Numerical Simulation and Experimental Study of the Tube Receiver's Performance of Solar Thermal Power Tower

AbstractA water-vapor tube receiver is a significant component in the solar thermal power tower plant. However, the tube flow performance is much different from others. Because semi-circumference of the tube is heated with an uneven heat flux, which is into a Gaussian distribution in this paper, and the other semi-circumference is insulated. A 5kW- Xe-arc lamp was used to simulate a solar light source. In this study, the effect of different entrance velocity on the flow performance and thermal efficiency of the tube receiver are investigated with numerical and experimental methods. The results of experiment and simulation agree well. The results show that the temperature distribution of water and tube wall are very uneven both in the axial and radial directions. The thermal efficiency of the tube receiver increases with the increase of entrance velocity

Lanthanide-MOFs as multi-responsive photoluminescence sensor for sensitively detecting Fe

Fast and selective detection of contaminants plays a key role in meeting human health and environmental concerns. Herein, two groups of isostructural lanthanide MOFs, [Ln(Hpta)(oxalic acid)]·

A series of lanthanide(iii) metal-organic frameworks derived from a pyridyl-dicarboxylate ligand: single-molecule magnet behaviour and luminescence properties

The reactions of LnIII ions with a versatile pyridyl-decorated dicarboxylic acid ligand lead to a series of novel three-dimensional (3D) Ln-MOFs, [Ln3(pta)4(Hpta)(H2O)]·xH2O (Ln = Dy (1), Eu (2), Gd (3), Tb (4), H2pta = 2-(4-pyridyl)-terephthalic acid, x = 6 for 1, 2.5 for 2, 1.5 for 3 and 2 for 4). The Ln3+ ions act as the nine-coordinated Muffin spheres, linking to each other to generate trinuclear {Ln3(OOC)6N2} SBUs, which are further extended to be interesting 3D topology architectures. To the best of our knowledge, the Dy-MOF exhibits a zero-field single-molecule magnet (SMM) behaviour with the largest effective energy barrier among the previously reported 3D MOF-based Dy-SMMs. The combined analyses of a dilution sample (1@Y) and ab initio calculation demonstrate that the thermally assisted slow relaxation is mainly attributed to the single-ion magnetism. Furthermore, fluorescence measurements reveal that H2pta can sensitize EuIII and TbIII characteristic luminescence

A substituent effect of phenylacetic acid coligand perturbed structures and magnetic properties observed in two triple-bridged azido-Cu(II) chain compounds with ferromagnetic ordering and slow magnetic relaxation

Based on two fluoro-substituted phenylacetate isomers, o-fluorophenylacetic acid (o-Hfpa) and p-fluorophenylacetic acid (p-Hfpa), two new Cu(II)-azido compounds, [Cu(o-fpa)(N-3)(C2H5OH)](n) (1) and [Cu(p-fpa)(N-3)(C2H5OH)](n) (2), have been prepared, and structurally and magnetically characterized. Single- crystal structure analyses indicate that compounds 1 and 2 consist of 1D chain-like coordination networks in which adjacent copper cations are linked by the alternating triple-bridges of mu-1,1-azido, syn, syn-carboxylate and mu 2-ethanol. For the two title compounds, the diverse charge distributions on the carboxyl groups caused by distinct substituent effects of the two phenylacetate coligands lead to the different structural parameters of intrachain Cu-Cu distances (3.218 angstrom for 1 and 3.168 angstrom for 2) and Cu-N-Cu angles (106.82(omicron) for 1 and 104.81(omicron) for 2), further resulting in the disparity of magnetic behaviors. The dominant ferromagnetic couplings between neighbouring Cu(II) ions in the two compounds (J = 87.08 cm(-1) for 1, J = 66.05 cm(-1) for 2) are due to the counter-complementarity of the multiple superexchange pathways, contributing to the interesting plots of a ferromagnetic order (T-c = 11.0 K for 1, 9.5 K for 2) and slow magnetic relaxation that are rarely observed in most of the reported azido-Cu(II) architectures. Heat-capacity experiments further emphasize the characteristic long-range ferromagnetic ordering in compounds 1 and 2. Magneto-structural relationships of 1 and 2 are investigated as well. Moreover, DFT calculations (using different methods and basis sets) have been performed on both compounds to provide a qualitative and quantitative theoretical explanation of their magnetic behavior

A new <i>β</i>-diketonate Dy(III) single‒ion magnet featuring multiple magnetic relaxation processes

<p>A <i>β</i>-diketonate mononuclear dysprosium compound, [Dy(TFNB)₃(bpy)] (<b>1</b>) (TFNB = 4,4,4-trifluoro-1-(2-naphthyl)-1,3-butanedione, bpy = 2,2′-bipyridine), has been prepared and structurally and magnetically characterized. X-ray crystallographic analysis reveals that <b>1</b> contains two crystallographically equivalent Dy(III) ions of which the eight-coordinate geometries uniformly behave as distorted square antiprismatic configurations (<i>D</i>_4d). Magnetic investigations demonstrate that <b>1</b> displays dual relaxation processes of SMMs behavior with the effective barrier (Δ<i>E</i>/<i>k</i>_B) of 23.44 K under 1200 Oe DC field, corresponding to the coexistence of two metal centers in the structure of the compound. The comparative studies of some Dy(III)-based SIMs with TFNB ligand have been conducted as well. <i>Ab initio</i> studies demonstrate that the Kramers doublet ground state is predominantly axial with the <i>g</i>_z tensors of two Dy(III) fragments matching the Ising-limit factor (20) anticipated for the pure <i>M</i>_J = ±15/2 state.</p

Coligand modifications fine-tuned the structure and magnetic properties of two triple-bridged azido-Cu(II) chain compounds exhibiting ferromagnetic ordering and slow relaxation

