. In addition, the fabricated nanofluid has high suspension stability. We use X-ray diffraction to analyze the structure of TiO 2 nanofluid. By measuring the Zeta potential of the TiO 2 nanofluid with different pH values, the suspension stability of the TiO 2 nanofluid is demonstrated. To verify the applicability of the TiO 2 nanofluid, this study also analyzes and compares the rheological properties and reaction to light absorption of nanofluids with different average particle sizes.