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In the present work, a numerical study is made on the fully-developed forced convective heat transfer of nanofluids in a curved square duct using Eulerian-Lagrangian two-phase approach. The curvature ratio of the duct is 0.02 and its hydraulic diameter is 8 mm. The Al2O3-water nanofluids contain spherical nanoparticles with particle diameter of 30 nm and volume fraction of 0.5%. Three different flow structures of nanofluids are obtained through the small perturbations generated by three different computers at the same conditions. The flow has a structural 2-cell, 3-cell or 4-cell at different Dean numbers and on different solutions, which leads to multiple non-uniform nanoparticle concentration distributions and multiple temperature fields. Multiple flow fields are symmetric in a low Dean number region and asymmetric in a high Dean number region, which leads to multiple symmetric (asymmetric) nanoparticle concentration distribution and temperature distribution fields, multiple symmetric (asymmetric) local Nusselt number and local friction factor along the outer wall at low De values (high De values), and finally lead to multiple mean friction factor and multiple mean Nusselt number. A significant enhancement of heat transfer (e.g. 23.79% at De of 335.2) can be achieved at the expense of a slight increase of flow friction (e.g. 6.84% at De of 335.2) in curved square duct through switching the solutions. This study could provide an explanation, from a new respect, for the inconsistent results of convective heat transfer of nanofluid in the literature.

With the rapid development of hydrogen production technology by using solar energy, the research of Solid Oxide Electrolysis Cell (SOEC) and Photovoltaic/Thermal (PV/T) system have become popular. A design scheme of hydrogen production system based on PV/T technology was proposed. The electrolytic cell combined photovoltaic panels, trough solar collectors and multiple heat exchagers to improve the overall efficiency of the hydrogen production system. The efficiency was predicted based on empirical models. The results showed that the hydrogen production efficiency of SOEC increased with increasing temperature and with decreasing current density. However, the balance between energy efficiency and hydrogen production rate of SOEC needed to be taken into account. The predicted hydrogen production efficiency of SOEC and overall system efficiency also agreed well with the results available in literature.

In order to alleviate the peak shaving pressure of power grid and further improve the deep peak shaving capacity of coal-fired units, this paper applies staged heat storage to condensing units. Under the condition of constant boiler load, the heat of regenerative steam extraction is stored to reduce the electrical load output of the unit. Taking a 660MW ultra-supercritical unit as an example,30%THA,40%THA and 50%THA were taken as the initial conditions of heat storage respectively to discuss the peak shaving range and power regeneration efficiency of different extraction steam positions for heat storage. The results show that the “storage 1# HP heater extraction steam” scheme with “two-stage three tank” heat storage and release structure has the largest peak shaving range of 37.3%~56.9% under 50% initial conditions. When the “two-stage three tank” heat storage and release structure selects the “storage 1# HP heater extraction steam ”scheme under 40% initial working condition, the “power regeneration efficiency” reaches the highest——78.3%. And the “power regeneration efficiency” of “two stage three tank” storage structure are always higher than the “single-stage” storage structure.

Long chain n-alkanes had been employed as the matrix of solid-liquid composite phase change materials due to the high latent heat. In this paper, paraffin-based composite PCM were constructed. To obtain the effects of the ratio of epoxide and hydroxyl groups on functionalized graphene, Molecular dynamics simulation had been used to calculate several composite systems. According to the obtained results, the interfacial thermal resistance surprisedly decreased by 48.68% when the ratio of epoxide and hydroxyl groups was 0.5. And the order parameter in x and y-directions showed the correlation on the interfacial thermal resistance. In terms of the melting point, the composite systems containing the functionalized graphene had lower value in chosen contrasting systems. The present findings were expected to reveal some intriguing thermal behaviors of the graphene/paraffin composite phase change materials with different ratios of epoxide and hydroxyl groups.

Based on the typical meteorological year data of Shanghai city, annual performances of solar water heating (SWH) system and photovoltaic/thermal (PV/T) system are comparatively analyzed under three different cases. The results show that when only solar energy is used, the effective day number of SWH system is more than PV/T system under the same case every month; for the PV/T system, heat loss at the nighttime dissipates most of the absorbed solar energy under the continuous heating mode considering the nighttime heat loss case; initial water temperature determines system electric efficiency. On the whole, PV/T system offers competitive performance only under the auxiliary heating mode, no matter from the points of primary efficiency and static payback period.