Employing two benzoate derivatives with different numbers of non-coordinated fluoro-substituents, 2-fluorobenzoic acid (2-Hfba) and 2,6-difluorobenzoic acid (2,6-Hdfba), two new azido-copper coordination polymers, [Cu(2-fba)(N-3)(CH3OH)](n) (1) and [Cu(2,6-dfba)(N-3)(CH3OH)](n) (2), have been successfully isolated, and then structurally and magnetically investigated. Single crystal structure analysis demonstrates that the metal cations in the two resulting compounds are connected by the alternating triple-bridge of mu-1,1-azido, syn, syn-carboxylate and eta 2-methanol, contributing to analogously linear 1D Cu(II) chain-like motifs with slightly different intrachain and interchain geometric parameters. The fine-tuned structures lead to variant magnetic properties in the two title compounds. Although a dominant ferromagnetic coupling between adjacent Cu(II) ions within each chain due to the counter-complementarity of the multiple superexchange pathways is observed in both compounds, the interesting plots of magnetic ordering and slow magnetic relaxation, which are rare in most of the reported azido-Cu(II) architectures, only occur in compound 1, while 2 behaves as an antiferromagnet consisting of ferromagnetic Cu(II) chains. The heat-capacity experiments further emphasize the characteristic long-range ferromagnetic ordering in 1 and the typical behavior of antiferromagnets in 2. Moreover, density functional theory (DFT) calculations (using different methods and basis sets) have been performed on both compounds to obtain the qualitatively theoretical interpretation of the magnetic behaviors

Coligand modifications fine-tuned the structure and magnetic properties of two triple-bridged azido-Cu(II) chain compounds exhibiting ferromagnetic ordering and slow relaxation

Employing two benzoate derivatives with different numbers of non-coordinated fluoro-substituents, 2-fluorobenzoic acid (2-Hfba) and 2,6-difluorobenzoic acid (2,6-Hdfba), two new azido-copper coordination polymers, [Cu(2-fba)(N-3)(CH3OH)](n) (1) and [Cu(2,6-dfba)(N-3)(CH3OH)](n) (2), have been successfully isolated, and then structurally and magnetically investigated. Single crystal structure analysis demonstrates that the metal cations in the two resulting compounds are connected by the alternating triple-bridge of mu-1,1-azido, syn, syn-carboxylate and eta 2-methanol, contributing to analogously linear 1D Cu(II) chain-like motifs with slightly different intrachain and interchain geometric parameters. The fine-tuned structures lead to variant magnetic properties in the two title compounds. Although a dominant ferromagnetic coupling between adjacent Cu(II) ions within each chain due to the counter-complementarity of the multiple superexchange pathways is observed in both compounds, the interesting plots of magnetic ordering and slow magnetic relaxation, which are rare in most of the reported azido-Cu(II) architectures, only occur in compound 1, while 2 behaves as an antiferromagnet consisting of ferromagnetic Cu(II) chains. The heat-capacity experiments further emphasize the characteristic long-range ferromagnetic ordering in 1 and the typical behavior of antiferromagnets in 2. Moreover, density functional theory (DFT) calculations (using different methods and basis sets) have been performed on both compounds to obtain the qualitatively theoretical interpretation of the magnetic behaviors

Single-Ion-Magnet Behavior in a Two-Dimensional Coordination Polymer Constructed from Co^II Nodes and a Pyridylhydrazone Derivative

A novel two-dimensional (2D) coordination polymer, [Co­(ppad)₂]_<i>n</i> (<b>1</b>), resulted from the assembly of Co^II ions based on a versatile ligand termed <i>N</i>³-(3-pyridoyl)-3-pyridinecarboxamidrazone. Alternating/direct-current magnetic studies of compound <b>1</b> indicate that the spatially separated high-spin Co^II ions act as single-ion magnets (SIMs). The present work represents the first case of a 2D Co^II-based SIM composed of a monocomponent organic spacer

Solvent-Induced Syntheses, Crystal Structures, Magnetic Properties, and Single-Crystal-to-Single-Crystal Transformation of Azido-Cu(II) Coordination Polymers with 2‑Naphthoic Acid as Co-ligand

Based on the solvent-induced effect, three new azido-copper coordination polymers[Cu­(2-na)­(N₃)] (<b>1</b>), [Cu­(2-na)­(N₃)] (<b>2</b>), and [Cu­(2-na)­(N₃)­(C₂H₅OH)] (<b>3</b>) (where 2-na = 2-naphthoic acid)have been successfully prepared. Structure analysis shows that the Cu­(II) cations in compounds <b>1</b>–<b>3</b> present tetra-, penta-, and hexa-coordination geometries, respectively. Compound <b>1</b> is a well-isolated one-dimensional (1D) chain with the EO-azido group, while <b>2</b> is an isomer of <b>1</b> and exhibits a two-dimensional (2D) layer involving the EE-azido group. Thermodynamically, density functional theory (DFT) calculation reveals that <b>2</b> occupies the stable state and <b>1</b> locates in the metastable state. Compound <b>3</b> consists of a 1D chain with triple bridging mode, which is derived from <b>1</b>, and undergoes a single-crystal-to-single-crystal transformation by soaking in ethanol solvent; the powdery product of <b>1</b>, namely <b>1b</b>, could be yielded after the dealcoholization of compound <b>3</b>. Magnetic measurements indicate that compounds <b>1</b>–<b>3</b> perform strong intrachain ferromagnetic interactions, experiencing long-range magnetic ordering and slow magnetic relaxation. Compound <b>1</b> features the metamagnetic behavior with a transition temperature of 15 K, while <b>2</b> and <b>3</b> display spin glass behavior with the phase transition temperatures of 15 and 12 K, respectively. Magneto-structure relationships are investigated as well