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Phase change materials (PCMs) have remarkable energy storage capacity and promising applications in the field of thermal control of electronic products. The problem of thermal property improvement and heat transfer of PCMs in metal-foam heatsinks is an important task for thermal management of electronic components. Mixed paraffin samples were prepared by mixing appropriate proportions of paraffin (mass) at various temperatures. Differential scanning calorimetry analysis revealed that the maximum enthalpy of 206.3 J/g is obtained by mixing 20% of 17°C liquid paraffin and 80% of 29°C solid paraffin. Heating and cooling cycling tests revealed that mixed paraffin exhibits excellent thermal stability and that the regulation method marginally affects thermal stability. Moreover, composites were prepared by embedding PCM into a copper foam by melt impregnation. The thermal conductivity of the composites increased to 4.35 W/(mK), corresponding to 20 times its original value. In addition, density functional theory and experimental results were in good agreement, indicating that the regulation method is practical and effective. [ABSTRACT FROM AUTHOR]

The development of automatic tracking solar concentrator photovoltaic systems is currently attracting growing interest. High concentration photovoltaic systems (HCPVs) combining triple-junction InGaP/lnGaAs/Ge solar cells with a concentrator provide high conversion efficiencies. The mathematical model for triple-junction solar cells, having a higher efficiency and superior temperature characteristics, was established based on the one-diode equivalent circuit cell model. A paraboloidal concentrator with a secondary optic system and a concentration ratio in the range of 100X–150X along with a sun tracking system was developed in this study. The GaInP/GalnAs/Ge triple-junction solar cell, produced by AZUR SPACE Solar Power, was also used in this study. The solar cells produced by Shanghai Solar Youth Energy (SY) and Shenzhen Yinshengsheng Technology Co. Ltd. (YXS) were used as comparison samples in a further comparative study at different concentration ratios (200X–1000X). A detailed analysis on the factors that influence the electrical output characteristics of the InGaP/lnGaAs/Ge solar cell was conducted with a dish-style concentrating photovoltaic system. The results show that the short-circuit current (Isc) and the open-circuit voltage (Voc) of multijunction solar cells increases with the increasing concentration ratio, while the cell efficiency (ηc) of the solar cells increases first and then decreases with increasing concentration ratio. With increasing solar cell temperature, Isc increases, while Voc and ηc decrease. A comparison of the experimental and simulation results indicate that the maximum root mean square error is less than 10%, which provides a certain theoretical basis for the study of the characteristics of triple-junction solar cell that can be applied in the analysis and discussion regarding the influence of the relevant parameters on the performance of high concentration photovoltaic systems. [ABSTRACT FROM AUTHOR]

The study of the phase equilibrium characteristics of CO2-ionic liquids (ILs) as new absorption-compression type refrigeration working pairs is of great importance. Three kinds of ILs, i.e., [emim][FAP], [bmim][FAP] and [hmim][FAP], were chosen as potential absorbents. The solubility of CO2 in these ILs was measured experimentally within 0 to 5.0 MPa at temperatures of 293.15 K to 333.15 K, and the effects of temperature, pressure, IL anion and cation structure and stirring action on CO2 solubility were also discussed and analyzed. The results showed that the longer alkyl chains in an identical IL family, the alkyl fluoride group in IL anions and the stirring action by a magnetic stirrer had positive effects on the solubility of CO2. In the three ILs, [hmim][FAP] possessed the best performance for CO2 absorption; the solubility of CO2 reached 0.7641 at a pressure of 5 MPa and temperature of 293.15 K, the maximum solubility measured in this work. The CO2-[hmim][FAP] binary mixture is recommended as a potentially applicable working pair for CO2 absorption-compression refrigeration systems. [ABSTRACT FROM AUTHOR]

A green, rapid and controllable synthesis of gold nanoparticles (Au NPs) was achieved using the mulberry fruit (MF) extract as reducing and capping agent at room temperature. Obtained Au NPs were characterized by ultraviolet–visible spectrum, transmission electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, selected area electron diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses. It could be found that Au NPs had a small size of 4.2–20.1 nm, face-centered cubic crystalline structure and homogeneous dispersion, indicating strong reducing and capping capacities of the MF extract. Meanwhile, the morphology (quasi-sphere/sphere) of Au NPs could be controlled only by adjusting the MF extract concentration. Furthermore, based on the 4-nitrophenol (4-NP) reduction reaction, as-prepared Au NPs exhibited excellent photocatalytic activity and stability in 30 days. Under sunlight irradiation, 4-NP could be completely reduced in 4 min and its rate constant could reach up to 0.91 min−1. And the rate constant could be linearly adjusted by the MF extract concentration or the amount of Au NPs hydrosol. In addition, it could also be found that the light source with short wavelength could obviously elevate the photocatalytic activity of Au NPs, attributed to the hot-electron effect. Clearly, as-obtained Au NPs can have great potential applications in wastewater treatment. [ABSTRACT FROM AUTHOR]

A packed-bed thermal energy storage (PBTES) device, which is simultaneously restricted by thermal storage capacity and outlet temperatures of both cold and hot heat transfer fluids, is characterized by an unstable operation condition, and its calculation is complicated. To solve this problem, a steady thermodynamics model of PBTES with fixed temperatures on both ends was built. By using this model, the exergy destruction, thermocline thickness, thermal storage capacity, thermal storage time, and other key parameters can be calculated in a simple way. In addition, the model explained the internal reason for the change of thermocline thickness during thermal storage and release processes. Furthermore, the stable operation of the PBTES device was analyzed, and it was found that higher inlet temperature of hot air, and lower temperature difference between cold and hot air can produce less exergy destruction and achieve a larger cycle number of stable operation. The work can be employed as the basis of the design and engineering application of PBTES. [ABSTRACT FROM AUTHOR]

The degradation of nitro and azo compounds has attracted wide attention due to their high toxicity and stability in water. Here, we reported the fast degradation of nitro and azo compounds by the direct injection of high-concentration noble-metal ions (Au3+, Ag+, Pd2+, or Pt4+) and discussed the degradation mechanism. The rate constants of the nitro and azo compounds degradation followed the order: K4-NP > K2-NP > K3-NP > K2-NR > KMR > KMO, explained by the substituent effect. The maximum of the degradation rate constant could reach up to 16 min−1, which can be attributed to the atom-nano catalysis motivated by the direct injection of high-concentration ions. Furthermore, based on the method, the highlighted conflicts shown in the nitro and azo compounds degradation could be resolved. Meanwhile, the recovery method (centrifugation, dissolution, and purification) of noble-metal ions was proposed by means of various characterization techniques, and then noble-metal ions were recovered and recycled for five cycles. Obviously, the above degradation technology can have great potential for applications in water pollutant removal and environmental remediation. [ABSTRACT FROM AUTHOR]