In the traditional PV/T collector, the temperature of thermal energy is always limited by the operation temperature of PV cells. Such a low-temperature thermal energy can hardly meet the demand in industrial application. To breakthrough the temperature limitation, a concentrating PV/T collector with fluid-based spectral splitting filter is developed in present work. The oleylamine solution of Cu9S5 nanoparticle is adopted in the filter to harvest the moderate-temperature heat. The performance of the collector is investigated by an outdoor experimental system. The results indicate that the PV efficiency of Si cell itself can be improved when the Cu9S5 nanofluid is employed as the optical filter in the collector. The maximum overall efficiency of present PV/T collector is 34.2%, which is 17.9% higher than that without a filter. The present collector has successfully obtained thermal energy with a temperature higher than 100 °C, which verifies the potential of Cu9S5 nanoparticles in fluid-based spectral splitting technique. Moreover, the particle concentration has a significant influence on the performance of hybrid PV/T system. The ratio of heat to electricity in PV/T system can be adjusted by changing the particle concentration to meet the requirements in various applications. In addition, the glass cover surrounding outside of the optical filter can improve the thermal efficiency, but it also increases the optical loss of the system due to the reflection on the surface of glass. Therefore, to realize higher performance, it is necessary to employ the glass with anti-reflection layer in the collector.

The high-power wireless charging system for the electric vehicle (EV) generates irreversible magnetic loss and quantities of heat during the charging process. Using thermal management with phase change material (PCM) can reduce the temperature rising rate and ensure the operation safety. A thermal management optimization for a 6.6 kW wireless EV charging system with PCMs was studied. The mathematical model of the heat transfer process in the charging system with thermal management was developed. It was solved by a MATLAB procedure and verified by an experimental measurement. A concept of effective time was proposed as the optimization index to evaluate the performance of the thermal management system. The results indicated that the thermal conductivity of the PCM needed to be improved for a better thermal performance. The modified PCM as paraffin with expanded graphite (EG) was adopted and the optimum thickness and thermal properties were obtained. The effective time by using the optimal PCM layer was 3 and 1.2 times that by using the original PCM layer for the charging system with 5% and 10% energy loss, respectively. The optimal layer can keep the temperature of the charging system below 60 °C in long-term operation.

Interaction potential plays a vital role on the friction. Potential energy of two contacts directly determines on the friction force. However, many mathematic models proposed, always abandon the instantaneous status during sliding to devote to a weighted average over lateral force, which might miss some information about friction behavior. In this work, the relation among potential energies, separation distances of two contracts, and positions in the sliding direction are studied to evaluate the instantaneous friction characteristics. Two hydrogenated diamond surfaces are used as the examined model. The results show that a watershed between positive and negative friction forces locates at the position with the minimum adsorption energy. A rapid decrease in potential energy occurs near the 2.5 nN external force, where the friction coefficient approaches zero at each position in the sliding direction. Therefore, a novel method may be developed to greatly reduce the friction coefficient between two surfaces by adjusting the contract pressure.

In order to improve the absorption rate of polycrystalline silicon thin film cells, an inverted pyramid structure was constructed and the metal nanoparticles were dispersed in the inverted pyramid structure. The absorption rate of the designed composite structure was improved by utilizing the LSPR effect generated by the metal particles, and the change of the absorption rate under different conditions was studied by changing the type, volume fraction and H/P ratio of the periodic structure in the composite structure. By using FDTD software to simulate, this paper finds that the designed inverted pyramid structure has a maximum absorption rate of 20% in the 0.4∼0.55um band. In the composite structure, the dispersed Ag nanoparticles have the best absorption rate in the 0.55∼0.8um band; The volume fraction of the particles in the inverted pyramid structure is found to increase slowly with the increase of volume fraction in a certain band. By changing the ratio of the depth of the inverted pyramid structure to the length of the period, it is found that as the ratio increases, the whole absorption rate will increase to some extent.

In order to reduce the moisture content of flue gas in coal-fired power plants, this paper puts forward a novel spraying system with upward spraying and downward gas flow (ST-UD). And the heat and mass transfer models of ST-UD in fluent were validated against experiment data. Then orthogonal simulation experiment was carried out to get the relationship between the four influence factors and the two evaluation indices. Through the range analysis and trend analysis, it can be found that the influence degree and the influence trend of factors on evaluation indices. The conclusion of this paper provides a reference for the heat-transfer performance optimization of other spray towers.

Photothermal conversion materials have promising applications in many fields and therefore they have attracted tremendous attention. However, the multi-functionalization of a single nanostructure to meet the requirements of multiple photothermal applications is still a challenge. The difficulty is that most nanostructures have specific absoprtion band and are not flexible to different demands. In the current work, we reported the synthesis and multi-band photothermal conversion of Ag@Ag2S core@shell structures with gradually varying shell thickness. We synthesized the core@shell structures through the sulfidation of Ag nanocubes by taking the advantage of their spatially different reactivity. The resulting core@shell structures show an octopod-like mopgorlogy with a Ag2S bulge sitting at each corner of the Ag nanocubes. The thickness of the Ag2S shell gradually increases from the central surface towards the corners of the structure. The synthesized core@shell structures show a broad band absorption spectrum from 300 to 1100 nm. Enhanced photothermal conversion effect is observed under the illuminations of 635, 808, and 1064 nm lasers. The results indicate that the octopod-like Ag@Ag2S core@shell structures have characteristics of multi-band photothermal conversion. The current work might provide a guidance for the design and synthesis of multifunctional photothermal conversion materials.

