The flow and heat performance of tree-like network heat sink with diverging–converging channel

A tree-like network heat sink with diverging–converging channel is designed, and effect of flow rate, channel diverging-converging angles on the flow and heat dissipation performance of the tree-like network heat sink is analysed and compared by numerical simulation. Results show that the diverging– converging angle of 2° can reduce the pressure drop by 14% when inlet mass flow rate is 0.00499kg/s. And the maximum temperature, the temperature difference between the maximum and minimum of the heat sink increases by 0.63K and 0.92K respectively. As the diverging-converging angle increases to 4°, however, it only reduces the pressure drop by 13% and can not bring more pressure drop due to formation of flow recirculation inside the tree-like network heat sink channel. Therefore, the diverging–converging fractal micro-channel heat sink with 2° has good heat dissipation performance with obvious lower pumping power

Catalytic depolymerization of lignin for liquefied fuel at mild condition by rare earth metals loading on CNT

A series of rare earth metals supported on carbon nanotube (CNT) were tested for the catalytic depolymerization of lignin. The supported cerium (Ce) and lanthanum (La) on CNT were firstly characterized by TEM and N-2-BET, respectively. The as-prepared catalysts were efficient to depolymerize lignin, whereas 86.1% liquefied fuel yield was obtained at the conditions of 260 degrees C,1 h with Ce/CNT catalyst. The catalyst presented high activity even after four times recycle and the yield of liquefied fuel still kept 82.0%. The liquefied fuel were evaluated to be a premium fuel with high contents of C and H and low content of O, together with high calorific value. From these tested results, it is clear to find that Ce/CNT is an effective catalyst which can depolymerize lignin under mild conditions. (C) 2016 Elsevier B.V. All rights reserved

Effects of KCl and CaCl2 on the evolution of anhydro sugars in reaction intermediates during cellulose fast pyrolysis

Reaction intermediates mainly consisting of anhydro sugars are the crucial transitional stage connecting the cellulose feedstock and the three phases of products during pyrolysis. For the first time, the effects of KCl and CaCl2 on the evolution of anhydro sugars in reaction intermediates were examined by using levoglucosan pyranose (LGA_Pyran), maltosan and cyclodextrin as model compounds. These compounds were subjected to fast pyrolysis on a Py-GC/MS, where dry samples were heated at a heating rate of 10 degrees C/s to 500 degrees C with a holding time of 20 s at 500 degrees C. The results indicated that KCl had a stronger inhibitory effect than CaCl2 on LGA_Pyran formation during cellulose fast pyrolysis. However, during the pyrolysis of the oligosaccharides, the catalytic effects of KCl were weakened by the low degree of polymerization and the lack of reducing ends, while the catalytic effects of CaCl2 were enhanced by a better distribution. This led to the reverse order of their effects on LGA_Pyran formation. Furthermore, much higher char yields from oligosaccharides under catalysis of CaCl2 than under the catalysis of KCl indicate the prominent influence of CaCl2 on the secondary reactions of reaction intermediates leading to secondary char

Wake Bifurcations Behind Two Circular Disks in Tandem arrangement

The wake bifurcations behind two circular disks in tandem arrangement are investigated through numerical simulations. The separation distance between the disks, S/d, is chosen at 1, 2, 4, and 6, and the Reynolds number, Re, lies in the range of 100 Re 500. The wake dynamics are examined in terms of the flow structures as well as drag and lift coefficient characteristics. Seven main wake regimes are observed in the considered (Re, S/d) space: steady state (SS), Zig-zig (Zz) mode, standing wave mode, periodic state with reflectional symmetry breaking (RSB), periodic state with double-helical (DH) structures shedding, periodic state with double-hairpin-loop (DHL) shedding, and weakly chaotic state. Among these bifurcations, the DH and DHL wake modes are reported in the tandem disk wakes, which are not observed in a single disk wake. Compared with the single disk wake, the first bifurcation leading to the SS mode is always delayed in tandem configuration, which is especially evident for the case of S/d = 1. For the second bifurcation leading to an unsteady state, some differences lie in the wake mode for different tandem configurations. The second bifurcation leads to the Zz wake mode for the cases S/d = 1, 2, and 4, and the RSB mode for S/d = 6. In the scenario of S/d = 1, the bifurcations are similar to those of a thick disk, suggesting that a shorter separation distance in this configuration has equivalent effects as increasing the thickness in the case of a single disk. In the scenario of S/d = 2, the bifurcations are complex and quite different from those in a single disk wake, indicating that the interaction between two disks in tandem arrangement is stronger when the trailing disk is located close to the end of the recirculation

Ruddlesden‐Popper‐type perovskite Sr3Fe2O7−δ for enhanced thermochemical energy storage

Abstract Perovskite has been considered a promising thermochemical energy storage material. Such materials can perform redox reactions reversibly under the control of oxygen partial pressure over a wide range of temperatures. Layered perovskites have been poorly studied as energy storage material, although their oxygen species exhibit good oxidation activity. In this work, Ruddlesden‐Popper‐type quasi‐2D perovskite Sr3Fe2O7‐δ and 3D perovskite SrFeO3‐δ were prepared for the testing of thermochemical energy storage properties. It was shown that the degree of reduction reaction for Sr3Fe2O7‐δ was much greater than that of SrFeO3‐δ, with change of non‐stoichiometry up to 0.79. The combined effect of thermodynamic parameters for samples on heat storage behavior was studied by Van't Hoff method. The reduction entropy of Sr3Fe2O7‐δ is much higher than that of SrFeO3‐δ, which explains the large promotion in the reaction degree of SrFeO3‐δ. The total reduction enthalpy of Sr3Fe2O7‐δ is about 2.8 times that of SrFeO3‐δ, with both reduction enthalpy and reaction entropy affecting the heat storage capacity. Sr3Fe2O7‐δ also has an attractive spectral absorption of 96.92% in the range of 300–2500 nm, which makes it advantageous in volumetric solar collector. Overall, Sr3Fe2O7‐δ offers improved performance in terms of thermochemical energy storage compared to SrFeO3‐δ