Heat transfer enhancement and performance of the molten salt receiver of a solar power tower

This paper investigates the interaction between the heat transfer performance and the thermal efficiency of a molten salt receiver used in the solar power tower plant. A test-bed is built, and a series of experiments of heat transfer enhancement for two types of molten salt receiver tubes, including smooth and spiral tubes, have been carried out under the high temperature and the high heat flux conditions. The experimental results show that the Nusselt numbers of spiral tube with heat transfer enhancement are in the range of 400-1200, which is about 3 times than that of the smooth one on average. The wall temperature of the spiral tube is decreased by about 30 °C comparing with that of the smooth tube under the identical heat transfer conditions. The results of the experiment show that, by using the spiral tube as the heat transfer tube, the heat transfer performance of the molten salt receiver is obviously improved, and the radiation and convection losses are significantly reduced. The results will be helpful for the design of the molten salt receiver.Molten salt receiver Heat transfer enhancement Spiral tube Radiation and convection losses

Synthesis and characterization of nitrogen doped ZnO tetrapods and application in photocatalytic degradation of organic pollutants under visible light

In this report, the nitrogen doped ZnO tetrapods are prepared by using the solid reaction of ZnO tetrapods and urea at 600 degrees C. XRD shows that the crystal structure of nitrogen doped ZnO is unchanged maybe due to the low percentage of the nitrogen doping. SEM proves that the nitrogen doping occurs on the surface of ZnO. Furthermore, the photocatalytic activity of the nitrogen doped ZnO tetrapods is evaluated for Bisphenol A photodegradation under visible light irradiation. The results show that the photocatalytic activity of nitrogen doped ZnO tetrapods is higher than those of pure ZnO tetrapods and Degussa TiO2 P25, indicating the great effect of nitrogen doping on the photocatalytic activity of nitrogen doped ZnO tetrapods. Finally, a mechanism is proposed to explain the photodegradation of BPA over nitrogen doped ZnO tetrapods photocatalyst under visible light irradiation. (c) 2013 Elsevier B.V. All rights reserved

INVESTIGATION ON DEPTH OF HEAT AFFECTED ZONE OF DISCHARGE SPOT BY HIGH REPETITIVE RATE YAG LASER-INDUCED DISCHARGE TEXTURING

It is known that the press formability and the elongation of laser textured sheet are improved, and the service life of textured roll is longer than that of the un-textured roll due to hardening of the treated surface. One of the goals to develop high repetitive rate YAG laser-induced discharge texturing (LIDT) is to get deeper hardening zone. By observing and measuring cross-section of LIDT spots in different discharge conditions, it is found that the single-crater, which is formed by the discharge conditions of anode, which is covered by an oil film and with rectangular current waveform, has the most depth of heat affected zone (HAZ) comparing with other crater shapes when discharge energy is the same. The depth of HAZ is mainly depends on pulse duration when the discharge spot is single-crater. The results are analyzed.Laser, heat affected zone, discharge

Synthesis of ZnO nanorod arrays on Zn substrates by a gas-solution-solid method and their application as an ammonia sensor

The design of the 1D nano-structured material arrays on substrates is required for the development of conductivity sensors. A simple method, the so-called gas-solution-solid, has been developed to prepare ZnO nanorod arrays on Zn substrate. The method consists of putting Zn foils above an ammonia solution for about 24 h to obtain the aligned ZnO nanorods on substrates. The sizes of ZnO nanorod arrays could be controlled by adjusting the concentration of the ammonia-water solution and reaction time. Moreover, the growth mechanism of the nanorod arrays was studied and proposed. In the proposed mechanism, the Zn source from the Zn foil is first oxidized to ZnO and Zn2+ by oxygen. Then ZnO nanorod arrays are grown with the help of ammonia in the solution as a transporter of zinc ions. The nanorod arrays growth mechanism involves oxygen gas, ammonia solution, and Zn foil, and is, therefore, named as gas-solution-solid mechanism. Finally, the NH3 sensing properties were measured and the results showed that ZnO nano-array sensor has high sensitivity and reversibility for NH3 sensing at the room temperature and the sensitivity increases with increasing gas concentration

Synthesis and characterization of hollow gold tetrapods

The development of different morphologies is desired in the field of nano-materials research. Gold is an interesting material for electronic nanodevice among many other potential applications and lots of morphologies have been prepared. However, hollow gold tetrapod has not been reported. In this paper, hollow gold tetrapods were prepared for the first time by using ZnO tetrapods as a template. HAuCl(4) as a gold source and ascorbic acid as a reducing reagent. The structure and growth mechanism were investigated and the results show that the hollow gold tetrapods are composed of gold nanoparticles with a mean diameter of about 7.0 nm. (C) 2011 Elsevier B.V. All rights reserved

Phase-transitions of alpha- and beta-Bi(2)O(3) nanowires

The transition temperatures for the alpha or beta to delta and the delta to liquid phase for alpha- and beta-Bi(2)O(3) nanowires were investigated. We found that there is a size effect for the delta to liquid phase transition but not the alpha or beta to delta phase transition. This is because the delta to liquid phase transition involves bond rupture as well as surface area reduction, whereas the alpha or beta to delta is only solid-solid phase transition, which requires only the reorganization of the bonds. This is the first time the phase transitions of the Bi(2)O(3) nanowires have been investigated and their size effect revealed. (C) 2010 Elsevier B.V. All rights reserved

Electrodeposition of manganese dioxide film on activated carbon paper and its application in supercapacitors with high rate capability

In this research magnesium dioxide (MnO2) is electrodeposited over activated carbon paper (ACP) to form a composited MnO2/ACP material. The as-prepared MnO2/ACP shows excellent capacitance performance with a high specific capacitance of 485.4 F g-1 calculated from a discharge curve with current density 2.0 A g-1, owing to its enlarged specific surface area and improved electronic conductivity. Moreover, the MnO2/ACP possesses remarkable rate capability due to the easy access of electrolytic ions, leading to complete utilization of MnO2 active material for supercapacitors. To summarize, the electrodeposition of MnO2 thin film on activated carbon paper is reported for the first time, and the composited MnO2/ACP is a promising electrode material for building up efficient supercapacitors