Photothermal conversion materials have promising applications in many fields and therefore they have attracted tremendous attention. However, the multi-functionalization of a single nanostructure to meet the requirements of multiple photothermal applications is still a challenge. The difficulty is that most nanostructures have specific absoprtion band and are not flexible to different demands. In the current work, we reported the synthesis and multi-band photothermal conversion of Ag@Ag2S core@shell structures with gradually varying shell thickness. We synthesized the core@shell structures through the sulfidation of Ag nanocubes by taking the advantage of their spatially different reactivity. The resulting core@shell structures show an octopod-like mopgorlogy with a Ag2S bulge sitting at each corner of the Ag nanocubes. The thickness of the Ag2S shell gradually increases from the central surface towards the corners of the structure. The synthesized core@shell structures show a broad band absorption spectrum from 300 to 1100 nm. Enhanced photothermal conversion effect is observed under the illuminations of 635, 808, and 1064 nm lasers. The results indicate that the octopod-like Ag@Ag2S core@shell structures have characteristics of multi-band photothermal conversion. The current work might provide a guidance for the design and synthesis of multifunctional photothermal conversion materials.

It is currently hard to estimate the reliability parameters of organic light-emitting diodes (OLEDs) when conducting a life test at normal stress, due to the remarkably improved life of OLEDs to thousands hours. This work adopted three constant-stress accelerated life tests (CSALTs) to predict the life of white OLEDs in a short time. The Weibull function was applied to describe the life distribution, and the shape and scale parameters were estimated using the least square method. The experimental test data were statistically analyzed using a self-developed software. The life of white OLEDs predicted via this software is in good agreement with that reported from the customers. The numerical results indicated that the assumptions of CSALT are correct, and that CSALT can be used to predict the life of white OLEDs. This work confirmed that the life of white OLEDs meets the Weibull distribution, and that the accelerated life equation conforms to the inverse power law. Furthermore, the precise accelerated param...

In this study, the effect of concentration of nanoparticles on the thermal storage properties of molten nitrate salt-based nanofluids with graphene nanoplatelets (GNPs) was investigated. Solar salt consisting of sodium nitrate and potassium nitrate was utilized as the base material for the nanofluids. Homogeneous dispersion of GNPs within the solar salt was observed through scanning electron microscopy analysis. For both solar salt and resultant nanofluids, differential scanning calorimetry was employed to measure the thermal storage properties, including characteristic temperatures of phase change, startup heat, and specific heat capacity (SHC). A maximum increase of 16.7 % in SHC at the liquid phase was found at an optimal concentration of 1 wt% of GNPs. At the same concentration, the onset temperature decreased by 10.4 °C, the endset temperature decreased by 4.7 °C, and the startup heat decreased by 9 %.

A prototype of a photovoltaic solar-assisted heat-pump/loop heat-pipe system (PV-SAHP/LHP) was constructed in this paper. The system was a combination of photovoltaic solar-assisted heat pump system (PV-SAHP) and loop heat pipe photovoltaic/thermal (LHP-PV/T) system. The combined system can carry out with two modes but using the same working fluid, and the two modes can switch operation freely. R600a was employed as the working fluid, and system performance under different working mode was presented in this paper. The results show that the day average photothermal efficiency & photovoltaic efficiency can reach to 43.6% & 11.3% under LHP-PV/T working mode compared with that of 57.5% & 12.1% under PV-SAHP working mode: Besides that, a day average COP of 3.66 was obtained under PV-SAHP working mode.

Due to copyright restrictions, the access to the full text of this article is only available via subscription. Micro- and nano-scale thermal radiation has become one of the fastest growing research areas because of advances in nanotechnology and the development of novel materials. The related research and development includes near-field radiation transfer, spectral and directional selective emitters and receivers, plasmonics, metamaterials, and novel nano-scale fabrication techniques. With the advances in these areas, important applications in energy harvesting such as solar cells and thermophotovoltaics, nanomanufacturing, biomedical sensing, thermal imaging as well as data storage with the localized heating/cooling have been pushed to higher levels.

The electronic and optical properties of Mn-doped 3C-SiC films are investigated by the first-principles calculation. The structure of Mn-doped 3C-SiC is modeled by substituting Mn atom for C or Si atom in 3C-SiC lattice. The results suggest that Mn-C and Mn-Si bonds can exist in the Mn-doped 3C-SiC. Mn location in 3C-SiC lattice significantly affects the crystal structure of Mn-doped 3C-SiC, and the Mn atom substitution for C or Si sites of 3C-SiC lattice can induce to the difference of indirect or direct band structure. The calculated results also show that some new impurity energy levels occur in the band gap of Mn-doped 3C-SiC, and the imaginary part of dielectric function of Mn-doped 3C-SiC shifts toward the infrared region in comparison with the primitive 3C-SiC. The adsorption spectrum of Mn-doping 3C-SiC, due to the transition of electrons between Mn 3d states, presents some new prominent peaks at low frequency. These results can further confirm Mn-doped 3C-SiC to act as a potential material for optical applications.